music, guitars & other obsessions


Pedal Board Planning

Clear out the “backlog” finally! I made PCB’s for the following effects:

6-Band Eq
Big Muff
Color Sound Overdriver
Color Sound Supa Tonebender
Crank Tone
Cranked AC
Echo Base
Engineer’s Thumb
Fat Booster
Highway 89
Keeley Booster
Keeley Centaur
Love Pedal Super 6
Meat Sphere McBeat
Phase 90
Ross Dynacomp
Supa Fuzz
Tremulus Lune

As you can see, that is quite a lot of effects to build one by one, so I am going to build them up a la modular synth style. Since this is a pretty complex project, I plan to follow the steps below:

Modular Effect Rack:
1. make and stuff the PCB’s (DONE);
2. make the power supply back-plane (DONE);
3. make the control PCBs to hold the pots and switches;
4. prepare the chassis with mounting rails and hardware to hold the modules;
5. mate the modules with their respective control PCBs and test;
6. debug and re-work the modules as required;
7. place the modules onto temporary front panels (made out of G4 board);
8. mount the modules into the rack;
9. re-position and optimize module placement and mounting hardware;
10. design front panel layout based on optimized placement.
11. wire the modules as simple effect banks until the Matrix Switch is done.

16×16 Matrix Switch
1. using Commonsound’s “beat matrix” design as the starting point, modify the design to accommodate one more Zarlink 8816 crosspoint switch;
2. re-write the code for the additional switch (see Greg Surges’ snake corral);
3. breadboard and test the switch;
4. integrate into the Modular Effect Rack when it’s ready.

As usual, the mechanical aspect requires the most effort, as there is no Eurorack available in China, so I had to come up with workarounds for everything – the chassis, mounting rail and assorted hardware, what a hassle!

After that, the front panel becomes the next big challenge, there are many good examples of modular synth modules that can serve as inspiration for the design. I think I will keep it pretty plain Jane as a start, since more elaborate designs could always be installed at a later date. The current plan is to use 3mm aluminum plates in two different widths – 40mm and 80mm to keep the complexity down. The modules will either have 3 or 4 controls per 40mm column. The control PCB is designed to handle either version.

The module will mate to the control PCB via 24-pin header. Each module is then connected to the power supply back-plane via a 10-pin flat ribbon cable. So it should be relatively easy to switch modules in and out of the chassis when needed. Ground planes on all the PCBs should also provide some shielding against noise.

The Modular Effect Rack will be powered via external 9V supply to keep the AC hum to a minimum.

First Try At Stompbox Graphic

The first try was not that successful, the image was printed on hi-gloss photopaper and tacked onto the pedal face plate with 3M 67 spray-on glue. There were a few problems with it:

1) the image did not line up with the actual hole locations, they were close, but not exact, you can see the whole image needed to be shifted up a few mm, it was too long on the bottom;
2) the cut out for the holes were not sharp enough, especially around the LED, I need to use a very sharp point knife the next time, and probably a LED holder to hide the cut out – it should give a more finished look;
3) the photopaper seemed a bit too thick for the job, I will try a thinner version and/or transparency next time.

From further away, the pedal does not look bad, but I think it will be much more attractive to use simpler color scheme in the future, instead of the “rainbow” colors in this image, I will use simpler, bolder images with two perhaps three colors only – that should give the image more punch…

Close-up shot of the Phaser 90

Breadboard for Pedals

Since I plan to build and test a bunch of guitar effects, I built a test bench breadboard – I found an old DVD player, took out the drive and controller card. The power supply has a bunch of different voltages, which will come in handy. In any case, I took the 12V tap and use a 7809 to get regulated 9V needed for the pedals.

Breadboard in a salvaged DVD player chassis.

A Simple Stompbox Build

After reading somewhere that using a buffer/booster could improve the sound for PC-based guitar sims – I suppose from proper impedance matching between the guitar and the soundcard, I decided to build one.

The design I chose was the Fat Booster, just a simple FET booster with some level and tone controls added, the schematic is shown below. The design is a derivative of Jack Orman’s MOSFET Boost, a very popular design. The unit is very clean as expected, but you have to be careful with the level and gain settings as not to overdrive the other effects down the chain. The kit only costed RMB99 (Chinese red case included), what a bargain;-)
The kit came with 2 PCBs, one is the main board, the other is the footswitch board, which I screwed up big time by turning the switch 90 degrees and made a mess of things, it took a couple of days to discover the stupid mistake 😦
Here are the exterior, interior shots and the schematic: