This is a basic reverb module constructed around the Belton BTDR-2H Reverb Module. From a single input, two channels of raw reverb are generated. Mix outputs are also provided, allowing the input/reverb mix to be controlled via a panel pot. An additional feedback function is provided for emphasizing the effect, or even for generating screaming feedback.
A little on how it works:
The schematic for Reverb module. PURPLE (A) components are only installed if you have a separate 5V power rail. GREEN (B) components are only installed if you have only +/-15V power rails.
C8, R3 and R4 are part of a high pass filter and gain recovery circuit. The values of these parts determine how "tinny" the reverb sounds. The http://www.accutronicsreverb.com/ web site has further details, a data sheet and so on.
Formulae for determining the values are:
High-pass frequency (Hz) = 1/(2π · C8 · R3)
High frequency gain (dB) = 20 · log(R4/R3)
If you do not require this high pass filter, short out C8. My prototype uses R3=100k, R4=15k, C8=10n(0.01μF). A 20k trimmer in series with R4 allows for gain adjustment.
The Belton BTDR-2H Reverb Module comes in three different delay lengths. Select the one that sounds most useful to you. I chose one medium delay and one long delay for my prototypes.
The 22pF capacitors marked * are to prevent the op-amps from oscillating, however, due to the high value of the feedback resistor, the form a low pass filter. At 22pF, the effect is fairly insignificant. If you have an oscilloscope and can check these outputs, you may try omitting the 22pF capacitors.
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