Re: [funwithtransistors] TDA2030 Amplifier Issues [1 Attachment]


Apr 19, 2014

 


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

#1700 Apr 19, 2014

Quick Question:



I'm building an amp using TDA2030 chips. The audio quality is not

great and I've been trying to discover why. It hit me tonight...I took

some voltage measurements and found that the applied voltages are

weird. There is a positive and a negative rail, and then there's an

output. The output should be at 0v but it is connected to ground

through the speaker. As far as my meter is concerned, this is

true...the output measures 0.0v when measured against ground.



Here's the funny part...when I measure the rails, the positive rail

measures 22.3v and the negative rail measures -1.7v. This tells me

that the chip isn't balanced enough to be left alone in the circuit.

The problem is that I don't know what to do about it; I could place

two 470-ohm resistors in series across the power supply and ground the

center of them. I don't know that it would be enough to balance the

power supplies. Another idea I had was using an active load where I'd

have a pair of transistors across the line which would hold the ground

point exactly equal distance from the rails.



That's all.

Ed



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

#1701 Apr 19, 2014

You should post a schematic. .Those chips usually have a feedback network. .The chip is really just like a big op amp.

On Sat, Apr 19, 2014 at 2:42 AM, J Ed jedwardsat1@...> wrote:

.Quick Question:



I'm building an amp using TDA2030 chips. The audio quality is not

great and I've been trying to discover why. It hit me tonight...I took

some voltage measurements and found that the applied voltages are

weird. There is a positive and a negative rail, and then there's an

output. The output should be at 0v but it is connected to ground

through the speaker. As far as my meter is concerned, this is

true...the output measures 0.0v when measured against ground.



Here's the funny part...when I measure the rails, the positive rail

measures 22.3v and the negative rail measures -1.7v. This tells me

that the chip isn't balanced enough to be left alone in the circuit.

The problem is that I don't know what to do about it; I could place

two 470-ohm resistors in series across the power supply and ground the

center of them. I don't know that it would be enough to balance the

power supplies. Another idea I had was using an active load where I'd

have a pair of transistors across the line which would hold the ground

point exactly equal distance from the rails.



That's all.

Ed



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

#1702 Apr 19, 2014

www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

The schematic I used was almost straight from the data sheet, maybe with some changed values for resistors. It's almost impossible to screw this up, even though I seem to have found a way. I first thought it was due to some power supply issues or oscillation but I saw the problem when I scoped the input and saw that all of the voltage excursions were positive and the negative half seemed to be getting cut off. It was at that point where I measured the voltages and found the voltage imbalance.

The more I think about it, I think I need something to keep the voltage supplies equal. They call it a rail splitter circuit. Look at this article full of circuits designed to work for a single-IC based headphone amplifier. I think they would work well for this too. It would be much better than simply using a resistive divider.

When I come up with a circuit that will work, I am going to post my results. First I need to find a suitable rectifier. UF4007 diodes won't be good enough because I need to find something with 2A or more rating.

Ed

On Sat, Apr 19, 2014 at 10:39 AM, Chris Albertson albertson.chris@...> wrote:

.You should post a schematic. .Those chips usually have a feedback network. .The chip is really just like a big op amp.

On Sat, Apr 19, 2014 at 2:42 AM, J Ed jedwardsat1@...> wrote:

.Quick Question:



I'm building an amp using TDA2030 chips. The audio quality is not

great and I've been trying to discover why. It hit me tonight...I took

some voltage measurements and found that the applied voltages are

weird. There is a positive and a negative rail, and then there's an

output. The output should be at 0v but it is connected to ground

through the speaker. As far as my meter is concerned, this is

true...the output measures 0.0v when measured against ground.



Here's the funny part...when I measure the rails, the positive rail

measures 22.3v and the negative rail measures -1.7v. This tells me

that the chip isn't balanced enough to be left alone in the circuit.

