DOD: 250

So by this stage, I think we can all assume that I'll be the only one making this.  I have a bunch of tin can LM741 opamps that I forgot about, so I thought why not...  

DOD 250 / DISTORTION + LAYOUT

MXR: Dyna Comp schematic

ORIGINAL MXR DYNA COMP SCHEMATIC 

MXR: Phase 90

Bit of a classic guitar effect - the MXR Phase 90.

Electrosmash has an excellent reference that covers all things Phase 90, including the schematic  https://www.electrosmash.com/mxr-phase90.

JFETS can be pesky, so make sure you match them as best as possible and buy from reputable suppliers.

The script switch is strictly optional.   It's one of those things that if you like a setting, you probably won't ever change.  

MXR PHASE 90 - VERO LAYOUT

Correction 25 Jan 2026:  Fixed resistors across JFETS.  Thanks Merlin

MXR: M-103 Blue Box

The MXR M-103 Blue Box is a sub-octave fuzz (two octaves down).  It's not a clean sub-octave either, pretty dirty really, well it's a fuzz...  kind of synthy on some settings.

Might want to check how many 56k resistors you have before starting this.  

MXR BLUE BOX - VERO LAYOUT

BLUE BOX OCTAVE MOD

Same again, but with the octave mod - this provides the option to switch between just one octave below or the standard two octaves below.  Very handy; I would recommend this over the stock version.

Another mod is replacing the 10n cap to ground on the output with a smaller cap, or remove it altogether, or putting it on a switch for the best of both worlds.  

The 10n does shave a lot of high frequencies off (see scope traces below) - even on a switch you may want a smaller cap.  

    

BLUE BOX ON THE SCOPE / FFT

Signal   440hz sine wave, approx 130mv TRMS

Out of the IC, on the 56k / 10k divider to drop the level to a reasonable amount (massive signal straight off the pin) - as you can see, it's pretty much a square wave now.

Blend set to max octave, switch on 2 octaves down, no cap across the output to ground.

 

Blend set to max octave, switch on 2 octaves down, 10n cap across the output to ground.

 

Blend set to max octave, switch on 1 octave down, no cap on output to ground.

 

 Blend set to max octave, switch on 1 octave down, 10n cap on output to ground.

M-103 BLUE BOX VIDEO DEMO

MXR: Distortion +

Something of a classic and many other designs are based on the MXR Distortion + so no real need for an introduction.

MXR DISTORTION PLUS - VERO LAYOUT

DISTORTION PLUS ANALYSIS

There's an excellent analysis of the Distortion + here on Electrosmash including a schematic (be prepared for some maths)

Note that I have used alternate pot values, compared to some of the schematics out there.   There’s evidence to support this on DIY Stompboxes.