MP32C64 is a simple adapter that allows connecting any audio source to the Datassette port of a Commodore VIC-20, 64, 128 or Plus/4 computer.
With this adapter, any audio source can be used in place of the proprietary Commodore Datassette, in order to load software into a Commodore computer through the dedicated port.
It was originally developed by the Spanish C64 freak Kopsec, probably inspired by the adapter that came with 1st CD-Edition.
As the name suggests, beside Audio CDs, MP3 files will also work, so a smartphone (provided that you have an old model with an audio jack...) or any other audio player can be used.
Another similar project, which works just as well as this one, is DatassetteAudioAdapter.
PRG files can be converted to audio using the WAV-PRG software suite.
Important
This adapter only works for playing back audio files, there is no support for recording.
The original adapter used 6.8k and 68k resistors, but I didn't have those values when I built the first prototype, so I used 4.7k and 47k and they worked well. Probably 10k and 100k would also work, so give these a try before buying new resistors for the purpose.
The adapter can either be built with a PJRAN1X1U01X RCA/Cinch connector or with a SJ1-3525N 3.5" headphone jack connector, according to your preference. Note that the RCA connector will point towards the back, while the headphone jack will point to the right.
The first thing to do is to set the playback volume: start with 0 and gradually increase it until the Signal LED is constantly on. You can still go up a few ticks from there, experiment a bit until you have successful loads.
Second thing is motor control: you have probably noticed that the computer is able to start and stop the Datassette motor at will, but of course it cannot stop an MP3 or CD player, therefore playback control will be on you: keep an eye on the Motor LED and pause the playback as soon as possible whenever it goes off, then restart it when it lights up again (for the latter you don't need to rush). This is particularly important when the "FOUND XXX" screen shows up in BASIC, as if you leave the player running, it might run past the data start while the computer is still waiting to start the loading. You can also press the space bar at this point, as it will abort the wait and start the loading immediately.
Also be aware of the NORM/INV jumper: this should stay in the NORM position for the vast majority of files. In case you know you have one that was encoded with inverse polarity, or if something just doesn't load, you can try the INV setting.
One last thing to keep in mind is that the adapter always behaves as if the Play button was pressed. Therefore, if a game explicitly asks to stop the Datassette, you will have to unplug the adapter, which is not very nice, so I don't take any responsibility for anything that might happen.
If you want to get this board produced, you are recommended to get the latest release rather than the current git version, as the latter might be under development and is not guaranteed to be working.
Every release is accompanied by its Bill Of Materials (BOM) file and any relevant notes about it, which you are recommended to read carefully.
The MP32C64 documentation, including the design itself, is copyright © SukkoPera 2025 and is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
This documentation is distributed as is and WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES whatsoever with respect to its functionality, operability or use, including, without limitation, any implied warranties OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A PARTICULAR PURPOSE or infringement. We expressly disclaim any liability whatsoever for any direct, indirect, consequential, incidental or special damages, including, without limitation, lost revenues, lost profits, losses resulting from business interruption or loss of data, regardless of the form of action or legal theory under which the liability may be asserted, even if advised of the possibility or likelihood of such damages.
If you want to get some boards manufactured, you can get them from PCBWay through this link:
You get my gratitude and cheap, professionally-made and good quality PCBs, I get some credit that will help with this and other projects. You won't even have to worry about the various PCB options, it's all pre-configured for you!
Also, if you still have to register, you can use this link to get some bonus initial credit (and yield me some more).
You can also buy me a coffee if you want:
- Kopsec for designing the original adapter.
- C64-Wiki for preserving the schematics and various information about the adapter.
- Kinmami for validating the design.