I bet you wouldn’t talk like that in person. In real life if someone is nicely trying to explain their point, a gentleman who knew more who than another might say, “Here is where you are mistaken- the sag/slew rate is not affected because of xyz. Component tolerance doesn’t matter cause xyz. Etc.”
I already said I am happy to learn more about design. You can even PM me, or move this over to the VTA discussion for others to be educated (I am not the only one who thinks this way- there is a whole other forum that does)…sorry everyone for cluttering the this Carver discussion
In my mind, these discussions are helpful. There is audio myth. It’s a myth that all tubes are designed to distort and have lots of harmonics. There is audio legend. Amplifiers that’s double down from 8 to 4 to 2 to 1 ohms are better. There are also “correct for the wrong reason.”
Myth: Tubes are only designed to have euphonic distortion. As you can see from SIY’s own measurements of some of his designs, they are really clean. Even the MC275 tested at Stereophile is pretty respectable for a tube amp. Tubes can be designed well or poorly, like NOS DACs versus oversampling DACs in solid state. Solid State can be designed well or poorly.
Legend: it’s hard to make amplifiers that are 1 ohm stable. Apogee ribbons used to go down to 1 ohm and kill amplifiers. Therefore, amplifiers that kept doubling down were great. The reason this is legend? Imagine that my average amplifier design gets 75W in 8 ohms and 100W in 4 ohms. I don’t double down. With a better power supply I should hit 150W into 4 ohms. However, imagine that I advertise my amplifier as 50W into 8 and 100 into 4. Suddenly I am doubling down when all I really did is pretend my 8 ohms is worse. Easy to do marketing around “doubling down”.
Let’s talk slew rate.
The faster the slew rate, the faster your voltage can change. Think of car making a sharp turn. You are driving along and now swerving at 20 kHz. You only need 6.3V/microsecond to get a clean 20 kHz by the math to achieve 50V peaks
I have seen a few discussions about slew rate and thought it might be a worthwhile thread. Slew rate is defined as the amount a signal (voltage, current, power, whatever) changes in a given time period. For the math types, it is the first derivative with respect to time. For a single-frequency...
www.audiosciencereview.com
Therefore “speed” is wrong when thinking about slew rate and sound. Even if you could hear beyond 20 kHz, you don’t need that much slew rate.
Fast slew rate can minimize TIM with poor designs.
Fast slew rate can increase risk of high frequency RF noise entering system.
Fast slew rate can increase risk of ringing or overshoot in complex loads.
This is where it gets tricky and
@amirm and
@SIY can put me in my place if I am wrong.
There are super high end amps with super high slew rates just because they can. It’s like going for SINAD 140 instead of 130. A high slew rate isn’t bad.
However there are plenty of “bad” high slew rate amps that will overshoot in transients. This could euphonically distort the signal to give you the sense of sharper transients because it is adding extra volume to transients which wouldn’t be added across the board linearly.
In theory, some loudspeaker drivers have faster and slower rise time. This is captured in the step response. In theory, if you amplifier had a bit of overshoot and that overshoot compensated for the slightly slower step response, it could work better…
Of course, a good speaker and good non overshooting amp is always the best engineering.
This quote which I took from this thread is helpful.
Post in thread 'Step Response: Does It Really Matter?'
https://audiosciencereview.com/foru...esponse-does-it-really-matter.1999/post-53005
To quote John Atkinson's digest version (on Stereophile) of his AES paper:
"Again, this is an aspect of loudspeaker behavior that has proved controversial. One school of thought holds that it is very important to perceived quality; another, which includes almost all loudspeaker engineers, finds it unimportant. Floyd Toole, now with Harman International but then with Canada's National Research Council, in his summary of research at the NRC into loudspeaker performance that is described in two classic 1986 papers [32, 33], concluded thusly: "The advocates of accurate waveform reproduction, implying both accurate amplitude and phase responses, are in a particularly awkward situation. In spite of the considerable engineering appeal of this concept, practical tests have yielded little evidence of listener sensitivity to this factor...the limited results lend support for the popular view that the effects of phase are clearly subordinate to amplitude response."
This is also my view. Of the 350 or so loudspeakers I have measured, there is no correlation between whether or not they are time-coherent and whether or not they are recommended by a Stereophile reviewer. However, I feel that if other factors have been optimized—on-axis response, off-axis dispersion, absence of resonance-related problems, and good linearity—like a little bit of chicken soup, time coherence (hence minimal acoustic phase error) cannot hurt. In my admittedly anecdotal experience, a speaker that is time-coherent (on the listening axis) does have a small edge when it comes to presenting a stereo soundstage, in terms of image focus and image depth. But time coherence does not compensate for coloration, poor presentation of instrumental timbres, a perverse frequency balance, or high levels of nonlinear distortion."
——
That is to say, it makes sense to have a perfect reproduction of the recorded waveform even if a lot of those characteristics may not be the primary impact on sound quality. No different that going for SINAD 140. But I wouldn’t pick a perfect step response over all the other critical things.
Going back to your comments on tubes. I have never heard a Dynaco or VTA but I do own the SFS-80 which is a Joe Curcio design of the Dynaco approach. The SFS-80 is a Sonic Frontiers product which we all know better as Anthem today.
You can see how well a Curcio ST-70 can be compared to the VTA70 or Carver measured here
Post in thread 'Review and Measurements of Dynaco ST 70'
https://audiosciencereview.com/foru...measurements-of-dynaco-st-70.7224/post-166287
The Curcio design sounds better AND measures better. But again, you only know how good a tube amp is if you also know what tubes are in it. Sonic Frontiers abandoned their tube line to focus on Anthem for both business reasons and in my opinion, supply chain issues.
If you want low distortion tubes, you need designs that want to be low distortion and tubes that were engineered and manufactured around low distortion.
You can spend a ridiculous amount of money to get great vintage tubes that really do perform well to get your tube to perform “close to solid state. Which in itself is incredible to me.
Last, I do think there is some euphonic alteration that occurs with tubes if only from the altered frequency response from a reactive load. That is just my opinions. In various threads I have described this as the voices in something like La La Land Soundtrack sounding larger than life and being artificial but still more preferable to listen to than a precise system where the non-professional singers sound “thin”.
For all I know, the VTA-70 and Carver amp will sound spectacular on the La la Land soundtrack and it sounds “better” with the distortion. But I think the real story is with the tubes looking a bit fishy to me.
