[sdiy] Clavinet C Preamp Problem

Paul Perry pfperry at melbpc.org.au
Thu Oct 11 02:36:42 CEST 2012


Most likely, this means that the circuit has a fault (probably a break) 
leading to incorrect bias of the transistors. Reversing the battery will 
lead to the caps having "strange' voltages on them.. and as luck would have 
it, this solves the bias problem until the cap in question discharges.

Alternatively, the 1.5K or 6.8K might be disconnected, which would lead to 
the transistor bias beign unstable, and the circuit might be working until 
the second one saturates.

In any case, checking the voltages on the transistors with respect to ground 
would give a pretty good clue.

----- Original Message ----- 
> The preamp is only putting out a very minimal signal.  Weird thing is, 
> when I reverse the battery terminals, holding the >battery on backwards 
> for a while, then flip it back right, the Clavinet will work perfectly for 
> about a minute or two, then a >little static comes and the volume drops 
> WAY back down again.  I can reliably repeat this process.

paul perry Melbourne Australia 




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