AC4 help

tbm

Long shot, but I thought I'd check. About 2 years ago I bought a modded AC4 on the old MR classifieds forum. I can't recall the chaps name, though I think his forum name was "Big(somethingorother)". Anyway, I'm punting the amp on, and I realized I can't actually recall the name or exact nature of the mod. I know he did it himself and that it sounds great. In various private messages he gave me more details, but they are now, alas, gone the way of the MR board.

I was hoping the seller had signed up here, or that someone would remember the amp or that someone would recognize the mod so I'd be able to advertise it correctly. Anyway, here's the amp. You can see the heatsink screw in the second pic:





The mod replaces the 1/4, 1 and 4 watt setting switch with some kind of attenuator. My brother-in-law bought an AC4 around the same time and at lover settings this sounds far fuller then his 1/4 watt setting. it can get quieter too!

Anyway, if you sold me this, remind me what you did! Otherwise if anyone can hazard a guess as to what was done can you let me know?

Thanks.

ICBM

Sounds like some sort of power scaling if it has an extra heatsink.

Can you take the back off and get a pic of what's inside?

tbm

ICBM said:

Sounds like some sort of power scaling if it has an extra heatsink.

Can you take the back off and get a pic of what's inside?

Good idea. I'll do that later and throw a pic up. Thanks.

tbm

This help at all?

thermionic

Looks very much like a VVR/power scaling mod to me. Pot, high voltage MOSFET bolted to the chassis (via an insulating pad), a 3 or 5W resistor and a couple of other components.

Misterg

thermionic said:

Looks very much like a VVR/power scaling mod to me.

It looks a lot like the Ampmaker VVR:

http://www.ampmaker.com/store/images/ak99a.jpg

http://www.ampmaker.com/store/VVR-kit-for-cathode-biased-amplifiers.html

tbm

S'all coming back to me now. It's a VVR mod alright.

Help much appriciated.

ICBM

I'm not keen on that taped wiring. Always a bodge, and the tape tends to come off after a while because the glue on it is crap.

Phil_aka_Pip

ICBM said:

I'm not keen on that taped wiring. Always a bodge, and the tape tends to come off after a while because the glue on it is crap.

and although it's not sticky enough to hold the tape in place, there's always an unpleasant layer of stickyness where the tape has been

thermionic

I should have spotted that, as I built an ampmaker VVR into my amp - as part of the power supply turret board though, not an add-on PCB.