Connecting a Pro amp. to LFE (consumer).

Discussion in 'Archived Threads 2001-2004' started by Mats Kellberg, Oct 11, 2001.

  1. Mats Kellberg

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    Hi!
    Anyone tried connecting a Pro level amp. to their LFE output to power a subwoofer ?
    I tried it and hardly any sound came out of the sub, after searching the net for a while it seems the signal levels are not compatible (consumer -10 dB, pro +4 dB).
    Would this be possible to solve by adding a pre amp between LFE-out and the Pro amp. ?
    If so, how much amplification do I need ? (I figure something like 4 or 5 times would be sufficient, but I'm in no way convinced this is correct)
    To me it seems the simplest solution would be adding a OP-amp circuit, which amplifies the signal 2-10 times (adjustable), has anyone tried this - did it work ?
    Or maybe I'm missing something big in this picture, so please help me out.
    /Mats Kellberg
     
  2. Brandon B

    Brandon B Second Unit

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    This is what everyone with a SVS CS sub and a Samson amp is doing.
    It should work OK. What kind of pro amp are you using? Possible problems I can think of:
    Gain is turned way down on your amp (i know it's obvious, just checking).
    Your amp has an internal input level switch (the Crowns I am using for this purpose do) that is set for too high an incoming voltage level.
    Your LFE out level is set too low with reference to the rest of your system.
    Your pro amp has a low frequency rolloff that is set to high (Mackie's and some others have this). Might be rolling everything under 40 or so off.
    BB
     
  3. Mats Kellberg

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    Thanx for the reply.
    The amp I'm using is a LAB1000B , which none of you have probably heard of it's swedish built with a rather good renommée. According to the manufacturer it has a frequency response of 10Hz-50kHz. I've tried adjusting the gain, but it sounds like the input level is way too low, but there is unfortunately no input level switch (the 1000B is an older model, twice as big as the amp in the link and without a fan). The LFE output is from a Yamaha DSP-A5, at the moment (if I remember correctly) it is set to +3dB (or maybe +4dB).
    Those who use the Samson - is it just to plug it in or do you use a signal level booster of some kind ?
    How do you convert from unbalanced (LFE) to balanced, or does the Samson have unbalanced inputs aswell ?
    I tried to use a cheat, which does not hum, and with the signalgeneratot I could get a strong enough signal to drive the amp and thus the sub.
    Oh, and by the way - I'm thinking of placing the IB in a compartment that might not be absolutely airtight (a large "cupboard"-like space in a room adjoining the listening room), will this be a huge problem ?
    Thanx again
    /Mats Kellberg
    ------------------
    Mats Kellberg
    Subsonic - can't beat the feeling!
    [Edited last by Mats Kellberg on October 12, 2001 at 01:01 AM]
     
  4. Vince Bray

    Vince Bray Stunt Coordinator

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    The specs in the link show input sens of .775 OR 1.7v. Are you sure there is not a switch for this selection on the back? If not, there is likely a jumper inside to make the switch. It sounds like it's on the 1.7v setting. My older Crest amp has a jumper for bridge that's inside, where the new ones have this feature as a switch on back. Crack it open and look on the preamp part of the circuit board for this switch, or give the manufacturer a call and they can surely help answer it.
    There's a huge difference between .775 and 1.7v!!
    Vince
     
  5. ChristopherJ

    ChristopherJ Extra

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    I have the same issue as Mats Kellberg described. I built a sonosub and am using the Samson S700 amp. The sound level is pretty week and I believe that if I could increase the volume to my subwoofer it would make the difference.
    So, "Would this be possible to solve by adding a pre amp between LFE-out and the Pro amp. ?" or "adding a OP-amp circuit, which amplifies the signal 2-10 times".
    What equipment would I need and do you know of a specific brand and model so I can look it up to start comparing?
    Sorry for stealing your thread Mats but it was exactly my question as well!!!
     
  6. Brandon B

    Brandon B Second Unit

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    Mats & Chris -
    I still think we're missing something. The LFE output from a pre/receiver really ought to be plenty to drive a pro amp to full gain if everything is set and calibrated right.
    Other thoughts. How are the voice coils on your subs wired? Series or parallel, and what is the impedance either way? And is your amp stable down to that level. Some pro amps cannot handle 2 ohm loads. Also, are you running your amp in stereo, or bridged or parallel mono? This can also affect whether the amp will drive the load properly.
    BB
     
  7. Mats Kellberg

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    Vince; You've probably got a point there, the amp I'm using is an older model without a switch, but I'll have a look inside and see if I can find anything that looks promising.
    The reason I have an older model is becuase it was a lot cheaper (second hand), it also lacked cooling fans which I believe is an added bonus (and of course its' size adding inches to my potency [​IMG] )
    Christopher; No problemo, your problem is my problem is everybody's problem [​IMG]
    I've spoken to a few people who all agree it should not be a problem connecting an OP-amp circuit between the units, if you do - please keep me updated.
    Brandon; I can (naturally [​IMG]) only speak for myself, personally I'm using two 8 Ohm drivers (single voice coil), one per channel. The amp (old as it is) cannot be bridged or "mono:ed", so I've split the outgoing LFE (could this be a problem ? - I reckon the voltage should stay the same, as long as the current doesn't increase too much).
    This weekend I went to a Sound & Light Pro exhibition, where incidentally the manufacturer (LAB Gruppen) had some stuff on display. I spoke to one of their engineers, who had a configuration similar to mine, he gave me a few tips which I will try out as soon as I have the time.
    (You know, the kind of stuff I already should have checked and I think I have, but just to be on the safe side...)
    /Mats
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    Mats Kellberg
    Subsonic - can't beat the feeling!
    [Edited last by Mats Kellberg on October 15, 2001 at 06:28 AM]
     

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