Ampeg 400T solid state rack amp

[Mars Amp Repair]

Hello folks,
I've also posted on the schemo request page...just don't know if that's viewed as often.

We are in need of the Ampeg SVT400T rack amp schemo. It has bipolar output transistors & is different than any of the other schemos I can find.

Through the power amp in, which seems to go directly to the power amp stage through one dual opamp, we have one channel that is very weak compared to the working one...but its signal is completely clean...kinda like if you had a weak coupling cap.

It is helpful to have the other identical channel that is working, but we've traced as far as we can (basically around in circles) so far. It's a little precarious trying to trace with the circuit board removed, too.

Has anyone experienced this type of symptom with one of these or does anyone have a schemo they can provide.

thanx, glen

[Enzo]

Wow, TO3s and TO39 drivers. How OLD is this thing? Ah, about 22 years. My first thought might be to look at the muting.

[Mars Amp Repair]

Hey Enzo,
Thanx for the schemo...you dah man! My tech looked all over the web for that thing, before he informed me of it. I just knew someone here would have it. Trying to ferret our way around w/o the schemo was proving to be rather difficult.

Yep, we're thinkin' about early 90's, too.

Interesting to see how the layout was the predicessor to the present day SVT4pro type series. As all, we sure wish Ampeg & these other companies would put access panels on the bottom...man that would make the job soooo much simpler.

You once mentioned that you had come to a kind of 'Zen' with the Peavey CS600 & similar series...we've kinda gotten that way with the SVT4Pro's. they suck to work on, but like anything you do enough of them & it gets to be kind of a personal victory & feather in your cap type affair.

I remember in the beginning I dreaded to even take that beast out of it's casing. Now it's just kinda 'what cha gotta do'. I've got one tech who takes those things on as a challenge. I just love it when my techs can approach things that way & not just piss & moan about it all day.

I used to do that when I was younger...now you just realize what a waste of energy that is & how if you just change your outlook, you can put that energy to good use & come out the other end having gained the experience & feeling ready for next one you get...suddenly you find yourself the 'expert' on that model just because you took the time to learn [ sometimes a dubious distinction, tho ;-] ]

Thanx again Enzo...glen

[Enzo]

Zen indeed. I recall one day it was 15 min before closing, so I thought I'd pop open the blown XR600 before me to see what it needed for tomorrow. Shorted outputs, etc. 11 minutes later, it was reassembled and running on the burn-in bench. No big pat on the back, just did enough of them. Now what can I do for the next 4 minutes...