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SVT4 Bridge problems / Smoke

V

vij

Nov 21, 2007
30
0
#1
My SVT4 started to smoke a bit. I opened it and found some burned resistors in one of the power amps. I replaced them but it just burns up again.

I called the local repair man and regarding this and his first question was if I was running bridged and yes I do.

He said that "they always break down if you run it in Bridge".

Is this truth?

Did any one have problems running SVT4 in bridge mode? I have heard about overheating but thats all. I had my amp (it is a used MIA) just a few months so I have no experience of this.

I have the proper Bridge cable and I am running a 410HLF 4 Ohm speaker.

Jocke...........
 
#2
I have never heard that SVT-4 Pros have ANY problem with bridged mono. I've had my SVT-4 Pro sitting in BM for two years on my 4 ohm 810E--never had any issues.

If multiple resistors are shot, then there is most likely something before those parts in the chain that have the problem. There could've been an electrical spike of some kind or a reverse-polarity issue. I would check out the transformer, preamp tube feed, and output transistors. Unless you're an old hand at working on SS amps, I'd have a certified Ampeg repair center or Ampeg perform the inspection and repair.

Which resistors were burned?
 
#6
Thanks for the answers. Some thing is for sure wrong. The funny thing is that it went to smoke and sparks between two songs when I was not playing.

We will see what comes out.

Jocke......
 
#11
2 ohms is a no-no bridged.

Absolutely no reason bridged at 4 and above should be any worse than stereo...... in fact it is a bit easier on the power supply. I'd suggest that bridged is THE way to operate the 4PRO........

if yu weren't playing it at the time, that makes it even odder........ raising the possibility of some form of mains surge, etc...... Hard to tell.

In any case, take it to a DIFFERENT tech, and get it fixed right. If there are any bad MosFets, make sure the tech knows to replace them with matched ones..... should be available from "Loudpeg" service... if they are NOT matched, problems will repeat...... I designed that poweramp circuit, actually originally for a different, earlier product, not the version in the 4PRO, and can assure you that it isn't a problem.

Just as a case in point, one of the tests that I ran as a verification for the original product was to set it up producing full output, short the speaker leads, and leave them shorted with the unit still set at full output for 4 hours. The unit worked fine afterwards, as expected.

The 4PRO version is a little different, but is still the same basic unit, with actually a bit more heatsink than the original.
 

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