Do you have a split supply that you could connect in the place of the regulators to see if that makes a difference? Leave the split supply on when switching the amp on/off.
I could connect an old computer supply up to the +/-15V rails for a test. Just lift the output leg of the regulators and "wire-in" the external supply?
Yes. Using that sort of supply, you might want to insert a 1 ohm resistor in series with the supply leads to offer some protection. I think a 1 ohm 1/4 watt would hold.
Results of that test are, I do not hear a turn on thump, and only one turn off thump instead of two now.
With main power off, switching the secondary power on and off does create small pops varying in loudness.
With main power off, switching the secondary power on and off does create small pops varying in loudness.
Do you think it has two problems since that didn't resolve everything?
Did it have this much of a pop when you previously had in installed.
Does this amp have the bias-defeat headers?
Did it have this much of a pop when you previously had in installed.
Does this amp have the bias-defeat headers?
I do think there are two different problems, yes.
Yes, and if we can't resolve all of them, it's the last one that is the loudest, that I would like to solve at least.
No, this amp does not have adjustable bias or dc offset pots so no bias headers either.
What is the purpose of CR29 and CR3? They are the diodes physically located near each regulator. They are connected between the main rails and the outputs of the regulators. They allow secondary voltage (minus the .6V drop) to be on the rails before I switch main power on. Seems like if those were to ever short it would allow main rail voltage to be on the secondary supply.
Yes, and if we can't resolve all of them, it's the last one that is the loudest, that I would like to solve at least.
No, this amp does not have adjustable bias or dc offset pots so no bias headers either.
What is the purpose of CR29 and CR3? They are the diodes physically located near each regulator. They are connected between the main rails and the outputs of the regulators. They allow secondary voltage (minus the .6V drop) to be on the rails before I switch main power on. Seems like if those were to ever short it would allow main rail voltage to be on the secondary supply.
It protects the regulator. I didn't know this and designed a circuit (a long time ago) that didn't use them and the regulators would fail when the circuit went into thermal shutdown. Page 3, item #2:
https://www.ti.com/lit/an/snva517b/...02863&ref_url=https%3A%2F%2Fwww.google.com%2F
https://www.ti.com/lit/an/snva517b/...02863&ref_url=https%3A%2F%2Fwww.google.com%2F
I just want to add a few of my own notes that may or may not be helpful to you, Perry, or future searches. Then i'm backing out.
1) I see the small signal caps that sit under the daughter board are not fully seated in your photo. On the PC450 model the tolerances between the daughter board and the main board are so tight that these MUST be fully seated or the cap tops make contact with the bottom of the daughter board. I don't know if this tolerance issue is present on this model, but with the daughter board installed you need to ensure this is not happening. They used a plastic insulator under the daughter board on the 450 to assist in preventing this.
2) Likewise all of those to92's you see folded over to accommodate the daughter board need to be checked to make sure none of the legs are touching the exposed legs under them. It's difficult to tell in your photo because it lacks dimension. But it's always good practice to make sure.
3) Occams razor. If the only difference between now and 8 years ago was 'sitting on a shelf' then you must consider the most perishable components. Or the problem was present at the time and you simply did not notice it.
1) I see the small signal caps that sit under the daughter board are not fully seated in your photo. On the PC450 model the tolerances between the daughter board and the main board are so tight that these MUST be fully seated or the cap tops make contact with the bottom of the daughter board. I don't know if this tolerance issue is present on this model, but with the daughter board installed you need to ensure this is not happening. They used a plastic insulator under the daughter board on the 450 to assist in preventing this.
2) Likewise all of those to92's you see folded over to accommodate the daughter board need to be checked to make sure none of the legs are touching the exposed legs under them. It's difficult to tell in your photo because it lacks dimension. But it's always good practice to make sure.
3) Occams razor. If the only difference between now and 8 years ago was 'sitting on a shelf' then you must consider the most perishable components. Or the problem was present at the time and you simply did not notice it.