Building A Runoffgroove Modified EA Tremolo

For a while now, I wanted to build a nice, good sounding tremolo effect. I built the vico vibe in the past but it's quite finicky to bias and has a volume drop when engaged, but compensating this with a simply SHO-style boost after it led to weird interactions. Once it's biased it sounds great, and works well with fuzz and overdrive in front of it. It's actually one of my favorite effects.

But in this case I was looking for something that would be more versatile and would simply work and be reliable. I read a few blogs and recommendations and one website that always intrigued me was Runoffgroove and their original circuits as well as their archive website homewrecker detailing clones and mods. This is where I found the "modified EA Tremolo", which is based on a circuit found on General Guitar Gadgets, which in turn was inspired by a tremolo circuit originally published in 1968 in the Electronic Australia Magazine. Phew.

I chose the ROG version because it is simpler and has a lower parts count. This is the schematic:

My requirements for this project were that I wanted to make a layout that has board-mounted pots, is reasonably small, allows for the pulsing LED to be used both as an on/off and rate indicator (to only have one LED for both), and I wanted it to fit Tayda's new predrilled enclosures. I'm tired of drilling them by hand and sometimes it's nice to use a painted predrilled enclosure and whip something up in an hour.

I made a layout in Eagle and got it fabricated at oshpark (here is a link to order my shared layout). During assembly and firing it up for the first time I though I had made a mistake because there was no sound when the effect was engaged. I also had weird voltages. However the trim pot needs to be adjusted until there are 4.5-5v at Q1 drain. This voltage does not come gradually, it's suddenly there at one point in the rotation and the range is really small, so be careful to get this right, otherwise there is no effect. I subsituted the BS170 for a 2N7000 (opposite pinout), the J201 for a 2N5457 and the 2N5088 for a BC547 (I think), as I had these on hand.

It came out great and sounds pretty good. More "gentlemanly" and subtle than the vico vibe, which I will present in another post (it's a longer story). Maybe I will add a sticker or paint something on it, or maybe I'll keep the bare black/aluminum look.