I picked up a PS-1A and after replacing all the electrolytics and a few of the power supply parts I'd like to understand it's trim pots. Is this something that can be done properly with a scope, or is it best to use guitar and ears?

Here is schematic that matches my unit: Maestro PS-1A

Step one is set JFET BIAS by turning oscillator amplitude trim pot all the way counter clockwise, and then set jfet bias trim pot in the middle of phasing sound. I don't see how you can hear phasing sound if oscillator trim pot wiper is grounded (on my unit trim pot all the way ccw has wiper at ground). Second step is to set osc amp trim pot for desired phasing depth. Can I use a sine test tone here to get this as close to ideal or again is it up to the ears?

-Tim

The closer to "ideal" is your sine wave source the far away from reality will be your trims...

Better use your own guitar together with your own ears..

(a resistor of 5-10% of trimmer value between Leg 1 and GND should be a good idea in case of having bias problems all the way CCW..)

Yeah I guess guitar is usually a better source if possible. I think I understand the calibration steps now. You vary the FET bias while a signal is present in the phaser so that you're actually manually "phasing" the signal by moving FET bias around (and thus drain source resistance). Then you can set osc amplitude. The question remains... isn't there a better way to find their center bias point? And a better way to find the oscillator amplitude that gets you the most modulation without hitting the FETs fully on and fully off points?

Still trying to bias this thing with a signal generator, I noticed this while attempting to bias FETs... this occurs when moving bias trimmer of the FET's from 0V in the negative direction (only goes negative of course). Yellow signal is my input, purple is output of last stage right on the opamp. Notice how a large positive DC offset starts to move signal upwards at a certain point (at about -1.5VDC bias voltage).