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

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

HTrookie wrote:

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.