A DIY valve overdrive pedal – Goldie

In an amongst the guitar building I decided to break out the soldering iron to build an overdrive pedal – as light relief. I had stumbled across the “Valvecaster” schematic and layout at Beavis Audio.

This is a very simple circuit that uses a 12AU7 valve, running at a low voltage. Because it is running at such low voltage it is very easy to overdrive.

The schematic specifies an operating voltage of 9v but I decided to bump it up to 12v to give a fraction more headroom. I chose one from the tangle of old wall-warts I have tucked away in a drawer. It could use a battery but I suspect that the current draw for heating the valve would suck a PP9 dry in a matter of minutes.

If you search for “valvecaster” at Youtube, you’ll find plenty of examples of the pedal in action. One of the common comments is that this is a naturally “dark” sounding pedal. This was not exactly what I was after and so I was going to experiment with different types of tone stacks. As laid out in the schematic it includes a simple treble cut tone control. Even turned up full this would only make the pedal darker, allowing treble frequencies to escape to earth. I decided, initially, to build it with no EQ, and then add it later. One of the results of this was that it is not a dark pedal at all. It is wonderfully balanced and punchy just as it is, and it’ll not be getting any additional EQ added. To remove the tone control I just eliminated the 10nF capacitor (C2) and the A100k potentiometer (VR2).

I reused an old enclosure I had laying around, which I shot with a coat of black nitro-cellulose and a very light top coat of gold (both left over from my Shaftesbury restoration). The gold coat is thin enough to allow just a hint of the black to show through.

The chemistry geeks amongst you may, by now, have worked out where the inspiration for the name and colour came from.

I have yet to print up and apply the decals for the pedal but there’s the standard 1/4″ input and output jacks round the back. The top has the valve, a true-bypass footswitch and the power toggle switch. On the front, left to right, are the gain, a dummy pot (filling up a surplus hole in the old enclosure) and the output volume.

When I was buying the parts for this I also got hold of a 12AT7 valve. This works well too. It is more subtle and has less gain, but in some ways is all the better for it; smoother, warmer and just a bit less wild.

You can listen to a quick demo of Goldie with the 12AU7, that I recorded for my friend Alfie Lanos, who was really helpful in helping me plan this one out.

It was recorded on my mobile phone so the sound quality is not the best, but gives you an idea of what the pedal does.