TheGreek Posted July 19, 2018 Share Posted July 19, 2018 For those who know how to play with electronics https://www.ebay.co.uk/itm/Ampeg-Svt3-Spares-Or-Repair/253762566117?hash=item3b156d77e5%3Ag%3AtLUAAOSwRNlbUKZI&_pgn=4&_nkw=repair&_from=R40&rt=nc Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted July 19, 2018 Share Posted July 19, 2018 One sets the bias on solid-state amps now..? Could be why it smoked..! Quote Link to comment Share on other sites More sharing options...
Bigwan Posted July 19, 2018 Share Posted July 19, 2018 Nice find! Quote Link to comment Share on other sites More sharing options...
paul_5 Posted July 19, 2018 Share Posted July 19, 2018 (edited) 5 hours use since the service and it smoked - I'd be having words with whoever 'biased' it... I'd have a go at this if it wasn't collection only. From Plymouth. Edited July 19, 2018 by paul_5 Quote Link to comment Share on other sites More sharing options...
Roger2611 Posted July 21, 2018 Share Posted July 21, 2018 I was talking to my local repairer a few months back and mentioned that I had the SVT pro 7 (now sold!) he said "get rid of it whilst it still works" apparently the Ampeg digital amps are incredibly complex and are near impossible to work on (something to do with different amp sections needing to remain linked whilst any work is done) possibly it was having issues before the "service" and the repairer was unable to do anything with it? Quote Link to comment Share on other sites More sharing options...
TheGreek Posted July 21, 2018 Author Share Posted July 21, 2018 I've sent the link to my local amp tech who normally works miracles...I'll tell you what he says. Quote Link to comment Share on other sites More sharing options...
Hellzero Posted July 21, 2018 Share Posted July 21, 2018 Ok, easy fix, replace the filtering capacitors that have simply blown. That's what the humming noise is. Will cost you a few quids if you can do it yourself. I used to run my own repair workshop some 20 years ago... Quote Link to comment Share on other sites More sharing options...
Hellzero Posted July 21, 2018 Share Posted July 21, 2018 On 19/07/2018 at 21:33, Dad3353 said: One sets the bias on solid-state amps now..? Could be why it smoked..! And "recently had all new valves and the biasing set on an oscilloscope"... In the preamp section, where the bias is useless as it's an automatic one. Funny repairer, indeed. Quote Link to comment Share on other sites More sharing options...
Hellzero Posted July 21, 2018 Share Posted July 21, 2018 As the amp is still turning on ("followed by a small amount of smoke from the back and loud humming"), it means that the ouput transistors are still sound and safe, otherwise the mains fuse would have blown. It could be interesting to know who that "Spike" is... Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted July 21, 2018 Share Posted July 21, 2018 42 minutes ago, Hellzero said: As the amp is still turning on ("followed by a small amount of smoke from the back and loud humming"), it means that the ouput transistors are still sound and safe, otherwise the mains fuse would have blown. It could be interesting to know who that "Spike" is... 'Still turning on' probably translates to 'the Power LED lights up. The 'small amount of smoke' is probably the o/p trannies frying, or the bridge rectifier, which would explain the hum. The mains fuse may well be a chunk of milk-bottle top. Difficult to be precise, of course, but from the description given, I'd say that it's in need of more than a wipe-down with a dry cloth. I'd give it a miss, myself. Quote Link to comment Share on other sites More sharing options...
Hellzero Posted July 21, 2018 Share Posted July 21, 2018 Yes, and if the Power LED lights up, than the bridge rectifier is still alive as in this circuit everything is operated after it, my guess, because remote repair is always a guess, is as I wrote the filtering capacitors that have blown as it's still humming, so "working". That said, I wouldn't bid any higher than 20 quids... Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted July 21, 2018 Share Posted July 21, 2018 (edited) 21 minutes ago, Hellzero said: ... the filtering capacitors that have blown... Maybe they just need biasing, and a smoke refill..? ... Edited July 21, 2018 by Dad3353 1 Quote Link to comment Share on other sites More sharing options...
