Cloning the Venerable Maestro PS-1A

The early 1970's saw an explosion of effects pedals with many well-regarded units making their debut. One of these was the Maestro PS-1 and PS-1A phasers, or more technically it was called a "phase shifter." I had a friend request one, and I figured it would be an entertaining challenge. Fortunately Lectric-FX has recently released the Altered State Phaser. This is not an exact clone of the original, rather it is a bit more user-friendly version of the original effect with some modern modifications. The effect now runs off of a normal 9V power supply, which still providing the effect the +/-12V it needs to function properly. There are also changes to the buffer, op amps, as well as a few optional modifications to the circuit. 

Another modification to the original is shrinking the board to fit in a 1590BB enclosure (I use a BB2 to give myself a bit more enclosure depth). Doing this required using smaller resistors. The instructions called for 1/8W, but I was able to find equivalently-sized Yageo 1/6W resistors from Mouser, so I decided to go with those instead. There are nearly 50 resistors on the board, so it will take some time to get everything populated. The film capacitors are a mix of Panasonic and WIMA. The electrolytic capacitors are mostly Nichicon with one Rubycon - the 220μF one.

The heavy lifting for the phase modulation is performed by a matched hex of transistors. The original used 2N4303 JFETs, but as those are difficult to acquire at this point, Lectric-FX offers pre-matched sets of 2N5485s for purchase on daughter boards. I went ahead and took this route rather than trying to acquire and match enough of the originals. The original 1458 op amps have been replaced in this circuit with TL074 op amps. I've built a total of three of these so far, and I unfortunately discovered that one of my sets of TL074s appears to be counterfeit as the circuit sounded horrible with those installed (yet recovered perfectly with known genuine op amps). There were also some visual differences, so I'm going to have to try and back-track and find out where I originally purchased the bogus parts.

There are also optional Feedback and Vibrato modifications to the circuit. I decided to just use the Feedback control as it adds a single potentiometer to the top of the enclosure allowing for more tonal variation in each of the three phase speeds. According to the build documentation, the Vibrato mode (which would need to be a separate toggle added somewhere near the already crowded top of the enclosure or routed off to the side) only works well when the Feedback mod is rolled off and is "most apparent in the fast mode." Given the limited configurations where it would be useful, I simply jumpered the two pads and omitted it.

Getting the phaser into the enclosure was a tight fit, but honestly not too bad as the board and daughter boards were all well-designed. Rather than the on/off switch and three rockers switches of the original, the Lectric-FX board uses the Slow switch as both a bypass and slow phase switch creating a modern true bypass effect. Boards for the Medium and Fast footswitches are also provided which have clear attachment points for power, ground, the effect, and the LED. I decided to go with blue, yellow, and red LEDs like the blue, yellow, and red switches on most of the originals (though the slow switch appears green on some models). The DC jack location is particularly tight, but it does limit the length of the power connection to the board from the jack.

I decided to go with an input star ground for this effect as there was only one additional ground pad on the PCB, and it was to the output side. All of the connections are insulated with heat shrink tubing. Mounting the main PCB to the enclosure for this build can be tricky if you don't include the optional Feedback mod as there would be no direct points of connection between the PCB and the enclosure. Lectric-FX therefore included mounting holes for standoffs. As I only had one point of connection on one side of the board, I decided to add a standoff to the opposite side of the board as well. 

As I was building this one for a friend, I sent him a couple of dinosaur ideas for the final name of the pedal, and this happy Polacanthus ended up getting the job to be the mascot for this particular pedal. According to Wikipedia:

“Polacanthus, deriving its name from the Ancient Greek polys-/πολύς- "many" and akantha/ἄκανθα "thorn" or "prickle", is an early armored, spiked, plant-eating ankylosaurian dinosaur from the early Cretaceous period of England.”

The dinosaur art and background of this enclosure are both licensed from online sources. The “Steggo” logo this time around has been designed as an homage to the original Maestro logo.

Once the pedal is together, it has to be biased using the semi-independent Bias and Range trimmers. This can be somewhat challenging as you want all three modes to sound as close to the original as possible. I ended up pulling up several demos of the real thing on YouTube, and kept adjusting until they sounded correct in all three modes - which took a fair amount of time! The end result is, however, a very lush and 70's sounding effect unit.