[jphone]

I would suggest this test to Jazz,
if you have a good sound card and a software that can generate sinewaves try to find your threshold of hearing detecting harmonic distortion. I could suggest something like a 1KHz fundamental and a set of harmonics (maybe simulate the Stereoplay curves?). I cannot detect (reliably at least) 1% distortion, see how you fare. Then try to explain why amps that have distortion under 0.1% almost unconditionally, sound different if you find this theory plausible.
I know that I was harsh in my critisism but you posted incomplete engineering data and you shifted back and forth between data and sound, mixing the two. Being an engineer and fooling around with audio for over 25 years I've seen a lot of truths come and go and the questions remaining. You have to see everything with a critical eye, the burden of proof is with the party that presents the theory. And the harder the critisism the better for the theory that can withstand it.

 

[lini]

jphone: The problem is just, that it's not JaZZ' but Stereoplay's theory - JaZZ just happens to think that it might be plausible. So however justified your critizism might be, putting the burden of proof on JaZZ doesn't seem fair.

JaZZ: Other influence factors... Sly question, actually.

Because, when I say something like "stability of the power supply, inner resistance of the whole circuit" or whatever, you'd probably ask back: "And will each of these not have any influence on the power related spectrum of harmonic distortions, lini?" And I'd go like: "Uhm... darn... dunno. You got me there. *whistle*"

Greetings from Munich!

Manfred / lini

 

[JaZZ]

ppl...

...your arguments are well-founded and more or less common knowledge (I don't know if IM distortion really is more important than harmonic distortion though...). Nevertheless, to judge the audibility of all the factors you listed you can do the simple test I mentioned a few posts above. You can even judge the neutrality of an amp. My conclusion from my tests is: the influence of the «complex load» represented by a headphone is near to zero - at least with the amps I've tested. Please do the test yourself! There may be very elaborated tricks to make an amp sound «good». But you can't prove if it is neutral if it sounds good.

To make this clear: of course the load-impedance curve has an impact on the sound, dependent on the amp's output impedance (and that's what you hear if you use the HA-2's 120-ohm jack). That's why I chose the HA-2 and the DAC2's line-out with their low output impedances as test amps, not the EMP. I have to admit that I didn't specify this.


jphone...

...maybe I'm not the most skilled writer (at least in English) when it comes to present technical issues accurately, but I'm not aware of your mentioned «mixing up». Are you sure it's not you whom this has happened? I was just speculating on the basis of the stereoplay theory. I (or stereoplay, resp.) even didn't present data which had any relation to a certain sound, just the measuring procedure. If my translation was misleading, then it's my fault, of course.

As to your distortion experiments: I'm interested on them, but have no concerning software. Nevertheless I don't think your sine waves are an adequate test signal. Maybe you're too much an engineer...

(meaning: a technocrat). I can't imagine to detect distortion-induced colorations in sine-wave signals.

One thing I can assure you: I don't «believe» in the stereoplay theory, and you may have noticed my own challenges. But one thing I'd like to read is still: what's the cause for the big sonic differences with amps, or electronic components generally, from your point of view - if you're sure it's not distortion? Still not the least personal statement from you...

What has convinced me most with stereoplay's theory is that obviously it's distortion - and be it in a special shape - that makes a good sounding (= euphonic) amp. So «good» sound is not neutral sound.


Manfred...

...that's a quite sly and prudent answer...

And thanks for taking the burden of proof away from me!

 

[jphone]

To Jazz:
Using sinewaves is the only way to induce repeatable and accurate harmonic distortion levels for this test. Their power is their simplicity. If you cannot detect 1% distortion level using a simple sinewave, you have no chance with a complex waveform. Recorded music is of no help either, since you have no reference to compare it to. Has nothing to do with being a technocrat, has a lot to do with being an engineer and having common sense and a lot with you being totally ignorand and not willing to spend the time to learn what you are talking about. Really, go read some more.

 

[JaZZ]

Quote:

Originally posted by jphone Using sinewaves is the only way to induce repeatable and accurate harmonic distortion levels for this test. Their power is their simplicity. If you cannot detect 1% distortion level using a simple sinewave, you have no chance with a complex waveform.

It will be interesting to read your proof to this theory of yours.

Quote:

Recorded music is of no help either, since you have no reference to compare it to.

Yes, you have: the original of the recorded music before you've added your artificial distortion.

Quote:

Has nothing to do with being a technocrat, has a lot to do with being an engineer and having common sense and a lot with you being totally ignorand and not willing to spend the time to learn what you are talking about. Really, go read some more.

It may be that it's you who's not willing to free yourself from some fixed ideas. Nobody was talking about perceivable distortion, but colorations resulting from distortion, appearing expressly in complex signals (= music!), not color-free synthetic signals.

And still no answer to my question... (Who's ignorant here?)

 

[jphone]

I seriously doubt that you know how to experiment with anything since the concepts or measurable and repeatable escape you.

