Thank you Lampie. The noise in the pots is exactly as if dirty; intermttent, louder, softer as you turn the pot. I can find a spot where they are quiet, all the way up on one and about at 75% on the other. No pre amp, direct to Oppo UDP205. As I mentioned, these are double Monitor 3(isobaric) so two sets of amps in use at once, same ic with Y connectors to same source So It's not the source since it happens in only one set. Stand by relay functions properly in all. They all go to the same power bar.
It looks like two of the HV resistors are not original in the first amp so most likely replacements. I have a utility box full of components for these amps I scored on the bay. I probably have what they need if it's not the pots. I've in the meantime bought new high quality instrumentation pots for them. I intend to replace them regardless just because my experience dictates at their age they are due anyway. But I'm still concerned there could be something else going on since it's both amps at once. I should point out that I acquired this set about 5 years ago from someone who stored them in an unheated shed for 15 years! When I got them they looked like they were in a flood. I cleaned them up, fired them up, and they've been running like a champ daily ever since. Amazing. Who said they're unreliable?? Pfft
It looks like two of the HV resistors are not original in the first amp so most likely replacements. I have a utility box full of components for these amps I scored on the bay. I probably have what they need if it's not the pots. I've in the meantime bought new high quality instrumentation pots for them. I intend to replace them regardless just because my experience dictates at their age they are due anyway. But I'm still concerned there could be something else going on since it's both amps at once. I should point out that I acquired this set about 5 years ago from someone who stored them in an unheated shed for 15 years! When I got them they looked like they were in a flood. I cleaned them up, fired them up, and they've been running like a champ daily ever since. Amazing. Who said they're unreliable?? Pfft
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Indeed it looks more and more like a dirty pot. Replacing them is not very difficult. Just try to get some with a metal housing that is grounded so they do not pickup static voltages just in case.
They are not unreliable at all !!! People who claim this have these modified "to death"or in a humid/smokey environment. Look at my pictures of the amps i got and you will see what i mean.
Many also remove the auto switch circuit. This also causes issues...
Naturally dust will be attracted by the high voltage and after 5 years it could use some dusting.
Many also remove the auto switch circuit. This also causes issues...
Naturally dust will be attracted by the high voltage and after 5 years it could use some dusting.
Those are not oem. Allen Bradley Mod Pot is what they were supplied with. But it really doesn't matter because they are intermediary. I would think as such they would most likely be linear, no?
Is that the gain potmeter on the back or on the PCB?
Both pots on the back are logarithmic.
Both pots on the back are logarithmic.
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I just checked them myself. They are logarithmic indeed. The numbers confirm this.
82A1A B28 F15
10K CCW Audio
82A1A B28 C23
500K CCW Audio
82A1A B28 F15
10K CCW Audio
82A1A B28 C23
500K CCW Audio
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Okay, but those are not oem pots in your hand🙂. The amp did not come with that Bourns pot. The original oem pots as I mentioned are Allen Bradley. Yours may very well be correct replacements but how can we confirm that?
On a side note, is there an op amp upgrade you could suggest for these amps?
Original is Texas Inst. TL084CN
On a side note, is there an op amp upgrade you could suggest for these amps?
Original is Texas Inst. TL084CN
These are the original pots (i have a bunch of those from all the dead amps). None of these ever needed replacing.
The opamp could be replaced by 2 opamps. I have modified the last amps i got a little but not much as i tried to keep it as original as possible.
Because i have build new amps (from scratch) i have sold my own set long ago. Now i only have some spare parts left over from the dead amps, mainly transformers, the metal work and some tubes as the rest is of no use.
The opamp could be replaced by 2 opamps. I have modified the last amps i got a little but not much as i tried to keep it as original as possible.
Because i have build new amps (from scratch) i have sold my own set long ago. Now i only have some spare parts left over from the dead amps, mainly transformers, the metal work and some tubes as the rest is of no use.
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Oh, I suppose they could have subbed in the Bourns sometime. Perhaps because of the issue mine are having. I have 3 sets acquired from different places at different times and they all have AB pots. When you say 2 opamps do you mean 2 duals or 2 different ones? What opamps would you recommend as an upgrade? I was thinking a straight drop in would be AD713.
You need no special opamp for the switching of the amp (auto on-off). So this can be a TL082. The other can be any good fet input opamp. Even a TL082 would be better as now there are more dedicated to do the job.
OPA1644 in this case...
The dual and quad versions feature completely
independent circuitry for lowest crosstalk and
freedom from interactions between channels, even
when overdriven or overloaded.
With modification i really mean modification... splitting 1 opamp into 2.
The dual and quad versions feature completely
independent circuitry for lowest crosstalk and
freedom from interactions between channels, even
when overdriven or overloaded.
With modification i really mean modification... splitting 1 opamp into 2.
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