Antique Sound Lab AV-20 Mods.

[Ricardo]

I mentioned I would do these mods in another thread, but decided to create a thread of its own.

I got these little monoblocks a couple of months ago, and even though I liked their sound, I wanted to do some mods to make them better. I guess a part of me really enjoys the DIY side of audio; it is very satisfying to modify something yourself and actually hear a difference, plus, you learn a lot. I was done with crossovers (no more to upgrade), so I needed a new project.

I started investigating what could be done to these amps; recently I needed the bias instructions/settings for these amps and emailed Divertech.com (ASL distributors), from where Tash Goka quickly replied with the document I needed, so I decided to try them. This same guy replied and suggested the following mods:
-Swap the power transformer with the one for the ASL AV-25; this would increase power plus eliminate any hum (which they had). Basically this is the only difference between the AV-20 and the AV-25.
-Change coupling capacitors, using Mundorf Supreme Silver/Gold; this single mod would increase the level of details, he used the word "amazing" to describe what this could do.
-Change a few resistors in the signal path, which would help achieve what the Mundorf cap could bring, plus reduce noise.

So I went ahead and ordered all the parts; transformers and Mundorf caps from divertech.com, and VISHAY resistors from partsconnexion.com

The work was relatively easy; cut and solder wires, swap components in a board, etc. The one "special" thing I had to do was enlarge the holes for the caps to make the leads fit.

I am using the monoblocks to power a pair of Von Schweikert VR-1 monitors. These monitors have great detail; from their web page: ..."Not only does this new tweeter sound extremely clean, it is also unusually lush, with a smoothness simply not found in common dome tweeters. If you like ribbon or electrostatic drivers, you will love the VR-1."...and as you all know, I loved them so much that I sold my AL-III's ;)

Results:

Quiet, quiet, dead quiet. Unbelievable how a tube amp can be this...yes, quiet. The hum really didn't bother me, but it's nice to see that it's gone.

Soundstage; it's wider; it projects beyond the speakers. I really have no idea what change did this, but I'll take it.

Details: the Mundorf require 100 hours to brake in; they have about three hours now, and I already hear MORE details than before. This also helps imaging a lot. Amazing what just one little capacitor can do. No more regrets for letting the ribbons go :)

So yes; I'm a happy camper; the bad news? Project is done. It won't be long before I start looking into something else...hmmmm...Mundorf caps for the SDA crossovers???


Some pictures:

[george daniel]

nice work Ricardo,, I see that you have your diy upgrade on :) Have fun ;)

[Ricardo]

Thanks George; yes, I really enjoy the DIY.....so far it has been only improvements, which are fine; it gets dangerous when you try to fix something that doesn't need it :)

[dorokusai]

Cool upgrade HT.....MillerLiteScott, you paying attention?...these are your future babies :D

[MillerLiteScott]

Hey DIY rookie sounds like some cool mods. What was your out of pocket for these mods because I just bought some ASL mono blocks from Doro.

It will be a while before make any modifications but I am a DIY kind of guy myself.

I am paying attention. I have been all over this thread.

[audiobliss]

Thanks for posting that, HTrookie! I'm not sure if I'll ever get brave enough to fiddle with audio equipment that works before I take it apart, but if I do, I'd be interested in this.

If you don't mind me asking, about what did all the parts run you?

[Ricardo]

Without the transformers it's around $100 (I think Millerlitescott got the AV-25??); Transformers were around $170 for the two of them, for Audiobliss that I think has the AV-20's??

[dorokusai]

The amps are almost identical, just capacity changes.

[audiobliss]

Without the transformers it's around $100 (I think Millerlitescott got the AV-25??); Transformers were around $170 for the two of them, for Audiobliss that I think has the AV-20's??

Yep, you got it right on both counts.

Not cheap, but not too expensive, either.