| GK 700RB II preamp failure
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I have a custom made dual channel preamp, where one channel is a copy of the 700 and 1001RB pre with an extra bass knob in the voicing filters and without the "Boost" knob and function. It sat on my desk for the better part of a year because I had to give up playing for a while, but when I put it aside it was functioning correctly.
I picked it up a few days ago to resume playing, and after 30 minutes of playing the volume started to drop slowly and steadily, taking about 10 seconds from initial volume to totally silent. No pops, no crackling, no squeaks, no smoke, no smell of burning cable, no noticeable warning of something wrong except the drop in volume. Also, while this was happening, the Clip led came on, first with the -10dB switch off (when I turned it on the light came off), then eventually it remained on regardless of the -10dB switch position. The other channel (Fender Bassman pre copy) was unaffected. Nonetheless, I shut it down, unplugged it and changed the power cable and the socket it was plugged into, to be on the safe side. No change, except that the GK channel remained silent. However, I noticed the following behaviour: The longer the preamp stays unplugged, the longer it takes for the Clip led to come on (as it did the first time, first the -10dB switch off, then with it on as well) when it is plugged in and turned on.
I took the casing apart and started checking for broken cables or connections initially, but the slow and constant drop in volume makes me think now of a component failure on the channel's PCB, like a capacitor, a pot, an opamp or a diode or something. I'm out of ideas so I thought I'd ask around in case it's an easy fix.
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Extended Range Bass Club Member #88
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