[The Monkey]

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Originally Posted by SmellyGas /img/forum/go_quote.gif Well part of the reason some of us are skeptical that headphone amps make a HUGE difference in sound quality comes from experience in home audio. At least 10-20 independent trials have been published, including a summary review in JAES, that essentially pointed to the inability of people to distinguish between loudspeaker amplifiers when not aware of the identity of the amplifier. When it comes to headphone amplifiers, the cheapest ones (i.e. built in to a receiver) have measured problems with frequency response with difficult loads, so yes, they CAN make a difference. But once you get into the amps that are above CMOY quality, then I am not confident that the differences are as dramatic as people report.

So it appears that you came in here with an agenda, and not just a question about an amp pairing with the O2. Nothing wrong with that. However, it's more direct to just state your position. Like this: "I'm skeptical that amps make much of a difference with headphones, and I think that includes 'stats. Convince me otherwise." Dispenses with a lot of the circular stuff.

Regardless, the debate itself will not be resolved here. Like cables, if you don't believe it, you don't believe it. Further, if the 252 provides you with a satisfying musical experience, huzzah! You get to spend more money on music. I suggest just buying it, as you appear to remain unconvinced that you need to spend more. I also encourage you to attend a meet where you can hear some of the other amps, or pick up a 717 used (you'll have no problem reselling it once you find it is the same as the 252) to hear how they compare.

 

[SmellyGas]

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Originally Posted by The Monkey /img/forum/go_quote.gif So it appears that you came in here with an agenda, and not just a question about an amp pairing with the O2. Nothing wrong with that. However, it's more direct to just state your position. Like this: "I'm skeptical that amps make much of a difference with headphones, and I think that includes 'stats. Convince me otherwise." Dispenses with a lot of the circular stuff.

No, no, actually I don't know, that's why I'm asking! With loudspeaker amplifiers, I think the evidence is clear. With dynamic headphone amplifiers, there are no good trials that I know of, so I have to extrapolate. With electrostatic headphone amplifiers, there is zero evidence to go on other than owner reports and what I know about electrostatics. The transducer, circuit topology, etc. are so dissimilar that I don't think it's possible to generalize my experience with dynamic equipment to electrostatic. I certainly could believe one amp sounds different from another, but if the explanation is that one amp is more powerful, yet I have a paper that talks about how the electrostatic current draw is near non-existent, then I start to scratch my head.

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Regardless, the debate itself will not be resolved here. Like cables, if you don't believe it, you don't believe it. Further, if the 252 provides you with a satisfying musical experience, huzzah! You get to spend more money on music. I suggest just buying it, as you appear to remain unconvinced that you need to spend more.

I'm considering it, but there are a LOT of reports of the 252 being inadequate. I'm not sure whether this is indeed the truth or if it's because people's expectations of a small wallwart powered amp have influenced their uncontrolled observations. So I might just pay a few hundred bucks more and get a mid-grade stax amp. Haven't decided yet.

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I also encourage you to attend a meet where you can hear some of the other amps, or pick up a 717 used (you'll have no problem reselling it once you find it is the same as the 252) to hear how they compare.

Yeah, if people are anywhere as uncivil during meets as they were in my HD800 thread, then no thanks. I have never seen so much DSM-IV activity over an inanimate object like a pair of headphones in my life.

 

[spritzer]

Wow, just wow. The level of ignorance in these posts is simply astounding. Electrostatics are far from a simple/easy load and you need a lot of power to overcome that. Given the way they work a low power amp will have a direct impact on the FR of transducer since it can't drive it to full swing. Since what you are doing is basically trolling then it's probably best to let the mods deal with you.

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Originally Posted by bjarnetv /img/forum/go_quote.gif yes... their best amp for the sr-007 was the 717, which they replaced with the inferior 727 for some reason (probably cost cutting).

It was actually licensing issues, they weren't allowed to use the 717 circuit any longer so they had to come up with one of their own.

