discovered something cool when messing with my sd-1

[ode2no1]

i had modded an sd-1 a while back and decided to buy another just to have one at home and one at the rehearsal studio. weird thing is the second one i bought sounded better for some reason with the exact same mods applied. just more natural sounding. anyway i was trying to figure out why i couldn't get the first one to sound like the second and socketed D6. after trying different diodes in there i ended up just removing D6 all together and bam! there it was...nice fat guitar tone. it's so much more open sounding and the low end is much bigger. one thing though...when the gain is turned up to just about noon and beyond low notes just completely crap out. is the IC just being overloaded without that diode there? i really wish i could find a way to work past this and keep that tone without this low note problem. is it possible?

[BAARON]

The sound you're hearing is diode clipping in one direction with supply rail clipping in the other direction.  Depending on what your clipping diodes are, you might be getting 0.6v on one side and ~4.5 v on the other.  I'd suggest replacing that empty diode spot with two LEDs in series, which keeps the clipping threshold high on that side (about 3.6v) without running into the disgusting op-amp clipping you're hearing at higher gain settings.

[R O Tiree]

Try an LED (approx 1.8 -> 3.0Vf depending on colour) one way and a Si diode (0.7Vf) the other... or any combination you desire.

[ode2no1]

hmm...thanks for the info. i'll give both suggestions a shot. i just don't want the tone to change much from what's going on right now even if it means i can't turn the gain up.

[BAARON]

Most tinted and diffuse LEDs have a clipping threshold around 1.6-1.8 volts.  Some super-bright clear ones have higher thresholds.

I'd aim to get as close to ~4 volts as you can in that socketed position, which is why I suggested two LEDs in series for a solid ~3.5 volts on that side, which will Definitely help you get that big, open sound you're looking for.

[ode2no1]

sweet. i actually have a couple of clear super bright green led's that i'm never going to use (cause they're not green enough when lit up and look terrible) laying around. i'll give this a shot after work tomorrow.

[MohiZ]

If you like what you've got now with gain below noon, take note that even if you put the LEDs in series there, the sound is still going to change when the gain is at noon or beyond. I guess if you really want the sound not to change at all, you'd need to run the op-amps at a higher voltage to yield more headroom. Or bias the input more to the side of the diode that clips sooner to give more headroom on the other side only.