kevin gilmore

well there are apex chips that do sound good. but they are stupid pricy. and require large heat sinks.

it could have originally been 2 different transistors for the darlington in which case the original diagram might have been correct. since this is 30 years old, any original ideas are long gone.

you are not looking carefully enough. there is much more wrong with this thing. hint: power supply

makes sense.

same push pull stacked circuit with higher voltage all smd parts. also this https://buyee.jp/item/yahoo/auction/d1165787088 ac powered version of stax d10 with the lower voltage apex parts.

this is why i have 4 sets of tires for 2 cars. seriously under 40 degrees F is death for summer only performance tires. besides which the tires will crack and then you have to throw them out.

koss pro4a ? definitely koss

with the sanyo transistors 5v results in about 500ma bias. which was the original design spec for this board.

you need to measure the voltage across q36 should be about 5 volts. if not adjust rv2 and if that is not enough change r36

minimum power supplies +/-24 might have to change a couple of resistors in the bias generator for this output transistor.

what is the name of the gerber file for the output board

super thin traces are never a good idea. just ask cavalli.

yes the distance matters. always put caps as close to the chips as possible. probably need a scope to see whats happening to the power rails. possibly one of the diodes on the input lines is in the wrong direction.

solder on some .1uf caps on the power supply lines on each chip close to the pins. also no diodes that i see across the relay coils.

much better. max sensitivity of the qa403. 60 hz and multiples are very hard to remove, moving wires around in the box and things will change. completely inaudible. the synchronous rectifiers may take out even more noise. mumetal shielding around the transformer is also a good idea. glad that more and more people are buying the qa403. higher quality diy coming soon

might want to try again with a good quality mylar cap say 1uf in series with the power supply outout. you should be able to get better resolution.

need to see the whole board. definitely missing the power supply caps at the lm339

pretty close to production now.

first picture is baseline with 6db antenna 0 to 100mhz 10db/major division 10mhz per horizontal major division top line -30dbm 1 inch from power supply. second picture is with the 600v power supply turned on and into a 1meg ohm load. 3rd picture is hall probe on the input power supply line. so 200khz flyback switching frequency.

i did some quick tests and they are pretty quiet. but i plan on doing more exact tests. cap.inductor,cap should be more than enough. spec sheet seems to imply 20mhz which cant be right. will get out the spectrum analyzer to make sure.

all three power supplies a total of $80.62 with shipping from china. fully regulated 12v to 18v input. i could not build these things for that price, no way.

after all these years we have finally found a solution for the power supply modules at a rational price. which means we can make a transportable electrostatic amplifier. similar to srmxh,srm252,srm270 etc. 3 times the power, +/-400v power supplys, no obsolete components etc. designed to be mounted to the bottom as a heatsink with silicone thermal sheet in between. should be about $250 in parts unless you go nuts with the volume pot. not sure of casing yet.

so this is the way to do it correctly. its the only way not to seriously effect the thd. unfortunately both opamps have to take the voltages of the output devices. which means they have to be opa445 you set rv2 to the maximum amount of current. Then B1 is a 10k pot to V+ and ground. r11 is actually 100k.

if it works right then yeah.

would like to see what effect this has on thd. especially large voltage swings. still think an optoisolator drive to the vbe multiplier.