If tubes amplifiers measure poorly, why are they perceived as sounding better?

[WisEd]

This was the standard we discused the amp should meet or better at full power at any impedance. This is Erins test which mirrors Atkinson"s
Qoute:

We see the typical decrease in THD+N as the amplifier moves out of its noisy region and into the distortion-dominated region at both the left and rightmost extremes, respectively. Ultimately what I see is an amplifier with low noise and extreme 2-channel power, hitting well over 500 watts into each of the 2/4/8-ohm loads while still being below 0.001% THD+N. That’s remarkable. More on power in the next section.

 

[WisEd]

Finally, though mostly scattered, non confirmed but persistent reports of "new" class D amp unreliability should give anyone pause of spending thousands of dollars on one. The consistent version .x updates to keep the investor confidence from crashing does not inspire a lot of confidence, at least in my book. In summary as shown from the unarguably unbiased data, they of yet have to meet AB amp specs that go back decades and their reliabilty is under the best scenario yet to be proven.

 

[NTK]

Finally, though mostly scattered, non confirmed but persistent reports of "new" class D amp unreliability should give anyone pause of spending thousands of dollars on one. The consistent version .x updates to keep the investor confidence from crashing does not inspire a lot of confidence, at least in my book. In summary as shown from the unarguably unbiased data, they of yet have to meet AB amp specs that go back decades and their reliabilty is under the best scenario yet to be proven.

Class D amp reliability not proven? Do you know what kind of amps pros use for live sound? You think they don't care about reliability?

 

[WisEd]

This is a thread about op-amp rolling, is it not???

As they often do it mutated!

 

[WisEd]

Class D amp reliability not proven? Do you know what kind of amps pros use for live sound? You think they don't care about reliability?

Those are not what we are talking about...at all. I have a pair of 1000W, wonderful, almost 10 y/o class D amps that have been happily chugging along....... In my subs. What we are discussing is full bandwidth, home audio, high fidelity amps. A whole other ball game.

 

[amirm]

This was the standard we discused the amp should meet or better at full power at any impedance. This is Erins test which mirrors Atkinson"s

You were talking about tube amps and now solid state? As noted, none of this related to the topic at hand. Please create a new thread or post in others with the same topic.

 

[reforminded]

The distortion is an additional endearing factor. Warmth is "comfortable". Its like listening to a guitar and listening to an amplified guitar. They are both excellent but slightly different. I own a Mcintosh MC462 paired with BW D803 diamonds. Probably the most "neutral" system you could find, yet I once in a while, I wouldn't mind a little warmth in the mix on the correct musical composition. The same thing with a good 45 RPM record and its high rez digital version, both almost identical but both with thelr own vharacter and flavor.

803 diamond neutral???

 

[mmuetst]

I tested with a forum member my Prima Luna KT88 push-pull tube amplifier against his own NAD M33 amplifier on a pair of Analysis Audio Omega speakers. The bass was picked up below 100Hz by subwoofers. The owner of the NAD amplifier wanted to know what tubes would do in his system, and the conclusion was that we didn't hear any significant difference (and I didn't hear any difference at all). However, I'm certain that the NAD M33 measures much better on paper than my Prima Luna. A clear test for the NAD owner and an answer to his question about whether he should invest in a tube amplifier—no, he didn't.

It was a very nice and educational afternoon

 

[Mike_Trueman]

Yeah nice setup there! My next amp will be the "NAD M33 V2" for my living room. I love NAD AllInOne amps, no extra wires needed for a streamer, DAC, PreAmp, Poweramp, ... so less distortion and no extra wire madness.

 

[Nicknack]

Hi there, regarding tube amps, I haven’t see anyone posted measurements of a good condition OTL tube amp. These amps ditch the transformers and use a lot of feedback to lower distortion and increase bandwidth and drive down the output impedance to the 0.1 ohm range. Very inefficient amps but curious to know their measured performance.

 

[Keith_W]

Ralph Karsten @atmasphere is on ASR. Do you happen to have any measurements of your OTL designs?

 

[atmasphere]

Ralph Karsten @atmasphere is on ASR. Do you happen to have any measurements of your OTL designs?

Yes. Most of our OTLs do not use feedback. So the distortion varies according the tubes. Unlike most tube amps, the distortion of the output section is actually quite low, contributing about 2-5% of total THD. Because we use a Circlotron output section which has no gain, all the gain of the circuit must come from the Voltage amplifier, since our driver circuit, being a cathode follower has not gain as well. The Voltage amplifier is a differential cascode; matching tube sections, particularly in the lower section of the circuit, is the key to keeping distortion down.

If no care is taken, THD is typically about 2-3% at full power; for example our MA-2, rated at 220 Watts into 8 Ohms, with no care to matching any tubes has measured 2.35%THD at clipping (230Watts). The distortion rises along a fairly linear curve. It is not affected by frequency in the audio band. If one matches the tube sections its no problem hitting 0.5% THD. In our smaller OTLs (S-30 and M-60), because more Voltage is needed to drive higher impedances like 16 Ohms, the distortion is slightly higher into those impedances. In such cases the distortion tends to be lowest driving 8 Ohms; into lower impedance for which the amp is not designed the output section distortion begins to dominate so the distortion rises.

If feedback is applied the distortion can be quite low. Earlier OTLs that were built with 12AT7 Voltage amplifier sections tend to have more loop gain so they can manage a bit of feedback, allowing full power distortion to be under 0.1%. But we've not actually manufactured the amps that way, although we have modified them to do that.

The old Futterman amps employed up to 60dB of feedback and were capable of 0.005%THD back in the 1960s. They had a reputation of being a bit on the unstable side as well- you had to be careful with them! Julias Futterman went to some lengths employing things like ferrite beads to stabilize his amps. He did not convey any of that in his schematics.