Very pleased in fact.
There’s nothing wrong with single ended triode amplifiers, but the major drawback with them is the output transformer. If, as is the tradition with SETs, you go for a zero negative feedback topology, apart from the inherent internal feedback mechanisms of the triodes themselves, then the output transformer has to be of absolutely unimpeachable quality. That costs serious money and it is an inescapable cost.
If you don’t have the money for such exotica (which I don’t) then a SET amplifier is always going to be compromised, soundwise, no matter how exotic are the caps and resistors in the circuit itself. Without the expensive output transformer, you are not going to realise the full potential of a SET amplifier - simple as that.
There are a group of guys on Audio Talk who do have the appropriate (read expensive) output iron, plus impeccable interstage coupling transformers (amorphous cores and silver wire) and frankly, the SETs they build are in a different league to anything I could come up with on my budget. Those who have been to any of our meets at The Owston Lodge will have heard these creations and will have heard the difference in performance they exhibit compared to some of the other stuff there. We’re all good designers, but as with any sort of craft, given similar design abilities, it is the ones with the best tools that will produce the finest work.
So after a very long time building SETs, I’ve given up on them. The 45 amp was my best effort by a long shot and sounds great, but still, I feel it is compromised by less than perfect output iron, so why bother? It’s my last SET.
Now this single ended ultralinear amp with feedback is more tolerant of cheap output iron than a feedbackless SET. To quote one of my AT mentors, James Doddington:
E-linear will be more tolerant of cheaper output transformers as the local feedback reduces the anode resistance making it a better option for a lower inductance transformer (better and more controlled bass) and for driving the parasitic capacitance at high frequencies both in terms of extending the frequency response and reducing overshoot by dampening it better (giving better midrange as well as h.f. and increasing transparency) It just doesn't help with the SE magic that some amps have - that's either there or not and only you know if it has it or not
So given this, why would someone like me on a budget, not want to build the amp I’ve just finished as opposed to making yet another fruitless attempt to get SET magic on the cheap?
The only thing you have to watch out for with single ended pentodes or ultralinear configurations and feedback is the inevitable generation of high, odd-order harmonic distortion products, caused by the non-linear transfer functions of the devices themselves when subjected to a feedback signal. These high-order distortion products need to be kept way below the 0.1% normally referenced for a low distortion amplifier. Even fractions of that 0.1% at 5th, 7th, 9th and above on the output will result in listener fatigue and then you might as well buy a good solid state amp, where feedback is par for the course and most designers have long ago minimised the high order distortion harmonics issue. You know, NVA for instance?
The E- Linear amp above sounds nothing like a SET, but it is low distortion, neutral, clear, dynamic and simply gets on with the job. That, to me, is what an amplifier should do. Enough of my ramblings.
Somebody’s telling me the latest scandals.
Somebody’s stepping on my plastic sandals. Joe Jackson (1979)
