Questions re:  GaNfet technology vs other designs.

@invalid ,

I quote,

No matter what speakers we used, every "difference" we thought we had isolated turned out to be there, in equal quantity, when we swapped amplifiers.

He probably could have and maybe just did most of his work with a resistive load adding in a set of speakers for verification. He wasn't going to give away all his secrets.

He did do things with his production models, but it would be good to question what are real sound difference, what is voicing, and what is marketing.

I would not be so quick to jump on the bandwagon

Bandwagon jumping?

I simply agree with Ralph’s succinct and clear explanation. I find it to be more on point and inline with the real world listening results people experience. Make no mistake, I appreciate your comment and perspective. I just find his more credible. That’s all. Good discussion.

Charles

You mean @atmasphere's unsubstantiated claim versus an effect (impedance impact on frequency response) that absolutely is undeniable. I find that most people make 0 correlation between listening results and the underlying cause so assigning cause to a result without knowing what it is does not lead to a valid conclusions. Bob Carver's challenge is a strong data point.

Read my words carefully. "MAINLY" comes from a non-flat frequency response. That is especially true of most tube amplifiers such as the high output impedance of your own OTL amplifiers.

@theaudioamp Our OTLs are intentionally designed to work without feedback and so do not operate on the principle of voltage driven loudspeakers. Like SETs, you have to be careful of the loudspeaker used to get proper response that isn’t colored. See http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html for more information. This is done with intention since its impossible to apply the kind of feedback you need to really get rid of distortion that is otherwise generated by the application of feedback itself (this occurs because the feedback node is always non-linear, which means that the feedback signal itself gets distorted before it can do its job). As Norman Crowhurst pointed out decades ago this causes generation of higher ordered harmonics. You need +30dB to get around that problem and since tubes won’t have the gain bandwidth product to allow for 30dB at all audio frequencies its a Sisyphean task. So zero feedback is how the harshness of feedback is avoided since in a tube amp you still have pretty good linearity if you’re careful.

So the OTLs were not a good example. If the amp has enough feedback or else a low enough output impedance to act as a voltage source then you really have to ask yourself why one can sound bright while another does not- because if its acting as a voltage source there is inherently no frequency response variation.

If you’ve not found any information about why the higher ordered harmonics are so audible when in such small amounts, its easy to demonstrate with simple test equipment. IOW you’ve not looked all that hard. The ear uses the higher orders to sense sound pressure. If there are higher ordered harmonics added to a signal, they will be perceived by the ear in two ways: louder, and also harsher. Because of ’louder’ that also means brighter (and Mr. Fletcher and Mr. Munson don’t help). If you need to know the procedure to demonstrate this to yourself let me know.

The ear/brain system has a variety of tipping points in its perception of sound. Since it assigns a tonality to all forms of distortion (the ’warmth’ of tubes for example being caused by the 2nd and 3rd harmonic) it will pay more attention to this sort of tonality than it will actual FR errors. You might be looking in the wrong place if you go to ASR and Stereophile; as best I can make out they don’t seem to have made the connection (yet) between measurements and audibility.

OTLs are an excellent example as they will have a totally colored response compared to probably virtually any other amplifier type with any given speaker. You can choose one that works best, but no matter what you do, it will sound different with other speakers. A quick review of your posts shows you pairing it with speakers that were not intended to be used as such.

Your interpretation of how the ear perceives harmonics is too simplistic to be useful as a rule. Here is a link to help: https://www.researchgate.net/publication/323914860_THE_EFFECTS_OF_DISTORTION_ON_THE_PERCEPTION_OF_LOUDNESS_IN_LIVE_SOUND Low feedback will result in mainly compressive distortion. Insufficient feedback will result in expansive distortion using their defined parlance.

W.r.t being easy to demonstrate with simple equipment, I agree. I low distortion amp, low distortion amplifier (across 20KHz), and low distortion headphones. Then use a distortion simulation program like Distorter (VST plug in) to simulate various level (and orders) of distortion, or Pkanes Distort. Sure if you did 0.1% distortion of purely higher order for a 500Hz tone, you will hear it before lower order distortion but you and I know that is not a realistic occurrence. And this is detecting with a pure sine tone at optimal frequencies. With real music, no way.

Take a perfectly digital source and low distortion SS amp. Then add in the distortion profile of a typical SET amp especially the 2nd/3rd distortion, at levels one could expect outside clipping. Then blind A/B them with music. It won’t sound warm or cold. On general music you will notice the distortion before you notice any warming ... and yes, I encourage everyone to repeat this experiment themselves if they have a low distortion DAC/AMP and preferably headphones as lower distortion but you could use speakers. Please don’t take my word for it. That whole "warming" due to typical distortion components of tubes is just Philelore.

Yes the brain does have a variety of tipping points, but it also has the ability to extract the underlying information out till things get really bad. It will not pay attention to this distortion tonality more than it will the raw frequency response.

So where should I be looking for this connection between measurements and audibility? Feel free to send a link with some sort of objective listening test of distortion (and reasonable levels) versus tonality, where the only variable changed is distortion. I don't know how you cannot find information explaining why higher order distortion is more audible. This is a readily known thing. Higher order harmonics will not be masked by the primary tone. That is for tones. They will be masked in music.  For pure tones, Fletcher-Munson comes in again, because at low frequencies, the higher order harmonics will be areas of higher sensitivity.  But SS amps typically don't have much distortion at those frequencies. Keep in mind with pure tones, the masked harmonics will themselves mask the higher orders for typical distortion profiles (to a point). That coupled with music again limits the practical audibility of higher order harmonics of real equipment. Philelore.