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Originally Posted by kintsaki /img/forum/go_quote.gif The Headfiers who own the O2 along with the super amp it takes to show its full potential (that extra 5-15%) are probably less than a dozen. First it was the T2 then the KGSS then the BH then the BHSE and of course the Egmonds, Mc Allisters, Single Power and so on. But the quest for the amp that will drive the O2 to its full potential is still on. Electrostatics used to be the fastest phones but had their shortcomings too. A lot of people do not like them and many more think they need that super amp to make them sound to their liking. And of course it make take you an afternoon or two to learn to bend the arcs of the O2 to angle them properly to obtain the proper seal and if you are still not satisfied you may have to replace the pads just in case the old ones have lost their elasticity. And then you must get properly recorded and mastered albums because the average recording will not sound good on them. But there are normally priced phones that are way faster and have greater acceleration than stats without the planar problems. It is all a matter of perspective. A musician, a recording engineer, a music lover that listens to live music more often than he does listen to recorded music, an "equipment-file" maybe kind like an "audiophile" and an electrical engineer or DIY hobbyist. I have been in the shoes of all of the above with the exception of the musician. At the end of the day I must agree with "Bullseys's" saying in his signature which i added to mine.

This has to be the most useless post I've read in a long time filled with nothing but BS.

 

[powertoold]

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Originally Posted by SmellyGas /img/forum/go_quote.gif I'm considering it, but there are a LOT of reports of the 252 being inadequate. I'm not sure whether this is indeed the truth or if it's because people's expectations of a small wallwart powered amp have influenced their uncontrolled observations. So I might just pay a few hundred bucks more and get a mid-grade stax amp. Haven't decided yet.

I think you're getting it wrong. I believe the skeptics say that amplifiers operating within their rated power limits will sound indistinguishable. With Stax amps, the more expensive ones are more powerful. They don't pretend to have some sort of special technology or snake oil. Electrostatic drivers need a lot of power, and not any weak amp is going to be adequate to drive them.

If you're going to say the 252 should be adequate, then that's like saying any speaker amplifier should be adequate for powering speakers of any load.

But anyway, it's pointless to argue any of this. If you think a 252 is adequate for all the drivers, then good for you. You've just saved a lot of money. Otherwise, arguing this subject is like an argument about religion and science.

 

[SmellyGas]

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Originally Posted by spritzer /img/forum/go_quote.gif Wow, just wow. The level of ignorance in these posts is simply astounding. Electrostatics are far from a simple/easy load and you need a lot of power to overcome that.

I don't really appreciate you implying that I am ignorant. Once again, according to an ancient paper on electrostatic amplifier design in JAES, "the load, the electrostatic transducer, is a capacitor, the current requirement under normal operation is...extremely low (if not nonexistent). ...it is advantageous to use a large series resistance in the DC supply...which provides a current-limiting resistor to reduce the total current available to an extremely low level...if an accidental short circuit is placed on the output of the supply, the total maximum theoretical current available then will be 200 MICROamps (=0.2mA)...the actual measured current is 60 MICROamps)."

So even at 500V, we're talking 100mW if the headphones had an impedance of 0 ohms (short circuit). So I'm honestly confused as to why a small amp couldn't drive the SR-007's.

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Given the way they work a low power amp will have a direct impact on the FR of transducer since it can't drive it to full swing. Since what you are doing is basically trolling then it's probably best to let the mods deal with you.

Can you explain that again? Even the 252 is rated at 4W, which is more than an order of magnitude more than the headphones could draw even at short circuit. Just because it's obvious to you, doesn't mean that it's obvious to everybody else, so there's no need to call people trolls. thanks.

 

[SmellyGas]

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Originally Posted by powertoold /img/forum/go_quote.gif I think you're getting it wrong. I believe the skeptics say that amplifiers operating within their rated power limits will sound indistinguishable.

That's a fair conclusion for power amplifiers based on a wide body of listening tests. However, I don't want to get into a debate about loudspeaker amplifiers because the data is not generalizable to electrostatic headphone amps, and the discussion isn't really relevant here.

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With Stax amps, the more expensive ones are more powerful. They don't pretend to have some sort of special technology or snake oil. Electrostatic drivers need a lot of power, and not any weak amp is going to be adequate to drive them.

