This design is largely based on the Belton BTDR-2 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.

TL Pedals

Official Product Video

Box of Hall