The problem is that I don't know what to do about it; I could place

two 470-ohm resistors in series across the power supply and ground the

center of them. I don't know that it would be enough to balance the

power supplies. Another idea I had was using an active load where I'd

have a pair of transistors across the line which would hold the ground

point exactly equal distance from the rails.



That's all.

Ed



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

#1703 Apr 19, 2014

The schematic as shown is intended to be used with a low impedance biploar,

positive and negative, power supply. A rail splitter will certainly work but it

needs to have an output impedance comfortably lower than the speaker impedance

which basically means using two TDA2030 amplifiers with one acting as the rail

splitter. If you do that, you might as well use them in a bridged configuration

to get 4 times the peak output power.



The alternative is to use a large output capacitor in series with the speaker

and bias the TDA2030 to the midpoint of the power supply.

On Sat, 19 Apr 2014 11:03:46 -0700, you wrote:



>www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

>

>The schematic I used was almost straight from the data sheet, maybe with

>some changed values for resistors. It's almost impossible to screw this up,

>even though I seem to have found a way. I first thought it was due to some

>power supply issues or oscillation but I saw the problem when I scoped the

>input and saw that all of the voltage excursions were positive and the

>negative half seemed to be getting cut off. It was at that point where I

>measured the voltages and found the voltage imbalance.

>

>The more I think about it, I think I need something to keep the voltage

>supplies equal. They call it a rail splitter circuit. Look at this article

>full of circuits designed to work for a single-IC based headphone

>amplifier. I think they would work well for this too. It would be much

>better than simply using a resistive divider.

>

>When I come up with a circuit that will work, I am going to post my

>results. First I need to find a suitable rectifier. UF4007 diodes won't be

>good enough because I need to find something with 2A or more rating.

>

>Ed







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

#1704 Apr 19, 2014

umm, i AM a newbe and all, but isn't that showing a bi polar power supply? the lower rail and ground aren't connected to ground directly.

in guitar pedal land, that usually means a +/- supply with ground somewhere in the middle.

jimi



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

#1705 Apr 19, 2014

Jimi, you are correct. What I did was connect a 24vdc supply across the amplifier. There really wasn't anything to tell the amp where 0v was supposed to be. My amps are finding it a few volts from the negative rail. The splitter I made up will set the ground point between the two supplies and the amp should self regulate from there. Like I said, there wasn't anything telling the inputs of the amp where to be biased.EdOn Apr 19, 2014 12:10 PM, "David" davidwhess@...> wrote:

.The schematic as shown is intended to be used with a low impedance biploar,

positive and negative, power supply. A rail splitter will certainly work but it

needs to have an output impedance comfortably lower than the speaker impedance

which basically means using two TDA2030 amplifiers with one acting as the rail

splitter. If you do that, you might as well use them in a bridged configuration

to get 4 times the peak output power.



The alternative is to use a large output capacitor in series with the speaker

and bias the TDA2030 to the midpoint of the power supply.



On Sat, 19 Apr 2014 11:03:46 -0700, you wrote:



>www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

>

>The schematic I used was almost straight from the data sheet, maybe with

>some changed values for resistors. It's almost impossible to screw this up,

>even though I seem to have found a way. I first thought it was due to some

>power supply issues or oscillation but I saw the problem when I scoped the

>input and saw that all of the voltage excursions were positive and the

>negative half seemed to be getting cut off. It was at that point where I

>measured the voltages and found the voltage imbalance.

>

>The more I think about it, I think I need something to keep the voltage

>supplies equal. They call it a rail splitter circuit. Look at this article

>full of circuits designed to work for a single-IC based headphone

>amplifier. I think they would work well for this too. It would be much

>better than simply using a resistive divider.

>

>When I come up with a circuit that will work, I am going to post my

>results. First I need to find a suitable rectifier. UF4007 diodes won't be

>good enough because I need to find something with 2A or more rating.

>

>Ed



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

#1706 Apr 19, 2014

Common as far as the signal input and amplifier can be wherever ever you want it

to be but if the speaker is using it for its return current as shown in the

schematic, then common is going to get pushed all over the place unless it is

low impedance.



