Sound Quality Vs. Measurements

[wahab]

Originally Posted by Wavebourn

By the way, what is inside of Denon AVR-591 receiver? I bought it an year ago to take it's Audissey digital processor and use with tube amps, but still never opened the case. It is the first stock budget solid state amp I like as is. It sounds almost like a tube amp.

It use likely the generic schematic of the AVR-XXX serie , as such ,
the most classical LIN you can imagine , differential + bootstrapped VAS + fast Darlingtons from SANKEN......

[ThorstenL]

Hi,

Originally Posted by a.wayne

Well considering that most tube amplifiers are power rated @1% thd and most SS at .01% from a pure technical position (taste's aside) it would appear tubes have more inherent distortion , more slewing, low damping and limited bandwidth (especially in the bass).

IT would appear that you prefer to repeat hearsay and mis-perceptions, compared to real information. There are too many to address all in one post, but I will try.

First, the current standard recommendations (including the US FTC) specify 1% THD as power limit. In the German DIN 45500 a distortion limit of 0.5% is set, however regardless of the FTC rules and DIN45500 we also often find maximum power stated at 10% THD.

In non of the standards and recommended practices is there a different limit for tube and solid state amplifiers.

Secondly, Tube Amplifiers generally use few stages with low gain and low or no feedback. This means they show relatively high measured THD at higher power and relatively high output impedances. This is not a direct result of using tubes but of circuit topology.

If use two gain stages composed of Pentodes and the normal output stage we can achieve open loop gain levels comparable to those in Solid state amplifiers and it is easily possible to achieve equally low measured THD and Low Output impedance. This is rarely done for a variety of reasons, but it has been done and can be done.

Thirdly, as feedback levels are low, available input voltage ranges in the input device (tube) and open loop bandwidth are generally (if feedback is used at all) Tube Amplifiers are not normally slew rate limited in the way soliud state amplifiers and the mechanisms through which TIM is produced even if the amplifier is significantly below slewing are absent. Also absent in tubes are several classes of distortion unique to solid state devices.

Low Damping is just as the apparent higher distortion a result of the specific circuits employed and a not a result of using tubes as such, again, increasing feedback levels can reduce output impedance dramatically.

Fourth, limited bandwidth in the bass is again purely a result of specific design choices made in a specific amplifier. Using a large enough core for the output transformer (expensive) and enough feedback can create performance comparable to transistor amplifiers.

Fifth, another fundamental question is why high Damping Factor and low THD are considered important qualities as such, given the behaviour of real speakers (where electrical damping is limited by the voice coil DCR and distortion at rated power often reaches double figures)... This is a major topic in itself, however it is sufficient here to note that there is no credible research that supports lowering amplifiers HD and Output Impedance past levels that are easily attained by most tube and transistor amplifiers.

Originally Posted by a.wayne

With all due respect, i find it interesting the cognitive dissonace of those building and designing tubes, where it does appear a lot of sound vs measurements is being practiced, especially when one consider their technical stance in other areas and the importance placed on such measurement for deciding good , better , best...

I cannot speak for others, but personally I am well familiar both with techniques needed to measure audio equipment and with the gear needed to do so. But I also understand how these measurements relate to the system a given device is employed in and how they relate to what people actually hear.

The persistent insistence on the important of measurements that have been illustrated as not being capable of giving meaningful information of the actual audible qualities (e.g. lower measured THD does not reliably correlate with lower audible distortion) and more, the representation that such insistence represents anything "scientific"; I find comical in a way that parallels how I find the behaviour of the peasants in the "She's a Witch" Skit in Monty Python's "Holy Grail" comical, even though it's more a tragedy than a comedy.

Ciao T

[ThorstenL]

Hi,

Originally Posted by wahab

This , is unrealisticaly exagerated and at odd with all known measurements/comparisons of best tube amps vs common SS amps

Just shows what is known, doesn't it? At least by you, that is. Known to me is this:

http://www.wolcottaudio.com/WA_Pres_specs.htm

To quote:

FREQUENCY RESPONSE @ 1 Watt 0 - .2 db 20 - 20 kHz
+/-0.5 db 3 Hz to >20 kHz; -3 db @ 65 kHz.

POWER OUTPUT
2 ohm load- 240 watts, 12 Hz to 20 kHz.
4 ohm - 280 watts, 16Hz to 30 kHz.
8 ohm load- 180 watts, 20 Hz to 30 kHz.
6 - 8 ohms, 350 - 400 Watts, 20 Hz - 30 kHz.

THD FULL POWER
Typical @ Rated Load Less than 0.01% midband
0.025% @ 20 Hz
0.1% - 0.2% Max @ 20kHz

IM: 60/7000 Hz, less than 0.02%.

TIM: Unmeasurable

SIGNAL TO NOISE RATIO: 95 - 100 db

DAMPING FACTOR: >500, 30-5000Hz

Then there was the Krohn Hite Amplifier designed by Dick Burwen...

