Tuesday, July 21, 2015

3VOD - Overdrive

You change and then you change again
Turning like a wheel inside your head

While working on my practice amp, I was looking around on the amzfx Lab Notebook pages and came across a section on low-voltage preamp circuit.  Towards the end, Jack Orman shares a fully-developed two-stage overdrive circuit.  With my bass project in mind, I put one together on my breadboard.

With the exception of two parts values, I built it as described and shown in the article.  It works the same way as the one I ended up with in my practice amplifier, with an NPN transistor stage pushing a JFET transistor stage.  It also has less parts and is powered by only 3 volts instead of nine.  As suggested in the write-up, my intent was to use a pair of NiMH AAA cells that should provide 900+ hours before needing a recharge.  So, what kind of sounds can you get out of so little?  As Jack wrote, "These low voltage boosters are not for making clean sounds but they excel in adding a bit of flavor. They will provide some additional tone colors for your musical palette..."  I was so impressed with this little circuit that I built a perf-board pedal version of it.

Biasing of the JFET is by means of a trim pot on the circuit board.

A small plastic junction box seemed like an appropriate way to house things.  The bypass switch is nestled between the drive and level-out pots, making for a compact set of controls.

It was a tight squeeze with all of the wires, but I left some extra length on the leads to make it easier to handle during the build and replacing batteries.

Some temporary labels came in handy during testing.

After passing initial testing, I added some lettering and sprayed on some clear coat.

3VOD is currently out on loan to a local musician who will provide some feedback on the sound and overall design...

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