Hi Nick, Do you want to make an amplifier from scratch or are you interested in making the amp from other pieces of equipment? If you are looking for something that is fairly low power you might use an amplifier that comes with auxiliary speakers for a computer. I have found that there are lots of these little amplifier systems sitting around and unused. You will have to get a small preamplifier so that you can raise the signal level of the guitar pickups enough to provide enough power to drive the input of the computer speaker amp. If you have two computer amplifiers you might be able to use one as the preamplifier and the second as the main amp. If you have more experience with electronics you could also use one channel of the computer speaker amp as the preamp and the other channel as the main amp. I have done some similar things for a couple projects. Of course it doesn't sound like a Fender Stage Amp but at least it is loud enough so you can hear what you are playing.
Hi Nick, Yes you could use an LM386 which can give you approximately 1 watt power output. You will also have to build a preamp to drive the LM386 as the voltage from your guitar pickups is fairly low. You might be able to use an op amp like a 741 for the preamp. If you lookup data sheets on these two components they may give you some basic designs that you can build. Don't expect a lot of power but you will get a lot of satisfaction when you build it yourself and it works.
Good idea with the LM386, it's still about the easiest-to-use audio amp around.
I know nothing about guitar pickups, but I recall the LM386 has a 'crazy gain' mode : ) where it can be turned up to huge levels (by adding or modifying one capacitor - the information is in the datasheet).
The Zout of an electric guitar is on the order of 30K ohms. Therefore, I would work on a preamp to get me out of this regime, where I could use Plain-Off-The-Shelf tech for the right-hand side of the gain-chain.
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.
Hi Nick, I found this simple 386 Guitar Amp Project in the Instructables Site. It looks simple and it would give you a start on your project with minimal parts. Here is the link.
