MiniAmp Replacement. Mono Audio Amp. Gain = 20

[cmh2001]

FYI, I think there are about 3 versions of the RS MiniAmp. The current version is 277-008C. I think there is also a version A and B. Attached is another version that claims to be official. The circuit P001-V2, is one that I drew out after I disected an mini-amp, and traced out the circuit and identified the parts. All versions that I have come across including the one I disected have different components.

I'm in the process of building the version that you sent me. I am short a couple of caps so I'll see if I can make it work after I get those.

 

[Audioguru]

Your capacitor C2 in series with the geophone coil is only 100pF which is MUCH too small for any audio and lower frequencies to be produced by the geophone coil.
A capacitor in series with the geophone is not needed anyway.