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Re: Question about transistor amp schematic


Jun 19, 2012

 


----------------------------

#843 Jun 19, 2012

I'm reading a book on solid state amps. . Here is a schematic I made based on the book. . I wanted to be able to study how it worked without actually constructing it. .This schematic has the best (lowest) distortion I can get without getting very complex. .Spice says it is 0.0005% THD at 1kHz. .I doubt it's really that good if build with real components.

I copied building blocks and I must admit I don't know 100% how some of them work. . One case is the block (lower center)..that contains Q4, Q5, Q16 and Q6. .This is a voltage amplifier based on a darlington pair and a cascode. . . But what is Q5 doing? .Is it simply providing a voltage drop to bias Q4. .Looks like it to me. . .Could I use a diode to do the same thing?



amp01.jpg





--

Chris AlbertsonRedondo Beach, California



----------------------------

#844 Jun 20, 2012

Q5 is providing NFB from the emitter of Q6 to the base of Q4 to stabilize

the operating point. The overall circuit is somewhat similar to my 200

watt per channel design.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Tuesday, June 19, 2012 4:31 PM

Subject: [funwithtransistors] Question about transistor amp schematic





> I'm reading a book on solid state amps. Here is a schematic I made based

> on the book. I wanted to be able to study how it worked without actually

> constructing it. This schematic has the best (lowest) distortion I can

> get

> without getting very complex. Spice says it is 0.0005% THD at 1kHz. I

> doubt it's really that good if build with real components.

>

> I copied building blocks and I must admit I don't know 100% how some of

> them work. One case is the block (lower center) that contains Q4, Q5,

> Q16 and Q6. This is a voltage amplifier based on a darlington pair and a

> cascode. But what is Q5 doing? Is it simply providing a voltage drop

> to bias Q4. Looks like it to me. Could I use a diode to do the same

> thing?

>

>

> amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#845 Jun 20, 2012

P S. I think the values for R12 and R13 are misprints. It seems that such

a low value in the base circuits would require a very high current in Q12

and Q11.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Tuesday, June 19, 2012 4:31 PM

Subject: [funwithtransistors] Question about transistor amp schematic





> I'm reading a book on solid state amps. Here is a schematic I made based

> on the book. I wanted to be able to study how it worked without actually

> constructing it. This schematic has the best (lowest) distortion I can

> get

> without getting very complex. Spice says it is 0.0005% THD at 1kHz. I

> doubt it's really that good if build with real components.

>

> I copied building blocks and I must admit I don't know 100% how some of

> them work. One case is the block (lower center) that contains Q4, Q5,

> Q16 and Q6. This is a voltage amplifier based on a darlington pair and a

> cascode. But what is Q5 doing? Is it simply providing a voltage drop

> to bias Q4. Looks like it to me. Could I use a diode to do the same

> thing?

>

>

> amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#846 Jun 20, 2012

On Tue, Jun 19, 2012 at 7:58 PM, Max Robinson max@...> wrote:

.Q5 is providing NFB from the emitter of Q6 to the base of Q4 to stabilize

the operating point. The overall circuit is somewhat similar to my 200

watt per channel design.







----------------------------

#847 Jun 20, 2012

On Tue, Jun 19, 2012 at 8:00 PM, Max Robinson max@...> wrote:

.P S. I think the values for R12 and R13 are misprints. It seems that such

a low value in the base circuits would require a very high current in Q12

and Q11.



----------------------------

#848 Jun 20, 2012

Actually, Q4, 5, 6 are a darlington dynamic current source driven by the current mirror Q14, 15, similar to Q7, 8 where Q5, 8 are the reference and feedback of a constant current source. You calculate the would-be current I=Vbe/R. Q16 is probably a higher voltage and power than the other 3 transistors.



Q9 is like and adjustable zener, R9 to R10, and Q9 should also be on the heat sink ner the power transistor to provide thermal negative feedback. This prevents thermal run away.



R12, 13 need to be more around 100 ohms.

--- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@...> wrote:

>

> I'm reading a book on solid state amps. Here is a schematic I made based

> on the book. I wanted to be able to study how it worked without actually

> constructing it. This schematic has the best (lowest) distortion I can get

> without getting very complex. Spice says it is 0.0005% THD at 1kHz. I

> doubt it's really that good if build with real components.

>

> I copied building blocks and I must admit I don't know 100% how some of

> them work. One case is the block (lower center) that contains Q4, Q5,

> Q16 and Q6. This is a voltage amplifier based on a darlington pair and a

> cascode. But what is Q5 doing? Is it simply providing a voltage drop

> to bias Q4. Looks like it to me. Could I use a diode to do the same

> thing?

>

>

> amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#849 Jun 20, 2012

Forgot to mention, in spice all transistors of the same number are identical, in the real world, not so much. That will have a direct effect on the real THD performance.

--- In funwithtransistors@yahoogroups.com, "Den" engineer_musician@...> wrote:

>

> Actually, Q4, 5, 6 are a darlington dynamic current source driven by the current mirror Q14, 15, similar to Q7, 8 where Q5, 8 are the reference and feedback of a constant current source. You calculate the would-be current I=Vbe/R. Q16 is probably a higher voltage and power than the other 3 transistors.

>

> Q9 is like and adjustable zener, R9 to R10, and Q9 should also be on the heat sink ner the power transistor to provide thermal negative feedback. This prevents thermal run away.

>

> R12, 13 need to be more around 100 ohms.

>

> --- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@> wrote:

> >

> > I'm reading a book on solid state amps. Here is a schematic I made based

> > on the book. I wanted to be able to study how it worked without actually

> > constructing it. This schematic has the best (lowest) distortion I can get

> > without getting very complex. Spice says it is 0.0005% THD at 1kHz. I

> > doubt it's really that good if build with real components.

> >

> > I copied building blocks and I must admit I don't know 100% how some of

> > them work. One case is the block (lower center) that contains Q4, Q5,

> > Q16 and Q6. This is a voltage amplifier based on a darlington pair and a

> > cascode. But what is Q5 doing? Is it simply providing a voltage drop

> > to bias Q4. Looks like it to me. Could I use a diode to do the same

> > thing?

> >

> >

> > amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

> >

> >

> >

> > --

> >

> > Chris Albertson

> > Redondo Beach, California

> >

>



----------------------------

#850 Jun 21, 2012

Since Q4 and Q6 form a darlington pair the loop gain is set by the gain of

Q5.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Wednesday, June 20, 2012 1:52 AM

Subject: Re: [funwithtransistors] Question about transistor amp schematic





> On Tue, Jun 19, 2012 at 7:58 PM, Max Robinson

> max@...>wrote:

>

>> **

>>

>>

>> Q5 is providing NFB from the emitter of Q6 to the base of Q4 to stabilize

>> the operating point. The overall circuit is somewhat similar to my 200

>> watt per channel design.

>>

>

> OK, NFB. What determines how much? Does it depend on the gain of

> whatever transistor is used?

>

> I had guessed that the transistor was always "on" and they were using it

> simply to drop volts like you light use a diode. have it in LTSpice so

> I'll look at some plots

>

> Thanks.

>

>

>> > .... But what is Q5 doing? Is it simply providing a voltage drop

>> > to bias Q4. Looks like it to me. Could I use a diode to do the same

>> > thing?

>> >

>> >

>> > amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

>>

>> --

>

> Chris Albertson

> Redondo Beach, California

>







----------------------------

#851 Jun 21, 2012

On Wed, Jun 20, 2012 at 8:52 PM, Max Robinson max@...> wrote:

.Since Q4 and Q6 form a darlington pair the loop gain is set by the gain of

Q5.



----------------------------

#852 Jun 21, 2012

Well, actually the signal outputs from Q4 and Q6 come from the collectors.

As it looks to me the purpose of Q5 is to stabilize the operating currents

of Q4 and Q6.



To do an open loop test on an amplifier on the breadboard you connect up the

feedback loop with the feedback resistor split into two equal parts half of

the original resistor. Then you connect a big capacitor from the junction

to ground.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Wednesday, June 20, 2012 11:13 PM

Subject: Re: [funwithtransistors] Question about transistor amp schematic





> On Wed, Jun 20, 2012 at 8:52 PM, Max Robinson

> max@...>wrote:

>

>> **

>>

>>

>> Since Q4 and Q6 form a darlington pair the loop gain is set by the gain

>> of

>> Q5.

>>

> Two unrelated questions:

>

> (1) Let's assume all three transistors are identical and have gain = "b".

> Then I think the darlington pair has gain of b^2 and if the feedback

> transistor has gain b the closed loop gain is b^2/b which is just "b".

