Profex 2 with buzzing in audio

Ken Fox · From: Nashville GA USA

I had two that came in with a buzzing sound in the audio, worse as the note died away. Similar sound that the not so good compressor makes as it dies away. This was on all settings. Scope revealed what looked like ringing pulses on top of the sine wave, when injecting a signal. Traced it to coming out of the digital to analog chip. Note temperature on the -12 volt regulators were running hotter than the +12 volt regulators as well.
I replaced the Burr Brown, PCM56P with a better PCM56P-K. The K series has a far better THD specs. Fixed both units.
By far the reverb sound in these was the best I have ever heard. Seems the upgraded chips were a great improvement. Also both regulator chips were running even and cooler in temperature.

Note I normally do not do any solid state repairs. I spent hours chasing down this at my own expense. Another reason I am only repairing tube amps now!

Ken Fox · From: Nashville GA USA

Just a note to add here. I do not stock or sell these chips. They were around $21.00 each and shipping from Mouser.

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