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In Reply to: RE: Thank you posted by Tre' on January 29, 2015 at 09:10:41
"It does not matter if your speaker does not go down to 31.25 Hz or not. If you are sending low frequency information to the amplifier, the amplifier will make the plate voltage move. If the plate voltage moves, the tube must spend bias current to charge and discharge the primary inductance as well as the actual primary load impedance. If the plate voltage or current "clips" because of low frequency plate excursions, the sound will suffer. "
"With 27 H, the load line is nasty. With a 27 H primary if there is any low frequencies making it from the preamp to the output transformer, I would expect the sound to be a bit nasty too. "
The practical implications for me; I just placed the high pass filter cap back in series with the input to my SET amp that drives my midrange (and tweeter) that only plays to 200Hz.
Thanks again Mike.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
That's a very important point that Voltsec made--- cause a lot of people will initially say I don't care what my amp is doing down at 50 or 40 or 30 hertz... cause my speakers only go down to X... but as Voltsec points out by then the damage is done....Your response--- using a high pass filter--- it's generally regarded as a taboo approach in hi end circles--- but I think the approach has a lot of initial merit to it. Frank Van Alstine in the mid eighties started using a high pass filter on the input of his ST-70 mod/circuit cause (his reasoning) it did not allow the circuit to be swamped with frequencies which it could not handle.
Or spec and use a transformer with really, really good capabilities in this respect (i.e., large signal goodness).
And to bring this back to "creative tapsmanship"-- i.e., ratioing transformer impedances-- don't do it--- your not likely on the vast majority of transformers to have enough "surplus" L to keep the loadline from becoming a beachball. And your tube really won't be all that happy with that.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Edits: 01/29/15 01/29/15 01/29/15 01/29/15
"Your response--- using a high pass filter--- it's generally regarded as a taboo approach in hi end circles--- but I think the approach has a lot of initial merit to it."If this was a full range amp I might regard it as taboo as well but this is a bi-amped system with a SS amp driving a pair of 15" JBL 2231s using an active 12db per octave low pass filter at 200Hz.
The JBL 2118J midrange speakers roll off on their own and are -3db at 200Hz.
I think keeping some of the LF out of the tube amp with a cap should help the issue that Voltsec points out and I believe this would be true even if my tube amp's OPT had "full" inductance.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 01/29/15
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