Cyanodore 64 Synthesiser

The Commodore 64 was an iconic home computer that was first introduced in 1982. The C64 SID chip aka the Sound Interface Device is what makes this machine suitable for a really incredible Synth. The Synthesiser software is free. You’ll need some adapters and with a little patience to get things up and working properly but it’s certainly worth it in the end. I will used the bread box aka „Brotkasten“ type made in West Germany – the model G Type ASSY 250469 (Rev.4).

In the Video

The Commodore 64 was an iconic home computer that was first introduced in 1982. While the Cyanotype process invented in 1842 by Sir John Herschel remains to this day a classic alternative photography process. I tackle both feats in this mash up crazy fun video. All the music was made with the Commodore 64 Synthesiser using Cythncart, Midi card and some major mods to make the whole thing portable!

You’ll learn how to build C64 synth and make a Cyanotype print with a UV box. Two increbile inventions and two fun projects to do!


Cyanotype of the Commodore 64
Cyanotype of the Commodore 64


My wish is to build a portable Commodore 64 synthesizer on a shoestring without much bother as quick as I can. The synth should have MIDI, stereo output with filter controls.

  1. Midi Interface Card
  2. Getting C64 Software to run from a SD card.
  3. The SID (Sound Interface Device)
  4. Software Synthesiser
  5. Adding Synthesiser Knobs
  6. Adding Stereo Outputs
  7. Adding 7″ Monitor LCD
  8. Run off USB battery.

MIDI Interface Card

There are a number of different card out there; Datel, Passport, C-LAB, Sequential, and Kerberos MIDI interface cartridges. I found a second hand one called, C-Lab cart for 40 euros. It usually came with the software Supertrack.

C-lab Midi Interface Commodore 64

I should also mention the Mssiah Cart too which is available from

Getting C64 Software to run from a SD card.

There are several software programs that can be used to turn a Commodore 64 into a synthesizer or midi sequencer. However to get your software up and running, in this modern age on a Commodore 64/VIC 20/128 you’ll need some magic.  It’s pretty easy voodoo to do, it’s called a SD2ISEC converter.

I found one, made by Max on Ebay. This should allow me to load up the software I need to run either a synth or a sequencer. The SD2IEC board basically a SD card reader that mimic itself as a Cassette player.  Once you find the software on the Internet, copy it onto the SD card and then plug it straight into the C64 and turn the puppy on!

Something to note here is, it still loads very slowly. This due to a bug in the Commodore’s kernel for disk drives and tape.  This can be fixed with a Fastload cart or better still replacing the EEPROM with JiffyDOS but that’s beyond the scope of this blog.

SD2IEC Convertor Commodore
SD2IEC Convertor Commodore

You could of course build your own adaptor but for 30 bucks including shipping why bother? There even a 3D printed side plate too :

The SID (Sound Interface Device)

The SID chip was designed by Bob Yannes, who also created the synthesizer company Ensoniq. The SID chip was a major breakthrough in audio technology at the time, and was capable of producing some of the most unique and interesting sounds ever heard in a home computer.

The SID chip was a three-voice synthesizer that could generate a wide range of sounds, from simple beeps and bops to complex musical compositions. The chip was capable of producing waveforms such as square, triangle, sawtooth, and pulse, and it also had a number of filters and modulation options that could be used to further shape the sound.

One of the unique features of the SID chip was its ability to produce realistic sounds, such as drums and bass lines. This made the chip a popular choice for electronic music producers, who could use the chip to create entire tracks without the need for any additional hardware.

Despite its popularity, the SID chip was eventually phased out in the early 1990s, as newer and more advanced sound chips were introduced. However, the chip remains a beloved piece of audio technology among vintage computer enthusiasts and musicians to this day.

Replacement SIDs

All being said many of the SID chips found in Commodore today are not completely functioning fully. Often they need replacing. Original replacements are expensive while alternative offer limited or missing functionality such as the joystick paddles. However one such SID seems to be a perfect modern replacement. Based on the ARM processor the ARMSID is available from the Czech Republic.

C64 CPU pins for ARM2SID
C64 CPU pins for ARM2SID

I’ve actually choose to use the ARM2SID with is two SIDs in one chip giving the possibility of stereo sound albeit with soldering in some extra wires and a few components which are included in the kit. You need to solder onto the CPU address lines and the cart port, not for the faint-hearted.

