Sound Quality Vs. Measurements

[jan.didden]

Originally Posted by tvrgeek

There is some irony here, as I put in my order to Digi-Key I was thinking of all the help I have received in an effort to "POOGE" an old Hafler. A process coined by, Mr. Pass. [snip].

Close, but no cigar . POOGE was coined by Walt Jung and Richard Marsh in Audio Amateur many years ago.
But I agree that NP has done more for the audio diy scene than anybody else I know.

jan

[dvv]

Originally Posted by tvrgeek

There is some irony here, as I put in my order to Digi-Key I was thinking of all the help I have received in an effort to "POOGE" an old Hafler. A process coined by, Mr. Pass.

His one transistor wonders are for those that need a 6W amp for their Louthers. He serves a market. If you need 100W, I am sure he can accommodate that after you get the mains to your house beefed up. If you read his papers, he is big on not making distortion in the first place, so many outputs are typical of his work. Even the original 60W Adcom 353 had triples. Actually, I am really tempted to snag a PA-5 or Forte off the Web.

How much actual power one needs is a moot point. As we would expect, the industry at large will always say as much as possible, simply because it promotes their more expensive models.

In my view, you need as much as is required to get you to at least (theoretical) 110 dB SPL in your room. 114 dB would be better. So, if you have speakers with an efficiency of say 92 dB SPL (such as mine), you would need (110-92) 18 dBW of power as the very least. That would be some 63 W or so. But if you own older gear, with say 87 dB SPL, you would need those extra watts, i.e. you'd need a good 200 W.

Trust me on this, I know what I'm talking about from first hadn experience, as one of my amps is declared as a 22 dBW (180W), and since my speakers do 92 dB, I do have a roughly 114 dB in room capability. It really does sound different all around, even at low power.

So for an output of 5-6 Watts, you would need prodigiously efficient speakers, like the Altecs of old, which used to do 105 dB SPL with just 1 Watt. Not many like that around.

In addition to this, I didn't find any of the designs to be particularly clean and clear, no more than other competently designed amps, although better than many strictly commercial offerings.

On the plus side, it's true Nelson Pass made a hell of a lot of people very happy by promoting the DIY angle. And a large fan base delivers fanatics in no time, always.

Also, I feel his designs did influence the audio industry by reminding us all of the KISS principle.

[planet10]

Originally Posted by dvv

As a firm believer that the amp should always be a constant voltage device, to me, this is completely unacceptable.

Well, there you go. You've painted yourself into a corner. There is a whole room to play in and you are missing out on some of the fun

dave

[VladimirK]

Coming back to the measurements vs sound, I could state that nothing is clear with such terms as "voltage amplifier" and "output impedance". None of these predetermines the bass signature (articulation) at a given system. Also, rated power of an amp helps not a lot for getting clear and articulated bass.
It is quite easy to observe, that 20W class D is better in bass than 200W class AB, or definite versions of 20W class A produce better bass and wonderful overall sound compared to various 100W...200W class AB amps.
These facts are hard to believe and to explain. At present, I see only one possible correlation: current NFB is much more preferrable than voltage NFB, resistive NFB divider with 40mA passing through it is much more stable against speaker back EMF than NFB resistive divider passing few microamps through it.

[DF96]

Originally Posted by VladimirK

current NFB is much more preferrable than voltage NFB, resistive NFB divider with 40mA passing through it is much more stable against speaker back EMF than NFB resistive divider passing few microamps through it.

Sensing the speaker voltage and sensing the speaker current are quite different forms of feedback with quite different outcomes. It is therefore quite unsurprising that they will sound quite different. In most cases it is voltage sampling (giving a low output impedance) which will correctly match a typical speaker. However, some people like listening to speaker bass resonances and may wrongly suppose that this is 'better' bass. They then have to come up with a nonsense explanation for their preference.

[dvv]

Originally Posted by planet10

Well, there you go. You've painted yourself into a corner. There is a whole room to play in and you are missing out on some of the fun

dave

Really?

And how would that be, pray tell, Dave?

Since 1966, I have learnt a thing or two about audio amps. I have a small collection of them, cosnsisting of Marantz (2 integrateds and one pre/power amp combo, made in 1978, all overhauled), Harman/Kardon (2 integrateds, one overhauled, other in the works), Sansui (1 from 1984) and 1 Karan Acoustics (from 2003), so it's safe to say I can verify most views I have. All the more so since I also have three pairs of very different speakers at home - my own (exceptionally easy load to drive, B&M Acoustivs 1041 Minitor), my wife's (JBL Ti600, floorstanding 3 way, reasonable load) and my son's (AR92, overhauled, changed suspensions, 2.5 way), which is a hard load to drive.

And lastly, a good friend of 30 years owns a pair of Apogee speakers, which are an evil load to drive.

I can't even remember how many amps went through all the hoops. Most dropped out with the ARs, and the rest, save a few notable examples, definitely flunked on the Apogees. And the ONLY common denominator with those who made the grade is that they were exceptionally load tolerant and delivered on their nominal voltage. Only one of them did not have full electronic voltage regulation, H/K 680 integrated (1999).

To me, this is very convincing proof of what I stated. If you feel differently, fine, you do it your way.

[SY]

Originally Posted by dvv

Since 1966, I have learnt a thing or two about audio amps.

Now it's time to learn a third thing. A careful reading of Mills and Hawksford's papers on current drive may be worth your time.

[dvv]

Originally Posted by SY

Now it's time to learn a third thing. A careful reading of Mills and Hawksford's papers on current drive may be worth your time.

Actually, I have most of Hawksford's papers downloaded, I consider them a lasting value which one should have at all times - even if one doesn't agree with everything he said.

Mills I don't know.

But I'm always pleased to learn something new. Did you have any particular paper by Hawksford in mind?

[VladimirK]

Guys, I my previous post I speak about low output impedance schematics for all cases (not about current drive mode at all). The point is, that current kind NFB in voltage amplifier gives rather definite sound effect, provided that both voltage NFB amp (resistors in the NFB divider like 47K and 2K) and current NFB amp (resistors in the NFB divider like 500R and 20R) have equal output impedances.
The current NFB chain is not possible to arrange in one-transistor schematics, except for the case if one allows 20R input impedance.

[SY]

Originally Posted by dvv

But I'm always pleased to learn something new. Did you have any particular paper by Hawksford in mind?

Yes, specifically Mills and Hawksford. The two papers on current drive amplification.