I am trying to fix an Adcom GTP-350 pre-amp that has signal leakage from input sources. This is happening before the tone controls, but there aren't many components before the source switch and those controls. Both channels behave the same and all sources leak into each other equally as far as I can tell. The volume knob seems to be steep on the gain, through headphones and out to my GFA-5300. On top of that, there is some hum, but I'll be replacing the caps in the power supply. It's a simple unit, I don't understand what would make it behave this way. Any suggestions?
Thanks!
Matt
Thanks!
Matt
Maybe the input switch is dirty and conducting on all pins...
The same thing could happen if the ground uniformity is not present, .i.e. if there's a ground break somewhere, the impedance goes high, and inputs start coupling between them - capacitively.
Posting well lit and in-focus photos always helps.
The same thing could happen if the ground uniformity is not present, .i.e. if there's a ground break somewhere, the impedance goes high, and inputs start coupling between them - capacitively.
Posting well lit and in-focus photos always helps.
I replaced all the PS caps (except for the big filter caps that someone already did), no more buzz, and less noise. I re-soldered all the internal interconnects and removed the glue.
Also, I removed the listen and record switches, testing them out of circuit, all OK. The only issue left is that unconnected sources still have signal leakage.
Adcom neglected to install 47K resistors across the inputs, should they be there?
Thanks; Matt
Also, I removed the listen and record switches, testing them out of circuit, all OK. The only issue left is that unconnected sources still have signal leakage.
Adcom neglected to install 47K resistors across the inputs, should they be there?
Thanks; Matt