Bigwan Posted July 24, 2018 Share Posted July 24, 2018 (edited) On 21/07/2018 at 19:33, Roger2611 said: I was talking to my local repairer a few months back and mentioned that I had the SVT pro 7 (now sold!) he said "get rid of it whilst it still works" apparently the Ampeg digital amps are incredibly complex and are near impossible to work on (something to do with different amp sections needing to remain linked whilst any work is done) possibly it was having issues before the "service" and the repairer was unable to do anything with it? The SVT3 is a different beast - a "lead sled" that is much more serviceable. The SVT7 is a class D and your repairer is quite right... repair folks are scared of them and won't touch them with a barge pole! Tempted by this myself... Edited July 24, 2018 by Bigwan Quote Link to comment Share on other sites More sharing options...
Twincam Posted August 24, 2018 Share Posted August 24, 2018 On 19/07/2018 at 20:33, Dad3353 said: One sets the bias on solid-state amps now..? Could be why it smoked..! Many solid state amps do indeed have bias adjustment. On 21/07/2018 at 19:53, Hellzero said: Ok, easy fix, replace the filtering capacitors that have simply blown. That's what the humming noise is. Will cost you a few quids if you can do it yourself. I used to run my own repair workshop some 20 years ago... No and yes. These amps are known for humming when bias is wrong. Indeed filtering capacitors when going do make an amp make humming noise. But then again many things can cause humming in an amp to just simply whip out the capcitors first in this amp would probably be wrong unless the caps had clearly blown. Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted August 25, 2018 Share Posted August 25, 2018 32 minutes ago, Twincam said: Many solid state amps do indeed have bias adjustment... Have you any examples to illustrate this..? We're discussing bias adjustment as a routine maintenance task, not the pre-set bias set by the manufacturer, and most unlikely to need attention, unlike a valve amp. It's true I've not been servicing amps for a couple of decades, but in my previous experience in both hifi (Cambridge Audio...) and as a music technician (most makes...), I never came across the need for biasing any SS amps, unless setting up as part of the manufacturing process, never as a maintenance task. Has this changed..? Quote Link to comment Share on other sites More sharing options...
Twincam Posted August 25, 2018 Share Posted August 25, 2018 23 minutes ago, Dad3353 said: Have you any examples to illustrate this..? We're discussing bias adjustment as a routine maintenance task, not the pre-set bias set by the manufacturer, and most unlikely to need attention, unlike a valve amp. It's true I've not been servicing amps for a couple of decades, but in my previous experience in both hifi (Cambridge Audio...) and as a music technician (most makes...), I never came across the need for biasing any SS amps, unless setting up as part of the manufacturing process, never as a maintenance task. Has this changed..? As much of a routine task say like many a valve amp then that would be no. But of course some valve amps also don't need biasing routinely or at valve change either. And I would suggest if any valve amp needs that regular biasing something might be wrong. Bias is as you know factory set on solid state amps and it drifts much less over the amps lifetime than traditional valve tech and may even never need to be touched within a reasonable time frame. Older solid state amps may (probably) need adjustment. And if there's an issue, blown transistor etc and it's replaced (Not that uncommon) biasing certainly needs to be done. I dare say that a solid state amps bias should also be checked on proper routine service and certainly on an older amps service. It may not be as critical an issue as valve tech but still can cause problems. So yeah solid state bias while less of an issue than valve is still part of maintenance. There are a few ampeg amps, solid state based that are known for some bias issues. From my experience the svt 3 pro and br2 need adjustment. Quote Link to comment Share on other sites More sharing options...
Phil_T Posted August 25, 2018 Share Posted August 25, 2018 I'm not techically minded so some of the might not 100% correct but - On the SVT 3 pro there is a tiny trim pot that sets the voltage being sent to the MOSFETs and it is known for either not being set correctly in the first place or drifting over time such that MOSETs become starved of power. It's an easy fix in principle but difficult to get right in practice because the trim pot is ridiculously sensitive making it very easy to run the MOSFETs too hot and blow something. There's lengthy thread on the other forum about this with all the info anyone needs to attempt it, 1 Quote Link to comment Share on other sites More sharing options...
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