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[Dylan]

I stumbled upon this while prototyping a mixer a couple months ago. It's extremely simple to make and very very very few parts.

Parts needed:

(1) LM324N Quad Op Amp (though you only use one amp. You may be able to get away with using a single op amp for this, I haven't tried)
(1) 4.7K ohm resistor
(1) 10K ohm potentiometer
(2) 1/4" audio jacks

Instructions for breadboarding:

1. Place your LM324N IC on the breadboard, connect pin 3 (Input + 1) to ground (pin 11) with your 4.7K ohm resistor.

2. Add your input jack to pin 2 (input - 1) and ground.

3. For your output, connect one wire to ground going to one leg of the jack, and connect a 10K potentiometer on the other leg of the jack with one of the outer legs connected to the center terminal. The center terminal is connected to pin 1 (output 1) on the IC.

4. Connect positive power (9V) to pin 4 and negative to ground (pin 11).

Plug in your guitar, bass, drum machine, synth, etc. and play.

Let me know if you run into any problems with the walk through or the schematic (attached below). I'm writing this from school and don't have my finished circuit here with me, so it's possible I screwed it up.

[Gordonjcp]

Stick another 4k7 resistor from the non-inverting input, and a capacitor from the non-inverting input to ground.  Stick a 1k resistor on the inverting input and feed your input sigal through that, and wire the 100k pot in series with a 1k resistor between the inverting input and output.  Then you've got an adjustable-gain amplifier that goes from 1x to 100x gain, great for distortion.

To make it even more distorted wire two "back to back" diodes (ie. anode to cathode, cathode to anode) across the output.  This will clip the output at about 0.6V and smash those peaks flat.  SMASH them, d'you hear me? SMASH!  It'll sound like Carlos Santana driving a lorry through a conservatory factory.

[Dylan]

Gordon, I love you.

[KitShunt]

hey Gordon!

you fancy posting up a schematic for those extra bits?
I'm not sure I understood all of what you said (still learning hehe).

Cheers!

[Bogus Noise]

The non inverting input is the +, pin 3 on the original schematic, and the inverting input is the - pin, pin 2 on the schematic.

Back to back diodes is two diodes in parallel, but facing in oppossite directions. A pair of 1N4148s would do it. Solder them between the output + and - wires. Found this image which shows neatly what's going on to the sound.

http://people.seas.harvard.edu/~jones/es154/lectures/lecture_2/diode_circuits/diode_clipper_1.gif

from http://www.shortscale.org/forum/viewtopic.php?t=15637

[KitShunt]

Ah nice one Bogus!
I'll give it a go

[KitShunt]

Actually, just a couple of questions (sorry!)...

"Stick another 4k7 resistor from the non-inverting input, and a capacitor from the non-inverting input to ground..."

I'm guessing these are in parallel to the original 4k7 resistor?
And what size cap would you suggest?

I'll get there eventually!
James.

[Bogus Noise]

Not sure, but looks like they go parallel. Cap size, I'd probably start with a 1uf and go from there, but I'm still learning as well 

Best bet is to breadboard it and see what happens! You won't break anything unless you turn everything up to 11 and put your ears against the speakers.

[KitShunt]

haha cool mate!
cheers for the help yo!

[Dylan]

Here's a sound sample of mine. Didn't do all of the mods posted here, mainly kept it the same except I put a 100K Pot between pins 1 & 2.

http://soundcloud.com/dylan-palme/mono-011