JimL

Depends on what its function is. As Kevin Gilmore points out, for a servo, an op amp with virtually no offset current (JFET rather than bipolar) and low temperature drift, that is slow (since the servo is monitoring for DC offset and is deliberately slowed down anyway), is good. OTOH may sound like crap as an amplifier, where the requirements for "good" are significantly different.

I would go with MM for a poor man's rig. MC tend to have lower output which puts more demands on the phono stage - higher amplification plus lower noise, or need for input transformer = more complication = more money.

Nice! BTW, probably the reason the BH is running cooler is that you've got 70+ watts sitting outside the case (those 4 EL34s at 9 watts filament power plus 9 watts plate dissipation per tube).

Partly that, but by all reports it sounds like Dan is a nice guy, so that likely rubs off on his headphones. OTOH if he was an SOB...

I like to run my filament 5% low, which is 6 volts. I believe David Berning, who designs for long tube life, likes to run his 12.6 volt tubes at 11.5 volts, and his 6.3 volt tubes at 5.7 volts, which is close to 10% low.

So, here's where a little math beforehand would have helped out. Now, the 10M90S is specified as having a thermal resistance of 80K/W junction to ambient (K = Kelvin, so 0 degrees Kelvin is absolute zero, each degree Kelvin = 1 degree centigrade), and the C2M10000170D is specified as having a thermal resistance of 40K/W junction to ambient. As these devices are rated to run below 150 degrees centigrade, what this means is that the 10M90S without heatsink is rated for less than 2 watts, and the C2M is rated for less than 4 watts. The 10M90S split the PS voltage between them (for as long as they were functioning), so 400 volts each at 20 mA = 8 watts. Running a transistor at 2 and 4 times their rated power dissipation will blow them in short order. If you've ever seen the actual size of the transistor inside its case you will understand why they can get fried quickly by being overstressed. Therefore, you need to replace ALL the C2Ms,all the constant current source 10M90S, and all the DN2540s as well, unless you're absolutely confident that the other devices protected them like a fuse. Which I doubt. Murphy's Law: a transistor protected by a fuse will blow first, protecting the fuse.

Probably because it's the cheapest amp around.

So, here's the thing. A post on HF suggests that what they want is to have one amp for both electrostatic and dynamic/planar headphones. Also, it appears that they want single-ended in. This circuit does all of that, but of course it's a compromise. It's not going to be as good as a dedicated stat amp, and it's not going to be as good as a dedicated dynamic/planar amp. I would add that I agree that a triode LTP in place of the pentode would work equally well as an input for single-ended, and also allow for balanced inputs, so you don't lose anything there. I suppose if you wanted to do tubes and all headphones, you could take the SRX Plus and stick a transformer on the end of it for dynamic/planars. That would give all differential, all balanced, and work for everything - assuming you are willing to accept transformer outputs for dynamic/planar headphones.

Now, the power supply, on the other hand, is "interesting." It appears to be a shunt regulated supply using the LM317 as a constant current source, and the TL431 shunt regulator IC. Both are protected from high voltage by tubes, the LM317 by a 5998, and the TL431 by the KT66. However, would expect the sonic impact of the regulator to be dominated by the TL431, which is the active shunt element, as the KT66 doesn't have any active role in the regulation. Nor does the 5998 play an active role in the constant current source, which is basically done by the LM317. Both are simply high voltage "umbrellas" to protect the solid state devices that are the active elements. So the tubes look nice but add the complication of filament supplies without (probably) contributing much if anything to the sound.

Actually, the schematic is in the first post in this thread, and is a copy of the classic Mullard 510 amp circuit from 1954, except with the feedback taken before the transformer instead of after, and the transformer being driven off the cathode of the triode-connected output tubes rather than the plate, so your head isn't sitting between several hundred volts. Nothing wrong with it, but nothing to be in awe of, either.

Possible 3rd party cables for electrostatic headphones - what could go wrong?!!? Oh, and notice this: "Energizers are available from Woo Audio, iFi and Stax, while amplifiers are available from HeadAmp, Malvalve and Stax." IIRC, Stax hasn't made energizers for a couple decades, the Woo WEE and iFi have questionable engineering, and notice that he left out the Woo WES (probably just as well).

