Stage Center Reverb Notes
Taken from GGG
| Stage Center Reverb |
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Craig Anderton’s reverb unit that appeared in the September 1976 Guitar Player magazine. The layout is for a TL074 op amp type pinout instead of the RC4136 op amp originally specified. This circuit is powered by bipolar power supply, I have included a wiring diagram with a charge pump to allow power from a single nine-volt battery without sacrificing any headroom.
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The two common ways to drive a reverb are current drive and voltage drive. With current drive the amount of *voltage drive* across the input terminals increases with frequency because the reverb inductance has an increasing impedance with frequency. Often with voltage drive the frequency response of the drive amplifier is shaped so it’s gain increases with frequency with an RC filter. If you use staight out voltage drive the current through the reverb input decreases with frequency which can sound a little rolled off. It’s not uncommon to roll-off the reverb with guitar. If you look at the center stage reverb the RC shaping parts are R4=22k and C4=20nF, so above frequency f = 1/(2*pi*22k*20nF) = 360Hz the voltage frequency response is flat.
The parts C1=220pF and R7=470k form a low pass filter will further adds to the roll-off, the cut-off for this filter is f=1/(2*pi*220p*470k) = 1.5kHz.
So all in all there’s a hell of a lot of roll-off compared to other designs – many designs have no roll-off or one roll-off at around 7kHz.
A simple mod to get rid of one roll-off would be to change C1 to 47pF.