The EctoVerb - a low-cost, Belton-brick-free lo-fi spacey reverb!

I love reverb effects, and I love building my own effects, but these two things aren't necessarily compatible as the only real option for DIY reverb, without going down the spring tank route, is the Belton (or Accutronics) brick.

They're a useful little brick, but not cheap, and instantly push your budget way up as they cost about £15. So I set about creating a reverb with multiple PT2399 chips, which apparently is all that's inside the BTDR-2H anyway.

My first design was based on two PT2399 chips set up in parallel, using an ultra basic configuration - using only LPF1 and OP2 to create a single repeat, and then a high-value resistor bridging pins 12 to 16 to induce the repeats (around 2M!) it's quick and dirty but it works!

I had 2 of these set up as below:

One with a short delay time and the other longer, with a 'balance' pot between them before ground for small adjustments. I also used a large pot (1M) with a 750K resistor instead of a 2M between pins 12 and 16 so I could dial in feedback amount.

It worked quite well, and I also used a series of jumpers (or a 3P4T switch, as above) to jumper the wet signal of chip 1 to the dry of pin 2, and vice versa, neither, or both, giving different reverb tones. 

It worked pretty well, but I struggled to hear the short delay tone when it came to the summing stage, it sounded a bit muddy, and I lost a lot of treble tone on the dry signal. So I went back to the drawing board.

Instead of running the chips in parallel, I ran the signal through the chips in series. This time I got a much better 'reverb' effect - a little delay before the effect came in which sounded much more convincing, and a more fluid, less choppy repeat sound. Very nice. Sound sample:

So as you can hear, some nice dwell (most of this clip is played with the delay mix quite low, straight into Ableton with a little saturation added) and it sounds a little bit like a spring reverb, but also strangely ghostly like an oil can delay or something. About half way into the clip I turn the mix up all the way to nearly 100% wet. It starts to oscillate a little bit and I've since increased resistance from the output of chip 1 into chip 2 to tame it a little bit.

 At some point in the late nights developing this, I used a JFET based buffer on the input with a wet blend to control wet/dry mix. The treble I lost on the input is now back and the mix works perfectly, from no reverb at 0 to complete drench at 10.

A video of it being played through an amp is here:


One thing I noticed is there's quite a lot of hiss, so that's something I'm still trying to iron out.  currently have very small capacitors across pins 15 and 16 so might tweak those for something larger. Otherwise, I'm pretty happy with it and have some boards on the way. It's a relatively low part count - around 20 capacitors and 12 resistors, one transistor and the usual 5v power management components for the PT2399s.

There are some kits available on eBay. The full build guide is available here.

EctoVerb!!!