The Maestro PS-1 Phase Shifter started the phase shifter craze of the 1970s. It's original box it rather large, and required a separate footswitch accessory unit if you wanted to toggle it with your feet. This bulky format lost out when the compact MXR Phase 90 and Electro Harmonix Small Stone entered the market.
The PS-1 was designed by Tom Oberheim (who would later make Oberheim keyboards). According to Tom's interview in Art Thompson's "Stompbox," Tom was inspired by the Leslie rotating speaker, and the use of reel-to-reel "flanging" that was popular 1960s recordings. He realized he could simulate these effects with solid state electronics. Tom notes that the Uni-Vibe was already on the market, but wasn't very successful, and Carl Countryman was making a studio phaser that lacked a LFO so you had to sweep the phase manually.
The PS-1 has a +/-15V internal power supply, probably chosen to get the best performance from the four dual op amps that are used for the phase shift stages, as well as the triangle oscillator. The variable resistance elements required for the phase shift effect are discrete JFETs. The schematic specifies 2N4303 JFETs. 2N4302 JFETs are seen inside actual units. The six phase shift JFETs must be a matched set for the unit to work properly. The original JFETs are usually painted to indicate they are a set. Other JFETs are used as switches to ramp the LFO speed up and down, and toggle the effect on and off.
The first version has an error where the output may have a very noticeable dc offset that the "output offset" trim pot cannot correct. I noticed this and came up with the same solution I later saw on the second version schematic. The error is in the input buffer amplifier. As originally designed, the output of the input buffer may have anywhere from 0.5V to over 1V offset that gets passed directly to the output in bypass mode. This can cause popping noise. The fix is to add a high value resistor (470k or 680k or 470k + trim pot if you want to nail it) from the input buffer's collector to base. This injects a small amount of -15V into the base, which pulls the emitter's dc voltage down. Too much -15V will make the output negative. The other obvious fix would be to use coupling capacitors, but that almost seems like cheating here. I add the resistor on the underside of the board.
One of the first versions came in that had obviously had a "overhaul" job where caps were changed out, and some fancy TL072 op amps had replaced the old 1458 op amps. Main symptom was "no phase." When I plugged it in, my scope filled up with screaming HF oscillation (in the kHz range). I immediately suspected the TL072s. Why? TL072s are "faster" than the 1458s. They can self oscillate, especially in high impedance situations like we have here. On the PS-1 schematic, optional 50pF caps are shown across the inverting input and output pins of each op amp. The schematic says this is to "eliminate RFI." Really what it is doing is putting a speed limit on each op amp so its gain drops significantly at high frequencies (high = well beyond audio). This model had no 50pF caps, and the TL072 would definitely need those. Rather than bother with that though, I simply installed 4x 1458 I had on hand. This was simpler, neater, and fixed the problem immediately. Phaser was working again.