Apple-1 SID interface
by Claudio Parmigiani PURPOSE Allow the Apple-1 computer to generate sounds and simple melodies via BASIC or Assembler. IMPLEMENTATION A SID (Sound Interface Device, MOS 6581) has been used. It is addressed through a TTL logic, which will be explained later. Some circuitry has been added to ensure compatibility with the MOS 8580. An amplifier has also been added in order to provide an adequate output level. CIRCUIT POWER 5V is taken directly from the Expansion Bus 12V (for 6581) or 9V (for 8580) is derived from the “12V Unregulated” on the Expansion Bus. Raw voltage is about ~20V (not stabilized). A jumper is used to select the right voltage. FILTERS Typical 6581’s CAP1/CAP2 filter capacitors value is 470pF. These capacitors are present on the board. It is possible to select other capacitors by switching another couple of jumpers. Alternative capacitors must be connected to the appropriate sockets. AUDIO AMPLIFIER A simple 1-transistor (