Autoformer Volume Control

uglymusic

Anyone come across this horrible looking thing?

Sounds interesting.

IslandPink

Should be very good - Dave's stuff is state of the art . I own a few items of Dave's ironwork, including some 300B output transformers . I'm not sure why it ended up in that plastic box ( not read all the article - probably one of Dave's prototypes ? ) because I'm pretty sure he has the AVC's in some very cool-looking enclosures, if you take the time to dig into his blog a little :
http://www.hifiheroin.blogspot.co.uk/
That should give you a flavour of what sort of gear he's into .
The tech forum for the DIY customers is here, Dave does a large amount of custom work :
http://www.intactaudio.com/forum/

One thing I'll say, is AVC's and TVC's need a decent amount of driving current ( eg. 20mA ) and a low-ish driving impedance of no higher than 1-2k to sound their best ; otherwise you're better off just using a good carbon-track pot .

IslandPink

Yes, plenty of info here :
http://hifiheroin.blogspot.co.uk/search?q=autoformer

uglymusic

Thanks. I'll give those a read

PAC

Hmmm, nothing wrong with Autoformers per-se. They're useful voltage step-up/down devices but I'm curious to learn how they deal with loading in that design as they're very sensitive to load impedance.  Better ways of achieving a volume control without the added difficulties that come using autoformers.  Tannoy use them very effectively in their crossovers for variable inductance and voltage levels but never seen them used in a volume control before.

IslandPink

...but a volume control is generally a much less demanding location than a speaker crossover, in terms of reactive loading (?) . The typical load for the AVC is an input resistor and/or the grid of a gain valve, neither of which presents much of a challenge.