Commodore 64 Synth Build Part 2

J. Fredrik Andersson continues his Commodore 64 Synth build in Part 2, transforming his classic C64 into a dual-SID stereo synthesizer. What started as a simple upgrade soon became a deep dive into chip behavior, voltage differences, and clever problem-solving that any retro enthusiast will appreciate.

He begins by breaking down the two main SID chip versions: the 6581 and the 8580. Both create the unmistakable Commodore sound, but each uses a different voltage. Mixing them on a standard stereo SID board can destroy a chip. To solve this, Andersson chooses the ARM2SID FPGA replacement. It safely emulates both chip types and removes voltage concerns.

After the theory comes the hands-on work. Andersson opens his C64C and removes the original chip. He installs a stereo SID board, solders audio outputs, and connects address select wires to the expansion port. Switches allow him to toggle between stereo and six-voice modes. His humor shines through, especially when he warns against frying “potato chips” instead of silicon ones.

The moment of truth arrives when he powers on the machine. Thankfully, the computer survives the test. Stereo mode sounds fantastic, but six-voice mode behaves oddly. One SID channel produces a distorted tone. Andersson suspects cable interference or signal noise. Even so, the stereo output proves stable and clear, giving him the confidence to continue developing the project.

Finally, he celebrates with what this Commodore 64 Synth build is all about: making music. He hooks up his C64 to a Roland D-50 and a virtual synth. The result is a smooth electronic jam that highlights the warmth and depth of dual-SID sound.

Andersson’s project shows how curiosity, patience, and creativity can turn a decades-old computer into a unique music instrument. For retro computing fans, this video offers practical insight, lighthearted humor, and real inspiration to start tinkering with their own setups.

Click Here to watch Part 1