Theoretical Distortion Pedal

[jayfroo]

Would it be possible to create distortion from a long chain of amplifier and attenuator stages in a single pedal? The principle is that each stage doesn't perfectly replicate the signal it receives. In the same way that a bucket brigade delays the signal by having many tiny short delays sum to a larger one, would a long alternating chain of opamps/transistors (gain of maybe 1.5-2, but not clipping) and attenuation stages compile to form an interesting distortion or just sound terrible? Has this been done?

[Thecomedian]

Like the Big muff Pi? The short answer is yes. You could use 20 transistor arrays in a stompbox if you wanted to, or perhaps a large number of op-amps. You may find there's not that much value in using excessive amounts of stages.

[idy]

Two stages like Big Muff, two or three when folks use CMOS invertors, three or four like a lot of amp simulators with FETs... some opamp amp simulators likes sans amp use a few (how many?) and the runoffgroove Thunderbird uses four diode clipping stage.

More stages means more noise, I think that's why practically speaking 2-4 stages seems to approach diminishing returns.

[idy]

And then we get a pedal board and run a booster into a 3 stage inverter pedal, into a 3 stage FET based amp simulator, maybe a dual opamp diode clipper at the end to add a little finish...
So its not that far out for a guitarist to be using quite a few stages before the amp, which itself has several opportunities for distortion.

[Keppy]

The principle is that each stage doesn't perfectly replicate the signal it receives. Would a long alternating chain of opamps/transistors (gain of maybe 1.5-2, but not clipping) and attenuation stages compile to form an interesting distortion or just sound terrible?

Stages with gain this low are probably too linear for this to have much effect. Active devices have much higher inherent gains than 1.5-2, and every method of reducing the gain that I know of amounts to some type of negative feedback, which tends to linearize the amplifier.

[Mark Hammer]

One of the projects in the Boscorelli "Stompbox Cookbook" actually uses such an approach.  It cascades a bunch of op-amp stages using an LM324, which he indicates as providing some coloration.  Nothing is pushed to its gain limits, and no diodes were harmed in the making.  It's apparently just a quirk of the 324, as he conveys it.  Haven't built it or seen a demo of someone else's build, so I couldn't tell you what it produces.  I'm just confirming that your idea is not an outrageous one.

[knutolai]

One of the projects in the Boscorelli "Stompbox Cookbook" actually uses such an approach.

what page may I ask? Can't find it..

[anotherjim]

Hmmm.. The Degrader! Good old LM324 is a touch asymmetrical at the output, is as slow as they come and  known for crossover distortion. With guitar, one or 2 of it's amps in the path isn't that noticeable - but all 4 could well get gritty. A factor would be what voltage the reference is set at. There's is a level where a small signal will pass quite cleanly, but it isn't Vcc/2.
Bear in mind the LM358 is the 8pin dual version if that helps with board layout.

[Mark Hammer]

One of the projects in the Boscorelli "Stompbox Cookbook" actually uses such an approach.

what page may I ask? Can't find it..

The Distort-o-matic IV, page 36.