preamp transformers etc

[Eddododo]

always curious about transformers... I have used products in which a transformer makes a DELICIOUS difference in the sound;
a  great example is the Origin Effects Cali76 compressor, which has the option of an additional transformer on the output. Comparing both options it just sounds... nicer with the tranny


I do not even know how to formulate a concise question on this, so I'll just bullet my thoughts...
-clearly just 'slapping on' any transformer will not do anything magical
-I'd love a link to any resources on transformer use (i KNOW this is broad, kinda hoping for a rosetta stone like a geofex article ) i do know about the jensen resources
- any short lists of transformers with that nice, ooey gooey sound?
-are modern transformers.. too 'good' to have the inherent distortion that people find pleasing?

thanks, I appreciate any thoughts or resources

[R.G.]

Two very good references:

Transformers for Electronic Circuits
Grossner, N. R.
This is the bible. I bought it in hard copy for ~$100 just to have one of my own.


Electronic Transformers and Circuits 
Carter, C. E., Lee, R., & Wilson, L.
Also very good.

Radiotron Designers Handbook, 4th edition
The section on transformers is quite good, if heavy reading in places.  This has the most lucid explanation of transformer distortion I've read.

Transformers are filters, among other things. The classical model of the transformer encapsulates the nomination nature of the filtering very well, in spite of what grizzled old amp techs and advertising literature will tell you. The texts also point out what happens when things go non-linear: core material B-H curve effects and nonlinear eddy current losses, as well as the signal-level-dependent inductance of the core, and other subtleties.

The problem you'll have is that although the details of what happens in a transformer are well enough known, mapping what these things do to sound is a difficult thing to do.