How to calculate impedance for reverb tank in a guitar amp
The opamp buffers at the input and output of the reverb unit mean that the circuit performance is not at all sensitive to the specific impedances of the unit.

Feel free to try any replacement unit you can get your hands on &mdash; you won't break anything.



The drive circuit (IC2A and IC2B) is functioning as a current source. First of all, IC2B is simply boosting the output current available from IC2A, and R94/R95 simply make sure that they share the current evenly.

The feedback is taken from the node between R96 and R97 (CN5 pin 2), which means that the signal voltage (IC2A "+" input) is also imposed across R97 (47 &Omega;). In order for this to happen, a current proportional to the signal voltage must flow through the reverb drive coil (connected across CN5).

The effective source resistance of this circuit is very high (it's actually limited by R96), which means that the actual impedance of the drive coil won't have any significant effect on the current that flows through it.