TBR Reverb
A Low-Parts-Count Reverb-ish Type of Thing
Overview
TBR, what is that? Well, it stands for Tiled BathRoom. Why? Well, reverb is a notoriously difficult effect to do right, and when it is, it's definitely not low parts count. TBR is meant to be a beginner-friendly way to add just a little space to your signal. It utilizes a single PT2399 and a couple of tricks to get something that sounds a little like a tiled bathroom. Not a large, suburban McMansion type of tiled bathroom, but a downtown, old European city kind of tiled bathroom. If you are looking for something a little more full-bodied, you can check out the Spare Room, T60, or Riptide reverbs that are right here at Scientific Guitarist.
How It Works
The basic idea for the TBR came from the Ersatz Verben by culturejam over at the FreeStompBoxes forum. It's a single delay stage, but I have simplified it further by eliminating the feedback and time pots. The idea here was as simple as could be. One thing you will notice is the absence of a traditional input buffer. Pins 15 and 16 and pins 13 and 14 of the PT2399 are actually opamp inputs/outputs that can be used for buffering and filtering. This plays to our advantage in a couple of ways. First, we can get rid of an input buffer, and second we can use a better way of mixing the delay with dry signal by using the second opamp as a summing amplifier. However, there is a drawback here, and that is that these opamps are running at +5V supply and are not the best opamps in the world. This means they have limited headroom. This necessitated a single MOSFET boost stage after the summing to bring signal level back up to unity gain. Trying to gain up the summing amplifier just results in unpleasant clipping.
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A second trick here is the use of a capacitor and white LED connected from pin 6 to pin 8. This idea came from deadastronaut who noticed that a resistor between the pins resulted in some modulation. I posited that some frequency-dependent modulation could be achieved with a cap in series, and he further discovered that a white LED adds some additional stability. The result is a super low parts count to get some mild modulation on your delayed signal, which helps reduce some of the metallic "clang" of a reverb/slapback that has a static delay time.
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Apart from those two tricks, it's a fairly basic PT2399 delay stage.
TBR Delay Stage
As mentioned above, using the built-in opamps in the PT2399 doesn't give a lot of headroom, so I needed a boost stage after the delay stage. This MOSFET boost (a bog standard stage made famous by the SHO) is set with a bias resistor that gives a unity gain output from the circuit relative to bypassed. Not a lot else to say here.
TBR Boost
The power section is a super simple +9V and +5V power section. We've seen this in a lot of my builds.
TBR Power Section
So there you have it! A simple but fun little effect to get just a touch of hard slapback space. Want to build one yourself? You can find build documents, full schematic, and board layout here.