Sabro Drive One

I’m a real novice when it comes to how these effects work, but I’ve always wanted to learn so I figured I’d try to “design” one myself. You got to start somewhere, right?

There’s nothing new here whatsoever. There’s an op amp gain stage of relatively low gain with clipping LEDs in the feedback loop. After having read R.G.Keen’s article about the tube screamer over at www.geofex.com I thought it would be interesting to place the gain pot so it would simultaneously increase the gain and shift the frequency at which gain is rolled off towards the bass. If I’ve understood this about right the frequency gain roll off starts at approx. 500Hz at minimum gain and goes down to about 200Hz at full gain.

I used a “James” tone stack from Duncan’s tone stack calculator as a base and, helped by component values from the Wampler Triple Wreck and a few minor tweaks, ended up with what you see in the schematic above.

To give the final signal a little amplitude I added a make up gain stage of about 3 at the end. The thought was to also give this thing some boosting properties.

I built this in a 1590B enclosure and realized I didn’t really have enough room for both the “Bass” and the “Clip” switch, so I decided to drop the “Bass” one.

I’m very happy with how the build came together. For some reason I really like those stars.

But, to be honest, I’m not really that happy with the circuit result. I like the tone stack, but the gain stage ended up sounding a bit gnarly and unpleasant. Not sure why that is, but it indicates I have much more to learn yet 😉

Not really a recommended build. More of a curiosity.

Update (29.11.2011): Added C13 to remove some of the high frequency harshness I didn’t really care for. Sounds a bit better now.