Ralph, I actually like the quality the base in my current system very much. So I disagree with your generalization that SET’s can’t play bass. Madfloyd,, a bass musician, shared his impressions of the sound of the bass in my system on page 2 or 3 of this very thread. He seems to also disagree with you about SETs not being able to do bass.
I heard your amps at a couple of shows. Perhaps your class D amps have even lower distortion. I wish you every success.
Thanks!
This seems like one of those things you have to hear to really appreciate. The deeper your speakers go, the easier this is to hear.
I've played string bass since 6th grade and still do (as well as keyboards) today.
Low E on a bass is only 40Hz. There's a whole nuther octave below that and some pipe organs can do 16 Hz. SETs simply can't play that stuff with any power (the type 45 power tube does it best but you can really only hear what it does on headphones since its power is so low).
If you have a gapped output transformer (and most SETs do) there is never enough inductance to play bass properly (let alone damping). The load line turns into an ellipse in the presence of low bass. The lower portion of that ellipse is not where you want to operate a tube. To prevent saturation of the OPT, most SET designers will cut off the lows earlier in the circuit so the mids and highs will be cleaner. This introduces phase shift in the bass region (since the cutoff is usually a 6dB slope) which extends to 10X the cutoff frequency. The ear perceives this as a lack of impact despite the frequency being in-band. That's why we extend our OTL amps down to 2Hz.
The other thing you might want to consider is what happens when you have a PP amp of the same class of operation and output power is the sacred SET. Such tube amps are hard to find! But if you do find one and its built properly you'll find it does not take a back seat to SETs in any way that audiophiles value.
Put another way, when SET lovers compare PP to SET, the playing field is never level. If you really want to hear what PP does, make that amp using the same tube complement as the SET with similar build quality. A 7 Watt 300b becomes 35 Watts. Topology is important too: as Norman Crowhurst (the tube guru of the late 1950s) points out, if you put a single-ended front end on a PP amp, thru algebraic summing you wind up with a 5th harmonic that's not masked very well by the 2nd and 3rd. My surmise is most of the PP amps compared to SETs have this problem.
So more about that: SETs express a quadratic non-linearity, which results in a dominant 2nd harmonic. If the amp if fully differential and balanced, a cubic non-linearity is expressed. The cubic non-linearity is inherently lower distortion. But if you combine the two, the 5th shows up stronger and I've no doubt that's why SET lovers disdain PP amps, not realizing the problem isn't PP but topology.
So the kind of PP amp you really want to hear is one that does not combine SE with PP but instead is entirely balanced and differential from input to output.