Inspired by a remark by Juanito Moore I made a euro rack version of a reverb unit based on a reverb board that one can buy at various places for less than 15 USD. Here is an example I found on aliexpress:
It contains some circuitry and a signal processor programmed with 100 different reverbs and/or reverb style effects. You can see it in the following picture attached to the module.
As you can see the circuit board comes with some cables. Note that the color coding of the wires may not follow standard conventions. So the red/black power cable may connect the black wire to the plus pole and the red one to minus (remedy is to reverse the connector on the pcb, or fiddle with the connector itself). I have 2 of these units, with one the polarity was reversed, the other one was as expected. Your mileage may vary!
The circuit runs on 5 Volt and is intended for use with line level signals. To adapt it to euro rack levels I added an input stage (TL071) that allows for connecting a euro rack level signal (which is attenuated), a level input which is copied, and a 2nd euro rack level input that can be used for another signal or as a feedback input. The FB pot can be used to either choose the level of the 2nd euro level input signal or when there is no jack inserted in the 2nd EIN, one of the outputs is connected (normalled) to the input circuit the pot can be used to choose its level. The dsp circuit outputs line level signals on 2 outputs (some reverbs result in a stereo signal), so I also added an output stage (TL074) that amplifies the signal to euro rack levels on 2 outputs. So the module has euro/line level inputs and euro/line level outputs. Finally I added a Dry/Wet pot.
The last picture shows that the circuitry is very simple indeed, just a few resistors and op-amps.
I found this list of effects on the net:
00~02 small hall,
03~05 medium hall,
06~08 large hall,
09 church,
10~12 small room,
13~15 medium room,
16~18 large room,
19 hal,84~85 Reverb+phase shift,
20~26 with metal acoustic reverb,
27~29 Spring reverberation,
30~35 Reverberation door,
36~39 Reverse reverb,
40~43 Early reflection,
44~47 Atmosphere effect,
48 stadium,
49 Ambient effect FX,
50~58 Delay
59 echo,
60~65 chorus,
66~69 Flange,
70~73 Phase shift,
74~79 Tone,
80-81 Reverb+chorus,
82~83 Reverb+chrome,
86~87 Reverb+tone,
88~89 Delay+reverb,
90 Delay+reverberation gate,
91 Delay+reverse reverb,
92~93 Delay+chorus,
94~95 Delay+chrome,
96~97 Delay+phase shift,
98~99 Delay+transposition
The reverbs are of reasonable quality (what do you expect for less than 15 USD !). And there is no way you can set any parameters. Juanito Moore has experimented with a VCO connected to the DSP which makes it possible to within limits sync the reverb to an external pulse. Iām going to experiment with that and see how that sounds.
Iāve planned to build a second one and add a schematic and some sound examples to this thread later, so stay tuned if you are interested.
Addendum 1
While I was experimenting with the DSP board I powered it from a DC supply and noticed that the board is a bit particular about the supply voltage. The chip wonāt process any sound unless the voltage is high enough. The 7 segment displays however will light up at lower voltages. So the fact that the 7 segment lights up is not a sign that you powered it up correctly and thus when fed with an input signal should be able to hear an output signal!
STL-files etc. can be found at the Reverb-O-Matic repository.
