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Ampeg SVT-8 Pro Power Supply Help
Ampeg SVT-8 Pro Power Supply Help
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Old 8th September 2014, 04:25 AM   #1
Upionics is offline Upionics  United States
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Join Date: Aug 2004
Location: Santa Fe, NM
Default Ampeg SVT-8 Pro Power Supply Help

I have an Ampeg SVT-8 Pro that has a weird story but basically died one day and the Fault and Limit lights stay on constantly. Preamp section tests out good and passes signal. I am somewhat sure that it is the Class D 2500 Watt power amp section that may just need to be replaced entirely.

But... I want to make sure the Power Supply is good. Testing seems fine, the rails have steady voltage and the +/- match fairly closely. Preamp tube section is getting power just fine. There are even LED's that light up.

And... here is the thing, some of the voltages don't match and I don't know enough to tell if/where the problem is or if there is a typo on the schematics.

Schematics for the power supply are attached and they were sent from Ampeg. My concern is at J2 and J3 on the second page, it specifies +/- 120V. But I am getting +/- 138V.

Then the real kicker is J7 on the second page. It specifies +/- 12 V Float and I am measuring +/- 120V!! I triple checked thinking I was crazy!

So is that just a typo on the schematics? Maybe the 138V is still in range? What else could be wrong?

I haven't gotten a quote on the power amp module yet, but I assume it isn't cheap and I would hate to blow it up without making sure the power supply checks out.

Thanks in advance!
Attached Images
File Type: png Ampeg-SVT8Pro-PS1.png (190.8 KB, 109 views)
File Type: png Ampeg-SVT8Pro-PS2.png (274.2 KB, 104 views)
File Type: png Ampeg-SVT8Pro-PS3.png (212.9 KB, 101 views)
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Old 2nd October 2015, 10:31 AM   #2
gzzdkj is offline gzzdkj
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Join Date: Oct 2015
Default i want svt8 amp schematics

i have a worry ampeg svt8. amp part is some worry.but i hanve not schematcs for this part . could you give me svt8 power amp schematis? thank you so much.
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Old 2nd October 2015, 11:51 AM   #3
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
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Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
J2 ans J3 are about right as it will be off load. J7 is + - 12V floating at 120V or 138V.
I would check your centre point on the power stage before doing anything else. I don't have a schematic on the amp section so if you need any further information, please forward it to my email address and I will help you repair it. jon@jonsnell.co.uk
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
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Old 2nd December 2015, 12:51 PM   #4
Ampeg is offline Ampeg
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Join Date: Dec 2015
Default Ampeg SVT-8 Pro Bust

Looks like I have a busted power amp section as well, disconnect the power amp board and it comes out of protect. Changed a shorted FET on the power amp board, but still in protect, so looks like more going on. Pre-amp section works fine. Any schematics for the power amp section available from anyone?

All help greatly appreciated.

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Old 22nd May 2018, 10:27 AM   #5
fieldsbart is offline fieldsbart
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Join Date: Feb 2015
I have a broken Ampeg svt-8 pro as well. I was wandering about the float circuit as well.
On mine j7 1st pin is - 127 2nd pin -108 and 3rd pin is -127, is that correct? I get signal up to the power amp
input ic10.
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