The minimal changes to make the schematic as show work with a single supply are:



1. Add a large capacitor in series with the speaker. Assuming 8 ohms with a low

frequency cutoff of 20 Hz, that value will be about 1000 microfarads.

2. Use a resistor divider with two 22k resistors to connect the non-inverting

input, pin 1, to ground and the positive supply.



The amplifier as configured is AC coupled and that is what is missing at the

output end to allow operation with a single supply.



The ST datasheet for the TDA2030 shows these very changes on the first page:



www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000128.pdf

On Sat, 19 Apr 2014 12:35:44 -0700, you wrote:



>Jimi, you are correct. What I did was connect a 24vdc supply across the

>amplifier. There really wasn't anything to tell the amp where 0v was

>supposed to be. My amps are finding it a few volts from the negative rail.

>The splitter I made up will set the ground point between the two supplies

>and the amp should self regulate from there. Like I said, there wasn't

>anything telling the inputs of the amp where to be biased.

>

>Ed

>On Apr 19, 2014 12:10 PM, "David" davidwhess@...> wrote:

>

>>

>>

>> The schematic as shown is intended to be used with a low impedance biploar,

>> positive and negative, power supply. A rail splitter will certainly work

>> but it

>> needs to have an output impedance comfortably lower than the speaker

>> impedance

>> which basically means using two TDA2030 amplifiers with one acting as the

>> rail

>> splitter. If you do that, you might as well use them in a bridged

>> configuration

>> to get 4 times the peak output power.

>>

>> The alternative is to use a large output capacitor in series with the

>> speaker

>> and bias the TDA2030 to the midpoint of the power supply.

>>

>> On Sat, 19 Apr 2014 11:03:46 -0700, you wrote:

>>

>> >

>> www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

>> >

>> >The schematic I used was almost straight from the data sheet, maybe with

>> >some changed values for resistors. It's almost impossible to screw this

>> up,

>> >even though I seem to have found a way. I first thought it was due to some

>> >power supply issues or oscillation but I saw the problem when I scoped the

>> >input and saw that all of the voltage excursions were positive and the

>> >negative half seemed to be getting cut off. It was at that point where I

>> >measured the voltages and found the voltage imbalance.

>> >

>> >The more I think about it, I think I need something to keep the voltage

>> >supplies equal. They call it a rail splitter circuit. Look at this article

>> >full of circuits designed to work for a single-IC based headphone

>> >amplifier. I think they would work well for this too. It would be much

>> >better than simply using a resistive divider.

>> >

>> >When I come up with a circuit that will work, I am going to post my

>> >results. First I need to find a suitable rectifier. UF4007 diodes won't be

>> >good enough because I need to find something with 2A or more rating.

>> >

>> >Ed

>>

>>







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

#1707 Apr 19, 2014

The preferred way to get a split power supply is to start with a transformer

with a center tapped secondary. Put a bridge rectifier on it and the

cathodes of the bridge will be the positive output and the anodes of the

bridge will be the negative.



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, April 19, 2014 1:03 PM

Subject: Re: [funwithtransistors] TDA2030 Amplifier Issues





www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg



The schematic I used was almost straight from the data sheet, maybe with

some changed values for resistors. It's almost impossible to screw this up,

even though I seem to have found a way. I first thought it was due to some

power supply issues or oscillation but I saw the problem when I scoped the

input and saw that all of the voltage excursions were positive and the

negative half seemed to be getting cut off. It was at that point where I

measured the voltages and found the voltage imbalance.



The more I think about it, I think I need something to keep the voltage

supplies equal. They call it a rail splitter circuit. Look at this article

full of circuits designed to work for a single-IC based headphone

amplifier. I think they would work well for this too. It would be much

better than simply using a resistive divider.



When I come up with a circuit that will work, I am going to post my

results. First I need to find a suitable rectifier. UF4007 diodes won't be

good enough because I need to find something with 2A or more rating.



