Sunday, 1 February 2009

Guitar Effects Mods

I don't play the guitar, but my flatmate does. He has a collection of electric guitar effects peddles and has recently expressed an interest in modifying one of his less favoured peddles to improve the sound. This interest was further motivated by an ebook which he received at Christmas detailing common mods made to a number of popular effects peddles.

So yesterday afternoon was spent taking apart the peddle apart, making some simple changes to it and then seeing if it made a difference. After reading the instructions for the mod, I was a little sceptical as to the difference it would make to the sound. The changes involved replacing one of the capacitors with a beefier one and replacing two diodes with three diodes (one was replaced with two in series). In addition, and at the insistence of my flatmate, the LED colour was changed, so that it was obvious that the peddle had been modified.

After a couple of hours wrestling with a horribly constructed PCB, we were finished. The unit worked first time, however neither of us were sure if our changes had made a significant difference to the sound. The aim was to make the distortion effect more 'responsive' and 'thicker'. Whilst my flatmate was certain there was a difference, I am less convinced. Despite this, I learned a few interesting things about this area of electronics:

Guitar effects peddles are remarkably easy to modify. There appears to be a lot of information including schematics and suggested modifications to be found on the internet.

Some effects peddles are custom made for bands and cost a phenomenal amount.

The design of such peddles seems to be a black art. The results are very subjective and I have no idea how one would go about designing to specification such a device. If I played the guitar then I would be tempted to build from scratch a simple effects peddle which allowed you to tweak component values quickly - as I suspect this is how most peddles are designed. Although this is entirely un-researched!


Smiler said...

Your last point is very likely to be spot on. Much like hi-fi equipment, you can't really design for it - you just tweak things until you're happy. Of course, this is made much easier for experienced engineers who have a sixth-sense for what a change might do... We had a technician at my school like that. He could tell whether a circuit would work just by looking at it.

I hope to be able to do that one day... one day. <sigh>

Gavin said...

I think they just use negative feedback with variable gain, don't they?

What was wrong with the PCB? No idea on the voltages/currents involved but I'm guessing it was pretty chunky and simple?

Btw, its pedal. To peddle is to sell door to door :p

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