SUB OUT VOLTAGE mismatch problems on Receivers

Discussion in 'Archived Threads 2001-2004' started by Mike Kao, May 15, 2002.

  1. Mike Kao

    Mike Kao Second Unit

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    I've heard of many people experience voltage mismatch problems when using pro amps to power their subs and connecting them to the sub out on their receiver. Unfortunately I've had the same bad experience with my previous receiver, the Harman Kardon AVR-510. B/C of the voltage mismatch, output drops significantly and requires the use of an external boost device. Using a buttkicker II and a crest pro amp, I connected the amp to my receiver's sub out only to first discover this problem... the problem precisely being that the sub signal drops. It required a sub setting of +10 (highest setting possible) and insane volume levels to get decent feedback from the buttkicker. I thought it may have been the amp, so I tried using two other brand amps (Samson and QSC), and experienced the same problems.

    Upon adding an SVS sub to my setup, I would encounter yet the same headache. I had previously used a Midiland sub in my setup that I ripped off my COMPUTER SPEAKERS (S2 4100), and quite honestly it outperforms the SVS, even when the SVS is driven at insane volume levels with the +10 sub setting! That gives you an idea of how bad this voltage mismatch problem is.

    Some have used the $50 Radio Shack SA-155 to boost the signal to the amp, but quite honestly it's quite a crude, cheaply constructly device that undoubtly degrades the signal. I've gone down the same route only to return the device a few days later.

    I've become and sick and tired of dealing with these problems so I finally decided to get a new receiver... one that doesn't exhibit these problems. As much as I LOVED the harman kardon (it really was a wonderful receiver), and in fact I even wanted to give the AVR-520 a try just in case it somehow miraculously doesn't have the problem, I really have to move on.

    So my question is, who here has experienced the same problem with their receiver? Please list the brand and model. Hopefully such a list may be useful for many others as well!
     
  2. Bruce N

    Bruce N Second Unit

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  3. Wayne A. Pflughaupt

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    Mike,

     
  4. Luke M

    Luke M Extra

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    This is a general issue with interfacing ANY consumer equipment with ANY pro equipment. You have to use a voltage level shifter (NOT AN AMPLIFIER! Sheesh whoever told you to use a RadioShack amp is an idiot) to convert up to pro levels.
     
  5. Wayne A. Pflughaupt

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    A “voltage level shifter?” What is that, and who makes them?

    Regards,

    Wayne A. Pflughaupt
     
  6. Luke M

    Luke M Extra

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    A level shifter, well, shifts levels. For example:
    http://www.swizzarmy.com/lls-2des.htm
    or
    http://www.rane.com/bb22.html
    No doubt there are others.
    These are passive transformer-based devices.
    When going from a higher to lower voltage (pro to consumer, not the case here) a simple attenuator can be used rather than a "fancy" level shifter.
    That's all I'm gonna write, if you want more, use the Force (er, Google).
     
  7. brucek

    brucek Second Unit

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    Luke,



     
  8. Cliff

    Cliff Stunt Coordinator

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    brucek,

    I have taken your suggestion about incorporating the X-30 into my setup, which also includes a receiver (Yamaha RX-V1), a parametric equalizer (Symetrix 551E), and a sub amp (Samson S-1000). I have a question about the sequence of connections between the receiver and the sub amp. Since both the equalizer and amp are pro gear, I would think that the most logical sequence is receiver -> X-30 -> equalizer -> amp. However, for logistical reasons, I have the connections going from receiver -> equalizer -> X-30 -> amp. Thus, the cabling switches back and forth between -10 dBV and +4 dBu a couple of times. Does this matter? Am I compromising performance, safety, or longevity of the equipment using the sequence of connections I have? I would appreciate your thoughts.

    Thanks,

    Cliff
     
  9. Bruce N

    Bruce N Second Unit

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    Here's what it says on that page:
    18dB of active gain allowing your surround receiver to drive virtually any consumer or pro-type high-power amplifier
    Isn't that what we're looking for here?
    Cliff,
    I have the same type of setup and I put the X-30 before the EQ.
    Pre/pro > X-30 > EQ > Amp.
    Bruce
     
  10. brucek

    brucek Second Unit

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    Cliff,

    I answered this question a few weeks ago (except the EQ was a BFD). I don't know the 551 to well, but I suspect the answer applies the same. Here's the advice I gave:

     
  11. Cliff

    Cliff Stunt Coordinator

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    Thanks, Bruce and brucek. The Symetrix 551E is an analog equalizer and therefore has no ADC/DAC processing. Neverthess, input level must be held within some optimal range, and thus the issues brucek described for the BFD are somewhat applicable to this device as well. But there does seem to be one difference: the 551E has a control for boosting or cutting input level up to 15 dB. In fact, the manual suggests using some boost when feeding a signal from a -10 dBV device (such as my receiver). I am actually doing this in the hookup I described above, where the receiver's sub output is fed directly into the equalizer.

    So, I assume that as long as the input level to the equalizer is appropriate, my setup is okay in which the equalizer's output is fed to the X-30, and the gain control on the X-30 is used to boost the signal to the amp. I guess my concern about the alternating sequence of the device types (-10 dBV, then +4 dBu, then -10 dBV, then +4 dBu) is not a problem.

    Thanks again.

    Cliff
     
  12. brucek

    brucek Second Unit

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    Cliff,

     

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