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Adapt XLR-F for Balanced to Unbalanced connection help - pins 1+3?

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Adapt XLR-F for Balanced to Unbalanced connection help - pins 1+3?

Postby Bexhill College Library » Wed Apr 01, 2020 2:20 pm

Hi,

I have a ZED R16 with unbalanced (0dBu) inserts. Via a patchbay, I am connecting a Drawmer 1973 hardware comp (Balanced XLR outs). With the particular topology of this compressor, when I connect the Balanced output to the patchbay/unbalanced insert, I loose 6dB of output from the compressor.

Drawmer support say that I should adapt the XLR cable at the output hardware output. I should 'connect PIN 3 and PIN1 ogether' and that this will return my 6dB of gain.

I've tried adapting the cable in 2 separate ways but with both, I'm still losing the 6dB of gain.

method 1: I made two 'legs' out of the copper ground wire and soldered one leg to PIN 3 and the other leg to PIN 1. This didn't bring back the 6dB.

method 2: I solder the XLR as normal, then took some extra copper wire and soldered a bridge between the cold and the ground wire thus 'connecting' them. This didn't bring back the 6dB either.

So my question: how exactly should I adapt the cable. Should I leave PIN 3 disconnected etc?

any help would be great.

Thanks
Bexhill College Library
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Re: Adapt XLR-F for Balanced to Unbalanced connection help - pins 1+3?

Postby Hugh Robjohns » Wed Apr 01, 2020 4:28 pm

Bexhill College Library wrote:...when I connect the Balanced output to the patchbay/unbalanced insert, I loose 6dB of output from the compressor.

Quite a common occurrence as a symmetrical balanced output places half the signal on each side of the balanced connection. When wiring to an unbalanced destination the cold side of the connection is either shorted to ground of left isolated, both options leaving only half the signal on the hot side*, and hence a 6dB reduction in signal level.

However, this is usually not a problem since unbalanced inserts often operate at a reduced operating level of -2dBu rather than the nominal line level of +4dBu anyway.

Drawmer support say that I should adapt the XLR cable at the output hardware output. I should 'connect PIN 3 and PIN1 together' and that this will return my 6dB of gain.

The manual for the 1973 is contradictory as in one image it shows the cold side (pin 3) being grounded to pin 1, and in another it says pin 3 should be left floating (isolated) when feeding an unbalanced destination.

*There are some active symmetrical balanced output configurations (cross-coupled types) where, if one leg is grounded the stage gain for the other leg increases automatically to provide the whole signal on the remaining output connection

This is effectively also the case for true transformer-coupled outputs.

And the 'impedance-balanced' output also puts all the signal on the hot side only to ensure a consistent signal level with both balanced and unbalanced destiantions.

I've tried adapting the cable in 2 separate ways but with both, I'm still losing the 6dB of gain.

I suspect the 1973 doesn't have cross-coupled active outputs nor transformer outputs, so it doesn't matter whether you leave pin 3 floating or grounded, you will only get half the signbal at an unbalanced destination!

If you can't live with the 6dB signal loss then the best solution would be to use a transformer line box to balance the insert points instead... but that will cost you around £50 per insert point, so not soemthing to be entered into lightly!
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