Guitar Electret Mic, Preamp & Practice Amp!

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DIY Cigar Box Guitar Electret Mic and Preamp AND Practice Amp

Ideal for Cigar Box Guitar (CGB)

  1. Power is switched on when the guitar lead is plugged in.
  2. Low cost
  3. Minimum number of parts
  4. As small as possible
  5. Easily available parts via Amazon, eBay & others
  6. Guitar-handling noise-reduction
  7. Only basic soldering skills and to be able to make a suitable hole in a guitar.
  8. Headphone Practice amp mode.  You may need a mono to stereo headphone adaptor OR use one ear!
  9. Ideal for Cigar Box Guitar! CBG!

Note: This is a mono device and NEEDS a mono only 1/4 inch jack input, or at least a stereo jack with the middle ring shorted to ground (barrel,) or the power switch mechanism will not work!

Electret Story

If you you believe in magic, you can skip over some techie stuff.

We are using this module: It is mass produced and normally lives in MP3 players, Door Intercoms and Baby Monitors. We can take advantage of this bulk production. From $1 to £10, the choice is yours!

Go into eBay and search for LM386 modules and find one of the many offerings looking identical to the pic. below.

This is a diagram of what is IN the module, which is of course MAGIC!

The Magic Module

electret circuit module 3

Please read all of below before even thinking of spending money!


Parts List


The Battery Container / Casing

PP3 Battery HolderI used this unit. It can hold a PP3 Battery and only needs a small hole in the guitar, which I found very easy to do. Your mileage may vary.



Jack Socket

jack socketEasily the most expensive item in my build.

£1 - £6.99

I used this but you could probably use one for £1 and a bit of cussing and filing, but this looked cool and would do the job

I did pay extra for fast delivery.


 LM386 Module

lm386Main module used.

£1.57 (£0.99 is acheivable).


PP3 Connector

PP3 ClipAre we not recycling men? Rip off the top of a PP3 Battery and use that! 0p! Or get a pp3 connector from anywhere, ideally NOT a 'T one' as it is a bit cramped in the battery compartment ;)

0p - £1

Electret PCB Microphone 2Pin Capsule


1 cm diameter standard electret. The subminiature ones have a worse frequency response.


120R 1/4 watt resistor.

120ROptional perhaps. Helped with a guitar longer lead.


Velcro Coin (or similar)

velcroI used Velcro to attach the module to the rear of the battery compartment, which also gives a measure of 'shockproofing' and reduces handling noise.

Follow the instructions and let the self-adhesive set properly before use.

You could use a 'sticky fixer', but that is more permanent and not so convenient if you need to rework anything.



Three small woodscrews to secure the module to the guitar.

Some thin electrical hook-up wire.

Assembly Instructions


Preparing the case and fitting the battery clip

The hole in the case is too small for the specified jack socket, so, I enlarged it so that it fitted. Not having a drill bit of that size, I found that my counter-sink was, so I used that!

Fit the the jack socket and secure it with the nut supplied.

Twist the wirpp3 leades on the PP3 clip and thread them though the case as shown.

Solder the red wire to the module hole marked VCC +

Solder the black wire to the terminal on the jack socket that is connected to the ring (not the body or tip)


Connecting the microphone


It has to be connected the right way around. The module has MIC + and MIC - holes marked.

The microphone will probably have its positive terminal marked with a '+'.

If it does not, then the negative terminal will be visibly connected to the metal case.

Insert the pins into the appropriate holes in the board and solder them in


Wiring the Jack Socket

female jack socketConnect the reamining leads according to the diagram.


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