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< MuffRat > TL072 easy DIY Distortion pedal project

Distortion Circuits and Schematics

< MuffRat > TL072 easy DIY Distortion pedal project

Postby maz » April 19th, 2014, 10:57 am

Quick Overview:

    - Level of complexity: 1/3
    - Nb of parts: 29
    - OP Amp IC: TL072
    - Type: Distortion
    - Buffered: Input - 2N3904
    - Nb of pots: 2 - (Distortion Level)
    - Schematic tested: Breadboard
    - Soundtracks: Yes
    - PCB Layout: Yes
    - PCB tested: no

The MuffRat Distortion is a simple distorted effect generated within 2 stages :

- A slightly overdriven 2N3904 NPN transistor input buffer inspired from the Big Muff PI
- A highly distorted stage using one side of a dual TL072 OP amp IC

With no LED at first clipping stage it reminds the fat saturation of these old cranked tube amps, but if you add (2) 5mm red leds there you will be amazed on how this pedal sounds different, much more "cut" and "modern".. So if you don't use the leds (with a switch), you miss something here! Leds can be replaced with 4 1N914 (or 1N4148) diodes, 2 of each seried and hooked symmetrically, like this :

---- >| ---- >| ----
---- |< ---- |< ----

As you play with the volume knob on the guitar, in addition with the "Vintage/Modern" switch (leds), you can reach many kind of distorted sounds. D3 & D4 should also be mounted using a DPST or DPDT toggle switch, given more clipping options, ie: one side with 1N914 pair and the other side with Germanium diodes,

You can try with different ICs having the same pinout, so think about using a socket.

The transistor (2N3904) at the input buffer can also be switched with any type of NPN (having the same pinout), just make sure to adjust the collector resistor to have 4.5V at the transistor collector pin. By the way here is the transistor gain (HFE), I really hate the little holes on these cheapo testers, much better modified using an IC socket:


The capacitor (C8) after the level pot is there as a "pre-setted" tonestack, you can experiment here.


:clip: Clip 1 (5.82Mb) - MP3 : Various music compilation at different setting.
Recording: Strat Guitar -> MuffRat -> Beltone AP-A tube amp (clean at low volume, 8 inches speaker) -> SM57 shure mic -> mixer (Flat EQ) -> soundcard -> software.

Schematic < Tested on breadboard > :


:pdf: Download the complete pdf project file for direct PnP transfer, layout, part list and schematic.

:txt: Download Bill of Materials in txt format.

* You access, view, download and use the content solely at your own risk. Trademarks are property of their owners.

Have fun!
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Re: < MuffRat > TL072 easy DIY Distortion pedal project

Postby bugs » April 24th, 2014, 6:34 pm

man this is so tempting
Posts: 10
Joined: April 15th, 2014, 12:56 pm

Re: < MuffRat > TL072 easy DIY Distortion pedal project

Postby hors_sujet » April 24th, 2014, 6:38 pm

Ill make a try for sure :mrgreen:
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