Electrostatic amplifiers VOODOO?
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Hello!

In the estat community both here on head-fi and on other sites, the usual chasing of the holy grail occurs. The most expensive way to achieve this is to get the most highly sought after electrostatic rig. Currently, this is the Stax SR-009 and SR-007 headphones. I will focus on the SR-007 as this is the most egregious example, but the same mantra largely goes for the SR-009. In short, the consensus is that if you really want to drive these headphones to their full potential, the amplifiers provided by Stax simply does not cut it - claims of "night and day" difference is commonplace, and the argument is basically that the Stax amplifiers cannot provide enough voltage swing (?). The recommended amplifiers are third party amps: Either a KGSSHV Carbon (6 000$), a HeadAmp Blue Hawaii BHSE (6 000$), or other even more expensive options like the T2 or T2 DIY. I lack a technical background, but having owned the SR-007 and the Stax SRM-727ii amplifier previously, and finding it the cleanest sound I've ever heard from headphones, and my understanding that the 727II does in fact provide enough power, I want to settle this once and for all by asking the fine experts here in the Sound Science forum. Calling out @castleofargh , @gregorio and @bigshot

I will now provide the specs for the headphones, and then the amplifiers in question. My argument is that the sound will not be different between the amps in question.

The headphones:

Stax SR-007

Type

Push-Pull Open Back Electrostatic Headphone.

Frequency Response
6 - 41,000 Hz (no tolerance specified).

Impedance
170 kΩ at 10 KHz.

Capacitance
94 pF, including cable.

Sensitivity
100dB SPL at 100 V r.m.s. at 1 kHz
.
Optimum Bias Voltage and Amplifiers
580V DC.
Works fine at 230V DC, but with reduced sensitivity (92dB SPL at 100 V r.m.s. at 1 kHz) and corresponding 8 dB reduction in maximum output level.

Stax suggests either of the current SRM-007tII (tube) or SRM-727II (solid-state) amplifiers, and they all work.

Stax SR-009

Type: Push-Pull Open Back Circular Electrostatic Headphone

Frequency Response: 5 - 42,000Hz

Electrostatic Capacitance: 110pF (including cable)

Impedance: 145k Ω (including cable, at 10kHz)

Sound Pressure Sensitivity: 101dB / 100V r.m.s. 1 kHz

Maximum Sound Pressure: 118dB / 400Hz

Bias Voltage: 580V DC

And now the amplifiers:

Stax SRM 727II

Specs:
  • Frequency Response: DC-115 kHz (SR-007 or SR-404, when using one unit)
  • Rated Input Level: 200 mV / 100 V outputs
  • Maximum Input Level: 30 V r.m.s. / at minimum volume
  • Amplification: 54 dB (x 500)
  • Total Harmonic Distortion: 0.01% / 1 KHz, 100 V r.m.s. Output SR-007 or SR-404 Signature, when using 1 unit
  • Input Impedance: 50 KΩ / XLR balance 50KΩ×2
  • Input Terminals: RCA×1 or XLR×1 (balanced)
  • Maximum Output Voltage: 450 V r.m.s. / 1 KHz
  • Standard Bias Voltage: 580 V DC
  • Power Voltage: 120-240V ±10%, 50 to 60 Hz (adjusted for your area)
  • Power Consumption: 46 W
I couldn't find the specs for the Carbon, but lets just assume they provide a lot more power in all areas.

Is there any reason for this amplifier to not be sufficent to drive either the SR-007 or SR-009, and would providing more power alter the sound?

Thank you for your time.
 
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castleofargh

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My expertise is on mangas and comics. And even then I can't remember the names more than half the time.
I know very little about electrostats and nothing about the amps for them.

Just very basic stuff, you're more likely to feed the amp with about 2v, so the gain isn't relevant as we can already can hit the maximum possible output with 2V. So let's just use 450Vrms as maximum output. unless of course, you specifically plan to feed it with some super weak Sony DAP like my old A15, or with a computer while setting the volume in your player at -30dB. if so, you probably need another amp, end of discussion.

