Hello!
This is a good question. Thanks for posting it!
Both Autoformers and transformers are using the same basic principle to control the level and to decrease the output impedance. I have played with both and either can work really well if done right.
The difference is that a transformer has a primary and secondary winding and an autoformer is just one winding - kinda like a secondary only.
We looked at messing with autoformers when we first came out with the TX102's but have not pursued it for a couple of reasons. One is that a sizable percentage of our customers want to run ballanced lines for outputs or inputs and do this in combination with some single ended stuff. The transformer can do this and from what I know an autoformer can run ballanced if you run 2 per channel but you need double the switch contacts and it can not do things like run single ended in and ballanced out (ie. conversion).
The other thing that is in the 'nice to have' catagory is to be able to isolate the grounds between your source(s) and your amp. This can be used to break a ground loop and eliminate a low level hum and in fact some transformers are sold just to do this function alone.
Anyway - hope that was not too confusing and explains why we have used the transformer instead of autoformers. I'll end by saying that with single ended only and with not needing to break a ground loop there is nothing wrong with autoformers at all. Dave Slagle's 'Slagleformers' in particular are really nice units.
Many Thanks!
John Chapman
www.bentaudio.com
