kevin gilmore

increasing the current resistors on the 900V supplies only.

those are the right thing. and the ebay clones, all did circuit modifications, some have half the output transistors, some messed with the bias etc. None are exactly the right thing

those are designed for cs3310 and not for anything else that i'm aware of

washers near the tubes are too close, use smaller washers

tree in the forest behind me cracked and totaled 1 section of fence. can't even get back there to take a picture

i have built a prototype from cfa2 boards and the ubaltobal board, so i know the design works. it sure is a lot of parts, all attempts to shrink the parts count usually ends up with something with very poor performance

nope and definitely nope one of them has one of the two words (well sorta)

version 6 of the lv boards posted, same as previous version except added the optional pot and resistors version 7 of the boards posted, 4.1 inches long, because one person wanted bigger power supply caps dual version 6 as previous version with the optional pots and resistors version 6 singles are 3.725 x 2.4 version 7 singles are 4.1 x 2.4 dual version is 3.67 x 4.32 with respect to the 2 singles in series, you really need 1 of each of the 2 boards, not 2 of 1 of them for lowest noise. (not that its really measurable on any dvm < about $5k)

Nope, not even close

actually a while ago, and I have not found it yet, I did a hybrid, because the cavalli supply blew up with no load. so what it actually did was lower the current under no load conditions so that the shunt transistors did not overheat. But in the end the performance was no better than the power supply at the time. And the golden reference HV versions are substantially less noise than any of the previous supplies. And probably not any more complicated.

the suspense is killing me

the polarization of the diaphram is something that changes on the order of minutes or longer, no way are they changing that. What they probably did is something similar to shure, shrink the distance beteen the diaphram and the stators and then run a lower voltage amplifier. There are p-channel fets that would allow a push pull amp with a very small class A bias that would run on +/-300v

you can be sure that the amp inside the headphones is a version of the hev70. that is, mosfet current source, mosfet driver. likely gain of 5 to 10. gain will have to be fixed because no feedback on the cable. and no room for output capacitors so the power supply is likely +/-300v or so because anything more would be very unsafe. (like +600 and 0) could i drive this headphone with a better front end, you bet. 8 tubes, how can you possibly use 8 tubes unless 4 of them are for the dac.

amazing, what kind of wood?

what you should do is schiit style. mount the things on the bottom panel.

one other thing, i went to bigger heatsinks since that picture when i'm driving both boards. the heatsinks are the ones from the blackhole amp driver

i had a variac on the power transformer and lowered the voltage to about 3 volts above the regulation minimum.So it really depends on how much voltage is on those transistors. With a total of about .5 amp, they can get warm.

At +/-200V power supplies and 200V bias, its super easy to do a real push pull electrostatic amplifier. All surface mount. You can be sure that there will be more iem electrostatics.

9.5 v from the pot to the opamp. production r6,r7 is 120 ohms. the offset pot is set a little high so that the servo can bring everything into range.

set the pot for 9.5V output, it works backwards, lower voltage is more current measure the voltage across either R6 or R7 and then adjust for 3V adjust the balance pot for zero volts differential out rinse and repeat

no they don't have to be rated at 450V. the unregulated input caps should be 350v if you are doing a 500v supply.

i think so, but have not tried it. the opto feedback controls the bias, so it should work in theory.

have a 34401A want a 3458a or keithely equivalent anyway!

updated schematic with diodes and right output transistors. (at least for the absolutely latest boards)

to92 and to220 do not have the same pinout