EffDub Audio

February 23, 2023 effdub

Box of Hall – DIY Reverb

I came up with the Box of Hall reverb circuit way back in 2012. The Belton BTDR-2 bricks had just come out, and I wanted to have the first working circuit out on the DIY scene. A whole LOT of people copied this design and called it their own, but this one is the original (from your old pal culturejam).

To be blunt, this design is largely based on the Belton application note’s example circuit, but I added a high-pass filter tone control and changed up other filter cutoff curves as well. I also added an op amp buffer for the virtual ground (VREF) used to bias the other three op amps in the circuit. A subsequent version also added a wet feedback loop to allow for better control of decay time, as well as wacky ambient swell capabilities. I will post that version sometime in the future. But for now, this is a nice, simple reverb circuit that anyone can build and that will sound great.

There is a fair bit of modulation happening in all circuits using the BTDR-2 brick, and that’s something that’s just a part of the brick. You can’t dial it out (but apparently you can drill it out). But, it sounds pretty cool and adds a nice extra layer of complexity in the background. So if you like modulated reverb, you definitely want to build one of these.

Download the Box of Hall Reverb file pack, which contains schematic and layout images, as well as Eagle CAD files (suitable for editing or ordering PCBs directly).

Here’s a demo of the Box of Hall Reverb done by some other guy:

Effects Projects

February 23, 2023 effdub

SmallBazz – Germanium Bazz Fuss for DIY

I can promise that you haven’t seen this exact circuit configuration in some over-priced boutique pedal. What we have here is my wacko take on the classic Bazz Fuss, a mainstay DIY favorite owing to its low parts count and surprisingly amazing fuzz tone. The original uses a darlington integrated circuit in a transistor-sized package (MPSA13), so I thought I’d spice things up with a discrete darlington arrangement but with germanium transistors instead of silicon. More mojo, amirite? Germanium Bazz Fuss is the coolest.

And to add to the quirkiness of this particular circuit, I decided to go with an oddball transistor: the NPN Germanium 2N1101, which is readily available from Small Bear Electronics. Why this particular part number? Two main reasons: 1) it’s NPN and much easier to deal with in terms of biasing and power supply setup, and 2) I’ve never seen it used in any circuit, and that’s enough for me. Also, it’s cheap and easy to source (at least for now as of 2023). The drawback? It’s not at all a standard package, doesn’t readily fit any existing PCB layouts, and doesn’t exist as a part in any of the common PCB creation applications.

So I created my own part for the 2N1101 in Eagle CAD and set off to create a fun new version of the Bazz Fuss. I added a few extra features: a switch to toggle between two feedback clipping diodes, a gain control, and a bias trimmer to dial in those finicky Germanium transistors. Here’s the schematic:

Once more for the SEO: Germanium Bazz Fuss.