kevin gilmore

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

if you pause the video at exactly the right place and expand, you see virtually all of the schematic. input is differential amplifier with resistive plate load and constant current sink vas stage is p-channel mosfets with resistive source loads. And likely the tubes are running at most 50v and outputs are stacked n-channel mosfets (futterman like) so top mosfet has no voltage gain, and bottom mosfet has quite a bit of voltage gain then wrap lots of feedback around it. LOTS of feedback. now I'm sure the real amp is slightly different, but from the prototype pictures, looks way simple. anyone see any specs, I sure didn't The price is WAY stupid. and reminds me of 2 completely brain dead cavalli designs (LF and LC) using an input tube with a plate load resistor is going to be much higher distortion than a Wilson current mirror. using resistors in the vas stage instead of current sources is another source of distortion. cavalli had to discount the liquid crimson by $1k (down to $1800) and i'll bet that sales of that thing are still slow and the few customers that paid full price are really pissed right about now, as one of them was trying to dump his used unit (only 3 weeks old) for $2300

the HV supply works great with the specified zener, so a 20v cap is ok. the higher voltage was if we needed to use a 24v zener. 20v caps ok for the lv supply too.

if the 8n80c shorts either drain or source to gate, then the zeners are going to pop. the 24v zener is strictly to protect the 8n80c on power turnoff, does not do anything for power on. suggest you purchase known real parts from mouser 8n80c needs thermal grease or thermal washer, but that does not have anything to do with the zeners blowing up.

i will look at the board layout later, but i thought it said 36 vac center tapped which is the same as 18-0-18 from now on, i will make that clear. the fat hvsic supplies are probably mislabeled too.

there was some discussion over there and calculations of the current needed to drive the headphones at full power at 20khz. That number is something like 18ma or so, the T2 is 16ma, a lot of the other amps are much less. at 20ma, the carbon has both a faster rise time and wider frequency response than anything else out there. So for a while it seems bright, then it seems more natural. Definitely a difference.

my guess is that there is a short on the 10m90 that i cannot see, or that part is dead resulting in way to much current to the zener string

its soldered, its just the back set of holes

so the default would be 25ma on the output stage and 15ma on the driver stage so 90 watts for the output stage and 54 watts for the driver stage (both at 900/450v) plus what ever differential on the power supply so close to 200W is probably right

you really want most of the power in the resistor and not the pot. that said, i don't think andy/steve have the servo turned on, but the thing is already so stable... i still have 2sa1968's and 2sc4686's available, i'm keeping the rest of the stuff. also have fqpf8n80c the circlotron is a must build, but way more complicated.

andy/steve have a the first working carbon from the group buy boards. (fat power supply boards) (400v) to hit 20ma, going to need to change the tail resistor on the offset pot probably to 100 ohms.