OTL Asylum

RE: From what I understand the Zero's...

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This Post Has Been Edited by the Author

In Reply to: RE: From what I understand the Zero's... posted by kablemetal@gmail.com on May 08, 2017 at 20:46:50

"Why do you have to put a transformer in an OTL??it's not OTL anymore!!"
As a general principle, I agree with you. To me, the term "OTL" has a very precise connotation, namely that there is no impedance-matching transformer between the tube output stage and the loudspeaker. This is a simple "yes" or "no" issue.
I find it to be a bit of a smokescreen when it is asserted that an autotransformer is allowable without invalidating the notion of OTL. As I pointed out before, if an impedance-matching autotransformer still allows one to call it OTL, then *any* tube amplifier could be easily made into an OTL amplifier by the mere contrivance of appropriately rewiring the output transformer so that the secondary was in series with the primary.
Of course, to use this argument would be rather absurd; I just presented it in order to demonstrate that one cannot take the autotransformer versus dual-winding transformer as the determining factor in deciding whether an amplifier is OTL or not.
The only other line of argument would seem to be that if the primary-to-secondary turns ratio is "sufficiently small," then it can still be called OTL. Thus with two-to-one the term OTL would still be allowed, but for twenty-to-one it would not. This is really just a matter of sophistry, though. One would now have to declare some arbitrary ratio, lying somewhere between two-to-one and twenty-to-one, as the cutoff between OTL and not OTL. This would really make little sense.
To me, the simplest and cleanest definition is just the obvious one; OTL if there is no impedance-matching transformer between the tube output stage and the loudspeaker, and non-OTL if there is.
An entirely different issue is the question of whether a particular system sounds better with, or without, an impedance-matching transformer. But I don't believe that it is helpful for these more subtle questions to be blurred by what, to me, are unconvincing claims that a set-up is still operating in OTL mode even when there is an impedance-matching transformer between the output stage and the loudspeaker.
Chris

Edits: 05/10/17 05/10/17

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