And I will leave you all with this diamond in the rough:

Quote:

Originally posted by JaZZ It may be that it's you who's not willing to free yourself from some fixed ideas. Nobody was talking about perceivable distortion, but colorations resulting from distortion, appearing expressly in complex signals (= music!), not color-free synthetic signals. And still no answer to my question... (Who's ignorant here?)

You can't even make up stuff like this!

 

[13DoW]

I haven't read through the Stereoplay material but anyone interested should have a look at this thesis on amplifier sound. It also claims the relative proportions of harmonics are important rather than the absolute amount.


http://www.audioasylum.com/forums/pr...ages/2816.html

Regards
13DoW

 

[ppl]

JaZZ. Actualy i have done tests on My own design headphone amps and the Measured performance with a resistive load and real headphones show slight improvements with resistive loads in THD and noise vs real headphones in the 24-64 ohm range. I admitt the most recent have been based on Right mark RTA that only measures 1KHz and is used to test sound cards. As most know my Headphones are Buffered High out put current low output impedance designs. so load driving sould be no problem.

Years ago the audio eng. society did a test of perceived THD in humans aand found most people could detect 0.1% THD at low levels and one frequency. at Higher levels the threshold was alot higher. when more than one frequency at a time is present the threshold went to about 12% what dose this have on the sound of an Amp I cant say. at that time I did this test myself and found I could detect these same levels but the threshold was10% with music and 0.01% at 2KHz. and 50 DB SLP at my ears via Headphones. rising to 0.5% at 90 dB SLP & 2KHz. i am sure that this has gotten alot worse now since that was 30 years ago i tried that test.

I still belive that there ear is alot more sensitive than we are thinking because no one can hear 100KHz yet AES testing havs showen that Amplifiers with less than 100 KHz bandwidth were detectable. now sure at -3 DB at 100 KHz is going to introduce Phase shift at the upper octave of the audio range, however this futher showes that using just one qualifier as the to the sound of an Amp is not IMHO Valid.

I do not dismiss your idea of the relation ship of harmonic content as at least one US Tube Amp maker Highlights the 2ed harmonic so as to dominate all the Others. this IMHO is Euphoric coloration.

 

[JaZZ]

Quote:

Originally posted by jphone I seriously doubt that you know how to experiment with anything since the concepts or measurable and repeatable escape you.

Another sample of technocratic approach. I guess you're referring to the proposition to use music instead of sine waves. Of course you won't get that exact and repeatable results as with sine waves. But at least it's not like searching an object under a lantern which in fact is lost somewhere in the dark.

Quote:

And I will leave you all with this diamond in the rough... You can't even make up stuff like this!

What's it that you're referring to? I imagine it's unimaginable to you that distortion as such may not be detected but nevertheless have an impact on the sound - with music, not sine waves.

Good example with the bandwidth, ppl! That's what I've xperienced myself with my Metaxas Solitaire after a modification which has increased the already wide bandwidth virtually by just removing some (0.05 ? mH) inductors from the output: the sound has gotten a lot smoother. You can't hear ultrasound directly, but you can hear some products of excessively increased bandwidth (or the other way round).

 

[ppl]

The use of an output inductor is a double edge sword. This output inductor is used in some Amp designs to isolate the Amplifier from the outside world at High frequencies. the Inductance, capacitance in addition to other parasitic will conspire to make the amp unstable. in addition Radio frequency contamination can also get picked up by the Loudspeaker Cables and feed directly into the amp and get into the critical Audio circuits via the Amplifiers negative feedback loop and cause real problems. Unfortunately this coil seriously degrades the Amplifiers output impedance (Called Damping Factor) at High frequencies. I have seen Amplifier's with a damping factor referred to 8 Ohms go from over 200 at low frequencies to less than 10 at 20KHz. since damping factor is the Load impedance divided by the Amplifier's output impedance. as you noted this also reduces the Amplifiers bandwidth since this coil is in series with the load. Most Amplifier's that are well designed will remains stable without an output inductor and removing this inductor is a popular modification. Manufactures however must include this coil to cover there but in this age of litigation since with the right amount of load parasitic any Amplifier can become unstable. Some manufactures resort to design topologies that can include operating the Amplifiers output stage outside the feedback Loop.

This same analogy can also be applied to other stability enhancing components like Compensation capacitors. All these components IMHO will seriously degrade the sound of any well Engineered Amplifire.

using real Music as the test is another interesting concept. One that comes to mind is the Halfler XL-280 Power Amplifier. In this unit David Halfler reintroduced an old Concept of using one Amplifier to Amplify the Distortion Components of the Amp under test. In this case One Amp is used to Amplify the distortion Of another Amp Any sound coming from monitor Amp is the distortion of the Amp Under test. I have used this method myself to evaluate Amplifiers and it is somewhat related to the amps sound. (See stereophile January 1987 for futher details)