Ed





On Sat, Apr 19, 2014 at 10:39 AM, Chris Albertson albertson.chris@...

> wrote:



>

>

> You should post a schematic. Those chips usually have a feedback network.

> The chip is really just like a big op amp.

>

>

> On Sat, Apr 19, 2014 at 2:42 AM, J Ed jedwardsat1@...> wrote:

>

>>

>>

>> Quick Question:

>>

>> I'm building an amp using TDA2030 chips. The audio quality is not

>> great and I've been trying to discover why. It hit me tonight...I took

>> some voltage measurements and found that the applied voltages are

>> weird. There is a positive and a negative rail, and then there's an

>> output. The output should be at 0v but it is connected to ground

>> through the speaker. As far as my meter is concerned, this is

>> true...the output measures 0.0v when measured against ground.

>>

>> Here's the funny part...when I measure the rails, the positive rail

>> measures 22.3v and the negative rail measures -1.7v. This tells me

>> that the chip isn't balanced enough to be left alone in the circuit.

>> The problem is that I don't know what to do about it; I could place

>> two 470-ohm resistors in series across the power supply and ground the

>> center of them. I don't know that it would be enough to balance the

>> power supplies. Another idea I had was using an active load where I'd

>> have a pair of transistors across the line which would hold the ground

>> point exactly equal distance from the rails.

>>

>> That's all.

>> Ed

>>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>

>

>





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

#1708 Apr 20, 2014

That much is clear to me. My problem was that the op amp input was referenced to ground. The circuit had no way of telling the op amp that ground was supposed to be half way between each rail. This caused it to find its own level near the negative rail.I built two power supply boards that are identical. They have large series capacitors and a transistor circuit that divides the power supply evenly. I could have gone with a resistive divider but didn't. Once the TDA2030 has a good ground reference, it does not need a rail splitter. It will end up doing that itself.EdOn Apr 19, 2014 1:57 PM, "Max Robinson" max@...> wrote:

.The preferred way to get a split power supply is to start with a transformer

with a center tapped secondary. Put a bridge rectifier on it and the

cathodes of the bridge will be the positive output and the anodes of the

bridge will be the negative.



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



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funwithwood-subscribe@yahoogroups.com



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

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

To: funwithtransistors@yahoogroups.com>

Sent: Saturday, April 19, 2014 1:03 PM

Subject: Re: [funwithtransistors] TDA2030 Amplifier Issues



www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg



The schematic I used was almost straight from the data sheet, maybe with

some changed values for resistors. It's almost impossible to screw this up,

even though I seem to have found a way. I first thought it was due to some

power supply issues or oscillation but I saw the problem when I scoped the

input and saw that all of the voltage excursions were positive and the

negative half seemed to be getting cut off. It was at that point where I

measured the voltages and found the voltage imbalance.



The more I think about it, I think I need something to keep the voltage

supplies equal. They call it a rail splitter circuit. Look at this article

full of circuits designed to work for a single-IC based headphone

amplifier. I think they would work well for this too. It would be much

better than simply using a resistive divider.



When I come up with a circuit that will work, I am going to post my

results. First I need to find a suitable rectifier. UF4007 diodes won't be

good enough because I need to find something with 2A or more rating.



Ed



On Sat, Apr 19, 2014 at 10:39 AM, Chris Albertson albertson.chris@...

> wrote:



>

>

> You should post a schematic. Those chips usually have a feedback network.

> The chip is really just like a big op amp.

>

>

> On Sat, Apr 19, 2014 at 2:42 AM, J Ed jedwardsat1@...> wrote:

>

>>

>>

>> Quick Question:

>>

>> I'm building an amp using TDA2030 chips. The audio quality is not

>> great and I've been trying to discover why. It hit me tonight...I took

>> some voltage measurements and found that the applied voltages are

>> weird. There is a positive and a negative rail, and then there's an

>> output. The output should be at 0v but it is connected to ground

>> through the speaker. As far as my meter is concerned, this is

>> true...the output measures 0.0v when measured against ground.

