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Jeri Ellsworth’s C64 bass keytar combined a bass-guitar neck, a modified Commodore 64 case, piezo string sensors, an FPGA and the computer’s original SID 6581 sound chip. The result was a one-off instrument built for Maker Faire—not a documented kit or a build with a published, complete parts list.
How the bass guitar and Commodore 64 became one instrument
Ellsworth removed most of a bass guitar’s body and attached its neck to the case of a nonworking Commodore 64. She altered the computer’s badge so the instrument retained the C64’s recognizable look. The bass neck supplied the strings and playing surface; the C64 case became part of the instrument’s body and housed the original SID 6581 sound chip, according to Hackaday’s July 9, 2012 account.
Make: also described the project as a Commodore 64 bass “keytar” using the original SID 6581 chip in a July 8, 2012 overview. That description was written by Make: writer Gareth Branwyn, not quoted from Ellsworth.
How the strings controlled the SID sound chip
Each string had a piezo sensor. The sensors picked up string vibration; their signals were amplified and filtered before being processed by an FPGA. Hackaday’s reports describe the FPGA as handling string detection and keyboard scanning, then connecting to the SID chip, which generated the sound.
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- Sense: Piezo sensors detected the strings’ vibration.
- Condition: The sensor signals were amplified and filtered.
- Process: An FPGA handled string detection and keyboard scanning.
- Generate sound: The FPGA connected to the C64’s SID 6581 chip.
The May 2012 Hackaday project item notes that the bass format related to the SID’s three-channel limit. That is a description of the chip’s role in this project, not a measurement of the instrument’s performance.
Why piezo sensors were chosen
Hackaday reported that Ellsworth chose piezo sensors because magnetic pickups could be unreliable around the Tesla coils at Maker Faire. This was the stated rationale for this build and event environment; the coverage does not provide measurements or establish that magnetic pickups fail around Tesla coils generally.
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What the reports say about performance
The May 2012 Hackaday item reported performance problems caused by string overtones. It did not quantify the severity, specify latency or accuracy, or establish whether later revisions changed the behavior. The available coverage therefore supports identifying overtones as a challenge, but not assigning a numerical performance result.
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What is—and is not—documented
The 2012 articles establish the broad design and signal path, but they do not identify the exact bass model, piezo sensor model, FPGA board, amplifier or filter circuit, power arrangement, or complete bill of materials. Make: said Ellsworth’s video covered the build and circuit designs, but the linked video was not available in the source material for this account. The reports do not establish whether the instrument was later revised.
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For someone exploring a similar approach, “piezo contact pickup for bass guitar” is a category to investigate, not a confirmed part used by Ellsworth. The sources call the components piezo sensors without naming a model or saying that a standard commercial pickup was used. Likewise, a C64 and bass-guitar modification supplies are component categories, not evidence of an assembled kit.
Quick Recap
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