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@padam awesome, just what I was looking for! Now I know I'm not crazy in thinking the Lambda Pro actually does sound very similar to the NB Lambda, with a few minor HF discrepancies. Sad to hear about wikiphonia, it was a treasure trove of info on vintage orthodynamics but I guess Faust didn't feel the need to continue hosting it. I also miss the Father of Orthodynamics, wualta. He taught us so much in a very endearingly quirky way @Craig Sawyers I purchased what I believe are PRO4AA pads awhile back... they are awful and don't fit the ESP6. There is a reason the Koss pads are $5. Even if I messed up and ordered the wrong pads (it's been a few years so I don't remember 100% and can't find any confirmation order email...), they are unusable for any purpose other than to enkindle. Hope you snag the ESP9 and report back!

You are not alone; I prefer the NB Lambda to 007 as well. It is one of my fav of the Lambda variants. I like to think of it as the headphone the AKG K501 (my first good headphone) wishes it could be. If you buy another pair of ESP6, try converting it to normal dipole operation (ripping out the circuit boards and recabling with a Stax cable). With some strong sound absorbing materials lining the cups the sound has potential to be pretty decent, and it actually weighs a normal amount for a headphone so no neck strengthening workouts needed. More problematic is the odd non-circular shape which makes pads that fit hard to find (the original ones have all leaked and hardened by now). I use SR-007 pads which sort of fit but are circular, so not really. Interesting.... but don't feed my GAS!! Could you point me to the measurements of the NB Lambda?

Thanks for the impressions! Never heard a SRA-3S but normal bias Lambdas are great. There's the old audiophile adage: If it sounds good but measures bad, you're measuring the wrong things. My fav headphone is still the SR-Omega, which I'm sure is less technically proficient in standard measurements than the SR-009. Other than an amp upgrade, is this pretty much your end-game setup? Most of the time I listen to $7 earbuds straight out of my phone or laptop, which sound just fine to me, so I get my enjoyment of this hobby from the quest to learn more than anything else. Since my end-game setup is no setup at all, I should probably sell everything off.

How did your ECR-400/500 refurb go? @edstrelow ESP6 converted to Stax dipole operation actually sounds quite good, other than the obvious backwave bass cancellation. I never heard the thing stock, as the deteriorated foam gunk shorted the circuit boards and as soon as I unscrewed the cups it was Staxifying time. I'll play around with some Dynamat lining and whatnot in the cups someday.

What are you rocking these days, Adam? SR-009 like in your profile pic? SR-5 Pro? How do they compare to the HE1060?

Way smaller than the first version boards, for sure! Thanks, Kerry and KG, for making this happen. I bought a rework station so things will hopefully go a lot easier than with the previous boards. I just finished the channel balance code, which parallels that of volume. A slider with a range of 256, so up to 128 on either end, and added +- buttons for fine control. Will investigate what's new with Android SDK in the weekend. I did some research on the RPi3 after you guys mentioned it, and saw they sell a companion 7" touchscreen for $60!! 7" is a bit unwieldy to put in an amp or DAC, though. What a time to be alive.

Balanced is a go. I'll work on a channel balance slider next weekend... maybe try to solder up a level shifter and scaler for the ADC. Anyone have recommendations for such a schematic to convert up to +-20v input signal to 0-3v3 input for ADC? The digital ps i protoboarded is the same (other than different capacitance values) as the one on the dynahi, so 7812, 7805, and murata 3v3.

Awesome, it would be nice to compare notes. I won't be getting the ADC boards for awhile anyway. Good idea, rp3 might be the best option for something universal for people to use, instead of all these different arduino/mcu options and the built in wifi and Bluetooth is nice.

Nvm, I just ran an i2c address scan and figured out the address situation. Got the code working on each attenuator board with a cloud-connected MCU which uses the 4D systems touchscreen LCD KG and Max are using as the input. 256 pixels for 256 settings, just like they wanted it, and +- buttons for fine control because these resistive touchscreens aren't very precise. I will write the code for balanced operation in the weekend, and I ordered some I2C ADC breakout boards for temperature sensors as well. Eventually the goal is to write an Android app for remote control; that way my lazy ass never has to leave the couch.

Speaking of the first version, sorry if this has been mentioned before but how did you guys change the I2C address pins for balanced operation? I believe all three address pins are grounded (L L L) on one PCF8574A per board, and the other one is adjustable with the ID pins? I suppose you could put in a PCF8574 for one, or mangle a PCF8574A pin and attach it to high. I see that the new boards use SPI. Also a bit obvious but, for anyone who hasn't soldered SMT resistors before, it might be a good idea to order two or three spares for each value just in case. Once you accidentally let one of these things fall to the floor it is very difficult to find. Maybe someone has a better way of finding them, or keeping them from flying off in the first place.

