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. .

. . .


sir sampleton (iOS)

cynthcart (C64)

synthcart (atari 2600)

seq. kit (atari 2600)

loopcart (atari 2600)

dot matrix synth

looper (win)


> and/or gallery

> artwork catalog

> spirit surfers

magic carpet (iOS)

pi house generator


> tree wave

> softoft techech ep

older music


marble craze game

game music hacks

homestar rpg (RIP)

> Atari 2600
programming guide







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-=*=- -=*=-

Cynthcart is a cartridge for the Commodore 64/128 that turns the computer into a standalone analog synthesizer. Its key-command user interface allows it to be played and controlled without a monitor, making it especially suitable for live performance. The original Commodore 64 piano keyboard overlay can be used (illustrated below), and Datel, Passport, Sequential, and Kerberos MIDI interface cartridges are now supported.

Cartridges are available on eBay through Tim Harris (he also often lists them on Ebay) or at Protovision. The current version of Cynthcart is 2.01


FEATURES (version 2.0)
+ 30 preset sound patches
+ Arpeggiator, portamento, vibrato, and tremolo effects
+ Analog filter control and effects
+ Control of attack, release, and other sound parameters
+ MIDI support including pitch bend, patch changes, and controllers
+ On-screen help
+ Color visualizer display
+ Mono stack, 3-voice mode, and 6-voice mode (with second SID)
+ No latency
+ SID hex editor for advanced users
+ Ability to turn off video chip to reduce noise
+ PAL and NTSC pitch tables with automatic selection
+ Copies itself to RAM (cartridge can be removed after booting)

+ Commodore 64 piano keyboard overlay
+ Datel, Passport, Sequential, and Kerberos MIDI interface cartridges
+ Paddle controllers in port 2 for filter, pulse width, vibrato, and pitch
+ 2nd SID chip for stereo and 6-voice sound
+ Works with Autodafe's Cynthcart MIDI editor VST


printable manual (one page front and back)


for most configurations running on a real C64 (MIDI autodetect, 2nd SID at $DF00)

for Kerberos cartridge or emulators with MIDI (Datel MIDI adapter, 2nd SID at $D420)

for emulators (MIDI disabled, 2nd SID at $D420)

for use with SID Symphony cartridge (MIDI disabled, 2nd SID at $DE00)


Cynthcart Midi Editor VST by Autodafe


Version 1.2.4 source and project: cynth1_2_4.zip

Version 1.1 manual cynthcart.txt

Creative Commons License

[Files and source are for personal use only, please do not sell cartridges online]

Where do I get the Commodore 64 piano keyboard overlay?

The overlay isn't required, but they show up on Ebay reasonably often. It's called "The Incredible Musical Keyboard" so try searching for something like "commodore musical keyboard". Also they sometimes can be found at thift stores and online retro-gaming vendors.

How do I get the audio signal from the C64 to my amp/mixer?

You can buy an A/V cable (on ebay all the time). It has a DIN connector on one end that goes into the C64, and RCA connectors on the other. It's also possible to make one out of a MIDI cable. Cut the cable in half and figure out which two wires are ground and audio and solder on a 1/4" plug.

Commodore 64 video cables typically have separate RCA connectors for chroma and luma video signals, so if you don't have separate chroma and luma video inputs on your monitor, then you will need a "Y" adapter to join the chroma and luma into a composite video signal.

What do I need to use the Cynthcart?

The minimum requirements are a Commodore 64 or 128, a power supply, and an A/V cable. Optional accessories are the piano keyboard overlay, paddle (rotary) controllers, a MIDI adapter, and a stereo SID cartridge or board.

If you're going to play live shows with your Commodore, you'll probably want to get a backup power supply and possibly a backup C64. Note that the off-brand C64 power supplies are usually much more reliable than Commodore brand supplies. More info about power supplies here.

What's the difference between the Atari paddles and the Commodore paddles?

Both will work, but I prefer the Commodore paddles because the Atari controllers have a smaller range of motion and are too sensitive. Atari paddles use 1 mega ohm potentiometers while Commodore paddles use 470K ohm.

Which model of Commodore 64 sounds best?

I have a slight preference for the 64C model (8580 SID) compared to the original model (6581 SID), but I use both.

How do I add another SID for stereo?

A secondary SID sound chip can be added either by installing an internal board like the SID2SID or by using a cartridge like the SID Symphony or SIDCart which is available through Shareware Plus.

There is no standard for where to put the second SID in the Commodore 64's memory, so the various solutions for installing a secondary SID chip are inconsistent about this. Version 1.2.4 and earlier versions look for a second SID at address $DE00 which is compatible with the SID Symphony cartridge and the SIDCart. Version 1.5 and later has the second SID address changed to $DF00 by default to avoid conflicting with midi adapters.

Note that the Kerberos cartridge is not compatible with SID cartridges because it has MIDI at $DE00 and a memory bank at $DF00. To use a second SID with Kerberos, the secondary SID must be installed internally and set to address $D420 using something like a SID2SID board.

More info about installing secondary SID chips here.

SID hex editor screenshot

Help screenshot

Cynthcart running with a Datel Midi adapter and SIDcart

A multi-cartridge adapter allows the SIDcart, MIDI adapter, and Cynthcart to all be used at the same time

Here's Cynthcart installed as a replacement for the C64 BASIC ROM (this was only supported in version 1.0)


changes in version 2.0
- now supports and autodetects Passport, Datel, Sequential, and Kerberos MIDI adapters (note: autodetect is incompatible with VICE)
- 8 new preset sounds
- added mono stack portamento modes
- new instruction manual
- moved secondary SID to $DF00 to work with SID cartridges again
- presets can have different waveforms and sustain/release for each voice
- added key to cancel out of the SID editor
- various UI improvements
- various bugfixes

changes in version 1.5.1
- fixed clock and sysex bytes causing crashes/stuck notes (0xF0-0xFF)
- fixed bad pitch bend startup value
- added non-omni midi modes for channel 1 and 5

changes in version 1.5.0 (major update for Kerberos)
- added MIDI support for Kerberos cartridge/Datel MIDI interface
- arpeggiator
- mono stack mode and 6-voice mode
- new filter and pulse width effects modes
- additional presets
- improved clarity of help screen text
- moved SID location for MIDI version to $D420 to avoid midi and Kerberos interfaces
- smarter note buffering system
- reworked patch parameter display
- made LFO and all pitch modulations use proper tuning/scaling
- various bugfixes

changes in version 1.2.4 (released 5-16-08):
- PAL and NTSC note tables and autodetection
- full-screen video mode
- second paddle controls pulse width, LFO depth, or pitch
- automatic activation for filter paddle
- improved keyboard layout
- onscreen help
- SID editor help and status display
- dummy SID register to edit 3 oscillators at once
- save an editor patch in memory
- fixed patch/sound change glitch when playing
- fixed bad notes in top octave

changes in version 1.1 (released 6-21-06):
- added SID HEX editor
- changed tuning keys to avoid accidentally changing the tuning
- added ability to turn the SID filter on and off

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