Behringer PMH1000 revisited

[drewl]

So, I had a PMH1000 with a DPA300-2 power amp that had a blown right channel.

After reading up, I rebuilt the power amp and it's up and running, so far it looks okay.
I've got about a 178khz signal on both outputs, about .7v ac.
Don't suppose this is normal is it?
Possible the output filters could have a problem?

I gotta' get some Neutrik adapters.

[soundguruman]

HF background oscillation in a behringer is pretty normal. Is the 178 khz there when the inputs are shorted to ground?
Anyhow, amps made in China do not have remarkable noise specifications. Sounds like some well placed snubber caps could improve the design. There is certainly some simple methods to kill response above 20khz.

[Jazz P Bass]

178K sounds as if it may be the switching frequency of the power supply (SMPS isn't it?)
Try going in the "power amp in" jack.
This will bypass the premp section.
If it still does it, either it is the power supply or you still have a problem in the power amp itself (filtering, as posted)

[Enzo]

My first thought at that HF noise signal is an artifact of the digital amp. That one HCA4001 handles both channels, and I'd be looking there.

Easy enough to look at the power rails for HF riding there.


Also, is that signal still present with a speaker load connected?