Only in audio would having pathologically bad bias setups that take eons to settle be considered a feature...what happens to an AB or push-pull class-A when it goes through a large traverse of output power? It's going to be yo-yo-ing around its quiescent bias point for ages (long enough to get disturbed again).
Now tubes certainly change their operating conditions as they come up to temperature, and certainly a/ab type amps, especially those with substantial heatsinking are going to take some amount of time to achieve equilibrium (more like and exponential convergence over 5 minutes than 5 hours though!). George's measurements above bear out the latter (especially since the bias current will have a secondary effect on the actual output, mitigated heavily by the loop gain).
But, given the option between seeing differences in -130 and -120 dB from adsorbed moisture or whatever mechanism of passives drifting (not unsurprising to see drift in the PPM to PPB range) and various other factors (mental or otherwise), plausibility suggests looking elsewhere. And it "being in someone's head" could easily mean the amount of time it takes to relax, clear one's mind a bit, and settle into the music, falsely attributed to the electronics warming up.
The trick is one of these is both infinitely less likely AND much easier to characterize than the other.
Now tubes certainly change their operating conditions as they come up to temperature, and certainly a/ab type amps, especially those with substantial heatsinking are going to take some amount of time to achieve equilibrium (more like and exponential convergence over 5 minutes than 5 hours though!). George's measurements above bear out the latter (especially since the bias current will have a secondary effect on the actual output, mitigated heavily by the loop gain).
But, given the option between seeing differences in -130 and -120 dB from adsorbed moisture or whatever mechanism of passives drifting (not unsurprising to see drift in the PPM to PPB range) and various other factors (mental or otherwise), plausibility suggests looking elsewhere. And it "being in someone's head" could easily mean the amount of time it takes to relax, clear one's mind a bit, and settle into the music, falsely attributed to the electronics warming up.
The trick is one of these is both infinitely less likely AND much easier to characterize than the other.
Hi Mark,
I don't think people are crazy at all. Mislead - yes, but crazy, no. Using your ideals, shouldn't people who bring forth these ideas be certain before releasing the information? Two examples for you that have been proved to be false. Both CD related. The green magic marker. If that wasn't enough, the green LEDs shining on the CD. Die hard colour green lovers behind these I guess. Do you know how many types of 12 Ga (equivalent) speaker cables I have tried over the years? The only time they affected the sound is when they made normal amplifiers unstable.
-Chris
Under those conditions the unit will never stabilize. The environmental humidity will cause changes in the water content in the part. Most good film capacitors are sealed and are rated for humid environments. So the constructor / designer of an audio product that decided to use unsealed capacitors is somewhat negligent, wouldn't you say? Just think of the long term effects of moisture content on the more reactive metals. Aluminium for example.
But Mark, I have a lifetime of experience on the bench in the high end market in a major urban market (Mississauga & Toronto in Ontario, Canada). I've been dealing with these issues specifically.
I don't think people are crazy at all. Mislead - yes, but crazy, no. Using your ideals, shouldn't people who bring forth these ideas be certain before releasing the information? Two examples for you that have been proved to be false. Both CD related. The green magic marker. If that wasn't enough, the green LEDs shining on the CD. Die hard colour green lovers behind these I guess. Do you know how many types of 12 Ga (equivalent) speaker cables I have tried over the years? The only time they affected the sound is when they made normal amplifiers unstable.
-Chris
I accept what you're saying may be true. To a point. However, have you listened to an amplifier like the one I described earlier? To remind you of the specifics:
* Collectors coupled to loads.
* Zero global NFB.
* High(ish) bias currents (typically - 100ma per output device).
* A thermal feedback system (using fans) to maintain output device temperatures to 55 degrees C (+/- 5 degrees C)
* Soft Voltage limiting.
* Benign current limiting.
* VERY large filter capacitor matrix, using large numbers of small value capacitors.
* A large number of output devices, relative to power output.
* All semiconductors matched to within 1% of Vbe and hFE.
* Compact output stage, ensuring wiring lengths are very short.
* No output inductors.
* No coupling capacitors.
Absolutely. In any zero global NFB amp, temperature plays a big part.
No argument from me.
Like you probably do, I cringe at some of the claims that come along. Yet, I am certain of every claim I have made, and no doubt some people find some of it hard to believe.
With regard to some possibility for proof: Unfortunately, like much of medical research, hearing research is hard and complex. Even people who have expertise, such as Earl Geddes, say a few to several tens of thousands of dollars would be needed for a merely preliminary study. Proving what can and can't be heard by the best listeners is not a task for amateurs. Earl said that new tests would have to be developed, and I would agree. So, asking people to provide their own proof is probably not practical. For such proof to be credible it would need to be performed and perhaps replicated in a way that would withstand scrutiny and overcome the doubts of skeptics. (I know you asked for certainty and not exactly proof, but I think it will probably require proof to establish that certainty can be sufficiently reliable or credible, so I decided to talk a little about that.)
