Hello users of DIY, my class A project is coming along very well but I have run into some issues in the final stretch. Here is the schematic of the amp:
The power supply runs perfectly and so does one channel. I completed the other channel and upon the first powered run the 10R resistor (farthest right in schematic) overheated and started to smoke. I thought this was strange so I checked all the wiring and circuit and it seemed to be fine, identical to the working one. The output transistors are also all working fine. So I turned it on again, and now my inductors in the power supply are emitting a high pitched squeal. The squeal isn't there with the other channel, it still works fine.
The speaker output reads about 30V AC and 10V DC. The squeal is also quite alarming and makes me think something is going to violently explode. I'm not too sure what to think what the cause would be.
An externally hosted image should be here but it was not working when we last tested it.
The power supply runs perfectly and so does one channel. I completed the other channel and upon the first powered run the 10R resistor (farthest right in schematic) overheated and started to smoke. I thought this was strange so I checked all the wiring and circuit and it seemed to be fine, identical to the working one. The output transistors are also all working fine. So I turned it on again, and now my inductors in the power supply are emitting a high pitched squeal. The squeal isn't there with the other channel, it still works fine.
The speaker output reads about 30V AC and 10V DC. The squeal is also quite alarming and makes me think something is going to violently explode. I'm not too sure what to think what the cause would be.
You know your stuff don't you. I did noticed the other channel amplifying some repetitive noise when both were running. Before I go on the hunt for oscillation knowledge, any suggestions on eliminating it?
Oh and I guess I didn't read the ESP disclaimer close enough, I'll take the schematic down.
Oh and I guess I didn't read the ESP disclaimer close enough, I'll take the schematic down.
It's Project 10 from the ESP site.
I went ahead and reheated all the solder joints and even tested the individual paths with an ohmmeter. The output transistors all work fine, and as far as I cant tell all the resistors on the board are working fine (might as well be sure). I'm positive none of the smaller transistors are oriented incorrectly and use plastic casings so no chance of shorting each other on the heat sink. The layout is about 98% the same as the working channel, the difference being I cut some leads shorter. The wires going to the output transistors which use snap connectors are also making good contact.
I think I'm going to start testing the transistors on the board to see if by fluke one of them is bad even though all parts are brand new. Once I'm certain all the parts are working perfectly I'm not sure what I'll do next...
I want to rule out layout and wiring because of it being an almost exact mirror of a working channel.
I went ahead and reheated all the solder joints and even tested the individual paths with an ohmmeter. The output transistors all work fine, and as far as I cant tell all the resistors on the board are working fine (might as well be sure). I'm positive none of the smaller transistors are oriented incorrectly and use plastic casings so no chance of shorting each other on the heat sink. The layout is about 98% the same as the working channel, the difference being I cut some leads shorter. The wires going to the output transistors which use snap connectors are also making good contact.
I think I'm going to start testing the transistors on the board to see if by fluke one of them is bad even though all parts are brand new. Once I'm certain all the parts are working perfectly I'm not sure what I'll do next...
I want to rule out layout and wiring because of it being an almost exact mirror of a working channel.
Link to the project -> http://www.sound.westhost.com/project10.htm
I can't believe my first circuit worked first try. I thought the next one would be just as simple. I'm going to start tearing it apart then. I'm sure I'll find something eventually.
Just a question before I go, will a DC line crossing a signal path potentially create noise or oscillation? This is point to point wiring so in some spots different wires cross or run beside each other or other components.
Finally, is it possible to edit old posts on this site?
I can't believe my first circuit worked first try. I thought the next one would be just as simple. I'm going to start tearing it apart then. I'm sure I'll find something eventually.
Just a question before I go, will a DC line crossing a signal path potentially create noise or oscillation? This is point to point wiring so in some spots different wires cross or run beside each other or other components.
Finally, is it possible to edit old posts on this site?
Well I'm officially a tool. 
After rebuilding half the circuit going through all the transistors and parts and finding nothing wrong I set my voltmeter across some other smoking resistors only to find the voltage to be about 3 times what it should. Well the voltage across those resistors are controlled by a multi turn pot which I was positive I had set to it's max resistance. It turns out it was at 0Ohms. I thought I had fried it, but after about 4 rotations it finally started to increase and about another 10 turns and it was at 1K. I thought I had these pots figured out. Guess not. So basically problem solved, all due to my dumb-assery.
After rebuilding half the circuit going through all the transistors and parts and finding nothing wrong I set my voltmeter across some other smoking resistors only to find the voltage to be about 3 times what it should. Well the voltage across those resistors are controlled by a multi turn pot which I was positive I had set to it's max resistance. It turns out it was at 0Ohms. I thought I had fried it, but after about 4 rotations it finally started to increase and about another 10 turns and it was at 1K. I thought I had these pots figured out. Guess not. So basically problem solved, all due to my dumb-assery.
I thought I spoke too soon, but well....not really.
With the source and load unhooked, the amp is silent when you turn it on. When you turn it off however, the inductor makes a noise like really small turbine spinning down. With the source and load hooked up everything is silent but that 10R still gets hot as hell. It'll burn you pretty good if you as much as poke it. Good news is it doesn't smoke anymore. I've yet to see if the other channel's resistor does that. If so, I'll just get some physically bigger ones.
