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Thread: FB3 - single or differential signal output?

  1. #1
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    Default FB3 - single or differential signal output?

    Question from those of you using the FB3 and conventional (differential signal input) scanner amps -

    Are you getting decent results using just the single-end connection from the FB3 and amps, or have you been converting the signal to a differential signal before going to the amps? I'm about ready to wire up my scanners from my "temporary" home while I'm on the road, and I don't want to worry with building any signal conversion circuits if they're not necessarily needed.

    I'm using an "older" FB3 with the SmartMedia card, and connecting to a set of ScanPro 30 scanners.

    Thanks in advance!

    RR
    RR

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  2. #2
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    I am using it as is. I too have the old style with the large smart media card.

  3. #3
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    im not up on differential signal input, could someone explain?
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  4. #4
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    Cool

    Differential signaling uses X+, X- and gnd. Single-ended signaling uses just X+ and gnd.


    Differential is preferred, because of the noise-canceling effect.

    Adam

  5. #5
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    ah i see .
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  6. #6
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    We have the older version of FB3, and have added differential buffers to them..
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  7. #7
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    does it really make that bigger difference?
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  8. #8
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    Hi all,

    This topic can be really confusing and, the fact of the mater is that most people don't understand it. Let me see if I can provide a few clarifying points.

    Differential is where there are two signals used -- DECODED BY THE RECEIVER in such a way so that noise picked up along long wires can be SUBTRACTED AND REMOVED BY THE RECEIVER.

    This is different from so-called "single ended", because, although single ended uses two wires to communicate information (a "signal" wire and a "ground" wire), the RECEIVER does not decode or SUBTRACT the two signals and thus, noise picked up along long wires can not be removed automatically.

    Now, there are a few very fundamental things to keep in mind here. First, the sensation of "single ended" or "differential" is purely ON THE RECEIVER, and has, essentially, nothing to do with the transmitter. It is the receiver (i.e. the scanner amps) that have the onus of "removing noise picked up along long signal wires".

    OK, lets look at another point here. Differential is really helpful when you have long signal wires (i.e. like hundreds of feet). Differential does not buy you much if your signal wires are 5 inches, and all inside the projector.

    Nevertheless, there are a few important points here. First, you would always want to use the + and - inputs on a scanner amp, and never use the ground (see another post). You do this regardless of whether or not your transmission system (in this case, some models of the FB3) is providing a true-differential signal or not. If it is not, you still get the full benefit of differential reception. Remember "THE ONUS OF DIFFERENTIAL SIGNALS IS ON THE RECEIVER, NOT THE TRANSMITTER".

    So, in a nutshell, differential or single-ended outputs from the FB3 or any other controller won matter for you guys. Trust me, it just won't -- as long as you always use the + and - inputs from your scanner amp, you are already benefitting.

    Now, one thing that you MIGHT benefit from is "twice the signal". If your scanner amp expects +10V and -10V to give you a full sized image, then this can't be had from the FB3 without our little (free) differential add-on. BUT!!! from what I have seen from these Chinese scanners that people send me to tune with the FB3, I can say a few things. First, these scanners really can't go very wide without either burning up, or being highly distorted. And second, the amps supplied with Chinese scanners don't seem to require -10V to +10V anyway.

    So -- bottom line -- this is a long discussion for absolutely no end-benefit. Scanner amps already give you the full benefit of differential signals (as long as you actually use the + and - inputs). And if you are using Chinese scanners with your FB3, then you probably can't use a larger signal and wider scan angle anyway.

    Best regards,

    William Benner

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