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out
MXR Distortion +
Originally released in the mid-1970's the MXR Distortion + has been a
popular pedal ever since. The gain is a bit less than what most of us would
consider as distortion, but the circuit is simple enough to provide ample
room for modifications. Take a look at the DOD 250 Overdrive project--you’ll
see that is almost identical to this one.
Mods!Diode clipping mods: try different values for D1, and D2. Try different diode types
and LEDs.
The standard single opamp is a 4558 dual opamp (only one of the opamps is
used). Use either the JRC or the RC version. Or use any other dual opamp.
The original circuit uses a B500K reverse log distortion pot. If you want to adhere
100% to the original, buy that value. But it won’t make a huge difference in tone.
The 10pf capacitor tames a bit of high-end in the feedback loop of the opamp (the
loop between pins 1 and 2). It also helps keep the circuit from oscillating. Try
different values here to see if you can make it sound better.
beavis board project
A100K
Volume
A500K
Gain
C2
10nF3
2
8
1
4
+
-
U1
4558
Input
9 volts +
C6
1uf
R410KΩ
R11MΩ
R21MΩ
C1
1uFR3
1MΩ
R710KΩ VR2
A100K(volume)
OutputD1
1N914
D2
1N914
C6
1nF
R61MΩ
C5
10pf
C4
4.7nf
VR1A500K(gain)
4558
in
1uF
+1MΩ
1MΩ
1MΩ
10nF
10KΩ
10pF
4.7nF
1N914
1nF
1uF
+
10KΩ
C3
1nF
R54.7KΩ
1nF
1N91
4
1MΩ
4.7KΩ
revision: 1.1 2/18/2009 © 2009 beavis audio research