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Author Topic: Peavey VSS-20 amplifier with chorus noise problem  (Read 242 times)

jpcar

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Peavey VSS-20 amplifier with chorus noise problem
« on: September 16, 2020, 10:48:25 PM »
I have a problem with the chorus on this amp. When the chorus is switched on it comes with a white noise type of hiss. The volume controls don't change the noise. Thankfully most of the 8 pin ICs are socketed, so I was able to easily change U3 (TL072). Same problem. I'm wondering if I should change the capacitors next: C52, C47, C48, C49. Might bad capacitors cause noise like this?
Or any other parts I should look out for?

Thanks,

Enzo

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Re: Peavey VSS-20 amplifier with chorus noise problem
« Reply #1 on: September 17, 2020, 12:50:41 AM »
U3 and all those caps are the chorus clock circuit, they are not in the audio path.

U2, U7 Q6, Q7 are the chorus path.  MAybe Q5 too but I doubt it.  Turn chorus on, you get hiss.  Power off, remove U2, power on.  His still there?  You won't get a chorus signal with U2 gone but we are looking for the noise now.  Still noise?  Remove U7, same question?

Make SURE not to install ICs backwards.

jpcar

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Re: Peavey VSS-20 amplifier with chorus noise problem
« Reply #2 on: September 17, 2020, 02:41:33 PM »
So,

Removing U2 the noise remains, but removing U7 and the noise is gone.

Now I need to find a MN3007 online.

Thanks!

edvard

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Re: Peavey VSS-20 amplifier with chorus noise problem
« Reply #3 on: September 19, 2020, 03:38:00 PM »
Make sure you buy from a reputable seller; there are some counterfeits ever since the MN-series bucket-brigade delay chips went out of production, though on eBay you're more likely to encounter salvage chips, which are a good deal if they aren't dead.  If they're actually listed as salvage and are cheap enough, I'd order two or more to make sure you get at least one good one. 


YouTube link: (Part2) Detecting Fake Ebay ICs Chips - Sound Test




Smallbear carries genuine NOS stock at somewhat of a premium ($10.95 at the time of this posting), but at least you know you're getting the real deal. 
Xvive is making re-issues, but they may be a little hard to find, and are on the expensive side ($25 and up from what I could find).  They sound as good as the originals, from what I hear.

« Last Edit: September 19, 2020, 03:39:01 PM by edvard »

jpcar

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Re: Peavey VSS-20 amplifier with chorus noise problem
« Reply #4 on: September 21, 2020, 07:34:27 PM »
Thanks for the advice!
I found a Xvive reissue on Ebay for $12 + shipping so I went with that. Should arrive in a few days.
I'll post how it turns out.