Janus Suitcase -30V coming through outputs

[craig]

Hey everyone. I'm working on a 77 Suitcase Janus-slider preamp version. The power amp fires up ok, and I get the +/- 15V where they should be (5 pin cable out, at the voltage reg board out), but  all I get is a loud buzz from any of the outputs (preamp out, speakers buzzing...). I'm not getting any piano signal  and I'm measuring -30V at each output jack. Both channels are identical at the speaker out (buzzing) and the preamp out from the power amp. Nothing visibly wrong/blown on any of the boards, no visible output transistor leakage (though that might not mean much). The buzzing is still there with the preamp unplugged. Anybody have any experience with anything like this? Any thoughts? Output transistors? Grounding issue? Thanks!

[Jenzz]

Hi :-)

Do you have both + / - 30 V from the power amp power supply (the 2 big caps)?

Check or replace the 1uF cap (C2) across the offset pot. If it fails / shorted, the output is totally out of DC balance and full supply voltage can be seen at the output. Had this issue on some Suitcase Amps in the past....


Jenzz

[craig]

I wound up testing the output transistors and they were all out of spec, probably the cause for the buzz. I replaced those, recapped the 15V power board and the amp modules as well. Power amp is great, now on to the preamp.