The thing with the inductors making the noise upon power down is quite strange indeed, at least to me. The power supply is simple enough being rectifier > +- rail > several caps > inductor > amp channel. The original plans placed the inductors farther back in the chain, between some of the caps but this caused a bad hum so I moved them to the end and problem solved.
It now produces sound just like the other channel so I want to say all is well but I feel as if something is not totally fixed. I'll hopefully abolish my suspicions as I get it all back together again.
With the source and load unhooked, the amp is silent when you turn it on. When you turn it off however, the inductor makes a noise like really small turbine spinning down. With the source and load hooked up everything is silent but that 10R still gets hot as hell. It'll burn you pretty good if you as much as poke it. Good news is it doesn't smoke anymore. I've yet to see if the other channel's resistor does that. If so, I'll just get some physically bigger ones.
The thing with the inductors making the noise upon power down is quite strange indeed, at least to me. The power supply is simple enough being rectifier > +- rail > several caps > inductor > amp channel. The original plans placed the inductors farther back in the chain, between some of the caps but this caused a bad hum so I moved them to the end and problem solved.
It now produces sound just like the other channel so I want to say all is well but I feel as if something is not totally fixed. I'll hopefully abolish my suspicions as I get it all back together again.
The 10R should not get hot at all. You have a problem with oscillation. You can't hear it because the frequency is too high. Do you have access to an oscilloscope ?? You could look at the output then and see the oscillation. The 10R should normally run cold. Hot = large oscillation = very bad. Warm = small oscillation = bad. Powering the two together probably just changes the characteristics (frequency) of the feedback (oscillation) enabling you to hear it. I agree with posting on the ESP forums, there should be someone there with first hand knowledge on this amp.
Hm, Rod doesn't show any rail decoupling caps on the schematic. That would be a good idea. Try some 330uF's onboard, with some 100-470nF ceramic or polyesters to bypass. Put them near where the output devices are.
Keep the ground for the 22K and 22uF parts isolated from the other grounds - especially the ground from the 100nF that is part of the Zobel network on the output.
Make sure you adhere to good grounding practice especially when you power more than one amp from the same PSU. All grounds should return to one STAR point, close to the PSU capacitor's ground point. Read Rod's article on PSU Wiring if in doubt
Rod loves his CFP output stages but personally I think they're too much of a b*tch to make stable. I'm also not keen on a 6K8 resistor as the current source for the LTP.
Keep the ground for the 22K and 22uF parts isolated from the other grounds - especially the ground from the 100nF that is part of the Zobel network on the output.
Make sure you adhere to good grounding practice especially when you power more than one amp from the same PSU. All grounds should return to one STAR point, close to the PSU capacitor's ground point. Read Rod's article on PSU Wiring if in doubt
Rod loves his CFP output stages but personally I think they're too much of a b*tch to make stable. I'm also not keen on a 6K8 resistor as the current source for the LTP.
Jaycee! First I split the grounds like you said. Nothing changed. So I grabbed a 470uF cap and tossed it on the positive rail, near the outputs. The inductor squeal was reduced significantly. I put the second cap on the negative rail and it was silent! The 10R is running cold now, like it should. I'm going to put these caps on proper, along with the bypass and put them on each channel. Once I get to this done I'll post a follow up.
! First I split the grounds like you said. Nothing changed. So I grabbed a 470uF cap and tossed it on the positive rail, near the outputs. The inductor squeal was reduced significantly. I put the second cap on the negative rail and it was silent! The 10R is running cold now, like it should. I'm going to put these caps on proper, along with the bypass and put them on each channel. Once I get to this done I'll post a follow up.Well I just absolutely **** my pants.
So I'm looking for 4 matching caps I can salvage off some equipment to use for decoupling. I find an old motherboard with a bunch of G-LUXON 330uF @25V caps. Perfect I assume. As I'm desoldering I ruined about 4 because the legs pulled out so easily. I actually ran a search on them because they seemed really cheap. With the good ones I decide I better charge them up and test to see if they're still good. I put it in the circuit which is providing 18V and as I grab onto to it to remove it (while the circuit is running) the damn thing starts expanding. I thought I was going insane but it blew up to about twice its size and exploded like a cap gun going off. I thought I had lost my eyes or something but well I'm posting so I guess not. Sheesh...I spend all my time tiptoeing around the mains wiring and a cap tries to take me out.
So I'm looking for 4 matching caps I can salvage off some equipment to use for decoupling. I find an old motherboard with a bunch of G-LUXON 330uF @25V caps. Perfect I assume. As I'm desoldering I ruined about 4 because the legs pulled out so easily. I actually ran a search on them because they seemed really cheap. With the good ones I decide I better charge them up and test to see if they're still good. I put it in the circuit which is providing 18V and as I grab onto to it to remove it (while the circuit is running) the damn thing starts expanding. I thought I was going insane but it blew up to about twice its size and exploded like a cap gun going off. I thought I had lost my eyes or something but well I'm posting so I guess not. Sheesh...I spend all my time tiptoeing around the mains wiring and a cap tries to take me out.
AndrewT - Saying "steal" is a bit harsh! Rod has put the circuit up with full values, so I guess he doesn't mind someone making their own board. Really, as long as no one is making boards for profit, I don't think he'll mind.
G-LUXON caps are... well DIYAudio wont let me use a harsh enough word. It sounds like you accidentally reverse connected that one though.
G-LUXON caps are... well DIYAudio wont let me use a harsh enough word. It sounds like you accidentally reverse connected that one though.
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