Frobnicator

This is my second try to get this right. I designed a PCB for this earlier but the errors were too great to get around.

Quick overview, Frobnicator is a tremolo by John Hollis, one of the original DIY crew. He designed a few very original effects that still exist on his site.

Frobinactor is built around the CA3080, which is a single OTA. These were available and used in a lot of effects before 2000. The chip went out of production and recently came back into production as AS3080, but went out of production again. Seems like you can still find these on the internet.

Frobnicator has a switch which brings the speed of the tremolo effect up to audio rates for pseudo ring modulator sounds. The depth control becomes a sort of mix control in this mode.

The ring mod sound is a little underwhelming but at low depths a it can add some subtle flavor.

I designed this PCB in Eagle PCB and had these boards manufactured at PCBWay.com. I fixed all of the issues with the first failed attempt.

I milled a bare 159B enclosure. I didn’t have any powder coated boxes left over and couldn’t find the first one I had made.

I wired everything up with one of these 4 conductor ribbon cables and a small 3PDT switch PCB.

The Frobnicator uses a weird bias scheme using two 3mm red LEDs. There is also a third 3mm red LED. I built one of these some years ago with a home made PCB. It worked well. I built another and didn’t work. I’m not sure what the problem was but I think it may have something to do with the LED bias. I seem to remember reading a post over at DIYStompboxes.com forum where it was suggested that these LEDs all need to have the same forward voltage and it was best to use LEDs from the same batch. Not sure if this is true or even if I’m remembering this correctly. I used LEDs all from the same order this time and it seems to be working.

Conclusions

Would I recommend building this? If you’re looking for an easy to build tremolo this is one of the easiest but it’s not easier than the base Tremulous Loon by Commonsound, or the EA Tremolo. If you’re looking for audio rate tremolo that’s something this circuit has that no others have, which might make this something you might want to built. If you just want to build an easy tremolo and have some spare CA3080’s on hand then this might give you some place to hang those parts. Otherwise there isn’t anything to recommend it over another tremolo and and the CA3080 might be harder to get.