kevin gilmore

not ideal, maybe find 20k?

+/-12v should be fine for a balnced setup. 50 amp power supplies would be perfect.

you need AC 120v not 12v and that is for low bias only

this is not a balanced input amplifier

wire the headphone grounds directly to the amp boards, not the power supply

The Thd is going to be higher at lower driver board voltages. Not a lot higher, but the idea is that the driver board needs to be able to fully drive the output board, so the driver board needs at least a couple more volts than the output board.

yum

i have a pair of 801 mk 3 that i still use as television speakers. with the arcici stands. in black. and the B&W bass alignment active filter somewhere.

for people building their own bh, one side of the filsment winding has to be connected to v-, not ground. also applies to all other tube output stax amp.

you better take a real good picture of the voltage selector block. there are many different kinds. if blue and purple are jumpered together then its 120v if brown and green are wired together its 100v white should be wired to grey the correct fuse for 100v should be 1.5 amp

take a look at the transformer and see if the 120v windings are cut or not. if they are intact, rewire for 120v. and replace the power electrolytics.

actually even easier assuming the drive is glass platters, open up the top and fill with battery acid. the plating comes right off the glass.

go to one of the sites selling magnets and buy a 1 tesla magnet, or bigger. they are cheap. take the drive apart all the way to the platters, and swipe the magnet on both sides of each platter several times in several directions. not even the nsa will be able to get the data back. one of these is way more than enough https://www.kjmagnetics.com/proddetail.asp?prod=DX0C

if you rotate the left transformer 180 degrees, makes the high voltage wires a lot shorter.

you can do up to 3 amps of class A bias with big enough heatsinks. The one feedback resistor, you can make into a resistor that is in series with a resistor that is in parallel with a cap. pick the numbers you want for appropriate bass boost. once in a while you get a bad transistor or low hfe etc, so always buy more than you need.

so its a balanced amp with only unbalanced inputs. only 2 gain stages so its already low on voltage gain, and then if you put in 12bh7 as output tubes it has even less voltage gain. stax jacks with what looks like heatshrink on the pins? no 5.1k safety resistors, relying instead on the current source to limit output stage current. electrolytics not secured to anything. nice chassis.

4 x 5.1k resistors in series with all 4 outputs L+,L-.R+,R- changing the bias voltage to negative means that any dust that gets inside the headphones will accumulate on the diaphram. Definitely not what you want.

if that is really MINUS 645 volts as the bias, bad things going to happen to the diaphrams. Flip directions of D3 and D6, change R10 to 5M

no 5.1k series resistors on the outputs is a super bad idea. definitely bad for the headphones and a safety issue if the mosfets ever short.

current version, front end at +/-35v power supplies, output section +/-24v from switcher, twice as many output transistors still need bass filter on the front end poweramp3a - CADCAM.ZIP poweramp3a.PDF

the jumper was supposed to be .1 newest software loves to keep switching to metric (fixed) forgot about the size of the caps, can always put them on the bottom. i had thought that 18awg was enough. size increased to 60th not going to be able to move the caddock resistors much. only 25th. then runs into the output wire

no it should not act like this. maybe it is oscillating in one mode. one person had a problem similar to this and fixed by adding 500pf B to C on the output transistor pair. Maybe the output transistors have changed over the years as i still have 100's of older ones.

The feedback is crossed for SS on all but the very latest board which was posted somewhere in here and is not in the archive.

r274x version of file but really you should find a manufacturer that does gerber x2 raalopamp - CADCAM.ZIP

if they are just making boards from the gerbers, i'm fine with that. But the people taking the gerbers and then re-editing the hell out of them causing all sorts of issues (like taking all the values off the resistors) or making clone boards like the one above that require obsolete parts are just causing people trouble. find the gerber you want and have boards made.