The Synthesiser Software

  • CynthCart:  A synthesizer program for the Commodore 64 computer designed with live performance in mind. Includes arpeggiator, portamento, stereo SID and MIDI support, realtime filter control, many other features.
  • Another Synthesizer program STATION64
  • Sequencer Software: If you are interested  you can also make a Midi Sequencer quite easily. Using , Steinberg Pro 16 or C-Lab Supertrack.

    micro rhythm
    micro rhythm
  • Drum machine:  MicroRhythm by Simon Pick.

Adding Synthesiser Knobs

C64 Synth Pots wiring
C64 Synth Pots wiring

To control filters and various other things four potentiometers need to be added to the joysticks internally inside the machine.

Only pins 5 and 9 are interesting to the Synth project. Bare in mind the red and black wires in the diagram below are the 5V and GND lines which could be taken from the board directly.
*Tip: As I need the voltage lines for the SD2IEC adapter, I would bundled them up from there.

Optionally, would be to add a switch on these pins, a double pole switch. This would allow the use of the joysticks for both making music and playing games.

Note: Cynth uses only two of these controls.

Update: Alternative version

Parts Required

Adding Stereo Output

Arm2Sid wire up for stereo
Arm2Sid wire up for stereo

Because I’ve decided on the ARM2SID, this gives the opportunity to have a stereo output. It is recommended to have decoupling capacitors wired to your output 1/4″ jacks. You can take the ground from previous points from the potentiometers.

You need to located the 6510 CPU chip on the C64 board and solder some wires to it too. In the ARM2SID kit I had to solder 2 diodes and resistor to the back of the cartridge slot and some wire. Not an easy feat for a novice but I’m a veteran with the soldering iron at this stage of my life.

More information and firmware available

There might be the possibblity to have an Audio Input and do some feedback looping too

Parts Required
Commodore 64 on USB battery!
Commodore 64 on USB battery!

Adding 7″ Monitor LCD

C64 with 7 LCD Screen
C64 with 7 LCD Screen

I mention to pick up an old LCD screen for 15 euros locally which works quite nicely with a stand too. Unfortunately this screen died over the weekend, so off to Amazon and ordered a “7 Inch LED Backlight TFT LCD Monitor for Car“.

It took awhile to get it one that displayed the image for the composite out of the C64. I use a 7” LCD screen which is larger enough and runs on 12-24 volts. I also hope to get this working on USB battery power too.

Parts Required
Commodore 64 on USB battery!
Commodore 64 on USB battery!

Run off USB Battery

Some of Commodore 64 boards can run on just the 5V line. However some things wont work, the user port, tape machine and the original SID chip which requires the 9V/12V line.  In our case the SD2IEC only requires the 5V line while the ARM2SID still might require the 12V line to decide which mode to operate. However there maybe a work around via the configuration software for the SID in the firmware.  This I’ll need to test.

After testing, it works out of the box on 5V with Cynth –  very nicely indeed.

Customising it as Cyanodore 64

Make it the Cyanodore 64

Adding the Tube Preamp

I’m using a 6J1 kit which is easy enough to get hold of. I did need to be cut it a bit to make it fit. There also a few hacks to improve the sound of this board, I’ve link and shown in the image gallery. Oh there are blue LEDs which illuminate the glass tubes!

It’s important to test this board before adding new holes to the Commodore!  Also the board relies on 12V AC power.  This doesn’t make the commodore portable with this mod.  However you could combine a simple bridge rectifier and capacitor circuit to supply the amp and the LCD display via mini power jacket socket.

Add Interrupt LED

This little modification will indicate interrupts and power in a single LED. Useful to know if the machine is locked up or if hardware activity is going on. This idea is taken from here

Commodore 64 IRQ Bicolor LED
Commodore 64 IRQ Bicolor LED


  • 1 x IC 74LS04.
  • 1 x Bicolor LED.
  • 2 x 330 ohm resistors.
  • Tiny wires.

How it work?

When the CPU generates an IRQ the green LED lights up, otherwise is red, if the IRQ is turned on and off quickly the led is orange.

By soldering to pin 4 for the IRQ on the cartridge port.


Adding Keyboard illumination

Adding blue illumination to the Commodore 64 keyboard  using a cheap kit found on Amazon

Step by step guide in the images

Add Oscilloscope


Other Resources and Mods

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