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In Reply to: Re: I can do that... posted by Ralph on December 27, 2006 at 11:51:43:
I am going to post my thoughts here. I am listening to a pair of A-S OTLs right now, on loan from local dealer.These are the things that occurred to me within the first few moments (I now have 4 hours listening):
1) They sound a bit 'thin' (compared to what I am used to), yet still VERY 'pure'.
2) The bass is astonishing. These are MA-1s run with 4 sets of tubes to simulate 60W M60s. It is far tighter and punchier than my 845 monoblocks.
3) Vocals, for whatever reason, are just not giving me the same tingles of realism.
I have never bought the "yummy 2nd-order harmonics" argument as explaining SETs' realism before because blind listening tests have shown up to 3% 2nd order HD to be inaudible, and no SET is producing that much when mated intelligently to speakers, except on transients. You may be right on the money about the distortion adding to the dynamic effect, but most vocal-only passages are drawing no more than a few watts in typical listening.
I am undoubtedly very conditioned to SET sound at this point. I'm quite open to the possibility that this OTL sound is, in fact, more correct, but I'll be darned if I know how to determine that.
One inescapable conclusion I can offer at this point is that these are fabulous amps. It is truly a unique sound, not like solid-state, or chip-amps, or transformed push-pull tube amps, or SETs. It's another category, and certainly does some things better than all of those.
Follow Ups:
> > I have never bought the "yummy 2nd-order harmonics" argument as explaining SETs' realismI don't buy the 2ndH argument either and posted some of my own findings in Tube DIY some time back. My own SET design has very low distortion, even 2ndH. In fact most well designed SETs have low distortion at normal listening levels, well under 1% in most cases but certainly under what is commonly accepted for SETs.
Anyway, I experimented with distortion cancellation between driver and OP stage and while I was amazed how great the human ear is at picking minute changes in distortion. Lower distortion sounded sweeter but the thing is, I heard it BEFORE I measured it so it wasn't a case of fooling myself. In fact I only took measurements in an attempt to explain what I was hearing because something initially wasn't adding up. BTW, my measurements were made using a very accurate spectrum analyser with an exceptionally pure signal source.
" I have never bought the "yummy 2nd-order harmonics" argument as explaining SETs' realism before because blind listening tests have shown up to 3% 2nd order HD to be inaudible, and no SET is producing that much when mated intelligently to speakers, except on transients. "It is true that with simple sine waves 2% of even ordered harmonics would be next to inaudible. With a full spectrum of music it is another matter!
What has been shown about even-ordered harmonics is not that we cannot hear them, but that we do not find them *objectionable*. We can definitely hear them- here are some terms that describe even-ordered harmonic distortion in ascending order of distortion present:
warmth
bloom
rich/richness
loose (as in bass)
muddyOne problem with our vernacular is real music has inherent built-in warmth as a function of the way a musician wants it to sound.
This neutrality v. richness issue is a tough one for many of us to get a good handle on. But I keep coming back to the way the SYSTEM sounds--simply more like music with SETs. But I've not heard an A-S OTL in my system!One thing I'm convinced of--SETs seem to have a much-more-linear distortion 'curve' than PP amps, that is, distortion rises more rapidly in the middle of the power band v. a PP amp's very gradual slope and then a sharp increase just before and at clipping. This caused me to buy higher-power SETs than others might have for my 97dB-sensitive speakers. My power indicators PEAK at only a few Watts, leaving my 22-Watters with LOTS of headroom.
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Tin-eared audiofool and obsessed landscape fotografer.
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