741 distortion?

[egasimus]

I'm thinking about designing a PCB for those single-opamp distortions that are so-similar; something akin to GeneralGuitarGadgets' idea - but with a few twists of my own.

First of all, my list contains the MXR Dist+, the DOD 250 (2 versions), the Ross Overdrive, and the YJM308 (any others?). I've been looking at the GGG schematics and wondering - what difference does the 100 ohm resistor make? Same goes with the entire bias network - does it actually sound different?

[egasimus]

bump...

[edvard]

...
I've been looking at the GGG schematics and wondering - what difference does the 100 ohm resistor make?

I've used resistors like that to limit the current draw of a given device.
Works well for those CMOS inverter-powered overdrives that tend to eat batteries.
Not as much of a concern with wall wart power.

Same goes with the entire bias network - does it actually sound different?

Different from... ?

It's a fairly standard bias network when not using a true bipolar power supply.
I tended to use 47k or 100k resistors in my op-amp designs, but once again that was just me being paranoid about battery eatage, not sonic quality.
One time I stuck a 100k pot in there instead of two resistors so I could vary the bias point.
Interesting, similar to the "Warp" control on a Tech 21 XXL pedal (the older ones, anyway).
470k to the middle is also standard as a high-impedance input bias connection; not much mystery there.
Anything from there to a few Megohms will do, actually.

[roseblood11]

If you want to try different variations of that circuit, have a look at the Vox 1902, aka Guyatone PS-102 Zoom Distortion.

[jafo]

I've used resistors like that to limit the current draw of a given device.
Works well for those CMOS inverter-powered overdrives that tend to eat batteries.
Not as much of a concern with wall wart power.

Hmm... wouldn't doing so shift the bias on the inverters for some asymmetry?

[aron]

I tried adjusting the bias for some of my op amp overdrives and found very little difference in sound. I think it's not worth it in the way I implemented it.

[egasimus]

My point is, will it somehow noticeably affect the sound of the different circuits if I use the same bias network. Something like the voltage changing just a little at signal peaks when the resistors are lower/higher, things like that. I guess not

roseblood11, thanks, I'll look into it

[roseblood11]

lowe resistor values = more stable operation

[edvard]

I've used resistors like that to limit the current draw of a given device.
Works well for those CMOS inverter-powered overdrives that tend to eat batteries.
Not as much of a concern with wall wart power.

Hmm... wouldn't doing so shift the bias on the inverters for some asymmetry?

Not really, because CMOS inverters self-bias to half of whatever voltage it has at it's power pins; it doesn't 'see' the larger circuit.
If you want asymmetry in a CMOS circuit, either bias it at the front end and put a cap in the feedback path, or use a NAND or NOR gate wired as an inverter.

I tried adjusting the bias for some of my op amp overdrives and found very little difference in sound. I think it's not worth it in the way I implemented it.

Yep, it makes a VERY subtle effect; only noticeable at extreme positions, and even that at low-to-middle gains so you can actually hear the forced asymmetry happening, if you can hear it at all. 
At high gains, it all turns to square waves, so the off-bias effect kinda gets lost.

[jafo]

I've used resistors like that to limit the current draw of a given device.
Works well for those CMOS inverter-powered overdrives that tend to eat batteries.
Not as much of a concern with wall wart power.

Hmm... wouldn't doing so shift the bias on the inverters for some asymmetry?

Not really, because CMOS inverters self-bias to half of whatever voltage it has at it's power pins; it doesn't 'see' the larger circuit.
If you want asymmetry in a CMOS circuit, either bias it at the front end and put a cap in the feedback path, or use a NAND or NOR gate wired as an inverter.

Cool, thanks. One day I'll overcome my need for even-order harmonics.

I tried adjusting the bias for some of my op amp overdrives and found very little difference in sound. I think it's not worth it in the way I implemented it.

Yep, it makes a VERY subtle effect; only noticeable at extreme positions, and even that at low-to-middle gains so you can actually hear the forced asymmetry happening, if you can hear it at all. 
At high gains, it all turns to square waves, so the off-bias effect kinda gets lost.

I do kinda like the idea of something which is asymmetrical at lower gains, then turns symmetrical at higher. Kinda... organic, I guess.

[WGTP]

Aron told me some time ago to listen and see if I really liked the asymmetry stuff.  After doing so, I have to say that I couldn't hear much difference.  Maybe you can see it on a scope.

In terms of CMOS and op amp stuff, I wonder if symmetry isn't one of those things that sort of gets scrambled when your overdriving things substantially?  Someone indicated that the CMOS stuff had more crossover distortion at lower voltages.

[edvard]

Yep.
After experiment after experiment, I have concluded that asymmetry is a VERY subtle effect, barely audible unless you know exactly WHAT your listening for, and mostly in lower-gain situations.
You'll see it on a scope WAY before you hear it.

I think I may have been the one who discovered the low-voltage crossover distortion in CMOS overdrives, but that's also a strange beast; you have to know what you're listening for to really hear it, and not everybody likes it.

[jafo]

Yep.
After experiment after experiment, I have concluded that asymmetry is a VERY subtle effect, barely audible unless you know exactly WHAT your listening for, and mostly in lower-gain situations.
You'll see it on a scope WAY before you hear it.

Indeed. Still, having been overly sensitized to it (waaay too much time on a DAW), a lack of it tends to hurt my ears -- sometimes I can't even listen to a flute or clarinet without wincing. Ah well, that'll pass eventually.

[edvard]

Ooog... flute.

I saw Guns & Roses years ago at the old Seattle Kingdome and the soundguy apparently had no idea that the woman playing a flute was going to sound like feedback... and not the good kind. 

The only show I ever saw that sounded BETTER with my fingers in my ears.