A SCMS killer circuit
The basic information of this page can also be found at the WWW home page for the DAT-heads mailing list
(will I ever find some time to update that page...??)


The circuit was invented by Dr. Horst Ludwig from Germany and published in "Stereoplay" (a German Hifi magazine) in September 1992. It's an additional board that should work with all DAT decks using the Sony CXD2601 signal processor IC (this chip can be found in many Sony decks and in the Pioneer D500). The SCMS killer circuit was tested by Dr. Horst Ludwig with the Sony DTC-55 and the DTC-57 and it works with my Sony DTC-670. Chances are good that it will work in other decks with a CXD2601, but I'm not sure about that. (So I can't answer questions like "Will it work with my Sony DTC-59?"). Don't blame me if you ruin your deck. I don't even fully understand what this circuit does. (Maybe someone else could explain this!?) Modifications at your own risk! It is very easy to damage your DAT! (By the way, this modification will void any warranty you may have!)

There are three images available:

The installation picture shows the additional board built into a Sony DAT-deck and on the close-up picture you can see the connections to the Sony board. (There are three wires going to the CXD2601, the other two wires are for the 5V power supply of the board.)

You don't need to change anything on the Sony board. Just connect the new board. The SCMS code on recordings made via the digital input is set to 00. The recorded tape can then be copied as often as you like even on unmodified decks. (Note: Recordings via analog input still have 11!)

That's it!

Which DAT-decks can I modify?

Since this page exists I received a lot of email with questions like "Will this circuit also work with my <insert any available DAT deck here>?". Sorry, but in most cases I just don't know the answer to this question. Fortunately I received a few notes from people who have successfully modified other decks than the above mentioned ones.

So here is the updated list of DAT-decks, that were successfully modified todate:

The DTC-790 uses a CXD2605 instead of the CXD2601 (for which the circuit was designed). So maybe the circuit does also work on decks using the CXD2605. (More info on the modification of the DTC-790 can be found at http://www.xs4all.nl/~fjkraan.)

The circuit _should_ work (but that's not verified yet!) with the following decks:
It probably won't work with the
because the DTC-1000 doesn't have a CXD2601 in it. It contains a CXD1052 and this chip doesn't seem to be a pin compatible predecessor of the CXD2601.

If you have successfully modified a deck that's not listed yet, please let me know, so I can update this page. Also if you have any comments, suggestions, corrections or additional technical information (like the following one), feel free to email me.

How the circuit works:

The following explanation was sent to me by Michel de Man:

What the circuit does -I have it already about 4 years built in successfully- is the following (as far as I can remember after 4 years):

The main board has it's own internal data stream extracted from the (digital) input signal to be copied (DAT-tape, CD, analog A->D converter). This internal data stream has also it's own copy prohibit bit (yes, just one). The value of this bit is determined by the combination of the two SCMS copy bits on the (digital) input signal to be copied (DAT-tape, CD, analog A->D converter). Whenever this bit is set to 1, the recording is blocked. So what the circuit does is pulling down the copy bit to 0 each time, no matter if the bit was already 0 or not. This bit is the N-th (don't know which bit anymore) bit in the data stream for which the circuit uses the clock signal as trigger. The circuit counts until the N-th bit and pulls down the datastream for one bit cycle to 0. At that time I checked it with a ocsilloscope and indeed it does what it says.
The result also is that the recorded tape can be copied infinit.

Michel H.L. de Man
Alcatel Telecom Systems

Additional Info:
(Just in case this is of interest for someone :-)

EXCK = Subcode I/O data transfer clock
SBSY = Subcode I/O sync signal
SDSO = Subcode serial data output

Special thanks to:

Jonathan Corbet, Fred Jan Kraan, Michel H.L. de Man, Eberhard Mattes and everyone who sent corrections and additional information. Thanks.


The author of this page is not responsible for any damage you may cause to your equipment (or to yourself :-) by doing this modification. Proceed at your own risk!

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Last updated on March 16, 1998.

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