I have a AmpegSVT 6 pro that had been experiencing volume drops. I sent it a Tech that I think has a lot of experience with these amps. He sent me back an explanation with the issue of a bad MOSFET failing causing other issues. For the total repair it will cost me 470 or so. Any opinions on this? I could go either way, 500$ could be a nice amount towards a new amp...So should I cut my losses? Or should I fix it?
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Advice on amp repair needed......Svt6 -pro
- Thread starter chandman1004
- Start date
In other words the Tech doesn't want to work on it. 
I would question that diagnosis unless they actually put it on a bench and measured it. A bench charge can be expensive itself but is usually refunded if you opt for the repair.
Maybe post a vid how it's loosing volume as I've seen some pretty good diagnosis of amp issues when people post vids/sounds and give more details.
You are right though $500 will go a long way towards a new amp these days!
I would question that diagnosis unless they actually put it on a bench and measured it. A bench charge can be expensive itself but is usually refunded if you opt for the repair.
Maybe post a vid how it's loosing volume as I've seen some pretty good diagnosis of amp issues when people post vids/sounds and give more details.
You are right though $500 will go a long way towards a new amp these days!
As an amp tech, not only does that repair quote seem ridiculously high, I also get the idea that he does not want to work on it and just gave you a super high quote so you would go away. Even if all the FETs had to be replaced it should not be that expensive of a repair.
One quick thing to check is the effects loop. If you run a patch cable from the send to the return on the effects loop does the problem go away? I have seen lots of these Ampeg SS amps come through with dirty Effects Loop jack switches causing volume fluctuations. Also do the same with the Pre-Amp out/Power Amp In jacks. there is also a switch in there that the signal passes through.
One quick thing to check is the effects loop. If you run a patch cable from the send to the return on the effects loop does the problem go away? I have seen lots of these Ampeg SS amps come through with dirty Effects Loop jack switches causing volume fluctuations. Also do the same with the Pre-Amp out/Power Amp In jacks. there is also a switch in there that the signal passes through.
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Yes,this is true... I did try the effects loop cable before I sent it off. Guess I'll just have him send it back. Anyone want a former shell of a SVT 6 pro cheap?
If you like the amp take it to an Ampeg Certified repair tech and get it done right.
I'm a tech, but not an amp tech. I have worked on amps before though. I agree that the quote you were given sounds high. Those amps are kind of a pain to work on, so perhaps he doesn't want to deal with it.
I'll second taking it to an Ampeg certified repair tech. If you're gonna pay to get it fixed, do it right.
I'll second taking it to an Ampeg certified repair tech. If you're gonna pay to get it fixed, do it right.
Agreed but do any of the amp manufacturers really check about the technical competency of a particular shop and their brand of amp? For that matter, do the authorized shops get access to tech repair updates?
- Feb 12, 2006
- 60,984
- 5
- 220,760
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The first thing that jumps out to me is that a defective or "failing" MOSFET is not going to cause volume changes like you describe. They are used in source follower mode and provide no voltage gain (in fact there is a small loss).
If a MOSFET (or the associated source resister) opens, you will hear no difference, but the current sharing between devices will suffer (which is the reason all QUALIFIED, PROFESSIONAL techs perform a current sharing test).
If a MOSFET shorts, it will generally open the power supply protection fuse(s) and trigger the DC offset protection. The amp will no longer work or be extremely distorted.
I am going to suggest that you find an Ampeg authorized service center that has a good track record with Ampeg, and had experience with this amp. Give the manufacturer's service manager a call and ask him who they would recommend.
On another note, I have recently seen a number of service shops (or techs) change their business model where they don't even repair anything but the easiest amps. They simply generate outrageously high estimates that guarantee nobody in their right mind will accept, and then pocket the (equally outrageous) estimate fee, often without ever testing, opening or even looking at the amp. When the actual repair is unrelated to what the estimate claims, that's when I call BS on a tech for shirking their duty of being honest to the customer. Small claims court often looks favorably on going after this sort of consumer fraud when challenged, but you have to have your paperwork in order, and you will only get your estimate fee back (which a tech that has any pride should offer anyway).
If a MOSFET (or the associated source resister) opens, you will hear no difference, but the current sharing between devices will suffer (which is the reason all QUALIFIED, PROFESSIONAL techs perform a current sharing test).
If a MOSFET shorts, it will generally open the power supply protection fuse(s) and trigger the DC offset protection. The amp will no longer work or be extremely distorted.
I am going to suggest that you find an Ampeg authorized service center that has a good track record with Ampeg, and had experience with this amp. Give the manufacturer's service manager a call and ask him who they would recommend.
On another note, I have recently seen a number of service shops (or techs) change their business model where they don't even repair anything but the easiest amps. They simply generate outrageously high estimates that guarantee nobody in their right mind will accept, and then pocket the (equally outrageous) estimate fee, often without ever testing, opening or even looking at the amp. When the actual repair is unrelated to what the estimate claims, that's when I call BS on a tech for shirking their duty of being honest to the customer. Small claims court often looks favorably on going after this sort of consumer fraud when challenged, but you have to have your paperwork in order, and you will only get your estimate fee back (which a tech that has any pride should offer anyway).
While I think everyone has good points, the person I sent it too worked for St Louis Music when they owned Ampeg. Possibly had a a hand in designing it. This is why I chose to send it out of state to him . That being said I have no idea on his honesty or business practices. He has offered a somewhat lower price to repair it and I may go with that .
- Feb 12, 2006
- 60,984
- 5
- 220,760
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Replacing all the MOSFETs is not a proper way to address your problem.
Proper diagnosis is necessary to identify what the actual cause is.
Proper diagnosis is necessary to identify what the actual cause is.
- Feb 12, 2006
- 60,984
- 5
- 220,760
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Agreed, perhaps there was a misunderstanding with what he said. PM me.
