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Mono Summing -- XLR cable or TRS adaptor?
Old 9th May 2015
Here for the gear

Mono Summing -- XLR cable or TRS adaptor?


Was wondering if anyone could explain to me why the mono summed signal coming out of my Radial USB Pro Direct Box (using only one of the two outputs) is louder when I use an balanced XLR cable versus an unbalanced 1/4 TS instrument cable (with an female 1/4 TRS to female XLR adapter attached to the Radial USB Pro and then to the 1/4 TS cable).

I guess I'm wondering if it's the cable or the adapter or both?

Is the unbalanced instrument cable not able to carry the whole summed mono signal? Or does the TRS adapter split the signal so the TS cable only gets (half) the signal?

This isn't a problem per se, I'm just going to use the XLR cable to play live as I like the louder signal and it doesn't seem to effect the overall sound quality if I use either cable. Just kind of curious as to why this is happening.

Old 9th May 2015
Lives for gear
Xander's Avatar
To put it crudely:

A balanced connection has three conductors: hot, cold, and ground. Most device outputs send the signal on hot, and the inverted signal on cold.

The input for a balanced connection has a differential amplifier that adds the difference of the hot and cold, giving you your signal and eliminating any noise picked up along the way.

If you only connect a hot and ground, as in an unblanced signal being plugged into your balanced input, you are essentially losing half your signal, which just makes it quieter.
Old 14th May 2015
Here for the gear


That's what I thought. Would a TRS stereo cable connected to a universal plug (ie QSC k10 ) yield the same signal ouput as the balance xlr? Like the below signal flow?

(This is hypothetical just trying to understand)

Laptop >>USB Direct box >> female xlr/female trs adaptor >> TRS stereo cable >> QSC K10 (universal input)

Here is the input impedance for the K10 :
XLR / ¼": 40 kΩ balanced / 20 kΩ unbalanced
XLR / ¼" MIC mode: 2260Ω balanced
RCA: 10 kΩ

Thanks again,
Old 24th May 2015
Lives for gear
Xander's Avatar
The specs that you quoted indicate that the 1/4" input is unbalanced. If you plug in a balanced TRS signal, the "R" (ring) actually just gets shorted to ground. So you won't gain anything. You will want to convert that TRS to XLR and go XLR input on the speaker. Make sure the mic/line switch is set to line if you are going in channel A. Channel B is line only, so you don't have to worry about it there.

With all that being said.... I just noticed you indicated the source was a USB Direct Box. Can you provide more info? A Direct Box is most often a device used to convert a 1/4" unbalanced instrument or line level signal to a balanced mic level XLR signal. Not usually associated with USB. Do you mean a USB audio interface?
Old 24th May 2015
Here for the gear

Its a new interface/direct box put out by Radial. A little more suited to live use, although not if you want multiple outputs. Sounds great, built like a tank etc etc ...
Old 24th May 2015
Lives for gear
Xander's Avatar
Oh cool, haven't seen that product yet. It's confusing that they call it a direct box. It's more so just a USB D/A converter.

It looks like the XLR outputs are balanced and adjustable level, so you can connect them to a mic or line input.
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