>>

>> Here's the funny part...when I measure the rails, the positive rail

>> measures 22.3v and the negative rail measures -1.7v. This tells me

>> that the chip isn't balanced enough to be left alone in the circuit.

>> The problem is that I don't know what to do about it; I could place

>> two 470-ohm resistors in series across the power supply and ground the

>> center of them. I don't know that it would be enough to balance the

>> power supplies. Another idea I had was using an active load where I'd

>> have a pair of transistors across the line which would hold the ground

>> point exactly equal distance from the rails.

>>

>> That's all.

>> Ed

>>

>

>

>

> --

>

> Chris Albertson

> Redondo Beach, California

>

>

>



---

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

#1709 Apr 20, 2014

On Sat, Apr 19, 2014 at 11:03 AM, J Ed jedwardsat1@...> wrote:

.www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

The schematic I used was almost straight from the data sheet,



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

#1710 Apr 21, 2014

Ed,I was out of town over the weekend so I don't know if you solved your supply problem yet. But I did find the attached schematic on the interwebs which seems to address the issue you're having. Unfortunately the splitter circuit seems to be more complex than your original amplifier circuit. John 

From: J Ed jedwardsat1@...> To: "funwithtransistors@yahoogroups.com" funwithtransistors@yahoogroups.com> Sent: Saturday, April 19, 2014 1:03 PM Subject: Re: [funwithtransistors] TDA2030 Amplifier Issues

 www.electroschematics.com/wp-content/uploads/2009/02/tda2030-diagram.jpg

The schematic I used was almost straight from the data sheet, maybe with some changed values for resistors. It's almost impossible to screw this up, even though I seem to have found a way. I first thought it was due to some power supply issues or oscillation but I saw the problem when I scoped the input and saw that all of the voltage excursions were positive and the negative half seemed to be getting cut off. It was at that point where I measured the voltages and found the voltage imbalance.

The more I think about it, I think I need something to keep the voltage supplies equal. They call it a rail splitter circuit. Look at this article full of circuits designed to work for a single-IC based headphone amplifier. I think they would work well for this too. It would be much better than simply using a resistive divider.

When I come up with a circuit that will work, I am going to post my results. First I need to find a suitable rectifier. UF4007 diodes won't be good enough because I need to find something with 2A or more rating.

EdOn Sat, Apr 19, 2014 at 10:39 AM, Chris Albertson albertson.chris@...> wrote: You should post a schematic.  Those chips usually have a feedback network.  The chip is really just like a big op amp.On Sat, Apr 19, 2014 at 2:42 AM, J Ed jedwardsat1@...> wrote: Quick Question:



I'm building an amp using TDA2030 chips. The audio quality is not

great and I've been trying to discover why. It hit me tonight...I took

some voltage measurements and found that the applied voltages are

weird. There is a positive and a negative rail, and then there's an

output. The output should be at 0v but it is connected to ground

through the speaker. As far as my meter is concerned, this is

true...the output measures 0.0v when measured against ground.



Here's the funny part...when I measure the rails, the positive rail

measures 22.3v and the negative rail measures -1.7v. This tells me

that the chip isn't balanced enough to be left alone in the circuit.

The problem is that I don't know what to do about it; I could place

two 470-ohm resistors in series across the power supply and ground the

center of them. I don't know that it would be enough to balance the

power supplies. Another idea I had was using an active load where I'd

have a pair of transistors across the line which would hold the ground

point exactly equal distance from the rails.



That's all.

Ed



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

#1711 Apr 21, 2014

John,

The TDA2030 is now working as its own phase splitter. Here are the facts...

- When my problem displayed, I was feeding the amp with +24v DC from a laptop supply.- The input terminals and the speaker were all referenced to ground. The amplifier is built in Manhattan Construction, meaning everything is soldered to small standoffs attached to a copper ground plane.- There was a totem pole of capacitors across the rail, two 100 uF / 50v, with the center point attached to the ground plane. There was no DC connection between the rails and the ground plane.

