Naim NAP 135 with Ultrasonic Oscillation

[rf7]

This amp has a 4Mhz oscillation on its output at all times. How do I fix that?

Bootleg schematics: Amp Circuit

Voltage Regulator

Any help would be much appreciated.

[Enzo]

Is R32 open? Over by the output.

otherwise, does it pass signal?

[rf7]

Is R32 open? Over by the output.

No, it measures OK.

otherwise, does it pass signal?

Yes, it passes signal, but with the 4Mhz wave riding the output. It was shutting down when used.

[Enzo]

Oh well, no easy points today.

Does this amp have a preamp or is it a plain vanilla power amp like the schematic? Is the 4MHz present at R3? Is it riding the rails? That power supply is some serious overkill, but its complexity could make it unstable, are the rails clean?

All those little caps hung all over it are there for stability, so check them.

[rf7]

Does this amp have a preamp or is it a plain vanilla power amp like the schematic?

It's just a power amp, basically a $3500 power amp.

Is the 4MHz present at R3?

No.

Is it riding the rails?

Bingo, you got it. Yes, it's all over the rails.

That power supply is some serious overkill, but its complexity could make it unstable, are the rails clean?

As above, no.

All those little caps hung all over it are there for stability, so check them.

Well, it was caps after all. I replaced all of the electrolytics in the supply --C101, 201, 105, and 205, and that did the trick.

Thank you so much! Is there a charity that I can donate to for you? Enzo, you're the man!

[Enzo]

Buy me a burger next time I see you.


Or, if you are in the mood, pop a donation to tboy to help support this terrific place he runs. Isn't there a donate button on the home page or something. We all should do that anyway from time to time.

[rf7]

Buy me a burger next time I see you.

LOL, you got it!

Or, if you are in the mood, pop a donation to tboy to help support this terrific place he runs. Isn't there a donate button on the home page or something. We all should do that anyway from time to time.

Sounds like a good idea.

[rf7]

Took me a while to notice the donate button, but I did make a contribution. Thanks again Enzo.

[Enzo]

I see the donate button has turned green lately.