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In Reply to: RE: If they work properly they don't tick. posted by PaulF70 on May 20, 2025 at 17:57:55:
Ralph has been waging a war on several forums against SET and those who think SET sounds better.
I, like you, have tried to move away from SET in the past only to rediscover the simple fact that they sound more like the real thing than other amp types.
I have done exactly what Ralph has prescribed by owning a couple of lower powered Class A PP triode amps (VAC 30/30, PureSound A30, WLM (made by Trafomatic) Class A EL84...etc.) and listening extensively to very good Class D (Mola Mola, Devialet etc.). None of them achieve what a good SET achieves.
The Class A triode gets pretty close because in Class A there is no crossover distortion; however, a push/pull circuit tends to cancel out even harmonics and this means the amps do not adhere to what Daniel Cheever calls the Aural harmonics, which Jean Hiraga also noted. You need an exponential decay of harmonics, starting with the 2nd harmonic, where each even harmonic is higher in amplitude than the following odd harmonic.
Ralph's OTLs and for sure his Class D amp do not follow this prescription for good sound because they have odd harmonics as dominant. This was noted by audio journalist Keith Howard as being the most offensive harmonic pattern of those he tried when he added distortion digitally to audio files. Of course he found the unadulterated to be the best but the least offensive was an even/odd pattern with the evens being higher in amplitude than the following odd.
Cheever found this also to be true when he developed a metric for evaluating amplifier quality. It is related to the ear's own self-distortion that the brain has evolved to ignore. That pattern is an exponential decay of even and odd harmonics. He posits that as long as the even/odd distortion of the amp is in the same pattern as the ear's own pattern and lower in level than that ear generated distortion then the distortion from the amp "hides" behind the ear's own distortion and the brain ignores it. The amp then sounds completely (or nearly) distortion free. This is consistent with audio journalist Jean Hiraga's assertions about a generation earlier.
It also fits with earlier attempts to develop meterics from the likes of D.E.L Shorter (BBC engineer) where he "weighted" the increasing harmonics in his equation to give greater importance to the impact on sound the higher the harmonic order was.
Ralph talks a lot about the SET limitations and the criticality of the output transformers. He is not wrong in the sense it is a critical component to getting a good sounding SET...so is the driver stage. Most SETs, especially those for reasonable prices, will necessarily skimp on the output and/or interstage transformers because they are the most expensive bits of the amp usually. An undersized transformer will make issues with bass saturation, which gives a significant coloration to the tube amp right up through the midrange. Really good SETs will have a properly sized transformer and the necessary winding complexity to allow good high frequency extension. Even very large core transformers can be wound in such a way to provide good extension.
The driver tube and mode of drive is also critical. I have found by owning a lot of SETs that I tend to prefer ones that are transformer coupled rather than cap coupled or direct coupled. The reason is dynamic contrast. They feel as if they have more macro and micro dynamics and simply more grunt. This was true of my 25 watt Aries Cerat Genus and Diana integrateds as well as my 3.5 watt Silvercore 2A3 amp. The SETs I have been most disappointed with were cap coupled using a 6SN7 as a driver tube, of which I have had a few.
Push pull amps can only completely avoid crossover distortion if they are running in full class A. If you look below there is a long running argument over this and I showed that there are a lot of modern Class AB amps that still visibly exhibit this very nasty type of distortion. I am pretty convinced that this is one of the big culprits in why a lot of amps sound simply synthetic and lack natural tone and body.
The other is negative feedback and interactions with the speakers. Your Quads will pump nearly 100% of the signal back into the output stage of the amp. If there is high negative feedback, then there is a pathway from the output back to the input, which is then reamplified. Of course what comes back out of the Quad looks nothing like what went into it.
The VAC 30/30 that I owned had an interesting feature on that allowed adjustment of the negative feedback from 0 to 8 dB. It invariably sounded the most natural on 0dB. Other amps that have had that feature in the past were also reported in reviews to sound the best either on 0 or on the minimum setting allowed.
I think the solid state amps from CH precision allow feedback adjustments as well and most prefer the minimum settings.
The discussions from Nelson Pass also indicate that he is an advocate of finding linearity without the use of negative feedback.
Ralph has now gone 180 from his OTL past into the Bruno Putseys Class D and ultralow distortion camp. I am not sure what to make of this but a lot of his anti-SET rhetoric on this and other forums seems like a large conflict of interest given he is now selling Class D amps, which are kind of the antithesis of SET.
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Follow Ups
- RE: If they work properly they don't tick. - morricab 05/21/2500:41:22 05/21/25 (9)
- RE: If they work properly they don't tick. - PaulF70 13:08:25 05/21/25 (4)
- I doubt that is due to crossover distortion - Ralph 13:05:45 05/22/25 (0)
- RE: If they work properly they don't tick. - morricab 08:25:12 05/22/25 (2)
- RE: If they work properly they don't tick. - PaulF70 09:48:39 05/28/25 (0)
- Yes, its not transformer insulation! - Ralph 13:02:59 05/22/25 (0)
- Ever consider writing novels? - Ralph 08:45:46 05/21/25 (3)
- RE: Ever consider writing novels? - morricab 12:01:13 05/21/25 (2)
- So please explain what class C is - Ralph 12:51:45 05/21/25 (1)
- RE: So please explain what class C is - morricab 06:32:40 05/22/25 (0)
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