Clavinet C with Very Low Output Volume

Tech Questions Regarding the Hohner Clavinet and Pianet.

Clavinet C with Very Low Output Volume

Postby analogsynth1 on Tue Oct 09, 2012 9:33 am

Hoping someone can steer me in the right direction. I've got a Clavinet C with a low output problem. I believe the pickups are good as I can hear sound out of each of them and they measure about 180 ohms across their leads (can someone confirm that is the right DC resistance?). The rocker switches were initially making a lot of static and crackling noise in certain positions, so I disassembled them and carefully cleaned the contacts. Now there is only a pop when I switch them back and forth.

In the preamp itself, I replaced all the electrolytics with new, good quality caps. I removed every resistor and tested to make sure the values were right and I sourced NOS AC151R transistors and swapped new ones in. Since the schematic doesn't have reference voltages, I was able to simulate the circuit in software and get expected voltages on the emitter, base and collector of each of the two germanium transistors. When I disconnect the pickup leads to the board (from the rocker switches), I measure voltages similar to what the simulation says should be there. When the pickups are reconnected to the preamp (load on the circuit), I am only getting 0.05 and 0.04 volts on the base and emitter of both, when I should be seeing over 10x that voltage (no matter which transistor, new or old, that I have soldered in).

I'm pretty much at my wit's end with trying to figure out the problem. The volume coming out of the output jack is about 10% what it should be (like volume on '1').

Weird thing this morning - I plugged the battery in, turned my guitar amp on, played a chord and BOOM- there it was in all it's glory for 2 seconds, then the sound disappeared again. I didn't touch anything when the volume went away.

Anybody seen this before or have enough electronics knowledge to know where the issue may be?

Thanks in advance!
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