Crate PA-B8350 Mixer

[TwinBeech]

I am still sorting out my Crate mixer amp and have found a strange occurance. I can put an audio signal sine wave into the mic low Z input and control it by the channel gain but the master pot is bad and has no effect except to cause noise and block the signal. When it is letting the sine wave through all the controls seem to work..

What is funny I can put a microphone into the channel and get nothing. All 8 channels work with the signal generator just not voice. Maybe the level of the signal generator is higher? It is a small 9volt powered DIY kit I got to troubleshoot this amp. I have ordered a Peavey pot to replace mine so when it comes in I will see if that makes a difference.

[The Dude]

The signal generator is probably closer to line level or at least hotter than mic level. (guessing without knowing specs). You could always add a pot to your generator so that you could vary the output.

[Jazz P Bass]

Not sure if you are in possession of the schematic or not.

Here it is: PA-B6350 _ B8350.zip

[TwinBeech]

Thanks so much for the files. I have the schematic and parts list from MusicParts.com that I got for $20. It has a parts placement scan also but is hard to read in spots. Still better than nothing.

[Jazz P Bass]

So, have you taken note of the voltage references?

[TwinBeech]

I suppose you are talking about the Test Points? Not really. Just tracing signals so far. My signal gen needs to be set up for 12mV P/P and I cannot get it any lower that 1/2 V P/P. I will try adding a pot and calibrating it. Waiting for the new master gain pot first.

[J M Fahey]

Add a fixed attenuator between generator and amp input.
100k in series with 1k (100:1) will output 10mV if fed 1V .

Scale for any other needed voltage/attenuation.

[TwinBeech]

That is good info. I was going to measure the current then figure out the R value. The little gen is happier at 1V P/P anyway.