For a headphone with 100dB SPL at 100 V r.m.s. At 1 kHz, that suggests you'll reach 113dB SPL max with that amp(with a normal DAC and maxed out digital volume on whatever source). I have no clue about the distortions figures at such output for that amp into that load, so I have no idea if it's a practical level or just some theoretical crap and the sound becomes rubbish long before? Not that I personally listen to music with 113dB peaks very often(never!).

With that said. When someone asks me about amps and I know nothing about him and his listening habits, I try to find an amplifier that can do at least 115dB. The 2dB difference isn't dramatic or actually important IMO, but it's just a tiny bit short of something I would usually recommend in term of power. Understanding that this 115dB target is sort of a worst case scenario, if the amp can do that into the headphone, then under almost no circumstances will we lack in output. It doesn't mean that suddenly the amp can't be used at all and everything has gone to crap.

Other than that, I typically ignore subjective feedback about voltage or power. Those are objective variables, so I like to see measurements as that's how they actually are defined. Unless the guy simply can't go loud enough(then he's right), he probably isn't talking about voltage or power and probably doesn't really know what he's talking about. That's my personal opinion.


All this told you nothing. you're welcome.
 
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gregorio

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I want to settle this once and for all by asking the fine experts here in the Sound Science forum. Calling out @castleofargh , @gregorio and @bigshot
It's reasonable to assume that "the consensus" regarding estat amps is the same as most other consensuses in the audiophile world, IE. Nonsense. However, this isn't the "Reasonable to Assume" subforum and although I heard some Stax estats (with stax's own amp) many years ago, I've never objectively measured/tested the performance of different third party stax amps or seen the results of anyone else who has. So like castleofargh, I can't tell you anything and you're welcome :)

G
 
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Thank you @castleofargh and @gregorio . How would I go about finding proof about the absence of sonic differences? The claim is that the Carbon (powerful third party amp) gives increased bass, better detail and so on. Having owned the SR-007 and 727II, I know you blow your ears off a long time before you reach the end of the volume pot, at least via schiit modi and a larger dac. What measurements, or what specification would you look for to find a difference in sound quality? If its only the power, given low enough THD, then its unlikely the 727II will in general sound worse than the Carbon, right?
 
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I can plug my LCD2 into my Denon receiver and blow my ears off. Or I can plug them into my La Figaro and do the same but experience better SQ. It is no different with STAX ear speakers and their amps or 3rd party amps.

I just sold a STAX SRM-T1 which sounded beautiful but lacked output compared to the Mjolnir Audio Octave III I also own that also sounds beautiful but has the power to really make my cans shine.

I suppose you just have to demo the amps to know for sure but the bottom line is, who cares? If that STAX amp rocks for you then rock on! That is all that matters right? Some of us will never purchase a $6k electrostatic amp for our STAX headphones and that's fine. I have better things to spend 6K on myself. I still want quality for my money and if I can find that spending under $1500 then I'm all the happier for it.
 
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Demoing won't prove anything. A controlled level matched, direct A/B switched blind listening test is the way to tell. Just make sure you are comparing apples to apples when it comes to a proper impedance match.
 
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I can plug my LCD2 into my Denon receiver and blow my ears off. Or I can plug them into my La Figaro and do the same but experience better SQ. It is no different with STAX ear speakers and their amps or 3rd party amps.

I just sold a STAX SRM-T1 which sounded beautiful but lacked output compared to the Mjolnir Audio Octave III I also own that also sounds beautiful but has the power to really make my cans shine.

I suppose you just have to demo the amps to know for sure but the bottom line is, who cares? If that STAX amp rocks for you then rock on! That is all that matters right? Some of us will never purchase a $6k electrostatic amp for our STAX headphones and that's fine. I have better things to spend 6K on myself. I still want quality for my money and if I can find that spending under $1500 then I'm all the happier for it.
I'm guessing the LCD 2 is clipping from the Denon receiver.

I used to believe that audio is an infinite journey upwards - that once I got a Carbon amp, the next upgrade down the line would be a DIY T2 or hopefully someone could create an even more powerful amp, making the highs even smoother and more detailed, the mids lusher, the soundstage deeper, the bass more authorative ... and so on. But now I don't believe that anymore. I believe its a bunch of bs.