> Is this correct? If so then I have to ask "why bother? I can get a gain

> of b with just one transistor."

>

> I guess I can look. I think there is a way to get Spice to plot

> mathematical functions of test points. I can have it find the ratio of

> Q16collector over Q4 base and see if it is linear. I think I can figure

> out how to do that

>

>

> (2) How do real people test a transistor feedback amplifier in real life

> without building the entire amp. I want to build the input section

> differential amplifier and try it out on a solder less breadboard but

> without the NFB applied to Q1 all the think does is clip. I can't test to

> see if the output is a linear function of the input

>

> In Spice there are magic components like effect AC voltage sources that

> allow me to simulate a section but how is it done on a breadboard with no

> NFB available.

>

> Tube amps use so little NFB that I can run them open loop but but this amp

> clips if run open.

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#853 Jun 21, 2012

--- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@...> wrote: >

> On Wed, Jun 20, 2012 at 8:52 PM, Max Robinson max@...>wrote:

>

> > **

> >

> >

> > Since Q4 and Q6 form a darlington pair the loop gain is set by the gain of

> > Q5.

> >

> Two unrelated questions:

>

> (1) Let's assume all three transistors are identical and have gain = "b".

> Then I think the darlington pair has gain of b^2 and if the feedback

> transistor has gain b the closed loop gain is b^2/b which is just "b".

With BJTs "b" is the current gain only while in some circuits it may be used a voltage gain device. Q5 is sensing the voltage across R11 and attempting to keep it at Vde by robbing current as needed away from the base of Q4 which inturn controls Q6, 16 current. Q14 takes most of the DC from Q2 while rejecting most of the AC maximizing it into Q4. That whole cluster of Q4. 5, 6, 16 is a very linear current/voltage amplifier to drive the darlington outputs. Q7, 8 are another CCS, constant current source, to pass all the DC and reflect all the AC to the outputs. Q9 is the bias/thermal FB for the outputs. >

> Is this correct? If so then I have to ask "why bother? I can get a gain

> of b with just one transistor."

As a control system the FTF, forward transfer function, is b^2 and the feedback is b. In the ideal world this would be the same as a FTF with a gain of b. In the real world that b is not a constant and very non-liniear. In a sense amplifing the NFB, negative feed back, improves the linearity. >

> I guess I can look. I think there is a way to get Spice to plot

> mathematical functions of test points. I can have it find the ratio of

> Q16 collector over Q4 base and see if it is linear. I think I can figure

> out how to do that

>

>

> (2) How do real people test a transistor feedback amplifier in real life

> without building the entire amp. I want to build the input section

> differential amplifier and try it out on a solder less breadboard but

> without the NFB applied to Q1 all the think does is clip. I can't test to

> see if the output is a linear function of the input

>

> In Spice there are magic components like effect AC voltage sources that

> allow me to simulate a section but how is it done on a breadboard with no

> NFB available.

>

> Tube amps use so little NFB that I can run them open loop but but this amp

> clips if run open.

NFB is a must for direct coupled amps, SS or VT. Without it they are highly unstable. You can make one stable in simulation only because nothing is drifting over time and temperature and all components are ideal and identical. Before simulation we did a lot of hand calculations and trial and error breadboards before a final design is realized. We also blewup a lot of components before reaching that point. >

>

> --

>

> Chris Albertson

> Redondo Beach, California

>







----------------------------

#854 Jun 22, 2012

OBTW Chris, this design has no output short protection. Do you plan on adding some? Looks like LT-Spice, I use it a lot. Denis.

--- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@...> wrote:

>

> I'm reading a book on solid state amps. Here is a schematic I made based

> on the book. I wanted to be able to study how it worked without actually

> constructing it. This schematic has the best (lowest) distortion I can get

> without getting very complex. Spice says it is 0.0005% THD at 1kHz. I

> doubt it's really that good if build with real components.

>

> I copied building blocks and I must admit I don't know 100% how some of

> them work. One case is the block (lower center) that contains Q4, Q5,

> Q16 and Q6. This is a voltage amplifier based on a darlington pair and a

> cascode. But what is Q5 doing? Is it simply providing a voltage drop

> to bias Q4. Looks like it to me. Could I use a diode to do the same

> thing?

>

>

> amp01.jpg dl.dropbox.com/u/28915695/amp01.jpg>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#855 Jun 22, 2012

On Fri, Jun 22, 2012 at 11:43 AM, Den engineer_musician@...> wrote:

.OBTW Chris, this design has no output short protection. Do you plan on adding some? Looks like LT-Spice, I use it a lot. Denis.



----------------------------

#856 Jun 23, 2012

Wow 250 WPC is a lot of PT, I don't have any iron that can do that twice. I'd have to make 2 mono blocks. 100WPC at 8 ohm is the one I built. Did you see it in the Photos here? I usually put an ohm or 2 in my LT-Spice voltage sources and/or a forward biased diode in series with it to make it a little more real. This was my second SS power amp design. I didn't like my first with the dynamic current source driving opposite the constant current source, waveform lacked symetry, I'm splitting hairs here, but the + half of the wave didn't match the - half as much as it could. So I did a full complimentary design from input to output, even the diff-amps. I did the single sided PCB with tape and knife on mylar back in the 70s. Check it out.



OBTW, for all that power don't skimp on the heat sinks. When Phase Linear first came out with the 400 and 700, they would blow up on the bench just trying to test them at full power for a THD measurement, not enough heat sink. Later Dynaco came out with their 400, lots of heatsink and a place to add a muffin fan. My band used one for the monitors, never failed.

--- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@...> wrote:

>

> On Fri, Jun 22, 2012 at 11:43 AM, Den engineer_musician@...> wrote:

>

> > **

> >

> >

> > OBTW Chris, this design has no output short protection. Do you plan on

> > adding some? Looks like LT-Spice, I use it a lot. Denis.

> >

> I just built this schematic to study.

>

> I think I will build the input and voltage amplifier sections first. I

> find that I can buy 2N5401 and 2N5551 for 4 cents each if I buy a 100 at a

> time. These are 100 volt transistors and seem to be the preferred part for

> this kind of amplifier.

>

> Then might make a cheap output section with TIP41C/TIP42C transistors and

> not care to much if one of those fails they cost 50 cents each.

>

> Then my plan is to make some kind of output protection and see if it

> degrades performance. I've read that it does and that I should simply use

> Speakon connectors that you can't short and fuse the power supply. I

> figure with cheat 50 cent output transistor I can experiment and

> intentionally short them

>

> My goal is a 250 WPC amp with THD in the 0.001 range to drive a pair of

> 1970's vintage infinity speakers like these:

> Infinity QLS www.bobbyshred.com/infinity/QLS.html>

> These are 82dB 3 or 4 ohm speakers and will suck up any amount of available

> power.

>

> I want an amp that can do 250 WPC into 8 ohms and more into 4 ohms. But

> I'll build it in modular parts. An input section with 2N5401/2N5551

> transistors, a power supply and an output stage so I can upgrade any of

> those.

>

>

> Eventually I'll build something based on it. I need to add some kind of

> sort protection and a real power supply as I cent seem to find those zero

> impedance LTSpice voltage sources anywhere.

>

> But first I think I'll build a cheaper/simpler amp using TIP41C/TIP42C

> output transistors

>



----------------------------

#857 Jun 23, 2012

If I wanted to build an amp with 100 WPC, what kind of power transformer would I need? I'd obviously get one that had between 150-200 VA of power but what kind of voltage and current ratings are we talking? When you have to take an AC power level, convert it to DC, and then back to AC, things get kind of confusing for me...

100 watts into 8 ohms requires a peak-to-peak voltage of 80 (E^2 / R = P...E = sqrt(PR)...sqrt(100 * 8)...28.28VRMS). This means I need to get a transformer that can give me a 40-0-40 supply (probably a 65-70 VAC winding) with a current capability of 3500 mA. I would probably look at a transformer with a capability for 70-0-70 VDC at 5A. Being that this is one channel, I'd probably have to go out and get a second transformer unless I wanted to buy one with an 8A capacity.

Granted, I'll never likely need the full 100w.Ed







----------------------------

#858 Jun 23, 2012

On Fri, Jun 22, 2012 at 10:35 PM, J Ed jedwardsat1@...> wrote:

.If I wanted to build an amp with 100 WPC, what kind of power transformer would I need? I'd obviously get one that had between 150-200 VA of power but what kind of voltage and current ratings are we talking?



----------------------------

#859 Jun 23, 2012

What if I took a broken welder or other high-power device and got the transformer out of that?