When you say "power," I interpret that by the electrical definition, which is Watts or Voltage x Current. Are you referring to something else, by chance? Because if you're referring to electrical power, based on a paper in JAES, the current draw is miniscule (<60 microamps) and my power calculation comes out to less than 100mW. I realize the voltage is very high, but because the current draw is so tiny, there is little power being delivered to the stats themselves.

I realize that virtually everyone familiar with stax amps believes that the more expensive stax amps are more powerful and that the smaller/cheaper ones are not. This might seem like a silly question, but how do you know this? Are you familiar with electrostatic headphone amplifier circuit design? Did you do some calculations on the schematics available? Or is this just an accepted assumption that everybody else knows, but nobody can explain in detail why? I want to know. I'm curious.

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If you're going to say the 252 should be adequate, then that's like saying any speaker amplifier should be adequate for powering speakers of any load.

Speaker amplifiers are designed to drive speakers within a very wide range of impedance curves and based on lots of testing in The Audio Critic, it is rare to find a power amp that has difficulty driving most non-exotic dynamic loudspeakers. But that's neither here nor there because they are a completely different beast. I'm just addresing the example you give.

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But anyway, it's pointless to argue any of this. If you think a 252 is adequate for all the drivers, then good for you. You've just saved a lot of money. Otherwise, arguing this subject is like an argument about religion and science.

I'm not arguing. I would just like an explanation of why the 252 is inadequate other than "it has no power," given the fact that electrostat transducers require very little power (using the traditional electrical definition). If nobody knows, that's fine too.

 

[kintsaki]

I must have made Birgir and Elephas mad.

I know Elephas thought that I suggested that musicians know better than audiofiles.

I just said musicians may have a different perspective to try to come up with a reason why some Headfiers don't care for stats and prefer dynamics.

I don't understand why it is wrong to try to associate people's preferences to their backround.

 

[The Monkey]

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Originally Posted by SmellyGas /img/forum/go_quote.gif Yeah, if people are anywhere as uncivil during meets as they were in my HD800 thread, then no thanks. I have never seen so much DSM-IV activity over an inanimate object like a pair of headphones in my life.

I'm not familiar with your HD800 thread, but in my experience, people are almost uniformly nice at the Meets I have attended. I think you would enjoy it.

 

[Cool_Torpedo]

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Originally Posted by SmellyGas /img/forum/go_quote.gif ... So even at 500V, we're talking 100mW if the headphones had an impedance of 0 ohms (short circuit). So I'm honestly confused as to why a small amp couldn't drive the SR-007's.

Excuse me? P=V^2/R IIRC. Anything /0 is infinite

500V into 1 Ohm is 250000 watts.

 

[spritzer]

The SRM-252 isn't 100% efficient so only a small portion of those 4W actually go toward making sound. With Class A amps it is quite normal for them to use 70-95% of their current draw to just giving off heat while the rest goes towards producing sound. The 717 draws something like 55W and gives off a lot of heat. I have the very rare Stax SRM-T2 sitting next to me and it draws in excess of 200w, most of which is converted to heat. Now this heat isn't all going to waste since running devices full time sounds a lot better then Class B and some of that heat stems from the standing power of the amp, i.e. how much power can it really give off.

As for the paper you quoted, it was always understood that electrostatics didn't need any current at all. While they have wild impedance swings the amount of current needed was small. Back in 1988 Stax set out to rewrite the rulebook on how electrostatics were designed by examining everything. The Omega lineup was the result plus the SRM-T2. On the amp front the saw then need to increase the current capability of the circuits as a whole with current sources for every stage to make sure enough power was always at hand plus seriously upping the amount of voltage the amps can swing. The output impedance of the amps was also lowered so that the slewrate goes up and the amps are more responsive to the load the "see". There was still room for improvement and that's where the BHSE comes in. Better PSU's, more standing power and even more current of tap.

 

[SmellyGas]

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Originally Posted by Cool_Torpedo /img/forum/go_quote.gif Excuse me? P=V^2/R IIRC. Anything /0 is infinite 500V into 1 Ohm is 250000 watts.