Audiophilia is one of the creepiest mass delusions I've ever come across, because I got completely fooled by it. I remember purchasing an amplifier for dynamic headphones and asking the designer about its "sound signature", and I remember being taken aback by his response, which was something along the lines of - "I'm not going to comment on sound characteristics, but I will tell you this amplifier can drive any headphone you throw at it". Its funny to look back at because he probably thought I was a complete idiot commenting about "deep bass and wider soundstage", parroting reviews about the amp I had read.

I've experienced "night and day" differences by upgrading DACs, usb to coax converters, upgrading cables - I lacked (and still do largely lack) the technical knowledge to understand why something would or wouldn't make the sound better, but if I'm being honest with myself, I always knew I couldn't tell my DAC or amp apart from another, as long as the headphones were properly driven. Hell, I was often disappointed by how similar my experiences with my expensive headphones were vs my cheaper ones, or the car stereo. And I definitely knew I could never tell the components apart in an ABX - only the headphones, nothing else.

Now, I find it extremely strange that an amplifier made by the largest electrostatic headphone company, for the headphones in question, would be underpowered to drive the headphones. If there was a change in sound going from one properly made and powerful amp A (727) to another properly made and powerful amp B (Carbon), which I already doubt, there is no way in hell anyone could ever pass a blind test. Now obviously none of the guys owning a Carbon will ever in their lifetime actually do such a test, but rather do as I did back in the day - argue about how blind testing "doesn't work". So I want to ask the guys with technical knowledge how it makes sense that the 727ii amp sounds "bad" (I mean its faultly amplifying the signal, right?).

The issue with your thinking about just being happy with an amplifier is this: A lot of audiophiles, me included, search for the holy grail, cost no object. People who believe the Carbon is necessary to get the most out of their headphones will do everything in their power to get their hands on them. But what if the sound isn't actually better, but rather its all in their head, as is so normal in audio? I was myself victim to such placebo. Wouldn't it be important to uncover whether the Carbon actually does improve the sound or not?
 
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I believe it would be important. But you need to set up the double-blind test: both amplifiers (the "good" and the "bad") connected to the headphone through a switch box invisible to the listener, volume-match both amps and then do the listening test with a person other than the listener operating the switch. Those owning a $6000 amplifier usually don't want to do it, because they don't want to know the result of the experiment.

I own a Koss ESP950 that uses a cheap looking plastic box as energizer, and all I can tell you is that it sounds great. I would LOVE to know if it really improves with a more expensive amp. But the only way I can do it is purchasing one. And if I do it, to hell with it, I won't want to know the answer.
 
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I had an expensive DAC/amp given to me by a company to evaluate. When I told them that their headphones sounded the same as just plugging directly into the headphone jack on my iMac, they wouldn’t give me free stuff any more!
 
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I believe it would be important. But you need to set up the double-blind test: both amplifiers (the "good" and the "bad") connected to the headphone through a switch box invisible to the listener, volume-match both amps and then do the listening test with a person other than the listener operating the switch. Those owning a $6000 amplifier usually don't want to do it, because they don't want to know the result of the experiment.

I own a Koss ESP950 that uses a cheap looking plastic box as energizer, and all I can tell you is that it sounds great. I would LOVE to know if it really improves with a more expensive amp. But the only way I can do it is purchasing one. And if I do it, to hell with it, I won't want to know the answer.
I've heard about the ESP950 supposedly sounding a lot better from other amps than the one it comes with, too.

@castleofargh explained why the 727ii could potentially, under some specific circumstance sound different from the Carbon. But what about the Stax top of the line amplifier, the T8000? This amplifier is universally revered as bad sounding - I've never read a single 009/007 owner say it sounds good. Does it make sense, considering its specs?

