Hattor Audio Autoformer Reference Preamplifier

@atmasphere - You do understand the autoformers (auto-transformers) being discussed here are being used as volume controls, right?

I certainly respect your work in designing balanced tubed electronics, and your adherence to the balanced line standard in your products, but I am not the person to convince since I have no dog in the fight, except as the owner of a preamp that uses four autoformers to adjust volume while providing balanced inputs and outputs.

I am not clear whether you are suggesting an alternative, or simply questioning why the designers are not using a single autoformer per channel.  Either way, the main commercial designers of these products (EM/IA-Jackson/Slagle, icon-Nagy, and Bent-Chapman, and now Hattor-Kallas) all use/used four autoformers to adjust volume when configuring their stereo preamp products for balanced operation. That would be surprising if they were aware that it was degrading CMRR by 20-30 dB.  Maybe you could figure out why they are not using just one per channel.

@mitch2 To your question, yes. 

I don't have a dog in the fight either. I'm simply presenting the facts. 

I'm still curious about this practice as you can see in my first post. 

@atmasphere - Ok, fair enough. If you have more than a passing curiousity, I suggest reaching out to one of the designers that I listed.  I would suggest Dave Slagle at Intact Audio and EM/IA, since many seem to use his autoformers.  If you find out anything, I too would be curious to hear about it just because I like to know how things work.