Saturday 29 December 2012

Hermanizer Power Pedal - A DIY Fuzz Box

For christmas gift to my brother I thought I'd try to make a guitar effect pedal. The main feature would be to have a nice sounding distortion effect, classic rock fuzz. I also found an article on Instructables by Harrymatic discussing adding a timer IC to the circuit to create a sound slicing/chopping kind of effect. This construction is based on his ideas.

So what you need is an amplifier IC, I used an LM386 circuit which can amplify a signal up to 200 times. To be able to control the amplification and the output signal, two potentiometers (resistors with variable resistance) acts as gain and volume controls. The sound slicing effect is created by a NE555 timer circuit which flips the voltage on its output pin high and low in a repeating fashion. The frequency of this is determined by a third potentiometer which is glued to a "effect rate" knob.

Circuit diagram of the effect pedal - click for larger picture
Depending on the state of the FX On/Off switches, pin 6 of the amplifier IC is fed by either a constant feed from the power source or a chopped up square wave from the timer IC.

So first step to try this out was connect everything on a breadboard.

If you buy your ICs with DIL8 sockets they will fit nicely on a standard breadboard. An important lesson from this setup is that you must ground both your input jack coming from your instrument and the output jack going to headphones/speakers/amplifiers or else you will get very disturbing hizzes and noises.

Once everything worked out on the breadboard I printed and soldered the circuits on a stripboard. The soldering is not shown in this picture since the circuits are on the backside of the stripboard.

For a case I bought a metal case and drilled the necessary holes for the potentiometers, switches and the power LED.

I bought the stuff I didn't already have at home from ELFA. It amounts to somewhere around 200 SEK. The integrated circuits are about 8 SEK each but the casing and the knobs turned out to be the most expensive stuff.

After stuffing everything inside the pedal works fine. When only using the distortion effect no hearable background fuzz is noticed. However, when enabling the chopping effect there is a constant background noise which is evident if no signal is coming from the instrument.
The final effect box
So how does the pedal sound? Well, this is the sound when applying quite a lot of distortion effect on an otherwise clean organ sound. I'm not a guitar player like my brother, but here's a few chords from my old Squire guitar lined directly into the effect pedal with pretty much distortion.

Here's a synth line which after a few seconds get the the chopper effect applied. In the end of the clip the rate of the effect is increased to maximum.