  • Frequency response:1~115kHz per channel
  • THD:<0.01% @1kHz per channel
  • Gain:60dB
  • Rated input level:100mV/100V
  • Maximum output voltage :470V r.m.s./1kHz
  • Input impedance:Unbalanced 50kΩ/ Balanced: 50kΩx2
  • Analog Input :RCA x2、XLR x1
  • Headphone output :Stax PRO bias output x2
  • Volume control bypass: Allows the use of an external preamp
  • Vacuum tube: 6922 x2
  • Power consumption :95W(58W when idle)
  • External dimension :320(W)×103(H)×395(D)mm / 12.6" x 4" x 15.6"
  • Weight:7.3kg / 16.1 lbs
  • Voltage: 120V/60HZ
  • Warranty: 1-year U.S. limited warranty

This is a 5,800$ amplifier that supposedly doesn't cut it sound wise for Stax amps.
 
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How would I go about finding proof about the absence of sonic differences?
Record your HP output using one amp then the other and null test the two recordings. You'll then have an objective measurement of the difference. This isn't quite as easy as it sounds though, you'll probably need a headphone recording setup (dummy head, etc.). The other way would be a blind/double blind test but that too has some potential problems if not done carefully. For example, level matching as bigshot stated, not moving the headphones on your head, etc.

[1] I can plug my LCD2 into my Denon receiver and blow my ears off. Or I can plug them into my La Figaro and do the same but experience better SQ.
[2] I suppose you just have to demo the amps to know for sure but [2a] the bottom line is, who cares?
1. This is the Sound Science subforum, not the "what you think you're experiencing" subforum.

2. Demo'ing components is one of the worst ways to "know for sure", even more so if demo'ing them at a retailer's! To "know for sure" requires objective measurements and possibly, well controlled double blind tests with good sample sizes. Even a little less than that and you don't "know for sure", you just know to some level approaching 100% sure. And obviously, a great deal less than that, say nothing more than audiophile marketing, audiophile anecdotes of sighted "experiences" and a personal, uncontrolled, sighted demo, and the level of surety is closer to 0% than 100%. This appears to be more than enough for the audiophile community to "know for sure" but for the Science community (and many others) it's only enough to be somewhere between "a guess" and "no idea whatsoever"!!
2a. Anyone interested in separating audiophile marketing/myths from the actual facts. Admittedly, that's not a lot of people in the case of third party amps for certain Stax HPs but one obvious example is the person who started this thread, to which you're responding!

G
 
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Record your HP output using one amp then the other and null test the two recordings. You'll then have an objective measurement of the difference. This isn't quite as easy as it sounds though, you'll probably need a headphone recording setup (dummy head, etc.). The other way would be a blind/double blind test but that too has some potential problems if not done carefully. For example, level matching as bigshot stated, not moving the headphones on your head, etc.

G
Considering these options are unavailable to me, is there any way of looking at the specifications of the amplifiers to understand how close they should be sounding in practice?
 
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If those specs can be trusted, and you think there really is a difference, (two VERY big assumptions) the likely suspect would be the frequency response. They list a very wide response, but they don't list a deviation tolerance. Without the +/-Xdb spec, response measurements aren't terribly useful.

If you can get ahold of the amp, I'd suggest doing a simple line level matched, direct A/B switched blind listening test. The equipment for that will cost about $50 and you can use it to test other amps and DACs as well.
 
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If those specs can be trusted, and you think there really is a difference, (two VERY big assumptions) the likely suspect would be the frequency response. They list a very wide response, but they don't list a deviation tolerance. Without the +/-Xdb spec, response measurements aren't terribly useful.

If you can get ahold of the amp, I'd suggest doing a simple line level matched, direct A/B switched blind listening test. The equipment for that will cost about $50 and you can use it to test other amps and DACs as well.
I definitely don't think there is a difference, but thats just based off my ears when listening to the 727ii. I had hoped we could discern a likely absence of difference in sound based on the published specs, but I guess not :frowning2:
 
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Proving an absence of difference would be proving a negative. You can only listen using one set of ears at a time and prove that there is a difference. My rule of thumb for stuff like this is that biased opinions are so prevalent in home audio forums, I tune out opinions of people who can’t be bothered to make an effort to eliminate bias and perceptual error in their comparisons. I’ll just continue like Diogenes.
 
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