Close
0%
0%

DCC Hacking

Reverse-engineering Digital Compact Cassette recorders

Similar projects worth following
The Digital Compact Cassette was invented by Philips and Matsushita as the successor to the analog Compact Cassette. It used a magneto-resistive head with 9 tracks per side, to play and record music digitally, using a lossy compression algorithm called PASC (Precision Adaptive Sub band Coding) which was an early version of MPEG-1 layer 1.

Arguably the most interesting DCC recorder ever was the DCC-175. This was a portable recorder made in Japan, but only available in the Netherlands. The interesting part was that it was possible to connect it to a computer. The cable to do this is very rare, and it uses a custom chip that makes it impossible to duplicate. Or not?

The plans are vague at this time, but I'm thinking along the lines of:
1. Find out what data goes over the cable
2. Make a similar cable with modern hardware
3. Implement computer connectivity on other DCC recorders

What we know

In the last few years, a lot of useful information has appeared about the secrets of DCC. Old magazine articles, press conference handouts, course material for technicians who needed to repair DCC recorders, service manuals and service bulletins, and datasheets have shown up on the Internet in digital form, and the DCC Museum has managed to get in contact with several people who worked on DCC behind the scenes.

At this point, I'm not sure what the question is, but here are  a couple of answers:

  • Philips mentions three generations of DCC recorders. They refer to the DCC-730 and DCC-951 from 1994 as the "Third Generation", with Turbo Drive and the ability to record song titles as distinguishing features.
  • The "first generation" was obviously the DCC-900 which was the first DCC recorder that came out in 1992. Several other manufacturers released recorders at the same time, which were all very similar to the DCC-900 on the inside. Marantz made two recorders that have a better D/A converter (TDA1547) and RadioShack sold the Optimus DCT-2000 which was designed by RCA but had Philips plugin boards and a Philips mechanism.
  • The "second generation" must then be what came in between: Philips released quite a number of DCC recorders in 1993 that were all based on the same hardware: The DCC-600, DCC-300, DCC-380 and DCC-450 (aka DCC-91) all have the same circuit boards inside but there are small variations (e.g. with remote control buses populated or not) and enclosures are different sizes.
  • The first and second generation recorders use the same chipsets (the first portable players used a different chipset). The third generation uses a different chipset.
  • The third generation chipset is more integrated that the first generation chipset. Modulation, demodulation, tape formatting and error correction are all done in a single chip in the third generation chipset.
  • For the first generation chips, there is almost no documentation, but the third generation chipset is very well documented. The datasheets are also clearly not just intended for technicians who merely need to understand why a recorder might have stopped working and how to repair it. They contain enough data to (theoretically) connect the chips together, slap them on a cassette mechanism with an MR head assembly and hook up a microcontroller to build your own DCC recorder. Just a few pieces of information are missing such as the format of the information that gets stored as SYSINFO (the data that is interleaved with the audio data) and AUXINFO (the data that's on the 9th track).
  • The DCC-175 was a portable recorder that was only available in the Netherlands. It could be connected to a Windows 3.1 or 95 or 98 PC with a special "PC-Link" or "DCC-Link" cable (naming is inconsistent). The cable was plugged into the parallel printer port and used a custom chip by Philips Key Modules for which no documentation is available. We know from a somewhat reliable source that only 1400 of these cables were made, and they are extremely rare at the time of this writing.
  • The DCC-175 and the PC-Link cable made it possible to copy music (in PASC format) from tape to hard disk and vice versa, and it could backup data files too, at the same 384kbps per second (which was rather slow even for 1995, by the way). It also allowed some light editing (copy-paste music fragments, play loops, place markers, change volume and fade in/out, change filter parameters, create compilation tapes).
  • In the late 1990s, someone started a reverse-engineering effort on the DOS backup tape driver that's included with the PC-link cable and found out that the hardware appears very similar to a parallel port tape interface by Shuttle Technologies. The reverse-engineering project was never finished, though.
  • The schematics in the DCC-175 reveal that the PC-link connection is directly connected to a 5V power supply in the recorder, a bidirectional synchronous serial port of a microcontroller in the recorder, and the...
Read more »

  • Exciting News: Incoming Data!

