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 version of the Commodore 64.

I've also made a video covering many of the items in this build along with a demo too which can be found on youtube https://youtu.be/qO_XLfV6d98

Supplies

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.

General

A working Commodore 64
26 AWG Wire,
Solder and Soldering Iron

SID

ARM2SID

Knobs

Sockets

LCD Screen

7 Inch LED Backlight TFT LCD Monitor for Car

Step 1: 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.

I should also mention the Mssiah Cart too which is available from https://www.mssiah.com/features.php#mssiahcartridge

Note: A midi cart is not essential but if you wish to connect a MIDI keyboard on a sequencer it's recommended.

Step 2: 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 article.

You could of course build your own adaptor but for 30 bucks including shipping why bother? There even a 3D printed side plate too : https://www.thingiverse.com/thing:3791063

Step 3: 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.

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.

Step 4: 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. https://www.qotile.net/cynthcart.html
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.
Drum machine: MicroRhythm by Simon Pick.

Step 5: Adding Synthesiser Knobs

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 (which I think might be better, I've yet to try it) https://midierror.blogspot.com/2014/04/make-commodore64-paddle-for-cynthcart.html

Step 6: Adding Stereo Output

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

Step 7: Adding 7″ Monitor LCD

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.

Step 8: 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.

Step 9: 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!

Change the sound with 6J1 Tube Pre Amp with override switches and feedback control.
Tube preamp mods https://www.diyaudio.com/community/threads/6j1-china-preamp-thoughts.309876/

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.