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Thread: Can I connect balanced output straight to Quad 405?

  1. #1
    Join Date: May 2020

    Location: NorthWest

    Posts: 42
    I'm Philip.

    Default Can I connect balanced output straight to Quad 405?

    Hi,

    I posted this question over on Pinkfish but it was a much longer post, possibly too long (I was just trying to add context) and no one has replied, so I’m trying the short version here. I’m new to hifi and do not yet understand the relationship between output voltages and input sensitivity. I’m rushing this a bit, trying to set something up for someone who’s health has taken a turn for the worse, and I don’t want to damage our speakers through my ignorance.

    So, short version; is it ok to take the x2 stereo xlr output from a 'Behringer Monitor2usb' which I assume is a balanced signal (I can’t find any more detail than that) straight in to a Quad 405 power amp (modded input sensitivity 1.5v) ?

    https://www.behringer.com/product.html?modelCode=P0BK8

    I feel like it would work but isn’t the best idea, and I’m not sure if it would be a case of “not enough to drive the amp” or “you’re going to blow your speakers”. I have a NAD1000 pre amp so I thought perhaps that could go in between. Then I would be concerned about having too many volume knobs, or is it just a case of balancing them?

    For what it's worth, these will be used by a responsible adult and never driven too hard.

    I appreciate any advice here…

    Thank you!
    Never underestimate the power of stupid people in large numbers...

  2. #2
    Join Date: Mar 2008

    Location: Galashiels

    Posts: 13,669
    I'm inthescottishmafia.

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    Yes it will be fine. I do the same, albeit the other way round- I run my Behringer bass amp from my passive pre, so feed into XLR from RCA.
    “Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”

    Hunter S Thompson

  3. #3
    Join Date: May 2020

    Location: NorthWest

    Posts: 42
    I'm Philip.

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    Thanks Ali!
    Never underestimate the power of stupid people in large numbers...

  4. #4
    Join Date: Sep 2013

    Location: North Island New Zealand

    Posts: 1,757
    I'm Chris.

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    If your Behringer has a balanced output it is comprised of a negative waveform called COLD, a positive waveform called HOT and ground. the three conductors are explained here:
    https://www.boxcast.com/blog/balance...the-difference You would need to arrange either the behringer to output unbalanced audio, or use a conversion
    of balanced to unbalanced - usually done with a transformer, but other methods are a operational amplifier explained here: https://www.jensen-transformers.com/...4/08/an003.pdf

    Your Quad 405 is designed for unbalanced audio - not balanced as such. You are better designing your attenuation as unbalanced, rather than dwelling between the two
    Opto coupling offers great advantage over balanced in terms of noise immunity explained here: https://lunainc.com/product/optocouplers/

  5. #5
    Join Date: May 2008

    Location: Surrey

    Posts: 7,103
    I'm Rob.

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    I have used balanced to unbalanced op-amp based converters, transformer based converters and by joining 2 of the internal connections of the XLR plug.

    Wiring diagrams here https://www.ranecommercial.com/kb_ar...p?article=2107
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  6. #6
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,853
    I'm openingabottleofwine.

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    Quote Originally Posted by Puffin View Post
    I have used balanced to unbalanced op-amp based converters, transformer based converters and by joining 2 of the internal connections of the XLR plug.

    Wiring diagrams here https://www.ranecommercial.com/kb_ar...p?article=2107
    The Quad 405 uses an unbalanced input, so the best way of connecting it to a source with a balanced output is to use the wiring arrangement Fig 4 in the above-mentioned link. This is the best and safest way to do it. You will suffer a 6dB loss, which given the high sensitivity of the Quad 405 (500mV) will not be a problem

    You can buy off-the-shelf XLR balanced to un-balanced RCA interconnects, but be aware in these the pins 1 and 3 of the XLR connector are connected together, thereby shorting out the 'COLD' connection. Depending on the actual item used having a balanced output, this may not matter, but it could cause damage to some items. I would strongly recommend you follow the advice discussed in the link above.
    Barry

  7. #7
    Join Date: Mar 2017

    Location: Seaford UK

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    I'm Dennis.

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    I think figure 2 is best.

  8. #8
    Join Date: Jan 2009

    Location: Essex

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    Quote Originally Posted by Pharos View Post
    I think figure 2 is best.
    The Quad 405 does not use a stereo (BTR) 1/4" jack socket, so Fig 2 is inappropriate. Figure 4 is the one to follow.
    Barry

  9. #9
    Join Date: Mar 2008

    Location: Galashiels

    Posts: 13,669
    I'm inthescottishmafia.

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    I use these to connect my Behringer to passive pre. Works fine. Did the same with my miniDSP which again worked fine.

    https://www.ebay.co.uk/itm/Neo-Oyaid...gAAOSwwgVeOEGr
    “Music has always been a matter of energy to me, a question of fuel. Sentimental people call it inspiration, but what they really mean is fuel. I have always needed fuel. I am a serious consumer. On some nights I still believe that a car with the gas needle on empty can run about fifty more miles if you have the right music very loud on the radio”

    Hunter S Thompson

  10. #10
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,861
    I'm Dennis.

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    Quote Originally Posted by Barry View Post
    The Quad 405 does not use a stereo (BTR) 1/4" jack socket, so Fig 2 is inappropriate. Figure 4 is the one to follow.
    I cant really see what difference the plugs and sockets make, it is the cct configuration which matters.

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