Ed

On Fri, Jun 22, 2012 at 11:37 PM, Chris Albertson albertson.chris@...> wrote:

.

On Fri, Jun 22, 2012 at 10:35 PM, J Ed jedwardsat1@...> wrote:

.If I wanted to build an amp with 100 WPC, what kind of power transformer would I need? I'd obviously get one that had between 150-200 VA of power but what kind of voltage and current ratings are we talking?



----------------------------

#860 Jun 23, 2012

ScrapSalvage��used to be a common way to get a transformer for Ham Radio Linearso I guess its OK here, but there a few points to watch:- Besure it isn't the transformer that hasn't failed besure its the right ratings besure its isolation is good..

Notsure about electric welders but many special purpose PSUs use "novel" techniquesto limit the current. So certainly in the UK a car battery charger will have atransformer that's deliberately designed to have poor regulation. Not sure if acar charger uses the same techniques... ��Personally I would look for a quality toroidal....��Dave Wade G4UGM

Illegitimi Non Carborundum ��

-----Original Message-----From:funwithtransistors@yahoogroups.com [mailto:funwithtransistors@yahoogroups.com]On Behalf Of J EdSent: 23 June 2012 07:59To:funwithtransistors@yahoogroups.comSubject: Re: [funwithtransistors]Re: Question about transistor amp schematic

��What if I took a broken welder or other high-power device and got thetransformer out of that?

Ed

On Fri, Jun 22, 2012 at 11:37 PM, Chris Albertson albertson.chris@...> wrote:��

On Fri, Jun 22, 2012 at 10:35 PM, J Ed jedwardsat1@...> wrote:��If I wanted to build an amp with 100 WPC, what kind of powertransformer would I need? I'd obviously get one that had between 150-200VA of power but what kind of voltage and current ratings are wetalking?



----------------------------

#861 Jun 23, 2012

Good start, I started at the speaker and went backwards from there. Yes you need a +/- 40V swing, but you also need to allow for the Vce of both output transistors at clipping. Since these are usually darlington voltage followers, that will much more than 300mV. My experience shows more like 3...5V when we include the emitter resistor for current sensing and short protection. Now that means the supply needs to be +/-45Vdc, but that's when fully loaded. Since no supply has 0 ohm source impedance, we need to allow for supply sag, 5...15% is a good rule of thumb. Let take 10%. that means we need to add an additional 4.5V to our 45V or +/-50Vdc with rounding. So our PT needs a 50Vpk or / 1.414 = 35Vac. So we need a 70Vac with a CT. To figure current 28.28/8=3.535Aac, double that for 2 channels, you'll need a 70Vac CT at 7Aac PT.

--- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@...> wrote:

>

> If I wanted to build an amp with 100 WPC, what kind of power transformer

> would I need? I'd obviously get one that had between 150-200 VA of power

> but what kind of voltage and current ratings are we talking? When you have

> to take an AC power level, convert it to DC, and then back to AC, things

> get kind of confusing for me...

>

> 100 watts into 8 ohms requires a peak-to-peak voltage of 80 (E^2 / R =

> P...E = sqrt(PR)...sqrt(100 * 8)...28.28VRMS). This means I need to get a

> transformer that can give me a 40-0-40 supply (probably a 65-70 VAC

> winding) with a current capability of 3500 mA. I would probably look at a

> transformer with a capability for 70-0-70 VDC at 5A. Being that this is one

> channel, I'd probably have to go out and get a second transformer unless I

> wanted to buy one with an 8A capacity.

>

> Granted, I'll never likely need the full 100w.

> Ed

>



----------------------------

#862 Jun 23, 2012

The transistor amp circuit that was used for years and is still used in some

amps, drives the speaker off the emitter of the top transistor on the

positive half cycle and the collector of the bottom transistor on the

negative half cycle. I have never thought that was a good amplifier

design. It was done for economic reasons. In the earliest days when

germanium transistors were all you could get NPNs were much more expensive

than the commonly used PNPs. When silicon transistors became available PNPs

cost a lot more. The standard circuit an example of which can be found in

the Heath AR 15, needed only one PNP transistor and the rest were NPNs.

Although the asymmetry can be cleaned up with NFB, this in my opinion is the

wrong way to design an amplifier.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

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www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

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----- Original Message -----

From: "Den" engineer_musician@...>

To: funwithtransistors@yahoogroups.com>

Sent: Friday, June 22, 2012 11:40 PM

Subject: [funwithtransistors] Re: Question about transistor amp schematic





> Wow 250 WPC is a lot of PT, I don't have any iron that can do that twice.

> I'd have to make 2 mono blocks. 100WPC at 8 ohm is the one I built. Did

> you see it in the Photos here? I usually put an ohm or 2 in my LT-Spice

> voltage sources and/or a forward biased diode in series with it to make it

> a little more real. This was my second SS power amp design. I didn't

> like my first with the dynamic current source driving opposite the

> constant current source, waveform lacked symetry, I'm splitting hairs

> here, but the + half of the wave didn't match the - half as much as it

> could. So I did a full complimentary design from input to output, even

> the diff-amps. I did the single sided PCB with tape and knife on mylar

> back in the 70s. Check it out.

>

> OBTW, for all that power don't skimp on the heat sinks. When Phase Linear

> first came out with the 400 and 700, they would blow up on the bench just

> trying to test them at full power for a THD measurement, not enough heat

> sink. Later Dynaco came out with their 400, lots of heatsink and a place

> to add a muffin fan. My band used one for the monitors, never failed.

>

> --- In funwithtransistors@yahoogroups.com, Chris Albertson

> albertson.chris@...> wrote:

>>

>> On Fri, Jun 22, 2012 at 11:43 AM, Den engineer_musician@...> wrote:

>>

>> > **

>> >

>> >

>> > OBTW Chris, this design has no output short protection. Do you plan on

>> > adding some? Looks like LT-Spice, I use it a lot. Denis.

>> >

>> I just built this schematic to study.

>>

>> I think I will build the input and voltage amplifier sections first. I

>> find that I can buy 2N5401 and 2N5551 for 4 cents each if I buy a 100 at

>> a

>> time. These are 100 volt transistors and seem to be the preferred part

>> for

>> this kind of amplifier.

>>

>> Then might make a cheap output section with TIP41C/TIP42C transistors and

>> not care to much if one of those fails they cost 50 cents each.

>>

>> Then my plan is to make some kind of output protection and see if it

>> degrades performance. I've read that it does and that I should simply

>> use

>> Speakon connectors that you can't short and fuse the power supply. I

>> figure with cheat 50 cent output transistor I can experiment and

>> intentionally short them

>>

>> My goal is a 250 WPC amp with THD in the 0.001 range to drive a pair of

>> 1970's vintage infinity speakers like these:

>> Infinity QLS www.bobbyshred.com/infinity/QLS.html>

>> These are 82dB 3 or 4 ohm speakers and will suck up any amount of

>> available

>> power.

>>

>> I want an amp that can do 250 WPC into 8 ohms and more into 4 ohms. But

>> I'll build it in modular parts. An input section with 2N5401/2N5551

>> transistors, a power supply and an output stage so I can upgrade any of

>> those.

>>

>>

>> Eventually I'll build something based on it. I need to add some kind of

>> sort protection and a real power supply as I cent seem to find those zero

>> impedance LTSpice voltage sources anywhere.

>>

>> But first I think I'll build a cheaper/simpler amp using TIP41C/TIP42C

>> output transistors

>>

>

>

>

---------------

>

> Always keep electrons and holes flowing in opposite directions.Yahoo!

> Groups Links

>

>

>

>







----------------------------

#863 Jun 23, 2012

Greetings from FixitLand!



Fearless Leader Max Robinson wrote:

> The transistor amp circuit that was used for years and is still

> used in some

> amps, drives the speaker off the emitter of the top transistor on the

> positive half cycle and the collector of the bottom transistor on the

> negative half cycle. I have never thought that was a good amplifier

> design. It was done for economic reasons. In the earliest days when

> germanium transistors were all you could get NPNs were much more

> expensive

> than the commonly used PNPs. When silicon transistors became

> available PNPs

> cost a lot more. The standard circuit an example of which can be

> found in

> the Heath AR 15, needed only one PNP transistor and the rest were

> NPNs.

> Although the asymmetry can be cleaned up with NFB, this in my

> opinion is the

> wrong way to design an amplifier.



