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Forum Home > Layout Gallery - GuitarPCB Build Documents, Mods and Tips > Dr. Phybes

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This is an Advanced Build with many uses and capabilities.

Not recommended for beginners.

Matched FETs are required for the project and for Support help.

Trimmer - Set it by ear till you hear the Phase. There is only going to be one sweet spot.

This is standard in all the MXR phasers etc.. of old because all FETs are not created equal.

Board Dimensions (W x H) 2.08” x 2.03” ca. 52.7 mm x 51.44 mm

Yes you read that right. Not much bigger than the MoWah board.

This means not only can it be mounted in a pedal but you can also mount it in a Wah Shell for foot control over the rate knob. You can make it a phaser or a vibe and have complete foot control over the rate.

Vibe Mod Foot Control Demo

There is also a hole available on the board for mounting it in a Wah Shell.

You must supply the screw, if you intend on using a Wah Enclosure.


The other option for Wah Shell mounting would be 3M Double Sided Foam tape.


You can also simply drop it into a 125B.

Dr. Phybes Build Document

Check the Forum for answers to many questions before posting a troubleshoot thread.

Do not miss the Easy Pedal Wiring Guide.

Namely the expansive Tips, Tricks and Tutorials section and the consolidated Crash Course Guide.


Mod 1:

Some people prefer the rotation of a B100k Potentiometer as opposed to the stock C500k

Just make sure you do all your wiring changes at the Pot Lugs and not the board so as not to damage the board with constant reheating etc...

Mods by Tonmann:

This mod concerns the LFO

The C7 Mod

Lowering the value of C7 will increase the LFO speed.. Again a Demo from Barry shows the effect.

Changing C7 from 22µF to 10µF is perhaps not a good idea but to be able to switch from one capacitor to the other via a DPDT ON-ON switch will increase the range of the Speed pot.

You can wire the capacitors directly t the switch as shown above or you can use one of Barry's DPDT Wiring Boards to make life easier.

Please note the orientation of the capacitors and the correct wiring to the board.

FURTHER MOD: If you use an On-Off-On DPDT switch, you can remove the LFO from the circuit and create a "stuck wah" effect. Demo w/Dr. Phybes + Mastodon fuzz

Mod to make this into a Cool Vibe sounding Circuit.

R17 - 100k

C2 - 6.8n

C3 -10n

C4 -220p

C5 - 2.2n

C7 - 10u

Here is a Quick Demo - Dr Phybes, Vibes


"Dr Phybes includes the famous “R28” or “Script” mod, this is R16 in the circuit. Some of the phased output signal is fed back to the second stage of phaser section via R16, although this makes the phased sound more pronounced, it adds some distortion at mid frequencies – for an idea of what this sounds like, listen to the demos at

The switch SW1 disconnects the feedback path. If you don’t envisage using the feedback feature, don’t install SW1 or R16. Another approach would be to increase the value of R16 to reduce the amount of feedback, although I would suggest something like 33k or 47k, a “socket it and see” approach would be better."

Rather than type the whole explanation, I've taken the text from the build documents.

On reflection there are a couple of better approaches than the "socket and see" method.

Replace R16 with a 100k pot, running wires from lugs 1 and 2 to the resistor pads (doesn't matter which way around).

Start off at 100% rotation adjusting back towards 0% rotation until you find the sound you like.

Switch SW1 to the off position, remove the power supply from the circuit and measure the resistance between lugs 1 and 2 of the pot.

Remove the pot and insert the appropriate value resistor for R16.

The second approach is similar but using a trim pot on a piece of vero board

Once you have adjusted the trim pot, glue some non-conductive material to the back of the vero board and then glue the board to the side of the enclosure - you can come back at  a later date and adjust the setting if you wish.

Rate LED Mod as posted by Tim Shelton

Patrick Garland (words) and Schectadon (picture for Dr. Phybes


1. Solder a Limiting Resistor to the POSITIVE side of the LED (Round) - on Blue LEDs I use a 3k9 Resistor

2. Connect a wire to the Resistor, and solder the wire to 9v

3. Connect a wire to the NEGATIVE side of the LED (Flat)

4. Connect NEG LED wire to lug 3 of Speed Pot

Tonmann: I wish every circuit was this interesting to watch:

Here is a recent build Courtesy of Jarrod.

Here is a Finished Build thread in a Wah Shell!

Courtesy of Playsforfun

For building a switchable Phaser and Vibe in a single enclosure read this:

November 12, 2012 at 10:51 PM Flag Quote & Reply

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