P=V^2/R is a correct formula for power. However, it is not the applicable formula here as you may have guessed when you came up with 250,000 watts. Obviously your wall socket could not deliver that. If you must use resistance, then I believe there is a very high-value series resistor installed, so even if your headphones went to short, the current delivery would still be very limited (which is why electrostatic headphones are generally safe from electrocution hazard).

P = voltage x current is probably a more applicable formula.

 

[spritzer]

Ahh you are mixing up the bias voltage (DC) and the music power (AC). The bias does indeed have next to how current and is protected with a ballast resistor so that next to no current flows. These are two very different things...

 

[SmellyGas]

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Originally Posted by spritzer /img/forum/go_quote.gif As for the paper you quoted, it was always understood that electrostatics didn't need any current at all. While they have wild impedance swings the amount of current needed was small.

Right! So what's all this talk about power? Even if the 4W SRM-252 is 10% efficient, that should still provide 400mW, which seems to be plenty.

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Back in 1988 Stax set out to rewrite the rulebook on how electrostatics were designed by examining everything. The Omega lineup was the result plus the SRM-T2. On the amp front the saw then need to increase the current capability of the circuits as a whole with current sources for every stage to make sure enough power was always at hand plus seriously upping the amount of voltage the amps can swing.

This part I don't quite follow. Why did they need to increase current capability when the current draw of the headphones was tiny?

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The output impedance of the amps was also lowered so that the slewrate goes up and the amps are more responsive to the load the "see".

This I'm not quite clear on either. I thought the impedance of electrostatic headphones was already very high (kohms), so would lowering output impedance of the amplifier help a lot? I think the paper mentioned this or something of the sort...

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There was still room for improvement and that's where the BHSE comes in. Better PSU's, more standing power and even more current of tap.

Thank you for the historical background and the circuit analysis. I'm still not quite sure where the current requirement comes from, though, given you agreed that the phones themselves require very little current. I appreciate this information, it's very helpful.

 

[SmellyGas]

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Originally Posted by spritzer /img/forum/go_quote.gif Ahh you are mixing up the bias voltage (DC) and the music power (AC). The bias does indeed have next to how current and is protected with a ballast resistor so that next to no current flows. These are two very different things...

Ya know, you could be right. While the bias voltage certainly should have low power requirements, according to:
HeadWize - Project: DIY Electrostatic Headphones by Andrew Radford
"the stators need around a 300V voltage swing, and need next to no current. So a high voltage, high output impedance amplifier is ideal"

I realize this a super-crappy amp, but the principal is the same. I could be wrong. But it seems to make sense. From what little I know, there is no actual conducted circuit through the headphones, which implies that the effect of two stators, with a non-touching diaphragm sandwiched in between, is essentially one fat capacitor.

 

[edstrelow]

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Originally Posted by SmellyGas /img/forum/go_quote.gif What's also concerning is that people seem to be under the impression that engineers design products so that they sound good. These people have apparently never talked to an engineer. Engineers design products so that they measure well. That's their job. Usually, these measurements are in areas that correlate with, but do not guarantee, accurate sound reproduction. For instance, someone designing an amplifier circuit doesn't listen with headphones and says "sounds too bright, I think I'll tweak this resistor here." However, he might measure the noise floor and improve power supply isolation if there was excess noise, for example. And then once the engineer's design comes out, it'll certainly get modified to keep costs low, and there will be compromises and parts substitutions that are mandated by other departments. .

Nonsense! Engineers are in business to make products which sell. They don't care any more (or less) about specs than about sound quality. The bottom line is the bottom line. Anyone who tries to sell any product based on specs rather than consumer acceptance will be looking for another job pretty quickly.

I seriously doubt that the type of specs you mention have much correlation with quality audio. Maybe at the extreme end of bad pertformance noise floor matters but not for most of the equipment being discussed in this forum.

Again you need some serious exposure to the type of equipment you are writing about. Otherwise you don't know what you are getting into or talking about.