That "El Cheapo" pseudo-complementary-symmetry amp is detailed on Rod

Elliot's audio pages:



sound.westhost.com/project12a.htm



We built essentially the same amplifier in high school back in

'71-'72. It used coils of Nichrome wire for the 0.47-ohm resistors in

the output stage, which caused no end of problems. That was probably

part of the training exercise. Lots of 2N3055 transistors got burnt

out in our class. Instead of 1000-uF output caps, we had 4700-uF

computer-type huge cans with screw terminals. Ours was the first

class to build solid-state amplifiers (darn it! I missed 6L6s by ONE

YEAR). Got mine to work (sorta) but it got stolen! A few years later

I built another one (sans the Nichrome wire!!) and used it for years

until finally building a 6L6 amp in 2007.



Take care,





Joe

--

"It is impossible for a lover of cats to banish these alert, gentle

and discriminating friends, who give us just enough of their regard

and complaisance to make us hunger for more."--Agnes Repplier

(1855-1950), U.S. essayist



----------------------------

#864 Jun 23, 2012

When I designed my 200 watt per channel amplifier I had a long debate with

myself about how much capability to give the power supply. Listening, as

opposed to musical instrument amplification, does not call upon the power

supply to deliver the full power. Even if you are listening at such a high

level that you hit occasional peaks at 200 watts the average power is still

about 1/4 of the peak. (SWAG). So the power supply could be much smaller

than you would think. Some manufacturers did in fact sell amps like this.

The only way to test them was to operate them from lab power supplies for

testing. I ended up putting in the full capability supply. I tested the

power supply with load resistors before finishing the amplifier. It

delivered plus and minus 60 volts at 5 amps.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

Music site: www.maxsmusicplace.com



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----- Original Message -----

From: "J Ed" jedwardsat1@...>

To: funwithtransistors@yahoogroups.com>

Sent: Saturday, June 23, 2012 12:35 AM

Subject: Re: [funwithtransistors] Re: Question about transistor amp

schematic





> If I wanted to build an amp with 100 WPC, what kind of power transformer

> would I need? I'd obviously get one that had between 150-200 VA of power

> but what kind of voltage and current ratings are we talking? When you have

> to take an AC power level, convert it to DC, and then back to AC, things

> get kind of confusing for me...

>

> 100 watts into 8 ohms requires a peak-to-peak voltage of 80 (E^2 / R =

> P...E = sqrt(PR)...sqrt(100 * 8)...28.28VRMS). This means I need to get a

> transformer that can give me a 40-0-40 supply (probably a 65-70 VAC

> winding) with a current capability of 3500 mA. I would probably look at a

> transformer with a capability for 70-0-70 VDC at 5A. Being that this is

> one

> channel, I'd probably have to go out and get a second transformer unless I

> wanted to buy one with an 8A capacity.

>

> Granted, I'll never likely need the full 100w.

> Ed

>



----------------------------

#865 Jun 23, 2012

1) Welding machines often��have a��duty cycle that is less than 100% (some less than 20%), so derate accordingly.2) Welding transformers are not designed to be especially quiet, so expect to hear them hum while they are running.��Jerry F.



From: J Ed jedwardsat1@...>To: funwithtransistors@yahoogroups.comSent: Sat, June 23, 2012 12:00:13 AMSubject: Re: [funwithtransistors] Re: Question about transistor amp schematic

��What if I took a broken welder or other high-power device and got the transformer out of that?

Ed

On Fri, Jun 22, 2012 at 11:37 PM, Chris Albertson albertson.chris@...> wrote:��

On Fri, Jun 22, 2012 at 10:35 PM, J Ed jedwardsat1@...> wrote:��If I wanted to build an amp with 100 WPC, what kind of power transformer would I need? I'd obviously get one that had between 150-200 VA of power but what kind of voltage and current ratings are we talking?







----------------------------

#866 Jun 23, 2012

Be careful with such a high current. You don't want your electrons to

get welded to their holes :)



Chris







Gerald Feldman wrote: >

> 1) Welding machines often have a duty cycle that is less than 100%

> (some less than 20%), so derate accordingly.

> 2) Welding transformers are not designed to be especially quiet, so

> expect to hear them hum while they are running.

>

> Jerry F.

>

---------------

> *From:* J Ed jedwardsat1@...>

> *To:* funwithtransistors@yahoogroups.com

> *Sent:* Sat, June 23, 2012 12:00:13 AM

> *Subject:* Re: [funwithtransistors] Re: Question about transistor amp

> schematic

>

>

>

> What if I took a broken welder or other high-power device and got the

> transformer out of that?

>

> Ed

>

> On Fri, Jun 22, 2012 at 11:37 PM, Chris Albertson

> albertson.chris@... mailto:albertson.chris@...>> wrote:

>

>

>

>

>

> On Fri, Jun 22, 2012 at 10:35 PM, J Ed jedwardsat1@...

> mailto:jedwardsat1@...>> wrote:

>

>

>

> If I wanted to build an amp with 100 WPC, what kind of power

> transformer would I need? I'd obviously get one that had

> between 150-200 VA of power but what kind of voltage and

> current ratings are we talking?

>

>

> A simple rule of thumb is to look at the total power output of the

> amp and then double that. So 100 WPC is 200VA total so get a 400

> VA transformer. Antek has them for $51. But for $57 you can

> have 500 VA. That would be my pick

>

> Chris Albertson

> Redondo Beach, California

>

>

>



----------------------------

#867 Jun 23, 2012

--- On Sat, 6/23/12, Gerald Feldman gfeldman2904@...> wrote:

> From: Gerald Feldman gfeldman2904@...>

> Subject: Re: [funwithtransistors] Re: Question about transistor amp schematic

> To: funwithtransistors@yahoogroups.com

> Date: Saturday, June 23, 2012, 4:06 PM

>

> 1) Welding machines often.have a.duty cycle that is less than 100%

> (some less than 20%), so derate accordingly.

> 2) Welding transformers are not designed to be especially quiet,

> so expect to hear them hum while they are running.



Some may have enough leakage inductance to limit the arc current

(Remember that an arc is a negative resistance creature, and, once

struck, will pull more and more current until something limits it.).

As such, the voltage regulation may be exceptionally poor.

. > Jerry F.



Dave



----------------------------

#868 Jun 24, 2012

I never liked the NPN transistor driving the (-) half cycle either, but in the circuits defence it did have a PNP driving it in a quazi-darlington configuration to make it behave sonewhat like an NPN darlington. Ge were mostly PNP and early Si were NPN, I was so glad to see Si PNP compliments becoming more common.

--- In funwithtransistors@yahoogroups.com, "Max Robinson" max@...> wrote:

>

> The transistor amp circuit that was used for years and is still used in some

> amps, drives the speaker off the emitter of the top transistor on the

> positive half cycle and the collector of the bottom transistor on the

> negative half cycle. I have never thought that was a good amplifier

> design. It was done for economic reasons. In the earliest days when

> germanium transistors were all you could get NPNs were much more expensive

> than the commonly used PNPs. When silicon transistors became available PNPs

> cost a lot more. The standard circuit an example of which can be found in

> the Heath AR 15, needed only one PNP transistor and the rest were NPNs.

> Although the asymmetry can be cleaned up with NFB, this in my opinion is the

> wrong way to design an amplifier.

>

> Regards.

>

> Max. K 4 O DS.

>

> Email: max@...

>

> Transistor site www.funwithtransistors.net

> Vacuum tube site: www.funwithtubes.net

> Woodworking site

> www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

> Music site: www.maxsmusicplace.com

>

> To subscribe to the fun with transistors group send an email to.

> funwithtransistors-subscribe@yahoogroups.com

>

> To subscribe to the fun with tubes group send an email to,

> funwithtubes-subscribe@yahoogroups.com

>

> To subscribe to the fun with wood group send a blank email to

> funwithwood-subscribe@yahoogroups.com

>

> ----- Original Message -----

> From: "Den" engineer_musician@...>

> To: funwithtransistors@yahoogroups.com>

> Sent: Friday, June 22, 2012 11:40 PM

> Subject: [funwithtransistors] Re: Question about transistor amp schematic

>

>

> > Wow 250 WPC is a lot of PT, I don't have any iron that can do that twice.

> > I'd have to make 2 mono blocks. 100WPC at 8 ohm is the one I built. Did

> > you see it in the Photos here? I usually put an ohm or 2 in my LT-Spice

> > voltage sources and/or a forward biased diode in series with it to make it

> > a little more real. This was my second SS power amp design. I didn't

> > like my first with the dynamic current source driving opposite the

> > constant current source, waveform lacked symetry, I'm splitting hairs

> > here, but the + half of the wave didn't match the - half as much as it

> > could. So I did a full complimentary design from input to output, even

> > the diff-amps. I did the single sided PCB with tape and knife on mylar

> > back in the 70s. Check it out.