    Jac Goudsmit02/16/2019 at 08:21 1 comment

    I fixed a few problems in the Synchronous Serial capturing program that catches the output of the microcontroller in the DCC-175, and behold: this was scrolling up my screen while I was playing my Grace Jones - Island Life prerecorded cassette!

    Read more »

  • First Signs of Life from the Analyzer (Update: Now in Hexadecimal!)

    Jac Goudsmit01/22/2019 at 08:46 0 comments

    I finally had some time to work on the Propeller software that interprets the synchronous serial data. The data in this picture are definitely completely wrong but at least the synchronous serial analyzer cog is generating data. For one thing, the Windows 98 computer was off during this first test and I don't know if the DCC-175 even talks to the chip in the DCC-Link in this state. Also the output format doesn't make sense: it should show a hexdump with lines that start with a memory address, followed by hexadecimal data, followed by filtered ASCII characters.

    Read more »

  • The Turkey Lab

    Jac Goudsmit12/25/2018 at 05:11 0 comments

    A quick update to show off the "Turkey Lab", so named because I attached all the parts of the project to the bottom side of our turkey cutting board. I used double-sided adhesive tape so that I can eventually detach everything again. At least I hope so: when I used the same tape to put blacklights on the wall for a Halloween party, it took parts of the wall with it when I tried to take the blacklights down again. Because of that, we now refer to this particular type of tape as Evil Tape in my house. So I suppose this must be a picture of the Evil Turkey Lab then ;-) .

    Read more »

  • Good News! No News.

    Jac Goudsmit11/25/2018 at 23:01 0 comments

    The other day, I wanted to do some work on this project again after it had been put away for a while. But to my surprise and disappointment, the DCC-175 that I was using for the project before, had completely stopped working. Normally when you push the Play button (or Rewind or Fast Forward), a DCC-170 or DCC-175 shows a message on the screen saying "Power On". But the screen stayed blank.

    This was depressing, because I got this DCC-175 a few years ago, after my first 175 stopped working in pretty much the same way. I couldn't find the problem in the first one, and I was afraid I would have to start looking for another replacement on eBay, and they are getting really rare. But then I thought: Maybe I should try connecting it to the computer and power it up that way?

    Read more »

  • Analyzing, Please Stand By. Your Call Is Important to Us.

    Jac Goudsmit08/19/2018 at 06:54 0 comments

    As I mentioned in the previous log, I found out that the microcontroller in the DCC-175 and the custom chip in the DCC-Link cable communicate in blocks of 32 bytes each direction. I've been wanting to set up a Propeller on a breadboard to do some deeper analysis but because it's crunch time at work, I haven't had time.

    Anyway, I thought it might be a good idea to do a brain dump of some of the details of my findings, along with some pictures of the logic analyzer screen for reference. That way I'll have all the information gathered here once I start programming. I'll also show some timing diagrams from the 3rd generation chipset datasheets.

    Warning: This might get a little dry, technical and boring so if you're here to see circuits getting soldered together (or breadboarded) and doing useful stuff, you may want to "sit this one out".

    Read more »

  • Now We're Talking!

    Jac Goudsmit07/21/2018 at 07:12 0 comments

    After the fiasco that I described in the previous log, where I had connected all the wires wrongly, I finally saw some data on the Logic Analyzer that made sense. In this log, I'll describe the signals for those who are playing along at home, and maybe haven't read the datasheets and service manuals as many times as I have.

    First of all, let's fix a mistake in the schematic in the DCC-175 service diagram:

    Read more »

  • Log All the Fails!

    Jac Goudsmit07/20/2018 at 06:01 0 comments

    I finally started to do something that I've been wanting to do for over 20 years: use a logic analyzer to figure out how the DCC-175 communicates with the PC. It didn't go so well but I fixed my mistakes. If you want, you can skip this log to go to the next log which will have some juicy interesting stuff (arguably?). If you want to find out how I made a stupid wrong assumption that threw me off for a few days, keep reading. 

    Read more »

  • Introduction to the DCC-175

    Jac Goudsmit07/18/2018 at 03:45 0 comments

    It shouldn't surprise anyone that a DCC recorder is significantly more complicated than a regular cassette deck.

    This article gives an overview of the general architecture of a DCC recorder, and the DCC-175 in particular.

    Read more »

View all 8 project logs

Enjoy this project?

Share

Discussions

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates