Some people get adventurous and drill holes in the guitars to add switches or knobs to allow for more control than the stock wiring affords. I decided to make a preamp that would allow any combination and polarity of the pickups (even time-varying ones) without requiring modifications to the guitar's body or pick guard.
And so, the Anubis preamp for Fender/Squier Stratocasters was born! There's a digital potentiometer and polarity switch for each of the three pickups. They're all controlled by a microcontroller. The control software can be edited and uploaded to the Anubis with an Arduino UNO board.
The volume and tone potentiometers have been replaced with a program selection encoder and two program value potentiometers. Here's a shot of the boards. The minimum order from the board house was 10 units, so I have some extras :)
And here's the board populated and installed on my Strat's pickguard. There's a single IDC breakout cable that goes from a header on the board to the switching jack, the pickups, the battery, and the programming cable.
I've made a mostly dry recording of the guitar (direct injected, a little compression and reverb added) to demonstrate a few of the programs I've written for it so far. In the order of recording they are:
1. Sample and hold: abruptly switching between randomly selected pickups.
2. Fast chorus: The pickups are amplitude modulated with low frequency sine waves that are 120 degrees out of phase with each other. Sounds kind of like a three tap chorus.
3. Slow chorus: same as above, but with a slower modulation frequency.
4. Some of the 13 different pickup combination and polarity options.
If I have time to do it over, I may try nice VCAs (like the SSM2164) instead of digital potentiometers to avoid the annoying stepping/zipper noise.
Here's a link to the GitHub repository for the microcontroller's software:
As promised, here's the schematic:
And here's the bill of materials:
|Description||mouser part number||unit price||quantity||line total||number on board|
|Amphenol flat cables||523-135-2801-020FT||1.75||1||1.75|
|regulator capacitors||77-VJ1206Y334KXJTBC||0.08||4||0.32||C13, C14, C15, C16|
|decoupling capacitors||77-VJ1206Y104KXJPBC||0.033||5||0.165||C7, C8, C12, C17, C11|
|crystal capacitors||77-VJ1206A220KXACBC||0.05||2||0.1||C9, C10|
|pull down resistors||652-CRT1206BY1002ELF||0.31||2||0.62||R8, R9|
|16 MHz crystal||774-ATS160SM-1||0.24||1||0.24||Y2|
|power supply resistors||71-CRCW1206J-100-E3||0.03||2||0.06||R10, R11|
|DG403||968-DG403DYZ||1.43||3||4.29||U4, U5, U6|
|9V battery holder||12BH610-GR||1.05||1||1.05|