> >

> > OBTW, for all that power don't skimp on the heat sinks. When Phase Linear

> > first came out with the 400 and 700, they would blow up on the bench just

> > trying to test them at full power for a THD measurement, not enough heat

> > sink. Later Dynaco came out with their 400, lots of heatsink and a place

> > to add a muffin fan. My band used one for the monitors, never failed.

> >

> > --- In funwithtransistors@yahoogroups.com, Chris Albertson

> > albertson.chris@> wrote:

> >>

> >> On Fri, Jun 22, 2012 at 11:43 AM, Den engineer_musician@> wrote:

> >>

> >> > **

> >> >

> >> >

> >> > OBTW Chris, this design has no output short protection. Do you plan on

> >> > adding some? Looks like LT-Spice, I use it a lot. Denis.

> >> >

> >> I just built this schematic to study.

> >>

> >> I think I will build the input and voltage amplifier sections first. I

> >> find that I can buy 2N5401 and 2N5551 for 4 cents each if I buy a 100 at

> >> a

> >> time. These are 100 volt transistors and seem to be the preferred part

> >> for

> >> this kind of amplifier.

> >>

> >> Then might make a cheap output section with TIP41C/TIP42C transistors and

> >> not care to much if one of those fails they cost 50 cents each.

> >>

> >> Then my plan is to make some kind of output protection and see if it

> >> degrades performance. I've read that it does and that I should simply

> >> use

> >> Speakon connectors that you can't short and fuse the power supply. I

> >> figure with cheat 50 cent output transistor I can experiment and

> >> intentionally short them

> >>

> >> My goal is a 250 WPC amp with THD in the 0.001 range to drive a pair of

> >> 1970's vintage infinity speakers like these:

> >> Infinity QLS www.bobbyshred.com/infinity/QLS.html>

> >> These are 82dB 3 or 4 ohm speakers and will suck up any amount of

> >> available

> >> power.

> >>

> >> I want an amp that can do 250 WPC into 8 ohms and more into 4 ohms. But

> >> I'll build it in modular parts. An input section with 2N5401/2N5551

> >> transistors, a power supply and an output stage so I can upgrade any of

> >> those.

> >>

> >>

> >> Eventually I'll build something based on it. I need to add some kind of

> >> sort protection and a real power supply as I cent seem to find those zero

> >> impedance LTSpice voltage sources anywhere.

> >>

> >> But first I think I'll build a cheaper/simpler amp using TIP41C/TIP42C

> >> output transistors

> >>

> >

> >

> >

---------------

> >

> > Always keep electrons and holes flowing in opposite directions.Yahoo!

> > Groups Links

> >

> >

> >

> >

>







----------------------------

#869 Jun 24, 2012

If I had a nickle for ever 2N3055 I replaced in the late 60s in amps that didn't short protection I'd be rich. What made me laugh even more were the ones that had fast blow fuses on the +/-DC supplying the output transistors. Back then we didn't know Si was way faster than fuse filiments. The outputs always blew first and then took out the fuses.

--- In funwithtransistors@yahoogroups.com, "J. E. Knox" rojoknox@...> wrote:

>

> Greetings from FixitLand!

>

> Fearless Leader Max Robinson wrote:

>

> > The transistor amp circuit that was used for years and is still

> > used in some

> > amps, drives the speaker off the emitter of the top transistor on the

> > positive half cycle and the collector of the bottom transistor on the

> > negative half cycle. I have never thought that was a good amplifier

> > design. It was done for economic reasons. In the earliest days when

> > germanium transistors were all you could get NPNs were much more

> > expensive

> > than the commonly used PNPs. When silicon transistors became

> > available PNPs

> > cost a lot more. The standard circuit an example of which can be

> > found in

> > the Heath AR 15, needed only one PNP transistor and the rest were

> > NPNs.

> > Although the asymmetry can be cleaned up with NFB, this in my

> > opinion is the

> > wrong way to design an amplifier.

>

> That "El Cheapo" pseudo-complementary-symmetry amp is detailed on Rod

> Elliot's audio pages:

>

> sound.westhost.com/project12a.htm

>

> We built essentially the same amplifier in high school back in

> '71-'72. It used coils of Nichrome wire for the 0.47-ohm resistors in

> the output stage, which caused no end of problems. That was probably

> part of the training exercise. Lots of 2N3055 transistors got burnt

> out in our class. Instead of 1000-uF output caps, we had 4700-uF

> computer-type huge cans with screw terminals. Ours was the first

> class to build solid-state amplifiers (darn it! I missed 6L6s by ONE

> YEAR). Got mine to work (sorta) but it got stolen! A few years later

> I built another one (sans the Nichrome wire!!) and used it for years

> until finally building a 6L6 amp in 2007.

>

> Take care,

>

>

> Joe

> --

> "It is impossible for a lover of cats to banish these alert, gentle

> and discriminating friends, who give us just enough of their regard

> and complaisance to make us hunger for more."--Agnes Repplier

> (1855-1950), U.S. essayist

>



----------------------------

#870 Jun 24, 2012

On Fri, Jun 22, 2012 at 9:40 PM, Den engineer_musician@...> wrote:

.Wow 250 WPC is a lot of PT, I don't have any iron that can do that twice.



----------------------------

#871 Jun 24, 2012

On Sat, Jun 23, 2012 at 1:03 AM, Dave dave.g4ugm@...> wrote:

.ScrapSalvage.used to be a common way to get a transformer for Ham Radio Linearso I guess its OK here, but there a few points to watch:- Besure it isn't the transformer that hasn't failed besure its the right ratings besure its isolation is good..

Notsure about electric welders but many special purpose PSUs use "novel" techniquesto limit the current. So certainly in the UK a car battery charger will have atransformer that's deliberately designed to have poor regulation. Not sure if acar charger uses the same techniques... .Personally I would look for a quality toroidal....



----------------------------

#872 Jun 24, 2012

That's true but you still have the asymmetry of two PN junctions between the

driver and the output on top and one junction on the bottom.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

Music site: www.maxsmusicplace.com



To subscribe to the fun with transistors group send an email to.

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----- Original Message -----

From: "Den" engineer_musician@...>

To: funwithtransistors@yahoogroups.com>

Sent: Saturday, June 23, 2012 9:12 PM

Subject: [funwithtransistors] Re: Question about transistor amp schematic





>I never liked the NPN transistor driving the (-) half cycle either, but in

>the circuits defence it did have a PNP driving it in a quazi-darlington

>configuration to make it behave sonewhat like an NPN darlington. Ge were

>mostly PNP and early Si were NPN, I was so glad to see Si PNP compliments

>becoming more common.

>

> --- In funwithtransistors@yahoogroups.com, "Max Robinson" max@...> wrote:

>>

>> The transistor amp circuit that was used for years and is still used in

>> some

>> amps, drives the speaker off the emitter of the top transistor on the

>> positive half cycle and the collector of the bottom transistor on the

>> negative half cycle. I have never thought that was a good amplifier

>> design. It was done for economic reasons. In the earliest days when

>> germanium transistors were all you could get NPNs were much more

>> expensive

>> than the commonly used PNPs. When silicon transistors became available

>> PNPs

>> cost a lot more. The standard circuit an example of which can be found

>> in

>> the Heath AR 15, needed only one PNP transistor and the rest were NPNs.

>> Although the asymmetry can be cleaned up with NFB, this in my opinion is

>> the

>> wrong way to design an amplifier.

>>

>> Regards.

>>

>> Max. K 4 O DS.

>>

>> Email: max@...

>>

>> Transistor site www.funwithtransistors.net

>> Vacuum tube site: www.funwithtubes.net

>> Woodworking site

>> www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

>> Music site: www.maxsmusicplace.com

>>

>> To subscribe to the fun with transistors group send an email to.

>> funwithtransistors-subscribe@yahoogroups.com

>>

>> To subscribe to the fun with tubes group send an email to,

>> funwithtubes-subscribe@yahoogroups.com

>>

>> To subscribe to the fun with wood group send a blank email to

>> funwithwood-subscribe@yahoogroups.com

>>

>> ----- Original Message -----

>> From: "Den" engineer_musician@...>

>> To: funwithtransistors@yahoogroups.com>

>> Sent: Friday, June 22, 2012 11:40 PM

>> Subject: [funwithtransistors] Re: Question about transistor amp schematic

>>

>>

>> > Wow 250 WPC is a lot of PT, I don't have any iron that can do that

>> > twice.