Ciao T

[ThorstenL]

Hi,

Originally Posted by tvrgeek

I wonder, with the basic tendency of a tube to act like a compressor more than a transistor does, maybe one raises the average level a little and the perception is more detail?

Tubes alone make very poor compressors. You need certain pentodes and adjust the screengrid voltage to get a good compressor (Variable Mu). Even BJT's actually compress much better.

Speakers on the other hand make very good compressors all on their own, almost as good as magnetic tape saturation...

Ciao T

[a.wayne]

Originally Posted by ThorstenL

Hi,



IT would appear that you prefer to repeat hearsay and mis-perceptions, compared to real information. .

Ciao T

Is this Hearsay...or mis-perceptions..?

Music Reference RM-200 Mk.II power amplifier Measurements | Stereophile.com

As did the original version of the Music Reference RM-200 amplifier, the Mk.II edition offers superb measured performance for a tubed design, particularly in terms of midband distortion and the ability to drive low impedances. And I remain impressed by the quality of its output transformers.—John Atkinson


Another : http://www.stereophile.com/content/c...r-measurements

Conrad-Johnson's LP125M measures well for a traditional tube amplifier.—John Atkinson



Notice a theme ...? and please spare me the innuendo's , I'm not anti-tube, just trying to find where you are getting your numbers from ..

[john curl]

Let's get real, engineers! The ONLY way to get really low distortion is to use a lot of paralleled parts and most probably the most feedback that you can put in the circuit.
I have made amps that have very low distortion for test equipment, but I don't think they are optimum for audio, because of the extra complication of nested loops, and potential instability with difficult loads. Now that is MY opinion, and others here might have another opinion, and that is OK with me.
It is well known that vacuum tubes are the most linear (standing alone) than any other active device. Also, as Wavebourn stated, output transformers are usually necessary with tube power amplifiers, and they are always a compromise. Also, it is almost impossible to apply a great deal of negative feedback with both transformers and capacitor coupling, and so, tube amps are usually limited to 20-30dB in feedback, rather than 60-100dB that is possible with solid state.
Now, two tube amp designs with rather different specifications have been put up here. So what? One amp is obviously designed with more parts, and more expensive parts to get its specifications.
It is interesting that solid state amps rarely measure very well either, unless a good deal of negative feedback is used. Just look at the Ayre power amps in Sterephile. AND they are made to the highest standard that is practical and possible. Take it from me, I wish I could do some of the approaches that Charles Hansen uses.

[Wavebourn]

All I know, John Atkinson has pre-suppositions about amplifiers and their parameters. I would say similarly, John Atkinson shows superb knowledge for an author of a popular magazine. No offense, just completely equal analogy in expressions.

If low THD and high DF are not typical for best sounding amps, the proper conclusions would be, they are less significant than other parameters.

[a.wayne]

Hence our discussion and current topic. Atkinson's opinion aside look at the numbers , not bettered by SS amps?
Maybe system distortion is where we need to look and not at any, one link ..?

[Chris Daly]

There are historically some good examples of this such as the Quad 405 that measures exceptional, but sounds average. If we were to believe the measurements alone and gone on our merry way- then the 405 should have sounded better.. but it did not And Pioneer technicians with their Legato Link appeared to temporarily abandon measurement in favor of listening. Were Pioneer naughty or had they stumbled upon something. Technology: LEGATO LINK CONVERSION PRO - KURO Projector

The benefit of measurement is quantifiable and repeatable result, The benefit of listening is to enjoy. Translating listening back to measurements where the two provide quantifiable result is the challenge. The ESL57 as a loudspeaker seemed to provide both good measurement - despite its awkward impedance and excellent listening. So it is possible. If we were to view the 57's impedance as poor, and try to find a better impedance curve - would we necessarily have a better sounding speaker ? Of course amplifier matching to the speaker answers some of this. But I think No, the 57 provided magnificent listening but its impedance measured all over the place... I am glad Peter Walker continued production and didn't stop production due to poor impedance, the 57 has proven as a huge success to everyone who has heard them .

Recent forum contributions in Solid State powering Op amps has touched on this as well where I have asserted that transistors for each polarity NPN arranged with collector as Vin, a resistor of 2K4 from collector to base and emitter feeding V+, and PNP arranged the same feeding V- of an op amp, offers much better spatial stereo information. Its an unconventional method of connecting transistors - but it sounds great.

Cheers / Chris

[ThorstenL]

Hi,

Originally Posted by a.wayne

Is this Hearsay...or mis-perceptions..?

It is.

Originally Posted by a.wayne

I'm not anti-tube,

Really, I couldn't tell, TBH.

Originally Posted by a.wayne

just trying to find where you are getting your numbers from ..

I measure, how else?

How do you get yours?

BTW, to repeat, i do not consider very low THD or very high damping factors relevant or beneficial, in the light of the whole system. However, I am familar with and have worked myself on tube designs that perform broadly comparable to solid state gear in these areas.

Ciao T