stevie Posted January 4, 2009 Share Posted January 4, 2009 I've just bought a Trace AH200 head from the bay, which has a mains hum/buzz that I'd like to try and fix, with your help. It is not coming from the bass, as the buzzing is there whether the bass is plugged in or not. It sounds very much like a transformer buzz or a single coil pickup buzz at 50/100Hz. It is present all the time and is not affected by either of the volume controls or the graphic equalizer. It appears on the headphone out and on the DI out. The mains transformer itself does not buzz physically. The level is such that it's a bit annoying in a domestic environment, and would be unacceptable in a studio, but it is not really a problem live. I've tried to trace the problem by plugging another head into the same wall socket, and have found that it does not have the same problem. Unfortunately, I have no idea how to unplug the umbilical cord between the pre and power amps, or I could be a bit more specific about the source of the problem. I have discovered, however, that there are three electrolytic caps at a late stage in the preamp that give off a loud hum when I touch the cans with an insulated screwdriver - which I find a bit odd. To get to the solder side of the PCB, I assume that I have to remove the two volume knobs, the graphic caps, and the jack socket nuts - or have I missed something? I'm handy with a soldering iron and have a good multimeter, but have no knowledge of amplifier electronics to speak of. I'm hoping that this is a common fault and that someone can point me in the right direction. If I can't fix it myself I'll just live with it, at least for now. Quote Link to comment Share on other sites More sharing options...
BassBod Posted January 4, 2009 Share Posted January 4, 2009 I had the AH150 (series 6?) head years ago and it developed a bad but hard to find hum after two or three years. Trace took it back and fixed for nothing (including carrier) because they knew what the fault was - the plastic connector block between the pre/power amp shrunk with heat/age and pulled the wires a bit. I never looked inside, but that was what they told me, and I never had a problem with it again (another two years before I went SWR). Sounds like a tech job - good luck! Quote Link to comment Share on other sites More sharing options...
stevie Posted January 4, 2009 Author Share Posted January 4, 2009 [quote name='BassBod' post='370207' date='Jan 4 2009, 06:53 PM']I had the AH150 (series 6?) head years ago and it developed a bad but hard to find hum after two or three years. Trace took it back and fixed for nothing (including carrier) because they knew what the fault was - the plastic connector block between the pre/power amp shrunk with heat/age and pulled the wires a bit. I never looked inside, but that was what they told me, and I never had a problem with it again (another two years before I went SWR). Sounds like a tech job - good luck![/quote] Interesting, thanks. I'll check that out when I look inside again. Quote Link to comment Share on other sites More sharing options...
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