>> > I'd have to make 2 mono blocks. 100WPC at 8 ohm is the one I built.

>> > Did

>> > you see it in the Photos here? I usually put an ohm or 2 in my

>> > LT-Spice

>> > voltage sources and/or a forward biased diode in series with it to make

>> > it

>> > a little more real. This was my second SS power amp design. I didn't

>> > like my first with the dynamic current source driving opposite the

>> > constant current source, waveform lacked symetry, I'm splitting hairs

>> > here, but the + half of the wave didn't match the - half as much as it

>> > could. So I did a full complimentary design from input to output, even

>> > the diff-amps. I did the single sided PCB with tape and knife on mylar

>> > back in the 70s. Check it out.

>> >

>> > OBTW, for all that power don't skimp on the heat sinks. When Phase

>> > Linear

>> > first came out with the 400 and 700, they would blow up on the bench

>> > just

>> > trying to test them at full power for a THD measurement, not enough

>> > heat

>> > sink. Later Dynaco came out with their 400, lots of heatsink and a

>> > place

>> > to add a muffin fan. My band used one for the monitors, never failed.

>> >

>> > --- In funwithtransistors@yahoogroups.com, Chris Albertson

>> > albertson.chris@> wrote:

>> >>

>> >> On Fri, Jun 22, 2012 at 11:43 AM, Den engineer_musician@> wrote:

>> >>

>> >> > **

>> >> >

>> >> >

>> >> > OBTW Chris, this design has no output short protection. Do you plan

>> >> > on

>> >> > adding some? Looks like LT-Spice, I use it a lot. Denis.

>> >> >

>> >> I just built this schematic to study.

>> >>

>> >> I think I will build the input and voltage amplifier sections first.

>> >> I

>> >> find that I can buy 2N5401 and 2N5551 for 4 cents each if I buy a 100

>> >> at

>> >> a

>> >> time. These are 100 volt transistors and seem to be the preferred

>> >> part

>> >> for

>> >> this kind of amplifier.

>> >>

>> >> Then might make a cheap output section with TIP41C/TIP42C transistors

>> >> and

>> >> not care to much if one of those fails they cost 50 cents each.

>> >>

>> >> Then my plan is to make some kind of output protection and see if it

>> >> degrades performance. I've read that it does and that I should

>> >> simply

>> >> use

>> >> Speakon connectors that you can't short and fuse the power supply.

>> >> I

>> >> figure with cheat 50 cent output transistor I can experiment and

>> >> intentionally short them

>> >>

>> >> My goal is a 250 WPC amp with THD in the 0.001 range to drive a pair

>> >> of

>> >> 1970's vintage infinity speakers like these:

>> >> Infinity QLS www.bobbyshred.com/infinity/QLS.html>

>> >> These are 82dB 3 or 4 ohm speakers and will suck up any amount of

>> >> available

>> >> power.

>> >>

>> >> I want an amp that can do 250 WPC into 8 ohms and more into 4 ohms.

>> >> But

>> >> I'll build it in modular parts. An input section with 2N5401/2N5551

>> >> transistors, a power supply and an output stage so I can upgrade any

>> >> of

>> >> those.

>> >>

>> >>

>> >> Eventually I'll build something based on it. I need to add some kind

>> >> of

>> >> sort protection and a real power supply as I cent seem to find those

>> >> zero

>> >> impedance LTSpice voltage sources anywhere.

>> >>

>> >> But first I think I'll build a cheaper/simpler amp using TIP41C/TIP42C

>> >> output transistors

>> >>

>> >

>> >

>> >

---------------

>> >

>> > Always keep electrons and holes flowing in opposite directions.Yahoo!

>> > Groups Links

>> >

>> >

>> >

>> >

>>

>

>

>

>

---------------

>

> Always keep electrons and holes flowing in opposite directions.Yahoo!

> Groups Links

>

>

>

>







----------------------------

#873 Jun 24, 2012

That's one of the original Murphy's laws. "A semiconductor device protected

by a fuse will protect the fuse by burning out first". This requires a bit

of suspension of disbelief. In fact the semiconductor shorts which then

takes out the fuse.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

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----- Original Message -----

From: "Den" engineer_musician@...>

To: funwithtransistors@yahoogroups.com>

Sent: Saturday, June 23, 2012 9:18 PM

Subject: [funwithtransistors] Re: Question about transistor amp schematic





> If I had a nickle for ever 2N3055 I replaced in the late 60s in amps that

> didn't short protection I'd be rich. What made me laugh even more were

> the ones that had fast blow fuses on the +/-DC supplying the output

> transistors. Back then we didn't know Si was way faster than fuse

> filiments. The outputs always blew first and then took out the fuses.

>

> --- In funwithtransistors@yahoogroups.com, "J. E. Knox" rojoknox@...>

> wrote:

>>

>> Greetings from FixitLand!

>>

>> Fearless Leader Max Robinson wrote:

>>

>> > The transistor amp circuit that was used for years and is still

>> > used in some

>> > amps, drives the speaker off the emitter of the top transistor on the

>> > positive half cycle and the collector of the bottom transistor on the

>> > negative half cycle. I have never thought that was a good amplifier

>> > design. It was done for economic reasons. In the earliest days when

>> > germanium transistors were all you could get NPNs were much more

>> > expensive

>> > than the commonly used PNPs. When silicon transistors became

>> > available PNPs

>> > cost a lot more. The standard circuit an example of which can be

>> > found in

>> > the Heath AR 15, needed only one PNP transistor and the rest were

>> > NPNs.

>> > Although the asymmetry can be cleaned up with NFB, this in my

>> > opinion is the

>> > wrong way to design an amplifier.

>>

>> That "El Cheapo" pseudo-complementary-symmetry amp is detailed on Rod

>> Elliot's audio pages:

>>

>> sound.westhost.com/project12a.htm

>>

>> We built essentially the same amplifier in high school back in

>> '71-'72. It used coils of Nichrome wire for the 0.47-ohm resistors in

>> the output stage, which caused no end of problems. That was probably

>> part of the training exercise. Lots of 2N3055 transistors got burnt

>> out in our class. Instead of 1000-uF output caps, we had 4700-uF

>> computer-type huge cans with screw terminals. Ours was the first

>> class to build solid-state amplifiers (darn it! I missed 6L6s by ONE

>> YEAR). Got mine to work (sorta) but it got stolen! A few years later

>> I built another one (sans the Nichrome wire!!) and used it for years

>> until finally building a 6L6 amp in 2007.

>>

>> Take care,

>>

>>

>> Joe

>> --

>> "It is impossible for a lover of cats to banish these alert, gentle

>> and discriminating friends, who give us just enough of their regard

>> and complaisance to make us hunger for more."--Agnes Repplier

>> (1855-1950), U.S. essayist

>>

>

>

>

>

---------------

>

> Always keep electrons and holes flowing in opposite directions.Yahoo!

> Groups Links

>

>

>

>



----------------------------

#874 Jun 24, 2012

I think the fuse is there not to protect a cheap 2N3055 but to protect the transformer. .At least that is why I fuse DC power supplies

On Sat, Jun 23, 2012 at 9:38 PM, Max Robinson max@...> wrote:

.That's one of the original Murphy's laws. "A semiconductor device protected

by a fuse will protect the fuse by burning out first". This requires a bit

of suspension of disbelief. In fact the semiconductor shorts which then

takes out the fuse.



----------------------------

#875 Jun 24, 2012

Without a doubt.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Sunday, June 24, 2012 12:34 AM

Subject: Re: [funwithtransistors] Re: Question about transistor amp

schematic





>I think the fuse is there not to protect a cheap 2N3055 but to protect the

> transformer. At least that is why I fuse DC power supplies

>

> On Sat, Jun 23, 2012 at 9:38 PM, Max Robinson

> max@...>wrote:

>

>> **

>>

>>

>> That's one of the original Murphy's laws. "A semiconductor device

>> protected

>> by a fuse will protect the fuse by burning out first". This requires a

>> bit

>> of suspension of disbelief. In fact the semiconductor shorts which then

>> takes out the fuse.

>>

>>

>>

> --

>

> Chris Albertson

> Redondo Beach, California

>







----------------------------

#876 Jun 24, 2012

I've read some articles on overload/short protection and have seen how some of them alter the sound. I was going to simply install rail fuses but I'm reconsidering now.

