dasbin
Well-known member
I bought an OSA API clone off eBay, and it had a REALLY rough shipment. This is a very old OSA model, which uses a Jensen input trafo, 2520 opamp, and original API output trafo. So it's basically an exact API clone.
I've basically resoldered every lead and joint in the whole card but I'm still having a problem.
Essentially, there is no volume change throughout the first 80% of the gain pot's range. It is a pretty static 30db of gain. This is not the pot's fault - I tried replacing it with another one, testing it with a multimeter, and most importantly, disconnecting it altogether with the volume leads not connected in any way... and I STILL got that constant 30db of gain.
The highest 20% of the pot's range exhibits some change, but, when you crank the gain pot to full, or simply short the two wire leads connected to it (zero resistance), the preamp just puts out this big "pop!" then refuses to let ANY sound through at all, except when you hit the mic or make a really loud sound into it, then it will just POP momentarily then fall totally silent again.
What could be going on here?
I've basically resoldered every lead and joint in the whole card but I'm still having a problem.
Essentially, there is no volume change throughout the first 80% of the gain pot's range. It is a pretty static 30db of gain. This is not the pot's fault - I tried replacing it with another one, testing it with a multimeter, and most importantly, disconnecting it altogether with the volume leads not connected in any way... and I STILL got that constant 30db of gain.
The highest 20% of the pot's range exhibits some change, but, when you crank the gain pot to full, or simply short the two wire leads connected to it (zero resistance), the preamp just puts out this big "pop!" then refuses to let ANY sound through at all, except when you hit the mic or make a really loud sound into it, then it will just POP momentarily then fall totally silent again.
What could be going on here?