Commodore Custom Built Circuit Bent Synth with Cynthcart and Screen

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via this eBay listing

"Listing is for a custom built circuit bent commodore synth with cynthcart and screen. This custom build device was made around 2009 and has been used a few times but mostly stored. Honestly forgot I had it. If I recalled I think the purchase price was around 600 from the person who built it.
Some of the knobs are blank for future wiring mods. The ones I checked I listed on with tape. Octave changes, Volume knob, Filter on off switch, Filter cutoff. The cynthcart is the sound module on a card for the commodore sounds and can be played on the darker keys. The device works and was tested before listing however since this is a custom build some functionality may vary. It played sounds and sounds as I remember.
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Listing is being sold AS IS so if there are any questions please just ask.
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Functionality for the cynthcart I found is listed below.
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cynthcart is a cartridge I developed for the Commodore 64 computer that turns it into a standalone analog synthesizer with MIDI support. The Commodore 64's SID is one of the most interesting 8-bit sound chips of all time, and I was unsatisfied with the available SID synthesizer software. Cynthcart supports the original Commodore 64 piano keyboard overlay (shown below), and MIDI interfaces by Datel, Passport, Sequential, and Kerberos. Cynthcart's key-command user interface allows it to be played and controlled without a monitor, making it especially suitable for live performance.
FEATURES:
● 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"