Ed

On Sun, Jun 24, 2012 at 9:51 AM, Max Robinson max@...> wrote:

.Without a doubt.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

Music site: www.maxsmusicplace.com



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----- Original Message -----

From: "Chris Albertson" albertson.chris@...>

To: funwithtransistors@yahoogroups.com>

Sent: Sunday, June 24, 2012 12:34 AM

Subject: Re: [funwithtransistors] Re: Question about transistor amp

schematic



>I think the fuse is there not to protect a cheap 2N3055 but to protect the

> transformer. At least that is why I fuse DC power supplies

>

> On Sat, Jun 23, 2012 at 9:38 PM, Max Robinson

> max@...>wrote:

>

>> **

>>

>>

>> That's one of the original Murphy's laws. "A semiconductor device

>> protected

>> by a fuse will protect the fuse by burning out first". This requires a

>> bit

>> of suspension of disbelief. In fact the semiconductor shorts which then

>> takes out the fuse.

>>

>>

>>

> --

>

> Chris Albertson

> Redondo Beach, California

>



----------------------------

#877 Jun 24, 2012

Ed. Think again. Rail fuses add a small amount of impedance to the power

supplies which already have a non zero impedance. Unless your power

supplies are tightly regulated electronically the added impedance of the

fuse will get lost in the natural impedance of the power supply.



Regards.



Max. K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

Music site: www.maxsmusicplace.com



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----- Original Message -----

From: "J Ed" jedwardsat1@...>

To: funwithtransistors@yahoogroups.com>

Sent: Sunday, June 24, 2012 11:57 AM

Subject: Re: [funwithtransistors] Re: Question about transistor amp

schematic





I've read some articles on overload/short protection and have seen how some

of them alter the sound. I was going to simply install rail fuses but I'm

reconsidering now.



Ed



On Sun, Jun 24, 2012 at 9:51 AM, Max Robinson max@...>wrote:



> **

>

>

> Without a doubt.

>

>

> Regards.

>

> Max. K 4 O DS.

>

> Email: max@...

>

> Transistor site www.funwithtransistors.net

> Vacuum tube site: www.funwithtubes.net

> Woodworking site

> www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

> Music site: www.maxsmusicplace.com

>

> To subscribe to the fun with transistors group send an email to.

> funwithtransistors-subscribe@yahoogroups.com

>

> To subscribe to the fun with tubes group send an email to,

> funwithtubes-subscribe@yahoogroups.com

>

> To subscribe to the fun with wood group send a blank email to

> funwithwood-subscribe@yahoogroups.com

>

> ----- Original Message -----

> From: "Chris Albertson" albertson.chris@...>

> To: funwithtransistors@yahoogroups.com>

> Sent: Sunday, June 24, 2012 12:34 AM

> Subject: Re: [funwithtransistors] Re: Question about transistor amp

> schematic

>

> >I think the fuse is there not to protect a cheap 2N3055 but to protect

> >the

> > transformer. At least that is why I fuse DC power supplies

> >

> > On Sat, Jun 23, 2012 at 9:38 PM, Max Robinson

> > max@...>wrote:

> >

> >> **

>

> >>

> >>

> >> That's one of the original Murphy's laws. "A semiconductor device

> >> protected

> >> by a fuse will protect the fuse by burning out first". This requires a

> >> bit

> >> of suspension of disbelief. In fact the semiconductor shorts which then

> >> takes out the fuse.

> >>

> >>

> >>

> > --

> >

> > Chris Albertson

> > Redondo Beach, California

> >

>

>

>







----------------------------

#878 Jun 24, 2012

I meant that the protection circuits I researched added distortion to the output signal. The reason I am not using fuses as an output protection (they will still be there) is to protect my transformer/power supply. Like someone said, the output transistors won't be saved by a fuse and they costs maybe $1.50 each. The transformer will be upwards of $40-60. I'm hardly worried about the fuse impedance.

I did once read a discussion about this by 'philes. One guy was bragging about how he sanded the endcaps of fuses with 400g paper to remove the metallic sound caused by the nickel coating. Another guy was boasting about the $80 silver fuses he special-ordered from Germany. I'm not kidding, this was a real thread.

Ed

On Sun, Jun 24, 2012 at 10:03 AM, Max Robinson max@...> wrote:

Ed. .Think again. .Rail fuses add a small amount of impedance to the power

supplies which already have a non zero impedance. .Unless your power

supplies are tightly regulated electronically the added impedance of the

fuse will get lost in the natural impedance of the power supply.

Regards.



Max. .K 4 O DS.



Email: max@...



Transistor site www.funwithtransistors.net

Vacuum tube site: www.funwithtubes.net

Woodworking site

www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

Music site: www.maxsmusicplace.com



To subscribe to the fun with transistors group send an email to.

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----- Original Message -----

From: "J Ed" jedwardsat1@...>

To: funwithtransistors@yahoogroups.com>

Sent: Sunday, June 24, 2012 11:57 AM

Subject: Re: [funwithtransistors] Re: Question about transistor amp

schematic





I've read some articles on overload/short protection and have seen how some

of them alter the sound. I was going to simply install rail fuses but I'm

reconsidering now.



Ed



On Sun, Jun 24, 2012 at 9:51 AM, Max Robinson max@...>wrote:



> **>

>

> Without a doubt.

>

>

> Regards.

>

> Max. K 4 O DS.

>

> Email: max@...

>

> Transistor site www.funwithtransistors.net

> Vacuum tube site: www.funwithtubes.net

> Woodworking site

> www.angelfire.com/electronic/funwithtubes/Woodworking/wwindex.html

> Music site: www.maxsmusicplace.com

>

> To subscribe to the fun with transistors group send an email to.

> funwithtransistors-subscribe@yahoogroups.com

>

> To subscribe to the fun with tubes group send an email to,

> funwithtubes-subscribe@yahoogroups.com

>

> To subscribe to the fun with wood group send a blank email to

> funwithwood-subscribe@yahoogroups.com

>

> ----- Original Message -----

> From: "Chris Albertson" albertson.chris@...>

> To: funwithtransistors@yahoogroups.com>

> Sent: Sunday, June 24, 2012 12:34 AM

> Subject: Re: [funwithtransistors] Re: Question about transistor amp

> schematic

>

> >I think the fuse is there not to protect a cheap 2N3055 but to protect

> >the

> > transformer. At least that is why I fuse DC power supplies

> >

> > On Sat, Jun 23, 2012 at 9:38 PM, Max Robinson

> > max@...>wrote:

> >

> >> **

>

> >>

> >>

> >> That's one of the original Murphy's laws. "A semiconductor device

> >> protected

> >> by a fuse will protect the fuse by burning out first". This requires a

> >> bit

> >> of suspension of disbelief. In fact the semiconductor shorts which then

> >> takes out the fuse.

> >>

> >>

> >>

> > --

> >

> > Chris Albertson

> > Redondo Beach, California

> >

>

>

>



----------------------------

#879 Jun 25, 2012

I agree that even a well designed active short protection will add some distortion, but it's very littl and only at full power. Besides if you consider the amount of distortion each peace of equipment adds to the signal the power amp is the least of your worries. The NFB in your power amp is there to reduce distortion and other things not important to this discussion right now. Your preamp has NFB for the same reasons. As long as these components are 0.1% or less I don't think you need to be too concerned about 0.001%. Speakers are a non-FB current device not voltage, the position of the voice coil is solely dependent on the current running thru it and not very linear at that. 10% THD is donig good for any speaker system, so who cares if you have 10.1% ot 10.001% THD. I challange any one to tell the difference in a true blind test where the only difference between 2 amps is the THD.



OBTW, there needs to be more attention to IMD as well as THD, and when ther is you'll discover that as THD goes down IMD goes up. I prefer a healthy balance between the 2. Either one alters the tone and timber of the sound.

--- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@...> wrote:

>

> I meant that the protection circuits I researched added distortion to the

> output signal. The reason I am not using fuses as an output protection

> (they will still be there) is to protect my transformer/power supply. Like

> someone said, the output transistors won't be saved by a fuse and they

> costs maybe $1.50 each. The transformer will be upwards of $40-60. I'm

> hardly worried about the fuse impedance.

>

> I did once read a discussion about this by 'philes. One guy was bragging

> about how he sanded the endcaps of fuses with 400g paper to remove the

> metallic sound caused by the nickel coating. Another guy was boasting about

> the $80 silver fuses he special-ordered from Germany. I'm not kidding, this

> was a real thread.

>

> Ed

>







----------------------------

#880 Jun 25, 2012

I didn't realize that speakers had such high distortion. It kind of puts things in perspective. I still need to read more on how to implement speaker and short protection devices...before I build my wild and crazy amplifier I want to be able to prevent it from blowing up expensive drivers.

