Effects Layouts Prismatic EQ (Boss GE-7)


Well-known member
Build Rating
5.00 star(s)
I just completed the Effects Layouts Prismatic EQ, which is based on the Boss GE-7 graphic equalizer.

Not a lot to say about this circuit, for me it's in the boring but essential utility category. I mainly use an EQ pedal for a deliberate mid-hump solo boost. I have the real commercial Boss GE-7, but I haven't yet done a side-by-side comparison (literally just finished this tonight). But I went through all the frequency bands and the sound changed more or less as expected. It sorta worked on first power-on: bypass worked, but as soon as I turned it on, it was just loud squealing! But as soon as I adjusted one of the knobs, the noise stopped, and it's been fine since. I think the problem was that I had the back off the case for the first power-up, and part of the circuit shorted against my pedalboard. At least I hope that's all it was!

This was my first Effects Layouts PCB build. It was delightfully unremarkable: nice board and good layout. The offboard wiring is just different enough from PedalPCB boards that you have to pay attention. See here for off board wiring documentation.

The enclosure is actually "take 2". On the first one, I put the knobs too far down, leaving insufficient room for the footswitch (let alone the relay board). D'oh!

Perhaps the most exciting part of this build was the use of my SMD relay bypass board. This is a simple relay bypass that uses an ultra-low power Schmitt-input hex inverter (CD40106 or 74HC14) to respond to the footswitch and (re)set the relay. I used the through-hole prototype version of this circuit in my recent Muroidea build. To shrink the board, I did a surface-mount version of the PCB. And as a first for me, I had it assembled by JLCPCB (everything except the actual relay). I sprung for the ENIG finish. I managed to use entirely "basic" parts, so no additional feeder loading fee. I had many of these made, so PM me if you'd like one, I'm happy to give a few away!

While I think my build looks halfway decent, if you want to see a truly top-shelf Prismatic build, check out @Guardians of the analog's Lucky 7 (GE-7 Graphic EQ) build!

Edit: fix typos.


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Taking a closer look at my pictures, I realized I used a relay with the wrong voltage - I used a 3v relay, it should be a 5v relay. The TQ2 datasheet says max allowable voltage is 150% of rated voltage, which would be 4.5v... I'm giving it 5v, although it's actually less than 5v due to the voltage drop across the MOSFET. Cutting it close either way! Double d'oh! 🙄