The Blue Clone
Pretty awesome analog drum machine (courtesy of CircuitBendersUK) and bass synthesizer! Very happy with this one.
The drums sounds are generated by a CB-55 board designed by CircuitBendersUK and modded by me. Check for info on the unmodded board here.
The bass synth is entirely of my own design, but is roughly based on a Roland Juno DCO.
An Arduino Uno generates trigger signals, DCO clock and takes care of the control and MIDI inputs.
Here's the quick demonstration video: watch here.
The Code
Lots of Arduino magic, download it here.
he code is heavily based on Drumique's, check that one out here.
The biggest difference is that Blue Clone also needs to generate the DCO clock, PWM and filter cutoff CV's.
Below's the entire bit of code for Blue Clone. Normally I have my code ordened and separated into different files (i.e. one for the drum machine, one for the bass synth, rhythms etc) but I've put it in one blob now for your convienience :):
The Hardware
The hardware is separated in 3 sections:
- Power supply, delivers +12V and +5V,
- Drum machine, the modded CB-55 board,
- Bass synth, DCO and VCF with various routing.
So let's go over each section.
THE POWER SUPPLY:
I used an old 15V AC wall wart, removed the transformer from it to be used as the mains transformer in Blue Clone. MUCH cheaper than having to buy a new transformer! I also salvaged a fuse holder with a proper fuse too. Don't want mishaps to be big mishaps :)
After that it's all pretty standard. AC gets rectified and smoothed to around 20V DC, then regulated down to 12V by a 7812. The 5V is regulated from that 12V by an 7805.
The 12V rail supplies most of the analog circuitry and the Arduino (on the Vin pin! The Arduino has its own 5V regulator).
The 5V rail supplies the 4016 switches, due to the 5V logic level used by Arduino.
THE DRUM SYNTH
I'm only going to list the various mods here, for details on/schematics of the board check the CircuitBenders link supplied at the top of the page.
Bass drum:
- BD decay: Replace R33 with a 10k pot.
- BD pitch: Replace R28 with a 500k pot.
- BD punch: Replace R35 with a 50k pot. This goes from a mellow tone to a punch in your face!
Snare Drum:
- SD decay: Replace R55 with a 100k pot.
- SD pitch: Replace R49 with a 50k pot.
- SD noise: Replace R52 with a 10k pot. Sets the noise decay.
Hats:
- HH decay: Attach to the top pin of R67 a 500k pot and 100nF capacitor to ground.
- HH decay: Attach a 68nF capacitor to the middle leg of T7, and a 20k pot between the capacitor and ground.
Rimshot:
- RS pitch: Replace R43 with a 1M pot.
THE BASS SYNTH
I've kept this circuit as simple as possible, as there wasn't a lot of space left while keeping things neat.
The DCO is a very simple one: a capacitor is charged through a resistor and discharged through an parallel transistor. The Arduino generates pulses in the frequency of the note played to reset the capacitor. Of course there's the issue with a lower amplitude at higher notes but I found this not to be an issue for a bass synth wich doesn't play that big a range anyways. It can do 4 octaves quite well though!
Two opamps of an LM324 are used, one as a buffer the other as a comparator to generate the PWM pulse.
The 2 signals go through an CD4016 analog switch, which is controlled by the Arduino and are then passively mixed to the input of the VCF.
The VCF is also very simple, I made my own vactrols from a 3mm red LED and an LDR that ranges from around 5 to 350 kilo ohms.
This allowed me to just put the vactrols in place where I needed a voltage controlled variable resistance.
The low pass filter itself is a very standard half-of-a-twin-T circuit, i.e. only the low-pass filter part of it. Simple but quite effective :)
I've had great success with TL081 opamps too, though they tend to be a lot more resonant (if that is your thing).
