Some comments

[R.G.]

Remember that this thing is not a stock IC opamp. Some apps will work, some won't.

The input impedance isn't all that high, the gain isn't all that high, and there is a big (30+ db) response hump out in the MHz region when it's connected as a follower.

But it will work for many things.

The softest clipping seems to be when running at full gain, no feedback, so try this:
make the feedback network be 100K-100K from output to input, and a 0.1uF cap to ground at the junction of the two 100K's.
Other possibilities are using really low gain transistors to get that soft and asymmetrical clipping at less than gigantic gains. Perhaps with piggybacking.

[Joe Davisson]

Yeah, it's really intended for making distortion, tone controls/oscillators should use IC opamps. I think diode capacitance may play a role in the sound, the 914 always sounded better, after trying base/emitter junctions, etc.

Maybe paralleling a bunch of 914's, or using varactors, would improve the sound. As each peak hits the diodes, they should react with a greater net capacitance?

The split feedback resistor works in other circuits so it should here, good idea. FWIW, I did a germanium version using B175 & 2N1308, with decent results. Kind of a fun thing to mess around with.

-Joe

[aron]

Thanks Guys. It works great in my Shaka pedal as I have said.

I like the entire range of this circuit. Very good!

[Matteran]

so what would this do in a booster, such as a MXR Microamp, i'll basically be modding a stock one.

[aron]

It makes it more "alive" and higher distortion levels have a more "compressed" feel.

Try it. It's a fairly easy build.

[MR COFFEE]

Joe,

Thanks again for sharing a nice snippet!  

You wrote:

I think diode capacitance may play a role in the sound, the 914 always sounded better, after trying base/emitter junctions, etc.

Maybe paralleling a bunch of 914's, or using varactors, would improve the sound. As each peak hits the diodes, they should react with a greater net capacitance?

The varactors might well sound interesting, but I believe their operation is meant to be in the reverse-biased condition for the variable capacitance effect they are designed to produce, which doesn't apply in this circuit topology, since the diode is forward-biased.  :cry:

IIFRC, varactors exhibit their effect when reverse bias causes the depletion region to expand more abruptly than the depletion region in ordinary signal diodes because of some fancy-schmancy doping of the junction. So even when biased correctly to take advantage of their variable capacitance effect, their capacitance values are small (I think I've seen ones that go as high as 200-300pf max.) but they do vary over a 10-to-1 range.

But since folks around here have found some interesting sound differences with other types of diodes in distortion circuits, it can't hurt to try a few and SEE what they sound like.

Happy experimenting!

[WGTP]

Is there an advantage to using an op amp rather than the Vulcan type stages?

Which part of the op amp are contributing most to the distortion, the 5087's or the 5089?

Does anyone remember this from Jay Doyle?

http://www.diystompboxes.com/pedals/schems/Shaka%20Discrete.pdf

[aron]

I'm not sure, but the Vulcan stages feel good. I have been using opamps since I started building and I rely on them for consistency.

Sure, they have a certain "feel" but I like them for some circuits.

I built Jays discrete Shaka as well. He was doing a lot of work in that area.