So, as of Friday, the official word: After a lot of tests this week we concluded we are able to add an outer barrier without audibly or measurably degrading the sound or performance parameters. Accordingly we will modify the driver stack to add an outer dust barrier so the driver is now "impermeable" to particulates. Since the changes are trivial to implement, won't materially impact cost, have no effect on schedule and could potentially improve long term reliability we've decided to make this change and the driver stack will be:1) outer metal grill2) protective super-fine screen3) mylar barrier4) outer metal stator5) diaphragm6) inner metal stator7) mylar shield 9) inner metal grill7) Fine cloth dust screen integrated to the ear pad optional filters which can be used for tuning; VOCE will include two filters for three different tunings (they can be above or below the the ear pad's screen). This is particularly fun, as you can instantly tweek the headphone to sound closer to a planar, with minimal loss of resolution. I hope people will enjoy this! Which means, TA DAH! Now it has dust covers, which it didn't have before. I'll let someone else draw the obvious conclusion.

So, it turns out he's bought an HE-1.

There's no accounting for taste. But seriously, credit where credit is due - all I did was update the original Stax circuit. Whoever designed that circuit deserves the credit.

Interested also.

Two other points (from Dan's post on Head-Fi): 1) "Yes. There's a fine mesh dust screen under the outer "web."" 2) "We have also taken steps to design this to be field service friendly, the driver is modular enough for field repairs to be a reasonable thing." Point 2 means that it shouldn't be too hard to rip apart. Point 1 could mean that ripping it apart periodically might be necessary. "Fine mesh" to me means dust permeable, unless the words mean something else that what I think they mean. Although they do say the box is to decrease dust accumulation on the stators, but they don't say anything about dust accumulation on the membrane, so maybe there is an impermeable dust cover underneath. I'm also not too thrilled with the spider-web ear cups. Looks like an open invitation for small children to stick something sharp into the open holes, like a pen, pencil or screwdriver. And that's from someone who doesn't even have children.

Yes.

So, the resistor that needs to be changed is the one which has orange, blue and green stripes on it - there are two of them, so the one to be changed is the one which has one end connected to the junction of all three resistors, and its other end going to the output socket. This should be replaced with a 4.7 megohm resistor. You can get a suitable one at Mouser electronics. Part number: 594-VR37000004704FR5 or VR37000004704JA100. It's only 19 cents, or 13 cents for the second option. Unfortunately shipping is around $7. The other orange-blu-green resistor should not be changed. You can tell this resistor because with an ohm-meter, there should be zero ohms (or very nearly) between the chassis and the end of the resistor that is away from the junction of the three resistors.

Then there's the input diff amp with resistors in the tail in the eXstatA - because it's cheaper than a current source and almost as good, according to Cavilli - which was duplicated in his LL because...who needs a little more expensive and better, for a spare no expense SOTA amp for big bucks?

That was the least of its problems.

Yes, but they're EXPENSIVE caps. Expensive caps add audiophool credibility!

I have both the 009 and the 007 Mk 2.9 with port mod. At the last Albuquerque meet, out of 6 listeners, 3 preferred one and 3 preferred the other, driven by a BHSE - I told them the 007 is less efficient so they needed to turn up the volume a bit to compensate. I slightly prefer the 007, as to my ears the 009 is a bit on the bright side, and the 007 Mk I is a bit on the soft/dull side. FWIW, recording engineer Bob Katz also prefers the 007 Mk 2.9 with port mod as being more tonally accurate, and Tyll at InnerFidelity seems to like Bob's modded 007 more than either the 007 Mk I or 009 based on his comments from Big Sound 2015.

What goes in may be sinusoidal, what comes out may be sine wave plus harmonics, i.e. distortion. For example, I have driven a woofer with progressively lower frequency sine waves, and at some point the pitch suddenly seemed to double because it was producing enough 2nd harmonic distortion that I heard the distortion as much as the fundamental, and the pitch sounded an octave higher. In fact, the term "doubling" refers to this phenomenon. So, yes, flapping can occur, or doubling (or tripling, or higher harmonics).

Below 20 Hz what you may be hearing is the harmonics of the tone rather than the fundamental - i.e. what you may be hearing is distortion, especially if you cranked it up.

If you're concerned about harshness, the 007 may work better for you than the 009. Not that the 009 is harsh, but it's a bit bright to my ears, and that can sometimes be confused with harshness.