Paul Speltz Zero-Box Autoformer With Tenor OTL

Mike,

I think you are talking about a linestage or passive volume control, including transformer/autoformer volume controls, whereas the original poster is inquiring about an autoformer inserted between the amp and speaker to reduce the output impedance of the amp (typically quite high with OTL amps).  I don’t know how this sounds, but this turns an OTL into an amp with an output transformer.

I'd be contacting Rockport and informing them of my situation before asking if they had any comment they would like to share.

@larryi

ok, you are right, i did not realize that was what an Auto-former did.

OTOH the magic of the Tenor OTL is it’s singular purity and sparkle. why would you do anything to dumb that down? why bother with an OTL then?

now 20 years later, my experience with the Tenor OTL’s with the Kharma is my all time reference sound that still guides me in my music reproduction journey. if they did not ignite regularly i might still have them. :-)

I’ve not heard an auto-former on any speaker so I don’t know how it sounds.  But, I too am skeptical about putting a transformer on an OTL.  Ideally, OTLs would be used with higher impedance speakers, so I can see why someone without the right speakers might cheat a little with an auto-former even if that is less than ideal. 

I had the first pair of Tenor OTL 70’s in the US, purchased directly from the NY audio show. They were with the volume controls, but as amazing sounding they were, suffered from reliability problems, and were fussy about speaker loads. Finally a lightning strike did them in. A few years back, I purchased a newly manufactured pair from the new Tenor Audio, with all the modifications and updates which are reliable, never an issue. They are still in my collection of tube amps, and I love them!! They sound beautiful with the built in volume controls, but I prefer driving them from my Audio Research 40th Anniversary preamp. It’s a sound that hooked me 25 years ago, and I missed it when I didn’t have it. Of course, with any OTL, speaker impedance is important. I don’t think it would be a good idea to try to change the impedance with an Autoformer, but I have no experience with that. I just think it would alter what makes these sound so great. Amazing on a Quad ESL 57, or a stacked pair wired in series.