I have a solid state guitar amplifier with a reverb tank. I have done a bit of research as to how these work. I now want to replace the reverb tank with an FX loop for normal pedals (instrument level). Therefore, the system in the amp that drives the reverb tank needs to be modified so it sends and returns correct levels. My guitar outputs about 800mV max. So the FX send needs to output about 800mV without additional gain from the preamp. The return signal of the reverb tank is obviously very weak and it is (just like the send signal) amplified with a 4558 amplifier ic. I have done a bit of reverse engineering and I have found out which part on the schematic refers to which part on the pcb.
Now my question is: Can anyone help me with modifying the reverb section so that the incoming signal and the signal that goes back to the rest of the system doesn't change, but just the send and return values?
Let me know which terminals I have to check with my multimeter when I have the amp on clean. This way I'm sure I won't give you useless information.
PS: The coils at send and return will be gone. Those refer to the reverb tank's systems. I will basically replace them with 1/4" jacks so J6 and J7 are positive and negative terminals (tip and sleeve). Same for J8 and J9.
Thanks!
Best Answer
Point X thru a 1k resistor and 10uF cap would do for an effects send I suspect, and if you lift the end of C41 connected to IC6A, that would do as a point to connect the FX return.
I would try that before doing anything more sophisticated.
The reverb mixing is done by IC5B, with the return muted by Q6 (when the gate is at ground), elsewhere there will be arrangements to pull the gate negative to enable the reverb doings. Point A,B switch the lead/rhythm channels in essentially the same way, these are mixed by IC5A.
IC6B causes the reverb tank to be driven current mode, you could use it to buffer the FX send, but would need to change the resistor values.