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. .

. . .


sir sampleton (iOS)

cynthcart (C64)

synthcart (atari 2600)

seq. kit (atari 2600)

loopcart (atari 2600)

dot matrix synth

looper (win)


magic carpet (iOS)

pi house generator

> catalog of my artwork

> spirit surfers

> and/or gallery


> softoft techech ep

> tree wave

older music

> palfloat


marble craze game

game music hacks

homestar rpg (RIP)

> Atari 2600
programming guide






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-=*=- -=*=-

Cynthcart is a cartridge that turns a Commodore 64 computer into a unique-sounding analog synthesizer. The program is designed so that the software can easily be used without a monitor, making it especially portable. Cynthcart can be played using the computer's keyboard or the original Commodore piano keyboard overlay (which unfortunately has become more difficult to find these days on Ebay)

The cartridge is available at AtariAge or on eBay through Tim Harris. The current version is the non-MIDI cynthcart is 1.2.4.

A MIDI version is also available through Frank Buss's Kerberos cartridge (which includes a new 1.5 version of Cynthcart with many new features, and also supports other C64 music software too)

SOUND DEMOS:   cynth1.mp3   cynth2.mp3   cynth3.mp3   cynth4.mp3  

* 3 Note Polyphony
* Works with the common C64 piano keyboard overlay
* Adjustable vibrato
* Portamento effect (sliding notes)
* Can change patches and settings while playing
* Filter, pulse width, vibrato, and pitch via paddle controllers
* Whammy (space) bar
* Control of attack, release, and many other sound parameters
* Support for 2nd SID chip (stereo chorus effects)
* Tuning adjustment
* Psychedelic rave color patterns
* On-screen help
* No latency
* SID hex editor for advanced users
* Can turn off video chip to reduce noise
* PAL and NTSC tuning tables with automatic selection
* Designed to be used easily without a TV/monitor
* Copies itself to RAM (cartridge can be removed after loading)


instructions textfile

concise online manual assembled by Juerg Maag

[NOTE: ROM and source are for personal use only, please do not sell cartridges online!]


PRG disk file, should work with most emulators or MMC64: cynth1_2_4.prg

BIN file can be burned to EPROM and used in an 8k cartridge: cynth1_2_4.bin



Creative Commons License


changes in v1.1 (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

changes in v1.2.4 (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

Where do I get that keyboard overlay?

You don't need the overlay to play it, but they show up on Ebay reasonably often and typically go for about $10. (UPDATE: they've become more difficult to find) It's called "The Incredible Musical Keyboard" so search for "C64 musical" or "commodore keyboard" or similar variations. Or check your local thift stores or maybe some 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. Or you can make one out of a MIDI cable. Just cut it in half and figure out which two wires are ground and audio and solder on a 1/4" plug.

What gear do I need to use the Cynthcart?

The core things you'll want are a Commodore 64 and power supply, A/V cable, piano keyboard overlay, and a set of paddle controllers. The piano keyboard and paddles are optional, but it really is a lot cooler with the paddles so you can control the filter in realtime. I'm sure you could learn to play it fine with the typing keyboard, but it's a little easier with the piano overlay.

All of these show up regularly on Ebay. You should be able to easily find a C64 with power supply and A/V cable on ebay for about $20-$25. You can use a monitor or TV with composite input to see the video output, but this really isn't necessary to use the Cynthcart.

The Cynthcart works with with both the original beige C64 and the later white 64C with the sloped front. Should also with with the C128 and SX-64, but I haven't tested this.

If you're going to play shows with it, 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. And probably the most reliable power supply is a Commodore 128 power supply modified to work with a C64. 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 very sensitive. It's been reported that paddle controllers work best when using 100k potentiometers and 4.7nanoFarad capacitors.

Which model of Commodore 64 sounds best?

I have a slight preference for the 64C model compared to the original model, but I use both.

How do I add another SID for stereo?

The easiest way is to get a SID Symphony cartridge (a somewhat rare cartridge with a second SID chip) and a cartridge expander that lets you use more than one cartridge at once. Another way is to install a second SID into your C64, but the current version of the Cynthcart doesn't support the SID addressing necessary and I haven't tested it. I can create a custom Cynthcart ROM if you have an internal SID. Future Cynthcarts will support multiple SID addresses.

Does it support MIDI?

Aiming to have one in 2013.

Hardcore! The Cynthcart installed as a replacement for the C64 BASIC ROM (so the C64 always boots to the Cynthcart).
More about replacing the ROMs on Nick Coplin's page.

A Magic Desk I cartridge which can be used to make a Cynthcart
(More about this on Nick Coplin's page too.)

ROMs removed and replaced with socketed EPROM. I should have put it in the upper left spot since that's the one that boots up first. I just cross wired the OE line from the EPROM.

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