Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
In Reply to: RE: You should go to their website.... posted by cpotl on May 06, 2017 at 16:34:40
The operating instructions for a Zero suggest placing them at the speaker, not at the amplifier end of the speaker wires. So think of them as a modification to the speaker, not a conversion from OTL to OTC operation. Semantics can make anything feel better.
Otherwise, I think this is beating a dead horse. If one doesn't need the Zeros, then one should not use them. If one does need them, then one can either get a different pair of speakers more suitable to one's particular OTL, or use Zeros to mate the OTL to the speaker. (Or buy an OTL with more output tubes, more power, and lower output Z.) I don't think anyone ever said that the Zeros are needed as a matter of course, or as an upgrade, with an OTL. My experience was as stated: the combo of OTL + Zero sounded better than any of several OTC tube amps I tried, but I do prefer the sound now that I have eliminated the need for the Zeros. (On the other hand, the speakers are way different now that I modified them; I daresay they would sound better now even WITH the Zeros than they sounded prior to the speaker mods, with zeros.)
I've got a used pair that I would sell cheaply, by the way.
"The operating instructions for a Zero suggest placing them at the speaker, not at the amplifier end of the speaker wires. So think of them as a modification to the speaker, not a conversion from OTL to OTC operation. Semantics can make anything feel better.
Otherwise, I think this is beating a dead horse..."
I agree that the talking points in this discussion are more or less played out. Reasonable people can agree to differ about fine nuances of interpretation!
However, my analytical side cannot let your first paragraph go by without a final comment. If one should think of the Zero as modifying the speaker, rather than the amplifier, since it is placed at the speaker end of the speaker cable, then what about an ordinary vacuum tube amplifier with a standard output transformer? Suppose now we remove the output transformer from the amplifier chassis and place it at the other end of the speaker cable, right up by the speaker. (So the speaker cable will now be connecting the B+ and output tube anode to the OPT primary.) Should we also now view the OPT instead as a "modification to the speaker," so that we would say the amplifier has become an OTL? I don't think that would satisfy anyone's reasonable criterion for calling the setup an OTL system. So I think the physical location of the matching transformer is not relevant to how one should describe the operation of the system.
Anyway, it sounds like you must have a great sound system!
I think the reason that what you describe is never done with an OTC amplifier is probably because of the high voltages involved. The speaker wires would have to carry thousands of volts in most cases, which is both unsafe and unwise. But I think Dave Slagle has implemented something like this with Quad 57 ESLs and one of his amplifier designs, where he has eliminated the step-up transformer at the input to the Quad in favor of a single transformer that effectively mates the amplifier to the Quad stators, directly. This is not direct-drive; there IS a transformer at the amp/speaker interface, except where you would usually have two transformers, now there is one. I heard this set-up at the Capitol Audio Fest, using stacked pairs of ESL 57s. The speakers are owned by a local friend. At home, he uses three panels per side. Quite impressive.
"I think the reason that what you describe is never done with an OTC amplifier is probably because of the high voltages involved. The speaker wires would have to carry thousands of volts in most cases, which is both unsafe and unwise."
Yes, I agree that one would not wish to do that in practice, for the reasons you mention. But I was really just considering it as a thought-experiment, to make the point that it would not, in any case I think, change the interpretation of the setup as an OTC system.
Actually one thing one could do, which I don't think is often done, would be to make something like a totem-pole or circlotron OTL amplifier, but just with more common or garden tubes like EL34 or whatever, and then use something more like an ordinary output transformer to match the relatively high output impedance of the amplifier to that of the loudspeaker. Then, the primary of the OPT would be at close to zero potential, and there hazards you mentioned would not arise, even if one did want to mount the transformer close to the loudspeaker. Also, for what it's worth, there would be no quiescent DC current passing through the transformer primary. Probably it would require higher HT voltages than is normal in an OTL, to get any decent power.
Of course I would not call the setup an OTL system, for the same reason that I would not call the system with Zero autotransformers OTL, but just thinking of it as a possible type of amplifier one could construct.
Your comment about driving ESL speakers puts me in mind of a crazy thought I once had, namely that one could envisage an OTL amplifier that would directly drive the ESL speakers without any step-up transformer at all. It would be a horrifically fearsome thing, I think, requiring something like a totem-pole or circlotron but with transmitter tubes and HT voltages being of order thousands of volts. Definitely not something I would want to make or have in the house!
I am interested in your Zero's so I can Bi-wire.
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: