Modifying in-built distortion: transistors in an op-amp feedback loop?

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Hi guys,

I can't remember who it was, but I know someone on here has used (with success) transistors in the feedback loop of an op-amp.
Thanks in advance,
Chris

I use this in conjunction with a guitar to get valve type distortion. There is a sweet spot on the pot that sounds very good.
 

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I use this in conjunction with a guitar to get valve type distortion. There is a sweet spot on the pot taht sounds very good.

That looks a bit similar in configuration to the one I posted, using PNP-NPN pair. Thanks for posting it.. now we have more circuits to cook up and play with. One thing that I have tried in the past with the Distortion plus circuit was to remove one of the clipping diodes from the circuit, which brings the sound more towards a subtle overdrive. I will try that as well with the transistor version. There is some tube/valve circuit theory going on behind that approach too.
 
I finally dug up my MXR Distortion + board. I had scavenged a couple of parts off it for another build but just a couple of jacks needed and a case to put back together..once I clean up the wires Once it gets going and add the FB transistors I will post and maybe start a new thread on a pedal build ..if anyone interested in continuing.
 

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yeah im quite interested in that, hehe yours looks a bir tidier than mine, mines just a breadboard in a aluminium box and it looks like ive just thrown some stuff in there... though it works quite nicely!
At least your circuit made it's way into a box! I was going to load it into a Hammond stompbox case but have decided on bigger one to leave room to modify etc.

Michael's post about Craig Anderton's Tube Sound Distortion circuit being one of the best out there, is right on the money IMO. His book Electronics Projects for Musicians is what got me into electronics industry way back when. Recommend building that circuit as well if anyone gets a chance..very worthwhile.
 
though just like any distortion most of it does seem to be in the EQ, a lot of bass roll off, and plenty of highs, then a little high cut and bass boost at the end
Here is an interesting article that analyzes the EQ and the importance on the distortion circuit, based on the well known green TS pedal. As you said it's all about tone.. and how the FB is applied.
Tube Screamer®'s Secret - BTE Audio
:eguitar::eguitar::eguitar:
 
I use this in conjunction with a guitar to get valve type distortion. There is a sweet spot on the pot that sounds very good.

Hi Nigel, thanks for posting that. I thought it was you that had mentioned it previously, but wasn't sure.

I'm currently running Ch1 with only one LED installed. When used in conjunction with pedal-based distortion, it sounds rather good, though the 4x8" cabinet I'm using is too bright and extended in the treble. I've left a chocky block in there (soldered wires to the board), so it's easy enough to experiment now. I'll give your circuit a try and report back.

Cheers,

Chris
 
hard/soft clip build

Cleaned up wiring on the Distortion + board and mounted in chassis. The chassis is bigger, as I want to be able to experiment a bit with various setups for hard/soft clip. I removed the 1N270 diodes from the op-amp output circuit, and will wire up a selector switch to be able to switch from them (at the output) to the transistors in the FB circuit. Aiming to add a Tone control after, as the original Dist + did not have one.
 

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