DCC recorders are complicated devices. But the service manuals and datasheets that are available online give great insight into how a DCC recorder works in general. They also give many subtle hints about how we could teach them new tricks.
Here's a list of the things that I want to make my recorders do:
- Extract text information such as song titles
- Extract audio in PASC-encoded format
- Store a cassette dump on an SD card inside or outside a recorder
- Play a dump file as if it's a cassette
- Record a dump file to a cassette
It will take a lot of effort to do all this, but I'm pretty sure the information to accomplish it is all publicly available. What I first need to do is figure out some details about how a recorder works, and find a way to improve it.
Third Generation DCC Recorders
The DCC-730 and DCC-951 "third generation" recorders were released around 1995, and by then, Philips were getting very good at making DCC recorders in a highly modular way. They released a System Description document that describes the Third Generation DCC system, and the following is roughly the same information in my own words, with extra focus on the parts that I need to use or modify for this project.
The heart of the 3rd generation recorder is the DDU-2113 Turbo Drive mechanism shown above. The DDU (DCC Deck Unit) is pretty much a standalone unit. In theory, if you would want to build a DCC recorder around a DDU, all you would need is:
- A power supply,
- A front panel with buttons, display and a microcontroller (and probably a receiver for remote control commands),
- Optionally, some digital (S/PDIF PCM, a.k.a. IEC-958 a.k.a. IEC 60958) audio inputs and outputs,
- Analog audio inputs and outputs.
Philips made two DCC recorders with the DDU-2113: the DCC-730 and the DCC-951. They also used the same electronics in the FW68 mini-set but because that unit doesn't have digital inputs and outputs, they left a chip and a connector unpopulated.
The block diagram above shows that all the essential electronics for an entire DCC recorder are on the DDU:
- The Analog board amplifies the signals to and from the heads
- The Deck Control board operates the mechanism
- The Digital board does... everything else!
Let's have a closer look at the Digital Board.
The Digital Board: The Heart of the DDU
The Digital Board is on the back of the DDU and it's what connects the DDU to the outside world.
- During DCC playback, it reads the bits from the tape via the Analog board. It performs error detection and correction, converts the PASC (MPEG-1 Layer 1) compressed audio stream to PCM, and converts the PCM stream to S/PDIF (IEC-60958) and analog audio
- During DCC recording, it converts analog audio or PCM digital audio to PASC, adds codes to help with error detection and correction, and records the bits to tape via the Analog board
- It communicates with the Deck Control board to change the state of the mechanism: Stop, Play/Record, Fast-Forward, Rewind, Search-Backwards or Search-Forwards, Drawer-open/close...
- It communicates with the Front Panel to receive commands from the user (buttons or remote control) and show text on the front panel screen.
- It can perform more complicated tasks too, such as recording and detecting markers and renumbering a cassette.
- When playing an analog cassette, the output signal from the Analog board is sent directly to the special ACC outputs which are connected to a Dolby decoder on the motherboard. The outputs of the Dolby decoder are looped back into the analog input of the ADC so that digital output is available for analog cassettes as well as DCC.
The most important chips on the board are as follows:
- The Main Microcontroller (MUP) communicates with the front panel and the deck control board, and controls...