If the beautiful analogue sound of the SID chip isn't suitable, maybe it's time to go digital instead? For this, we've created the DigiMAX. When plugged into your User Port, it provides four 8-bit digital sound channels (in stereo) through a separate output on the card. With appropriate cables and mixer (not included), one can even use the SID and DigiMAX together!
Here's what Vanessa herself has to say about the project:
Despite the C64 being able to do 8-bit audio with various methods, I always thought it could use a proper 8-bit DAC, if for no other reason than to eliminate the extra CPU time those methods take, so I created the DigiMAX. The original hand-wired prototype is somewhere unknown, but I did find a copy of the schematic buried among the documents on my CMD HD. It was a snap to re-create with proper schematic capture tools, and this time it is based on a somewhat cheaper version of the chip the prototype used.
The original prototype was directly wired to female a user port connector (two legs of the chip were actually soldered directly to of the edge connector's mounting pins). Board layout and schematic updated to v0.1.4 (Couldn't get any audio -- fixed by changing the four 100 ohm resistors to 3.3k and the two 10uF caps next to them to 1uF. Also replaced User Port footprint with a lower-profile version to shrink the board).
The board is based on the TLC7226 whose pinout can be seen to the side. It has 2 address lines for addressing the 4 DACs, and a write signal line and 8 data lines for writing to it a byte at a time via CIA2's Port B.
Here's what the TLC7226's Spec Sheet has to say for itself:
The TLC7226C, TLC7226I, and TLC7226M consist of four 8-bit voltage-output digital-to-analog converters (DACs) with output buffer amplifiers and interface logic on a single monolithic chip.
Separate on-chip latches are provided for each of the four DACs. Data is transferred into one of these data latches through a common 8-bit TTL/CMOS-compatible 5-V input port. Control inputs A0 and A1 determine which DAC is loaded when WR goes low. The control logic is speed compatible with most 8-bit microprocessors.
Features:
Here it is, in a custom case, and in action.