BFD & SVS Black Box - Connection order?

Discussion in 'Archived Threads 2001-2004' started by MarkFrab, May 10, 2002.

  1. MarkFrab

    MarkFrab Agent

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    My Pre/pro (Sunfire Theater Grand II) to Sampson S1000 connection required an SVS Black Box to get the signal level up for proper amplification.



    I just received a BFD which I am going to use to flatten some wicked room nodes.



    The BFD has a -10dBV/+4dBu source level switch, so it could be placed in two ways:
    1. TGII -> BFD -> BlackBox -> S1000
    2. TGII -> BlackBox -> BFD -> S1000
    Which setup would be better - and why? Does it even make a difference?



    My thinking is that option 1 (with BFD set to -10dBV) would give the BFD a known level and probably avoid any clipping in it's signal path, but I'm afraid that it might also raise the overall noise floor, as any noise would be amplified twice.



    On the other hand, sending the BFD a boosted signal might make achieving a flat in-room response easier because there is only a single amplification step after wards.



    Each piece of equipment except the Black Box can use balanced interconnects, so that is another issue that may affect how the setup should go.



    I just don't know - any opinions?
     
  2. Steven Hen

    Steven Hen Stunt Coordinator

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    Mark,

    I have no idea if one way is better than another, but I go..pre/pro > blackbox > BFD > S1000. With it set up this way, it makes it easy to set the input level for the bfd just by adjusting the blackbox. If theres a better way, I'd sure like to know.
     
  3. brucek

    brucek Second Unit

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    So what's a black box?

    brucek
     
  4. Steven Hen

    Steven Hen Stunt Coordinator

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  5. brucek

    brucek Second Unit

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    Oh, it's a line amp...

    OK, well then it would be best to place the line amp between the BFD and SVS power amp for several reasons. Feeding the line amp from the processor is a bad idea.

    Use the -10dBv switch setting on the BFD...

    The BFD is not an amplifier, it's a unity gain device. Since it's digital and you're feeding an ADC/DAC chain you want to optimize its input level to take advantage of all the bits available. By this I mean to take maximum advantage of the dynamic range provided by the analog to digital converter in the BFD or any ADC for that matter, you need to provide it with a maximum input signal level that takes advantage of the greatest number of bits to represent the resultant voltage samples.

    If the range from your weakest signal to the strongest signal was only half the required maximum input level, you would be robbing yourself of dynamic range and subsequently increasing your signal to noise level. To get the most out of this system you would like the maximum signal sent to the BFD to "just" not turn on the red LED. If the yellow LED comes on in explosions etc, that would be fine. The BFD has no compressor or limiter on its input, so you can easily overdrive it and clip the output.

    This means once you've reached and set this level, you can't increase the level any more even if you wanted to. So it's the output analog signal that you want to amplify, not the input signal which is easily set to optimum by your processor.

    The BFD's unity output (or less if filters are applied) can then be amplified to your hearts content with the line amp. If the line amp can create 18dB gain, then it will "all" be available to you, instead of being limited if you placed the line amp before the BFD.

    Certainly if you're able to, I would recommend the use of the balanced inputs to the BFD. The BFD has a tendancy to create some nasty ground loops when single ended connections are used, usually requiring the unadvisable use of a cheater.....

    brucek
     
  6. Richard_M

    Richard_M Second Unit

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    Bruek wrote

     
  7. Richard_M

    Richard_M Second Unit

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    My apologies BruceK on the misspelling of your name!!

    Richard
     
  8. brucek

    brucek Second Unit

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    Richard,
    Yeah, just use these type of converters:
    http://www.radioshack.com/product.as...uct_id=274-320
    It does put the system the same as using unbalanced as you said. Certainly lots, if not most people use the unbalanced route and everything is fine, but the BFD does seem to create more trouble with loops than most devices. I was just suggesting if you have balanced outputs on your processor you should take advantage of them.
    brucek
     
  9. Richard_M

    Richard_M Second Unit

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    Thanks for that Bruce,

    Currently I have 2X M&K subs which don't have an earth, But I have on order 1X HSU VTF-3 which does use an earth pin. I have used a sub previously with an earth and there was a slight hum (was quite loud until I put a line isolator on the TV circuit, and used 2X high filtered(& expensive) power boards one on the BFD and the other on the sub, these must have given abit of earth isolation not sure)

    Anyway I will get some of these adaptors and also I'm going to use RG6 quad shield coax as the feed circuit from the BFD to the subs. I was talking to the local distributor of HSU, and he informed me that alot of hum can be caused by the signal lead not being shielded.

    regards,

    Richard
     

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