Decompression Overdrive - another approach to diode clipping

[midwayfair]

Were using pretty standard op-amps here that sure aren't able to swing from rail to rail.

Well, the TLC2272 is a really good sounding OP amp with good rail-to-rail capabilities if that's a concern.

I'm wondering about something: what happens if we put that assembly in the feedback loop of IC1? I'm intensely curious. I really need to get this on the breadboard ...

[samhay]

Were using pretty standard op-amps here that sure aren't able to swing from rail to rail.

Well, the TLC2272 is a really good sounding OP amp with good rail-to-rail capabilities if that's a concern.

I'm wondering about something: what happens if we put that assembly in the feedback loop of IC1? I'm intensely curious. I really need to get this on the breadboard ...

It's only the second op-amp clipping that we have to worry about and, as the clipping stage usually eats most of the signal - see the next post, this is not usually going to be a problem. If it is, you can turn down the gain.

I thought about putting this is in a feedback loop but in the end I couldn't figure out how this would make it work any better.

[samhay]

Here are some oscilloscope traces that might give you an idea of what it sounds like.

[samhay]

I got it boxed up. The enclosure is nothing to look at, but here's a gut-shot below.
Getting four 16 mm pots into a 1590A is a PITA and I don't think I am going to do another one for a while.

I've spent quite a bit of the evening playing with it, which must be a good sign. There is a fair bit of redundancy between the decompression and asymmetrical clipping pots, but I haven't decided if one or the other of them is redundant yet as they both sound a bit different.
Having worked quite hard to clean up the clipping, I have grown to quite like it with the gain maxed and the decompression and asymmetry pots at minimum. There is a hint of fizz that might be from the op-amp clipping and a fair bit of high gain squeal that sounds like stadium rock to me.
I had a couple of technical hitches so won't be doing any sounds clips for a little while. Sorry about that.

[samhay]

After a bit of a nudge from tca on a related thread, here's a quick sound clip to give some idea of how the 'decompression' effect works. Apologies for the sloppy playing.

https://dl.dropboxusercontent.com/u/11996927/DCOD.mp3

0:00 - clean (Tele neck + bridge single coils straight to sound card via effect
0:11 - effect: gain, max; decompression, min; asymmetry, min
0:24 - effect: gain, max; asymmetry, min; decompression increased from min to max
0:32 - effect: gain, max; decompression, min; asymmetry increased from min to max
0:39 - effect: gain, 12 o'clock; decompression, 12 o'clock; asymmetry, 12 o'clock
0:53 - effect: gain, 2 o'clock; decompression, 9 o'clock; asymmetry, 9 o'clock
1:25 - clean
The volume was not adjusted (it was about 10:30) to give an idea of how much the 'decompression' effect has on the signal level.

Bare in mind that the frequency response of this effect is flat, so it doesn't have the typical overdrive mid hump. This is not a feature of the clipping stage, but rather how I set up the filtering. It's probably not for everyone.

[tca]

^ It sounds a bit dark, but I like it, have to test the Crowhurst's "Fuzz" and listen to the differences.

Cheers.

[samhay]

Glad you like it. My tastes seem to run a little darker than most and I generally have my tone knob rolled all the way down.
It would be easy enough to use more convential fltering to get a brighter sound - significantly decreasing C2 and/or C6 would be a good start. Replacing the Ge diodes with Si (e.g. 1N4148s) also brightens up the sound a bit.

[Jarno]

Does anyone have the updated schematic of this and the build info?
Am doing a layout of the Secret Sauce and I want to make sure to incorporate improvements (or at least, put the option in to add alternative components), like the gain adjustment of the first stage.

[bluebunny]

I think there was only one schematic.  This is the one I built mine from:

[Jarno]

Thanks! That's quite different from the "Secret Sauce" actually, but gain adjustment in the first stage is similar to what I now have in my schematic.