I believe that, because of these things, the input of the TDA2030 had no reference that would show it where ground should be in relation to the DC rails. In building a rail splitter, I show the amplifier chip where the DC point should be. It could have been as simple as two resistors across the supply with the center tap set to ground. Instead, I opted for a circuit like the one below:



This has the added benefit of being able to compensate for the input bias current to the TDA2030. Now that the TDA2030 has an idea of where ground is supposed to be (halfway between VCC and ground), it puts it there and doesn't need the rail splitter. It performs as its own.

Ed



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

#1712 Apr 21, 2014

Ed,Good job. Your ckt is an even simpler one than the one I attached previously. John 

From: J Ed jedwardsat1@...>

To: "funwithtransistors@yahoogroups.com" funwithtransistors@yahoogroups.com> Sent: Monday, April 21, 2014 12:11 PM Subject: Re: [funwithtransistors] TDA2030 Amplifier Issues

 John,

The TDA2030 is now working as its own phase splitter. Here are the facts...

- When my problem displayed, I was feeding the amp with +24v DC from a laptop supply.- The input terminals and the speaker were all referenced to ground. The amplifier is built in Manhattan Construction, meaning everything is soldered to small standoffs attached to a copper ground plane.- There was a totem pole of capacitors across the rail, two 100 uF / 50v, with the center point attached to the ground plane. There was no DC connection between the rails and the ground plane.

I believe that, because of these things, the input of the TDA2030 had no reference that would show it where ground should be in relation to the DC rails. In building a rail splitter, I show the amplifier chip where the DC point should be. It could have been as simple as two resistors across the supply with the center tap set to ground. Instead, I opted for a circuit like the one below:



This has the added benefit of being able to compensate for the input bias current to the TDA2030. Now that the TDA2030 has an idea of where ground is supposed to be (halfway between VCC and ground), it puts it there and doesn't need the rail splitter. It performs as its own.

Ed







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

#1713 Apr 21, 2014

John,

What you posted looks like the circuit to boost the 2030's output. If you use the 2030 to drive a pair of power transistors, you could easily get 100 watts out of the amplifier.

I can see myself building one of these to make an audio modulator for a transmitter in the future. If I created a 25 watt transmitter, I could use this to modulate it by placing the output in the power line for the finals.

Ed



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

#1714 Apr 21, 2014

Ed,The circuit I attached in my email is an active "virtual" GND circuit. R1 and R2 form a voltage divider that biases the plus input of the op-amp to half of the input supply (how close to half depends on how closely theresistors are matched). Since an op-amp always tries to keep both of its inputs at the same potential, the op-amp's output will drive the transistor bases to whatever level is required to bias the emitters ofthe transistors, which are fed back to the op-amp's minus input, to the same potential as the plus input. Thus, the emitters form a relatively low impedance "virtual" GND that always remains at half of the input supply over a fairly wide voltage range. John

 

From: J Ed jedwardsat1@...> To: "funwithtransistors@yahoogroups.com" funwithtransistors@yahoogroups.com> Sent: Monday, April 21, 2014 2:35 PM Subject:Re: [funwithtransistors] TDA2030 Amplifier Issues

 John,

What you posted looks like the circuit to boost the 2030's output. If you use the 2030 to drive a pair of power transistors, you could easily get 100 watts out of the amplifier.

I can see myself building one of these to make an audio modulator for a transmitter in the future. If I created a 25 watt transmitter, I could use this to modulate it by placing the output in the power line for the finals.

Ed



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

#1715 Apr 21, 2014

Exactly. The problem was that my ground had NO reference to the DC rails except through the amplifier's output and speaker. Therefore, the amp had no idea where ground should be. There was no speaker DC current but there was also nowhere for the amp to move in the negative direction. This caused everything to go wrong.

Ed



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