-560V is just a -60V supply tied to the -500V rail as reference, so focus on something connected to the -500V rail. If the CCS LEDs aren't lighting up on the +250V and +500V rails something is wrong on that end, too, since the required forward voltage is not being dropped across them. If everything measures fine on the other channel, the PS should be fine so check the amp board.

Are you grouping these boards for shipping with the attenuator boards for those who ordered both?

Depressing how 100 pages of the HF thread are dedicated to the so-called 6kHz spike which the response graph clearly states is based on their developed measures ideal diffuse field curve.

Tautologically, that's indeed how HRTF works. This is a nice intro to the subject, although the differences are exaggerated with the rubber "ears": http://lib.tkk.fi/Dipl/2008/urn012834.pdf Concha-related Helmholtz resonance is approximately 6 to 10 dB in magnitude at around 4-6kHz. If one can't hear a few dB difference at 5kHz he/she should probably have his/her hearing checked out by a doctor. This is an interesting read on approximating with reducing anthropometric measurements, though: http://arxiv.org/ftp/arxiv/papers/1005/1005.5137.pdf Another read on the correlation between aging of the external ear and resonance: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-17822014000200112 The best one can do when designing a headphone is to take some sort of average, and then there's the whole free field vs. diffuse field debate, and baseline volume in equal loudness contours. @comzee Not 100% sure on that, I was just going off of what (IIRC) someone said earlier. I haven't tried buying either.

Agreed, there are many other factors involved including user variance (error?) in regards to positioning/earpads and in manufacturing with all these different versions (not even mentioning mods like the spring and port mods, upstream components), so it's difficult to replicate and compare when there are almost no control variables in a veritable sea of them. Someone would have to experiment and crunch numbers to compare magnitudes of difference between, say, earpads and concha shape. I happen to agree with you that the SR009 that I heard, in the conditions I heard them in, with my ears, etc., has a bit of a hyped treble but that's just an additional possibly meaningless data point in context... another one being that if the SR009 has basically been on backorder since its inception, clearly some people do like its sound. I have not been a fan of the SR-007s that I've heard, enough that it has never interested me to purchase one to mod and fine-tune; of course, there are plenty of people who do like theirs. tl;dr ymmv

Everyone has different-shaped pinnae, which mean different resonance peaks. We need to model pinna-related transfer functions with parametrization over anthropological measurements to even attempt to "equalize" frequency response.

I can confirm

I recently watched an old review of his on the taket h2 and the ultrasonic tweeter and it was fairly negative. However, Jude's approbations on the Shangri-la don't offer any substantive sentiments on sound quality. The fact that this is the same company that made the jade -- some of the worst-made headphones in existence -- does not inspire a surfeit of confidence in build quality and long term longevity. No one wants to end up with a 10 grand paperweight. Also, copying some of the design elements of rival Stax and Sennheiser electrostatic headphones seems rather hackneyed.

Nah nah nah nah nah nah nah nah nah yeahh

https://www.digikey.com/Web%20Export/Supplier%20Content/Stackpole_738/PDF/Stackpole_ThickFilmXThinFilm.pdf?redirected=1 KG was probably referring to something like the Caddock non-inductive film resistors? Have you tested the 2sa1486es to make sure they're real? I think it's easier to just use stn9360s; they're cheaper than any real 2sa1486es and in production so no worries about fakes.

When's the HC trip to Amsterdam?

All Stax and AKG K1000s suck, no one buy any

Replace your zener strings with fresh zeners, they should not be measuring near shorts. 100V zener should in fact measure ~100V. You should measure ~320VAC*1.414 so around 450VDC across the 430k bleeder resistor.

Everything including the voltage across each zener in the string should be what you expect on the negative rail since you're getting -345VDC output, then you can figure out what is wrong on the positive rail. Be careful and also measure the voltage across the 430k resistor. Does anyone's wall voltage measure less than 120V these days? I only have a couple test points, which ranged from 122-126V. It would make choosing transformers and other parts easier.

Don't forget to replace that 10m90s as well. An easier option to finding the right shoulder washer is to use an insulating screw, such as the aforementioned nylon. Joehpj has a different PCB version; our negative rail isn't next to the bias.