I don't know what the answer is, but it would be great if we could figure out something agreeable to work on to make some progress in this area.
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Wouldn't it be be nice to have an amplifier about the size of a breeze block that you could carry easily under your arm, was efficient enough to not need skin shredding heatsinks and transparent enough to wow users and reviewers alike. That would be progress.
</sark>
</sark>
If you have enough money, there's always this stuff (which is quite nice):
Expert pro: the ultimate audiophile system - Devialet
a testable assertion?
Scott, PMA have posted BBC/Blecher, AP/FastTest type multitone analog loop back plots from low cost 'pro-sumer' soundcards with inter-tone noise near the spot noise floor ~-130 dB
the soundcards of course using only indifferent quality by audiophile standards op amps on input and output
if you don't take that as evidence for global feedback behaving cleanly then what test would you suggest?
Scott, PMA have posted BBC/Blecher, AP/FastTest type multitone analog loop back plots from low cost 'pro-sumer' soundcards with inter-tone noise near the spot noise floor ~-130 dB
the soundcards of course using only indifferent quality by audiophile standards op amps on input and output
if you don't take that as evidence for global feedback behaving cleanly then what test would you suggest?
"The best of both worlds. Our pioneering hybrid amplification technology combines all the linearity and sophistication of Analog (Class A) with all the power and compactness of digital (Class D). Working in parallel, they deliver unbeatable performance. At every turn."
C'mon, that's new, they've invented a digital amplifier, unless, they are cleverly not actually referring to the amplifier
C'mon, that's new, they've invented a digital amplifier, unless, they are cleverly not actually referring to the amplifier
No, it's QUAD-style current dumping, just with a class D dumper. Maybe they thought a low feeback class A stage would negate the huuuge feedback of the class D?
It's like when Ford in the UK tried to persuade us that a 1.8 litre engine would give us the power of a 1600 and the economy of a 2 litre. Or was it the other way around?
(For those of an older an non-euro persuasion I remember 750cc VWs and learned to drive in a Ford with a mighty 1098cc engine it confused me for years how detroit managed to make a big block produce only 220HP in a station wagon. And yes I know there are a suprising number of old healeys on the road in the US).
It's like when Ford in the UK tried to persuade us that a 1.8 litre engine would give us the power of a 1600 and the economy of a 2 litre. Or was it the other way around?
(For those of an older an non-euro persuasion I remember 750cc VWs and learned to drive in a Ford with a mighty 1098cc engine it confused me for years how detroit managed to make a big block produce only 220HP in a station wagon. And yes I know there are a suprising number of old healeys on the road in the US).
Sure. Don't Quad still build that Class A/Class C current dumper system they've been running for decades?
That said, the Devialet is one of the few Class D amps I could live with. It actually sounds quite nice. Oh yeah, it looks drop dead gorgeous too.
You drove an Anglia? Yikes!
Over here, I loved my Escorts (I owned 4 of them). A 1.3L push-rod, then a horrible, 1.6L push rod (unique to Australia, to cope with emission controls -it was a dreadful engine - 5,500RPM redline, Dieseling problems, etc), then Ford Australia, very cleverly, fitted that beaut 2L SOHC Cortina engine to the Escort. WOW! Quick, economical and so easy to manage (loverly twin choke Weber carbie -felt like it was turbo charged, when the second choke opened). One of mine used to rev to 7,000RPM. Some guys turbo'd their 2L Escorts! The only really quick, factory, Escorts we saw over here were the 1.6L Lotus twin cam ones. Similar power to the 2L, but without that low down torque of the 2L and a lot more 'fiddly'. I do miss the induction noise of that Weber. Damned Subaru just gets on with it's business with almost complete silence.
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How much did that cost (if I may be so rude to ask)? Looks like a whole lot of fun. What engine?
I don't think we ever had the 1.1L Escort in Australia (Oops. I just checked. We did get the 1.1L engine). I did hand the keys of one of my 2L ones to a mate, who used to rally a Renault. His words after a short drive on bitumen:
"It doesn't handle brilliantly, but it is very 'chuckaboutable' and very, very predictable. I get why they rally these things."
I sold my last 2L to an apprentice. He did rather well for himself (he's on his third Ferrari - wife drives an S-Class) and he rallied his Ferrari. Once. After the thing went off-road, he decided to go another way. He bought an old 2 L Escort and promptly dropped AUS$100k into the thing. Apparently, it handled very well and accelerated quicker than his F360 to 200kph.
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I take it you are referring to 'inter-signal silence' as mentioned in your earlier post.
The only test that I can think of is to compare recordings (eg Diffmaker) to extract differences that can be post analysed.
I have tried using Diffmaker to compare recordings of throughput/output when applying my filters to gear, but have been thwarted by timebase instability, soundcard resolution and Diffmaker crashing.
Excess noise behaviour is the major differentiator between subjective findings, THD and IMD not so much.
Dan.
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