Using a 25-2's DBX as external decoder?

Discussion in 'TASCAM Analog Forum' started by DEDKOwh, Nov 6, 2019 at 8:51 PM.

  1. DEDKOwh

    DEDKOwh New Member

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    I'm digitizing a bunch of 70's submasters.

    Some of them were mastered with DBX on a 25-2.

    The 25-2's pretty rough on these old tapes, so I'm using a BR-20T for transport.

    I don't have a manual for the 25-2. Is there a way to route the signal from the BR-20 through the 25's DBX decoder?
  2. SkywaveTDR

    SkywaveTDR Active Member

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    It is much easier to just get an unlocked DX-2D or DX-4D and go from there.
  3. DEDKOwh

    DEDKOwh New Member

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    Bummer - so it isn't just plug-n-play.

    I *do* have a DX-8. I reckon I could just use 2 channels from that guy, huh?
  4. SkywaveTDR

    SkywaveTDR Active Member

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    People think all this stuff is so easy- it is not. Some older unit were play OR record not both and so in the RX9, DX4, DX44 and DX-8 they all require signals from the switching portion of the deck to control these functions. Then I am not sure what levels they specify as for input and output. The service manual for the unit would say but with the known history of the DX series other than the DX-4D or 2D these are notorious for relay related failures causing channels to cut out and sometimes change levels. It is those relays that were a real design problem. If someone would figure out a DIP relay retro fit then this would be the way to fix the cards but the dBx cards themselves had a good amount of failures from cracks and bad Tantalum caps which we replaced with new Electrolytics. Even in decks as new as the X2000R C363 a Tantalum cap still is found shorted on some units and so is common to be replaced with a cap that is an electrolytic.
    Yes you might be able to use the DX-8 but it might also be a lot of trouble to do so. The levels have to match when you use such a unit as dBx is level sensitive which is exactly how they work.
  5. SkywaveTDR

    SkywaveTDR Active Member

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    Most facilities that have good equipment will have a dBx unit in a rack so they can patch it in if needed. The DX-4D is a unit like that which could be patched into a rack. The DX-4D is a fixed level processor while the actual dBx units that have level adjustments on them are better for those jobs where the signal level is not referenced to -10dBV. The DX-4D as well as 2D need a FV signal system bypassed or modified. DBx required Tascam put a system in the decks to allow ONLY Tascam unist to be used with their dBx units. They did not want a DX-4D being used with a Studer , Fostex, Otari or other brand as it then affected their sales. It did not take long for those enterprising Technicians to figure out the FV signal was a 1Hz TTL square wave that could be generated by any NE555 IC but that why go to all this trouble when the detection circuit could be cut out or bypassed.
  6. DEDKOwh

    DEDKOwh New Member

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    I've a stack of precious DBX-encoded 1/4" masters which I need to decode.

    I appreciate the detection circuitry explanation. And the susceptibility to failure of the relays. Either may explain why a casual attempt to route 2 channels of audio through the DX-8 didn't appear to have any effect.

    If this were easy, I wouldn't be asking for advice in a specialists forum!

    Is anyone aware of legit software decoding of DBX1? I understand that there are licensing concerns, but surely some pro DAW has sorted this out. I haven't run across the right solution, though.

    Here's a guy who did figure out DBX decoding, but - due to licensing - is unable to share the actual code: https://www.bobweitz.com/dbx_webpage/dbx.html