Hello Everyone!
I have a problem with my ESP P3A amp. It works beautifully up to a certain high volume level. When I turn the volume loud (not really loud), on certain songs where there's strong bass, I hear a slight fuzz *tststs* sound. This only happens on one of the two channels. I'm using the same components on both channels. Another thing is, when I turn the good channel off, the channel that fuzzes does not fuzz anymore. Does this point to a problem in the power supply? I don't think it's clipping because one channel does not ever exhibit this problem. Any suggestions would be appreciated?
Thanks
I have a problem with my ESP P3A amp. It works beautifully up to a certain high volume level. When I turn the volume loud (not really loud), on certain songs where there's strong bass, I hear a slight fuzz *tststs* sound. This only happens on one of the two channels. I'm using the same components on both channels. Another thing is, when I turn the good channel off, the channel that fuzzes does not fuzz anymore. Does this point to a problem in the power supply? I don't think it's clipping because one channel does not ever exhibit this problem. Any suggestions would be appreciated?
Thanks
Secondary breakdown? I've replaced the power transistors already when trying to fix this issue. So are the driver or first stage BJT's susceptible to secondary breakdown as well?
I'm using 10,000uF on the rails. I was thinking about dropping this to 4,700uF to see if it would help. Does it make sense to try this?
Thanks
I'm using 10,000uF on the rails. I was thinking about dropping this to 4,700uF to see if it would help. Does it make sense to try this?
Thanks
I'm pretty sure it's not a ground loop hum. It's a white noise sound like jnb describes. I am more inclined to think it is a transistor, but wonder why it only occurs when both channels are playing. The noise does not occur if only the one channel is playing. Could it still be the transistor?
Thanks
Thanks
Hi blap0220,
Once a transistor has gone into secondary breakdown, it has become a piece of wire that only looks like a transistor. Your problem is not a transistor.
I would support some of the other posters here like darkfenriz who is on the right track with ........
All these members are pointing along the same path, even though it may not appear that way.
-Chris
From ...
No.
Once a transistor has gone into secondary breakdown, it has become a piece of wire that only looks like a transistor. Your problem is not a transistor.
I would support some of the other posters here like darkfenriz who is on the right track with ........
ACD with ...
AndrewT with ...
who I completely agree with. The instability could be caused by a number of things, so recheck all you work and solder joints carefully.
All these members are pointing along the same path, even though it may not appear that way.
-Chris
Well. I'm reluctant to believe it's a solder issue because I've touched every joint over. Doubt it's because of ground loop, because there is no hum. And the other channel works just fine. My wiring is pretty good as far as the layout. I am most interested in JNB's suggestion because he says that he has encountered this buzz before. Can a transistor be someone degraded but still functional?
THanks
THanks
blap0220 said:
My guess would also be loop problem. The fact that you have no hum doesn't mean there is no ground loop. The ground loop may be problematic for higher frequencies as the wiring L comes into play. That will cause occasional bursts of oscillations, exactly what you describe. The fact that it changes when you turn off one channel points in the same direction: if there is only one channel there is no mutual influence through the ground loop.
I would look at any part of the supply (return) wiring and/or the signal ground wiring that both channels share. Try to run those for each channel separately. Do you use a start ground?
Forget about transistor problems - you don't have them.
Jan Didden
I would agree with Janneman. It also guess it is a loop problem, but could be worse than just a ground loop. It is something Nelson Pass hinted several time here, the "signal loop". I've experienced this (the hard way
). Somewhere in the cct, part of the output signal is being feeded back to the input (can be input "input" or a certain stage's "input"). It's weak parasitic radiation signal, so it only appears when you play your amp quite loud. You can add more stability caps or you can change the physical layout/PCB layout. I found out that more of the so called "amp oscilation" is actually this signal loop problem, not purely oscilation problem.
Hi blap0220,
I think you are barking up the wrong tree myself. Your amplifier is unstable at high frequencies. You may have a cracked trace or something not making good contact.
-Chris
Edit:
Yes. Small signal transistors that have gone into reverse breakdown E-B. Most often the differential pair. Output transistors can be leaky, but that would be very definite with temperature.
I think you are barking up the wrong tree myself. Your amplifier is unstable at high frequencies. You may have a cracked trace or something not making good contact.
-Chris
Edit:
I just can't see any connection unless the amp is unstable anyway. Then bias current levels may affect it, but that isn't the problem.
This is an indication that the fuzzy channel may be OK as far as damaged components are concerned.
The PS voltage may be lower when both channels are drawing current. Depending on the design, the bias current of the fuzzy channel may drop below critical threshold when both channels are at full potential.
If the builder used the common colorband metal films then one of them may have a production flaw. They are cheap because they have minimum quality control. An endcap may be loose. Using RN55Ds is worth the money. IMHO , Mark
Ok. I think I've made some progress on this issue. I have a dual power supply for the two channels. When I swap the power source of one channel with the source powering the other channel and vice versa, the fuzz problem transfers to the other channel. In other words, the problem is following one channel of the power supply. I am using two rectifiers and two sets of filter caps. I tried swapping the rectifiers and caps to see if they would follow those components, but they don't. It doesn't make sense to me because the rectifier and caps are the only components in the power supply other than the transformer. Any ideas? Thanks for all your suggestions btw.
This last try points even more to a grounding issue. Poiwer supplies don't give off 'buzz' but it is quite common that ground noise couples to an amp input through shared wiring.
Would it be possible to sketch out your physical power supply wiring?
One thing you could try is to look how one channel wiring is different from the other. How/where are the two ground connections of the input signal lines coupled together and to the ground return?
Jan Didden
Would it be possible to sketch out your physical power supply wiring?
One thing you could try is to look how one channel wiring is different from the other. How/where are the two ground connections of the input signal lines coupled together and to the ground return?
Jan Didden
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