How do you set bias or dc offset in SX-727?

[tusntuk2]

Hello the the Pioneer group! I'm a recent old member, just reintroduced myself from Arkansas. I successfully repaired a NAD with fellow AK er's help, and it inspired me to recap a SX-727 - wow! I'm stunned by the clarity, it's like, um, retirement, you know? There's this big build-up to it and then, when you do it, it's, it's, well it's actually nothing. No noise. No static. No distortion. No snap-crackle-pop. No freq holes. Nothing, it just works. The receiver becomes like nothing, you just hear the music and forget the machine. Well, I was really amazed. I read a lot about the bias and the offset, but while I recapped it, and will probably swap out some transistors in the head amp, I did not do anything for the bias and offset. What do I do, how do I measure and set that? Thanks in advance to the group, I've been peeking in a for a while. (Currently running the 727 and a 626)

 

[zebulon1]

I found this Quote from Mark Posted in 2010:
I searched Google using this: "pioneer sx-727 offset and bias idle settings audiokarma"

10 millivolts across an emitter resistor is a reasonable compromise in the lack of concrete information. The 828 shares 30mA across two channels which would call for 7.5 mV. No such info is on the 727 manual.

The 2.2k pots on the outside edges of the board control the idle current - BE VERY CAREFUL, the type of circuit used - a Vbe multiplier - has a WIDE voltage swing, and could dial in way too much idle current.

The 4.7k pots clustered together in the center of the board are for dc offset adjust , which of course should be as close to zero volts as possible.)

That would be 20 millivolts between pins 11 & 13 on one channel, and 12 & 14 on the other.

that's 20 mA idle current across two 0.5 ohm resistors.