Diagnosing Preamp / Receiver channel drop + static

September 6, 2018 9:19 PM

I have a Adcom GTP-400 Preamp / Receiver and a GFA-535 amplifier. I have had issues where a channel (it can happen to either channel) will drop low and have some static. See inside for further explanation, but how can I try to fix this myself?

I have a Adcom GTP-400 Preamp / Receiver and a GFA-535 amplifier.

I have had issues where a channel (it can happen to either channel) will drop low and have some static. When I push the power button on the amplifier and hold it in, the channel will clear and return to full volume, and if I turn it off and on, it will also clear and return to full volume.

This led me to believe it was the amplifier causing the problem, so I swapped it only to find the problem was still happening.

• I have swapped cables between the audio source (it happens both from a record player and an Apple Airport Express)
• I have swapped cabled between the Preamp and the Amplifier
• when headphones are plugged in the same channel drop and static happening with the speaker happens with the headphone.

Any ideas of where to start?

I know I can take it to a repair place, but I also like learning new things and trying to repair things myself.

Thanks!!!

posted by apetpsychic to Technology (2 answers total)

I did a little bit of Googling and your issue seems to be recurrent with that model of preamp, and seems to be related to the input selector knob. It may have a fleck of dust in it, there maybe slight corrosion, or a solder joint could be a little loose. One way to diagnose would be to wiggle just that one knob when you're hearing the problem.

People have resolved it by twirling the knob a lot, using tuner/contact spray, or resoldering joints.

Hope this helps -- definitely google the model number and "static" to see the pages I found.
posted by seanmpuckett at 6:58 AM on September 7, 2018 [2 favorites]

I'm a big fan of Nu-trol contact cleaner for cleaning controls and switches. Sounds like your issue is definitely in the preamp if you hear the channel dropouts through the headphones. (This wouldn't be true in the case of most stereo receivers, where the headphone output is derived from the power amp output, but in your case with separate pre/power amps, the headphone output comes strictly from the pre amp.) +1 on seanmpuckett's advice; gently wiggle controls and switches when the issue is happening to see which control correlates with the problem.
posted by Larry David Syndrome at 7:21 AM on September 7, 2018 [1 favorite]