Sound Quality Vs. Measurements

[tvrgeek]

dvv, gootee,
I notice in one of the application guides for l-MOSFTES they are really specific to get both the gate resistor and tons of bypass right at they devices. I know in my digital logic days how critical it was to keep the bypass caps right at the legs. Some "bright" engineer wanted to save money and instead of a .001 at every chip, put a .01 at the end of the row. It was not cheap to lay out new boards ( 6 layer) and do it all over again. A class I tool from AMP in interconnection pretty much said you should put a bypass cap on anything that uses power and turns on or off. This is of source where the art of board layout gets hard.

Changing to the HEXFRED rectifier and new main caps, the ripple on the rails is about 25% less. About 12mV on the input side, 40 on the output side. No surprise. The shape of the little "burp" where the diode turns off looks a bit more rounded. I will try to look at the residual distortion today. I did keep a "before" graph.

[ThorstenL]

Hi,

Originally Posted by TheShaman

I'm sure Jan will be happy to publish an article with the "correct" math. As I said before, it's easy to talk the talk but harder to walk the walk.

Why should I care?

If Bruno likes he can correct what he has written.

BTW, the effects are quite easily measured.

Originally Posted by TheShaman

Then again one might argue that if the HiEnd industry could afford bright scientist to do some solid R(esearch) before they actually get down to D(evelopment), we would see some real progress and not the recycling of 1970's technology.

Sorry, I don't do '70's tech. It's either 1910's tech (Vacuum Tubes) or very recent.

Originally Posted by TheShaman

Regarding Bruno's preference, he's stated in numerous occasions that a properly built statement Class A amp will be untouchable by any Class D design.

And? Has that anything to do with the topic?

Originally Posted by TheShaman

But his definition of "proper" is not what we're used to seeing - esp. in the "less is more", "the 1st watt is the best", "feedback is bad" DIY world we live in.

He is welcome to his definition. I know several of his designs quite intimately.

But let's recap.

For starters, up to now, not one Technocrat has provided proof positive that low THD is a valid design goal, in fact much evidence exists that show that comparably high distortion levels (of a certain spectrum) are in fact inaudible.

Secondly, Bruno's article elected to ignore significant factors that would have changed his analysis, meaning his analysis needs improvement. In fact the only value of the article I can see was that it attracted a range of criticism which ultimately gave a new insight (from BP), namely: "Negative feedback does not attenuate the harmonics of the open-loop nonlinearity, but of its inverse."

This should make it even more clear why disregarding distortion of distortion is a crucial fallacy.

Anyway, whoever may wish to believe BP's article is the ultimo ratio on the whole feedback subject is welcome to their beliefs.

Ciao T

[CopperTop]

Originally Posted by ThorstenL

For starters, up to now, not one Technocrat has provided proof positive that low THD is a valid design goal, in fact much evidence exists that show that comparably high distortion levels (of a certain spectrum) are in fact inaudible.

Presumably high THD = high IMD, and conversely low THD = low IMD..? It would take a very sophisticated (digital) box of tricks to provide harmonic distortion without intermodulation distortion. Are you therefore saying that high levels of some types of IMD are also inaudible? With what source material?

[tvrgeek]

Power supply improvement for DH 120. Put in the Hexfred rectifier, new main caps of 2200uF instead of the 6600 and they have half the esr.

Referenced to 1.68v as 0DdB. 60Hz improvement of 6 dB, 120 Hz of 19 dB, 180 Hz of 13 dB. Drop in higher order in the 2 to 3 dB per harmonic. No residuals above 1K as was the original case. Noise floor below 60 Hz dropped by 5dB to -113.
So I am back to where I started from, confirming some basic power supply improvement.

I am happy it is an amplifier again. Hard to probe and work on the way it is stuffed in the case. I think I had best continue learning Spice and breadboard some of it rather than apply my bad vision and fat fingers to tight quarters.

[ThorstenL]

Hi,

Originally Posted by CopperTop

Presumably high THD = high IMD, and conversely low THD = low IMD..?

Yes.

Originally Posted by CopperTop

Are you therefore saying that high levels of some types of IMD are also inaudible?

Yes.

Originally Posted by CopperTop

With what source material?

Music, pure tones. SPL plays a role here. More HD/IMD is tolerated at higher levels.

Ciao T

[jan.didden]

Originally Posted by ThorstenL

Hi,

If Bruno likes he can correct what he has written.

[snip]Ciao T

He has shown that your arguments are in error, many pages back. Funny how memory deteriorates when you get older...

jan

[tvrgeek]

Could use a DC servo. Watching how the offset moves around from 4 to 25 mv depending on input. It is slow enough to suggest thermal effects.

[ThorstenL]

Jan,

Originally Posted by janneman

He has shown that your arguments are in error, many pages back.

My memory must be indeed bad. I do NOT remember him providing numbers for "distortion of distortion" that allowed simple dismissal as unimportant, but please, what is the post where he does so?

Ciao T

[a.wayne]

Originally Posted by Wavebourn

You never heard class D tape recording amp, did you?

You know i can't recall ever hearing one ....

Originally Posted by dvv

I'm not so sure about that.

I've come across some really wild loads; retracing Otala's steps, I tried AR3a Improved, Yamaha NS-1000,etc, all the way to the notorious "amp killer", the Apogees.

The thing is that amps, the behavior of which with the 1uF cap proved better than with others, ALSO drove the said speakers more to much more convincingly than the others did.

So, while I do not claim that an amp which "fails" that oversimplified test cannot sound good, I am claiming that an amp which does pass that test has a better chance of sounding good with real world speakers than the one which doesn't pass the test.

+10 , those that pass will go on to bigger and better things .....

[DF96]

Recognising that with high feedback ratios we are actually seeing the inverse of the amp response is surely equivalent to 'distortion of distortion'? That is where the algebra leads us.