kevin gilmore

back board in the power supply next to the high voltage opamps has what looks to be a pair of 3 terminal regulators. one low voltgage power supply needed to drive all the input relays.

that does look like the right thing. 12au7 for gain driving 300b cathode follower. 70ma definitely pushing the tube pretty hard. not balanced.

i've been searching for over 24 hours now and cannot find a single example of a 300b used as a cathode follower. All 300b preamps seem to use an output transformer. And this completely makes sense as the voltage grid to cathode for a 300b is 75 volts. used as a cathode follower its performance has to be poor. and the opamp used for the headphones, from the apex website, this device runs class C. no output stage bias. furthermore the maximum voltage swing bandwidth is 3khz. and the slew rate is 8 volts/us. this has got to be a miserable sounding thing. there seems to be another amp just like this (for over $30k) that likely has some significant amount of solid state on the internal heatsink. 300b are great tubes when used as outputs in a push pull circuit. thats about it.

to do 10 amps you are going to need to boost the drive current. probably lowering the value of r1 to 120 ohms. same with r4.

golden reference was designed for only 5 amps.

measuring stuff like this correctly while avoiding ground loops and transformer radiation is very hard.

yep

here you go cfp3largeT.ZIP

m2's owned by someone else. too big for my room.

the 45k miles is a joke. i had 4 sets of the as3,3+ over the years and never got more than 30k. completely even wear. different car of course, but would expect the suv to be worse. those high mileage tires are not going to ride as nice.

its still 2 boxes. but sure if you want to build it that way.

nope, going to need two boxes. no easy way to stack the front end board onto the heatsinks. the 2 boards will take up much of the bottom. zero feedback generally ends up with a lower damping factor. so to boost the damping factor need more output transistors in parallel. and the sanken parts are actually 2 die in each package. and are to3p. i could go to 3 or 4 pairs of output transistors for even lower output impedance. the idea is to drive jbl m2's with the amplification they deserve. not a pair of crown industrial amps. and things like the susvara.

its already a split board. the power resistors make it impossible to shrink. joamat may come up with a solution but i doubt it. but you can download some free layout software and try to come up with something smaller.

won't fit in a 2u. if you do all the transistors on 1 edge its too long for the case. unless you want to do fully custom

soo to get it into a dissipante 3u chassis

actually 12.7 x 3.85 at the moment. size may change a bit

the board will be about 15 x 4.

i have plenty of speed. 495hp + 640hp in the garage.

making larger in progress

oops, to3pf according to the datasheet spacing .75 inch instead of .5 inch. board is about to get bigger. or i find different transistors.

yup. not available at mouser, lots in stock digikey.

i'm trying hard not to get this to uberamp size there are wonderful t03p transistors that would be great but then the heatsink would be 8 inches high instead of 3.57

4 more transistors added so yep its longer.

going to have to buy one, have not figured out which one yet, then test. i did a uberamp with a smps, it was fine. i have a couple of lambda smps that i use for testing, absolutely dead quiet.

gerbers will be available after much more checking. lots and lots of editing was done. but if you really want to be first, i can arrange for gerbers to be delivered. you can do the checking before making boards. i got to hear a cfa3 driving vintage klipsch belle. stunning. also it was running stupid hot. so this will take care of all of that. should make all the raal owners real happy. (and deaf) (and fried diaphrams) connex switching power supplies recommended. a linear power supply would be very large and heavy.