Jazzer Posted May 6, 2012 Share Posted May 6, 2012 Hi, I need some help please... I have a Trace Elliot GP12 SMX head... Occasionally when I turn the mains switch on there is an awful loud buzz... this happens with or without a bass plugged in [b]and with the standby switch on[/b] (which I thought should stop anything getting to the speaker??) After turning it on and off once or twice, the amp switches on normally / silently and works without the buzz. Does anyone have any idea what the problem is..?? I'm worried that this intermittant problem will become permanent (maybe on a gig!) and I'll be stuck. Many thanks for any help or advice. Please PM if you can help me. Quote Link to comment Share on other sites More sharing options...
Jazzer Posted May 8, 2012 Author Share Posted May 8, 2012 Just in case it's helpful, the head is a Model 4001 GP12SMX 280Wattt RMS (580W peak) Many thanks for any advice... I can'tunderstand how I can get a buzz when the standby switch is on?? Is it a relay or a cap or diode about toi fail in the power supply? If the above is twaddle, I'm sorry..... a little knowledge is dangerous... I really need any suggestions or help on offer. Many thanks Quote Link to comment Share on other sites More sharing options...
thepurpleblob Posted May 8, 2012 Share Posted May 8, 2012 The circuit diagram I have for the GP12 doesn't show a standby switch but there do seem to be a bunch of different takes on that amp. If it sounds like a "motor boat" then, yes, I would peer suspiciously at the big smoothing caps in the power supply. However, we are both guilty of forum-based guess work. It's probably easiest to take it down to an amp tech and get it sorted. It's unlikely to get better and will most likely get worse. Quote Link to comment Share on other sites More sharing options...
Japhet Posted June 13, 2012 Share Posted June 13, 2012 These apparently had a problem where a star washer was missing on the earth strap to the chassis. I've only just found this out and have already blown mine up twice so it's worth checking this out. It was a manufacturing fault which costs a few pence to sort out. Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted June 14, 2012 Share Posted June 14, 2012 (edited) For a moment I thought that this amp does not have a Standby switch, but it does - I looked at the amp manual. The problem is that most probably it does not work as in valve amps. When the switch is in "off" position in valve amp the power supply voltage for the power amp (valves) is disconnected. But this is not the case in SMX 12 . It has only one valve in the preamp section so most probably the standby switch turns off only the valve - the rest of the amp still works. It means that you shouldn't worry for the switch but rather give the amp to a tech to fix it. Or, maybe try to replace the valve first. EDIT: it can be also a problem wit a power amp - depending on what you mean by "loud buzz". Can you record the sound and post it somewhere (and post a link to it here)? You can still investigate the problem a little bit by pluging a cable directly into the Power Amp Input and not into the Preamp Input. Do you still get a buzz in this case? Mark Edited June 14, 2012 by MarkBassChat Quote Link to comment Share on other sites More sharing options...
Subthumper Posted June 17, 2012 Share Posted June 17, 2012 Sounds like it might be a smoothing cap issue. I've seen quite a few Traces and Ashdowns(very similar power amp pcb) with failed solder joints on the main smoothing caps.This will cause horrible hum and buzz as the amp will be running on an unsmoothed supply. Its a very easy job to fix as removing the pcb is just 4 screws and then resolder the joints. Be careful removing the screws at the back as the heatsink may well be carrying some stored charge from the caps and will short out to the screwdriver. Whilst its out check the whole board for bad joints plus all the wire connections. Good luck cheers Just Quote Link to comment Share on other sites More sharing options...
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