A Doppelganger Doppelgänger - Building Aion FX's Quadratron

The Lovetone Doppelganger is a four stage optical phaser pedal with a huge number of tone options. Once again, this is currently a very expensive pedal, with examples going on Reverb north of $1000. However, Aion FX offers a version which you can build for a fraction of the cost of the original, though it is a challenging build! As you can see below, the PCB itself is vary large, though it isn't packed as tightly as some other manufacturers' offerings are. As this is a fairly complex build, I'm actually going to go through the process step by step rather than glossing over some of the more gory details.

The Doppelganger was first produced in 1995, but the PCB as provided by Aion FX represents the pedal as updated in 1999. That version of the phaser included a dry out, square wave toggle which provides a "chopped" effect, and a "Slow" toggle which allows the modulation on LFO 1 to be tuned to even slower rates.

Following best practices, I start low and then move to taller components in all of my builds. That means resistors and diodes go first, then I generally will attach any IC sockets as I can put them on a flat surface (usually the metal base of my magnetic "helping hands" set up which provides a massive heat sink when I solder the sockets to the PCB). In this case I'm using all metal film resistors from Mouser with a 1% tolerance. Most of them are Yageo, but there are a few other brands I had to use because Mouser was out of the Yageo SKU with the appropriate resistivity. The diodes were nothing exotic just 1N914s and 1N4001s (and as per Aion FX usual there is a 1N5817 on the 3PDT / bypass board).

I then moved to the taller components, and some of the more challenging portions of the build. The film capacitors were next. Again, most of these were from Mouser and are WIMA or KEMET film capacitors. Unfortunately they were completely out of any 2.2uF capacitors that would fit on the board, but I was able to find some alternatives, I believe from Pedalhacker. This let me use the acoustically superior film capacitors as opposed to the electrolytic capacitors (the open C10, C12, C14, and C16 slots on the silkscreen).

Squarely in the center of the board is one of the most delicate parts of this build - the four optical resistors and LEDs. The build notes provided a part number and source for the LDRs (if you're in the US, you can get a 20 pack cheap from Amazon) and suggested an appropriate LED from Tayda which provide the appropriate brightness to get the right sound out of the finished unit. Apparently these are all open in the original unit, so you do get "cross-talk" between the LDRs. So shrink wrapping the pairs or using vactrols would give the pedal a completely different tone. Of course, the open nature of the optical system means testing the pedal before it is boxed is extremely difficult.

Then it was just a simple matter of dropping in the ICs and adding the wiring. I ended up using ribbon cable to connect the two sets of six wires from the dual 3PDT daughter board to the main PCB. This simplified construction greatly and made the enclosure look a bit neater. After I'd initially boxed it up, the LFO rate for LFO #1 didn't appear to be working properly (once I figured out the toggle switches!). I suspected a cold joint as it would work intermittently, so I went back into the enclosure and re-heated the joins to the switches and potentiometers. Sure enough, a couple of them looked a bit starved, so I added a little more solder to them (and I double checked the stomp switches as well while I was at it).

While this is an absolutely epic pedal, unfortunately the enclosure is a bit mundane at this point. I may try and build a second pedal someday with an upgraded enclosure, but that will take a bit of work both in terms of layout and design work. Part of the problem is I'm still learning Adobe Illustrator, which limits what I can get Tayda to UV print. Custom decals are also typically fairly expensive, but it may be worth it. Sadly my little MXR Phase 90 now has to compete with this beast, as those are really the only two phaser pedals I have at this point. The MXR is tiny, though so fits on the "normal" board a bit better likely saving it for the time being!