Ed

On Sun, Jun 24, 2012 at 5:36 PM, Den engineer_musician@...> wrote:

.I agree that even a well designed active short protection will add some distortion, but it's very littl and only at full power. Besides if you consider the amount of distortion each peace of equipment adds to the signal the power amp is the least of your worries. The NFB in your power amp is there to reduce distortion and other things not important to this discussion right now. Your preamp has NFB for the same reasons. As long as these components are 0.1% or less I don't think you need to be too concerned about 0.001%. Speakers are a non-FB current device not voltage, the position of the voice coil is solely dependent on the current running thru it and not very linear at that. 10% THD is donig good for any speaker system, so who cares if you have 10.1% ot 10.001% THD. I challange any one to tell the difference in a true blind test where the only difference between 2 amps is the THD.

OBTW, there needs to be more attention to IMD as well as THD, and when ther is you'll discover that as THD goes down IMD goes up. I prefer a healthy balance between the 2. Either one alters the tone and timber of the sound.



--- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@...> wrote:

>

> I meant that the protection circuits I researched added distortion to the

> output signal. The reason I am not using fuses as an output protection

> (they will still be there) is to protect my transformer/power supply. Like

> someone said, the output transistors won't be saved by a fuse and they

> costs maybe $1.50 each. The transformer will be upwards of $40-60. I'm

> hardly worried about the fuse impedance.

>

> I did once read a discussion about this by 'philes. One guy was bragging

> about how he sanded the endcaps of fuses with 400g paper to remove the

> metallic sound caused by the nickel coating. Another guy was boasting about

> the $80 silver fuses he special-ordered from Germany. I'm not kidding, this

> was a real thread.

>

> Ed

>



----------------------------

#884 Jun 25, 2012

Hi Ed, I started putting fast blow fuses in my speaker cabs so I could protect them at their power rating even if I put them on an amp way more than that.



I used one of the more typical short protections in my design in the Phosos here.

--- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@...> wrote:

>

> I didn't realize that speakers had such high distortion. It kind of puts

> things in perspective. I still need to read more on how to implement

> speaker and short protection devices...before I build my wild and crazy

> amplifier I want to be able to prevent it from blowing up expensive drivers.

>

> Ed

>

> On Sun, Jun 24, 2012 at 5:36 PM, Den engineer_musician@...> wrote:

>

> > **

> >

> >

> > I agree that even a well designed active short protection will add some

> > distortion, but it's very littl and only at full power. Besides if you

> > consider the amount of distortion each peace of equipment adds to the

> > signal the power amp is the least of your worries. The NFB in your power

> > amp is there to reduce distortion and other things not important to this

> > discussion right now. Your preamp has NFB for the same reasons. As long as

> > these components are 0.1% or less I don't think you need to be too

> > concerned about 0.001%. Speakers are a non-FB current device not voltage,

> > the position of the voice coil is solely dependent on the current running

> > thru it and not very linear at that. 10% THD is donig good for any speaker

> > system, so who cares if you have 10.1% ot 10.001% THD. I challange any one

> > to tell the difference in a true blind test where the only difference

> > between 2 amps is the THD.

> >

> > OBTW, there needs to be more attention to IMD as well as THD, and when

> > ther is you'll discover that as THD goes down IMD goes up. I prefer a

> > healthy balance between the 2. Either one alters the tone and timber of the

> > sound.

> >

> >

> > --- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@> wrote:

> > >

> > > I meant that the protection circuits I researched added distortion to the

> > > output signal. The reason I am not using fuses as an output protection

> > > (they will still be there) is to protect my transformer/power supply.

> > Like

> > > someone said, the output transistors won't be saved by a fuse and they

> > > costs maybe $1.50 each. The transformer will be upwards of $40-60. I'm

> > > hardly worried about the fuse impedance.

> > >

> > > I did once read a discussion about this by 'philes. One guy was bragging

> > > about how he sanded the endcaps of fuses with 400g paper to remove the

> > > metallic sound caused by the nickel coating. Another guy was boasting

> > about

> > > the $80 silver fuses he special-ordered from Germany. I'm not kidding,

> > this

> > > was a real thread.

> > >

> > > Ed

> > >

> >

> >

> >

>







----------------------------

#887 Jun 25, 2012

Fast-blow fuses are all well and good, but if I for some reason decide to hook the speakers up to a tube amplifier, it endangers the entire output stage in case the fuse decided to open.

Ed

On Sun, Jun 24, 2012 at 9:22 PM, Den engineer_musician@...> wrote:

.Hi Ed, I started putting fast blow fuses in my speaker cabs so I could protect them at their power rating even if I put them on an amp way more than that.



I used one of the more typical short protections in my design in the Phosos here.



--- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@...> wrote:

>

> I didn't realize that speakers had such high distortion. It kind of puts

> things in perspective. I still need to read more on how to implement

> speaker and short protection devices...before I build my wild and crazy

> amplifier I want to be able to prevent it from blowing up expensive drivers.

>

> Ed

>

> On Sun, Jun 24, 2012 at 5:36 PM, Den engineer_musician@...> wrote:

>

> > **

> >

> >

> > I agree that even a well designed active short protection will add some

> > distortion, but it's very littl and only at full power. Besides if you

> > consider the amount of distortion each peace of equipment adds to the

> > signal the power amp is the least of your worries. The NFB in your power

> > amp is there to reduce distortion and other things not important to this

> > discussion right now. Your preamp has NFB for the same reasons. As long as

> > these components are 0.1% or less I don't think you need to be too

> > concerned about 0.001%. Speakers are a non-FB current device not voltage,

> > the position of the voice coil is solely dependent on the current running

> > thru it and not very linear at that. 10% THD is donig good for any speaker

> > system, so who cares if you have 10.1% ot 10.001% THD. I challange any one

> > to tell the difference in a true blind test where the only difference

> > between 2 amps is the THD.

> >

> > OBTW, there needs to be more attention to IMD as well as THD, and when

> > ther is you'll discover that as THD goes down IMD goes up. I prefer a

> > healthy balance between the 2. Either one alters the tone and timber of the

> > sound.

> >

> >

> > --- In funwithtransistors@yahoogroups.com, J Ed jedwardsat1@> wrote:

> > >

> > > I meant that the protection circuits I researched added distortion to the

> > > output signal. The reason I am not using fuses as an output protection

> > > (they will still be there) is to protect my transformer/power supply.

> > Like

> > > someone said, the output transistors won't be saved by a fuse and they

> > > costs maybe $1.50 each. The transformer will be upwards of $40-60. I'm

> > > hardly worried about the fuse impedance.

> > >

> > > I did once read a discussion about this by 'philes. One guy was bragging

> > > about how he sanded the endcaps of fuses with 400g paper to remove the

> > > metallic sound caused by the nickel coating. Another guy was boasting

> > about

> > > the $80 silver fuses he special-ordered from Germany. I'm not kidding,

> > this

> > > was a real thread.

> > >

> > > Ed

> > >

> >

> >

> >

>



----------------------------

#888 Jun 25, 2012

On Sun, Jun 24, 2012 at 10:18 PM, J Ed jedwardsat1@...> wrote:

.Fast-blow fuses are all well and good, but if I for some reason decide to hook the speakers up to a tube amplifier, it endangers the entire output stage in case the fuse decided to open.



----------------------------

#890 Jun 25, 2012

Wow, I forgot about the flyback issues of an open output on VT amps, good one, so far I had used these only on SS amps... Waite a minute, this is "funwithtransistors" you've turned this board into a hybrid... waite a minute does that mean this board gets more mpg, where's the battery... I'm so confused...

--- In funwithtransistors@yahoogroups.com, Chris Albertson albertson.chris@...> wrote:

>

> On Sun, Jun 24, 2012 at 10:18 PM, J Ed jedwardsat1@...> wrote:

>

> > **

> >

> >

> > Fast-blow fuses are all well and good, but if I for some reason decide to

> > hook the speakers up to a tube amplifier, it endangers the entire output

> > stage in case the fuse decided to open.

> >

>

> The neat protextion device for a tube amp is a 470 ohm sandstone power

> resister wired arcoss the output terminals. In normal use it robs a very

> slight bit of power from the speaker but not much. A 470 in parallel with

> an 8 or 4 ohm speaker is still close to 8 or 4 ohms. But if you blow a

> speaker or forget to plug one in then 470R is MUCH lower than infinity.

> I've used 270R resistors too. Better protection but more power loss.

>

> I know first hand these work. I've run a few amps on just the 470R safety

> load.

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>



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