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Behringer XENYX 1222FX Mixer output wirings.

Discussion in 'Recording' started by dgian, Oct 15, 2008.

  1. dgian

    dgian Guest

    I'm using a Behringer Mixer Xenyx 1222FX. I have to connect the Main Outputs of the mixer to the unbalanced line-in of a Dolby stereo amplifier which uses 2 RCA connectors. In order to make the correct wirings (balanced XLR -> unbalanced RCA), I have to know if the output stage of the mixer uses:
    transformers,
    active balanced output stages based on low-output-impedance amplifiers or
    floating cross-coupled output stages.

    Can anyone help me????

    Thanks
     
  2. Boswell

    Boswell Moderator Distinguished Member

    They are electronic balanced, i.e. two separate op amp outputs carrying the phase and antiphase signals, so it would be OK to take just one output as an unbalanced signal.

    However, I wouldn't bother wiring up an XLR cable specially. The RCA tape outputs carry the same signal, so just use those. Beware that the +22dBu FS level could well be too hot for your stereo amp and you may have to attenuate it.
     
  3. dgian

    dgian Guest

    Thanks!!!
    I'd prefere to connect the Main Out's (and not the Tape out's) to be able to use the Graphic Equalizer of the mixer.
    The RCA inputs of my Amplifier are specified as 50 KΩ 130mV ... 6.3V at Dolby level (85 dBC in the auditorium).
    As the output stage of the Xenyx Mixer is not a transformer nor a cross-coupled stage, I have to use the configuration "4b" in the attached Rane Corporation's Note, is it ok?? Wirings.jpg http://www.4shared.com/file/67256308/feecf2b0/Wirings.html
    This configuration causes a loss of 4 dB.
    Can I connect the mixer to the amp directly or have I to use a pad atenuator??
    :D
     
  4. Boswell

    Boswell Moderator Distinguished Member

    The 130mV to 6.3V spec on your amplifier corresponds to -18dBV to +16dBV (about -16dBu to +18dBu), so you would need to attenuate the mixer's +28dBu output, even allowing for the 6dB loss when using the output unbalanced.

    I suggest you wire a pair of 4K7 resistors in series across pins 2 and 1 of each of the mixer XLR main L-R outputs and take the resistor junctions to the L and R inputs respectively of your amplifier. XLR pin 1 goes to RCA ground, via the cable shield. With a little care, you can fit the resistors inside the XLR connector.
     
  5. GeckoMusic

    GeckoMusic Guest

    Boswell,

    Can you walk me through your calculations? I'm not sure what "50 KΩ 130mV ... 6.3V at Dolby level" is. If 6.3 is the max Vpp then:

    22 dBu = 27.6 Vpp

    6.3 / 27.6 = 23%

    R / (R + 50k) = 23%

    R = 15k

    Or you could just keep the volume knob low.
     
  6. dgian

    dgian Guest

    My ampli system is composed by a Dolby CP500 SR/D Cinema Processor + 2 Crown CE1000 + 1 Crown CE2000.
    The Non-sync 1 stereo RCA input of the Dolby Processor is specified as:
    50KOhm input impedance
    "Non-sync 1 will accomodate input Dolby levels between approximately 0.18 and 6.3 volts. Dolby level represents about 85 dBC in the auditorium"

    I'll try the connection by the resistive attenuator as soon as possible!!!
    15K + 50K or 2x 4K7?

    Regards
     
  7. Boswell

    Boswell Moderator Distinguished Member

    First of all, let's deal with the 50KΩ figure. If the output impedance of whatever resistive divider you use is less than on-tenth of this figure, you can ignore it, as it will have negligible effect on the attenuation. Since we are talking somewhere around 2-3KΩ Zout, ignore the 50KΩ.

    Next, it's not clear whether the 130mV ... 6.3V spec is nominal or peak. Since it's such a wide range of adjustment, we can afford to take it as the maximum r.m.s. value rather than risk overload by assuming nominal value with a peak of 20dB above this. So 6.3V r.m.s. = +16dBV (about +18dBu).

    Note we are dealing with r.m.s. levels here, which is where the confusion over peak or peak-peak values may have come in.

    The FS balanced level from your mixer is +28dBu, so an unbalanced connection from that output would be +22dBu. That gives a minimum value of 4dB needed from the attenuator (22dBu down to 18dBu). It's easier on the brain cells to use equal value resistors in a simple voltage-divider configuration, hence my original recommendation of a pair of 4K7 resistors to give an attenuation of 6dB. Note that the output impedance is about 2.4K, justifying neglecting the 50K input impedance of the amplifier.
     
  8. dgian

    dgian Guest

    Thanks a lot!!!!!

    By the way, I'm searching for some info (possibly a schematics - but I think it's quite impossible) of my Dolby CP500 SR/D processor, in order to know if its input sensitivity (130mV ... 6.3V ) is a nominal or peak value.

    Regards :p
     
  9. Boswell

    Boswell Moderator Distinguished Member

    A few milliseconds of searching turned this up:

    http://www.csst.net/manuals/cp500.pdf

    I'm not sure where you got the 130mV - 6.3V spec for the input sensitivity, as that sheet gives 50mV - 2.5V. These figures will be nominal values.

    If this information is correct for your amplifier, you will need to increase the attenuation, as 2.5V equates to +8dBV (approx+10dBu). That means you need at least 12dB. Use a 1K resistor to ground across the amplifier input and 3K in series with the mixer output.
     
  10. dgian

    dgian Guest

    The CP500 has 2 Non-Sync input:
    Non-sync 1 will accomodate input Dolby levels between approximately 0.13 and 6.3 volts.
    Non-sync 2 will accomodate input Dolby levels between approximately 0.5 and 2.5 volts.
    Dolby level represents about 85 dBC in the auditorium.

    I've chosen Non-Sync 1 which has the wider input range!

    :D
     

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