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Thread: An oddball (maybe) cabling question...

  1. #1
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    An oddball (maybe) cabling question...

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    Thinking ahead to the cabling to interface my Ampex MM-1000 and my Soundtracs MX desk...and even further out to when the Ampex is setup for 2" 16-track operation.

    The snake from the Ampex to the mixer is a no brainer...I have a 16' 16-channel TRS-TRS snake I made some time ago...the TRS plugs at one end of the snake will be replaced with XLR plugs...Ampex XLR outputs 1~16 to mixer line inputs 17~32...done.

    My question is about the cabling to interface the mixer outs to the Ampex. I'm going to be using the Soundtracs' 8 group outputs, but I want each of those group outs to interface with two tape machine inputs (just like you'd do when using something like a Tascam M-300 series mixer to an 8-track...only think 8 groups to 16-tracks instead of 4 groups to 8-tracks).

    My crux...I want to just use an 8-channel snake and daisy-chain the connectors at the tape machine rather than use 16-channel snake cable...so what'll happen, for instance, is channel 1 of the snake will go from the mixer group 1 output to the tape machine input 1 and then in series to input 9 (so inside the plug connected to the tape machine input 1 jack will be two sets of 3-conductor cable...the cable coming from the mixer and the cable continuing on up to the plug for input jack 9.

    Does that make sense? Any negative issue in doing this?

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    Sounds like it would work fine. As long as you don't need to record like 1 and 9 at the same time. I don't believe the extra cabling will take away from the source.
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    So this like a Y-adapter? I'm not familiar with the switching mechanisms of the tape deck, but I'm guessing the input impedance/load remains the same for both tracks in all operational states, armed or disarmed, or re-routed, or whatever. Should be OK.

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    In any parallel split, the impedance will drop, just like speakers do. So this will mean a harder load for the mixer to drive.

    I'd use a patchbay instead and run a proper 16 channel snake to the deck. For switching connections this will be the easiest to work with. Keep in mind this will require more cabling and jacks but its balanced anyway so no biggie if you have the inventory.

    Cheers!

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    I'm thinking Ghost is spot on about impedance difference. Note the Fostex 80 is setup this way with the inputs to channels 1-4 normalled to 5-8 so you can use it with a 4 buss mixer and not repatch. I'd suggest taking a look at the schematic for that and see how they do it. I have a pdf of the sm, pm me and I can email it to you.

    I think you could accomplish this with some kind of buffer/splitter though if you wanted to go the extra work to avoid a patch bay.

    Take a look at the Jensen website, I'm assuming you could use some of the same mic splitter technology to make a buffered splitter. Craig Anderton's spluffer would likely work too: (This is in his classic Electronic Projects for Musicians)

    https://img530.imageshack.us/img530/...plufferji7.gif

    Note the IC in that circuit is unavailable, so you can't use his PCB, but there are numerous alternatives. generalguitargadgets has a pcb layout. I don't have EPFM in front of me now, but I think you eliminate the pots for a splitter.

    Obviously, you're adding an active or passive stage between the board and the deck by any of these methods, transformer or opamp.

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    So how does Teac/Tascam get away with doing this on so many of their mixers (albeit the split is at the mixer output with the parallel group out jack pairs)?

    Also, FYI, at this time it is unbalanced. The Soundtracs MX group outs are unbalanced XLR's as standard. There is a transformer output option which I may build up at some point, but it'll be unbalanced until that time.

    Ampex input impedance is 100kohm...Soundtracs output impedance is 50ohm so one split should be fine....shouldn't it? That would still be an impedance ratio of 1000:1 which is plenty AFAIK...

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    100k? Wow.

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    Quote Originally Posted by The Ghost of FM View Post
    In any parallel split, the impedance will drop, just like speakers do. So this will mean a harder load for the mixer to drive.---
    If one parallels speakers the resistance will drop not the impedance.

    So what Cory may experience here is an increase of resistance which increases the load which may decrease the volumes passed.

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    there should be no impedance issue doing this. But I suspect you will end up recording over a good take at some point.

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    Quote Originally Posted by FALKEN View Post
    there should be no impedance issue doing this.
    This is correct.

    Impedance is a factor of an AC current moving through a wire coil in a DC (magnetic) field.

    None here unless Cory's magnetic personality affects the issue.

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