Any Ampeg SVT-II (non-pro) schematics??? - diyAudio
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Old 7th May 2008, 12:11 PM   #1
spirus is offline spirus  Greece
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Default Any Ampeg SVT-II (non-pro) schematics???

I have this SVT-II but the only schemos I managed to get were the SVT-II Pro which from what I've heard differ a lot, don't they?
Any one can help around?
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Old 7th May 2008, 03:26 PM   #2
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Default Re: Any Ampeg SVT-II (non-pro) schematics???

Quote:
Originally posted by spirus
I have this SVT-II but the only schemos I managed to get were the SVT-II Pro which from what I've heard differ a lot, don't they?
Any one can help around?
Try checking this page:

http://users.aol.com/bluemuse/schematics.html

If the schematic isn't there, it tells you where to get it. The St. Louis Music produced Ampeg stuff pretty much requires you to get the schema right from them.
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Old 7th May 2008, 04:25 PM   #3
GordonW is offline GordonW  United States
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Default Re: Re: Any Ampeg SVT-II (non-pro) schematics???

Quote:
Originally posted by Jim McShane


The St. Louis Music produced Ampeg stuff pretty much requires you to get the schema right from them.
If it comes to that, I hope the OP has better luck with them than I seem to, generally. LOUD Group is now the owner of all the St. Louis Music companies, including Crate, Ampeg, and SLM. In addition, they also own Mackie and EAW, among other companies.

Since the buyout, parts and service info has become like pulling teeth without anesthetics. Many parts are simply not supported, and it can take them as long as a week to get back to you (if at all).

I've started steering people away from any new equipment made by any of the companies the LOUD Group owns. I really hate "disposable" gear...

Regards,
Gordon.
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Old 9th May 2008, 11:00 AM   #4
spirus is offline spirus  Greece
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Default ahmmm

thanx guys
but the schematics there have little to do with the amp I have in front of me!
they seem alike but not the same circuits!

as for the LOUD group, I think I should not try to contact them for a schemo, right?
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Old 10th May 2008, 09:41 AM   #5
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What's the problem you are having with the SVT II.

This amp has a common problem with mosfet bias drift, resulting in noise, dsitrotion or low output, there is a simple procedure that I was given by an Ampeg engineer, if this what you are chasing let me know and I'll dig out the procedure.

Michael
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Old 15th May 2008, 06:23 AM   #6
spirus is offline spirus  Greece
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Default well not exactly...

well junction
the problem I'm facing is not exactly that...
the real problem is that they brought it to me and it has no output so I'm searching for a schematic to follow the signal path and see where it's put to gnd!

by the way, what u r refferring sounds "good"...
if you'd like to share that knowledge with us, I'd be more than happy to know what the common problem is and how it is solved, as I may run into this problem as I check the amplifier further on...
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Old 15th May 2008, 07:09 AM   #7
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I must have been brain dead when I read this, because the one I worked on was the Pro version, your's is clearly the non pro version, I'll post the details anyway, because it may be the same circuit in the mosfet power amp stage, maybe??

This info came form someone who used to work at Ampeg;

Adjust the trimpot closest to the mosfets for 25mv across the 0.47 ohm resistors in the mosfet source circuit. Average, so check each bank to be sure they are matching pretty well. No signal no load, obviously.

Be sure to have the pot at the LOW end of the bias voltage range to start with, or it will immediately draw a lot of current...........

If the mosfets are not matched for their Vgs(on), within 0.3V, they will never share well, and may fail at high currents. That was the factory spec, and the mosfets were sourced pre-matched and color dotted.

Before that procedure was followed there was a too-high failure rate. Once we introduced matched mosfets, there were a lot less failures.
.................................................. ...................
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Old 15th May 2008, 12:03 PM   #8
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SVT-II and II Pro are tube amps, no MOSFETS. Both are rackmount, but the Pro has a couple of extra features in the preamp (more bands on the EQ, different line-out, etc.)

Are you thinking of the SVT-3? That's an SS amp.
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Old 15th May 2008, 12:44 PM   #9
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Thanks for that note. sounds just like the SVT-4 I just rebuilt.
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Old 15th May 2008, 04:08 PM   #10
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Quote:
Originally posted by pharaohamps
SVT-II and II Pro are tube amps, no MOSFETS.
Yeh I really screwed up, okay my reference to Mosfet biasing is only applicable to SVTIII-Pro.

Sorry for the bum steer

Michael
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