DIY Korg PME40X External Selector "Clone"

I am a PME40X user, and I like this multi effect very much. Sometimes I feel the need to place an external stompbox in my effects chain, but this is not possible without the external selector Korg realized for this pourpouse.

I have not one of these at hand, nor schematics unfortunately, but, as you can see, Korg placed some useful indication on the module front, soo...

.. let's go and realize a replacement for this!

Modules Pinout

First thing first, we need the pinout for these modules in order to make good use of signals coming from and going into the power supply / FX selectors base.

The most important thing to notice here is that the power supply is +15V, not the now "standard" +9V. This means that we cannot power most of our external stompboxes directly, but they will need a separate PSU.

Hardware and Assembled Module

The module in a nutshell is a pair of unity gain amplifiers, one at the module input, the other immediately after the return path. It uses a very small amount of cheap and common components, the op-amp being the "prom Queen".

Even if the module is simple, cutting a perfboard to the right size and then soldering the nedded components following a scheme could be time consuming. It's way better to have a pre-sized module manufactured and then solder some component, is't it? :)

The components you will need to assemble the module are (BOM):

1x External Selector Module PCB

2x jack socket, 6.3 mm, mono, female

1x 8 pin precision socket

1x op-amp (NJM4558 or any other pin compatible

4x 1M ohm resistors

2x 0.1 uF poly capacitor

2x 10 uF electrolitic capacitor

8x angles pinheaders

I think the module looks good, but most important: works great! 

I tested it with different amplifiers, and they all worked well: NJM4556, NJM4558, TL072 and NE5532. Even if some amp could be better on paper for audio use, in this application I couldn't honestly hear any difference between those I tested: the module is always quiet and "transparent".

The module PCB you can see in these pictures has been manufactured and sponsored by those nice guys at PCBWay - PCB Prototype The Easy Way. Their customer service is very good and PCB quality excellent. Thanks guys!

The module was designed and sized around my PME40X. It's tested, so don't worry!

Final Words

This was a simple project because simple is the module's function. As I said I have not an original Korg external selector and it would be interesting to see what's "hidden" under that plastic box. In case anyone has one, or schematics: please post a pic or a link!

Now, having the pinout opens a lot of potential for DIY project: I hope some of you will chime in with brand new exciting effects for our beloved PME40X!