Two things to mind when working with such a weak signal are EMI and shot noise. You should probably use a (grounded) metal box. You should consider an inverting op-amp scheme, maybe using a current-mode (Norton) amp.
Two things to mind when working with such a weak signal are EMI and shot noise. You should probably use a (grounded) metal box. You should consider an inverting op-amp scheme, maybe using a current-mode (Norton) amp.
Electric guitar signals are often huge - on a recent customer project we decided that we needed +/- 3V headroom on the input of the amplifier to cope with even a reasonable range of instruments. Noise is not an issue. To avoid loading effects on the guitar/cable combination you should aim for an amplifier input impedance of greater than 1M ohm.
Norton amplifiers are not very low noise. With conventional op amps the inverting op amp configuration is much noisier than the non-inverting.
Although a bit old hat now the TL071 fet op amp is not a bad choice for the input - cheap, low noise but needs a fair bit of PSU headroom so for a guitar amp input you'll need a 10V supply (or +/-5V).
LMP7701 is a better choice for a modern part but comes in SOT23 package, OK with supplies down to 6V with guitar but will work down to 3V OK with reduced headroom.
However since the OP is talking about using an LM386 I assume he wants to keep it cheap - so I would go for a TL071 connected as a unity gain buffer with a 2.2M resistor to ground across the +ve input, driving a 10k volume control pot, then the LM386 with gain set to 20 and use a 12V supply.
Max power will be about 0.7W which is hardly in the big league of power amps.
If Nick wants more welly there are lots of other power amp ICs to consider.
