Behringer Xenyx Q802USB: impedance-balanced or unbalanced Main Out?

[Alan45]

I've just downloaded the Q802USB manual from the Behringer site. Page 7 says " The MAIN OUT connectors are UNbalanced mono jacks." On page 10, under "4. Specifications", it says "MAIN OUTPUTS 1/4 " TRS connector, BALANCED".

Is one of these statements wrong, or could this be an instance of impedance-balanced? For the trivial cost of a 120-ohm resistor, and use of a TRS jack socket in the mixer, this could be a useful feature - especially for me, as I have to drive a 100-foot cable. Has anyone checked out the Main Out jack on the Q802 with an ohm-meter? If it's truly not balanced, then I'll have to fudge a cable with resistor externally.

[tomas]

Alternatively, you improve your chances of obtaining balanced signals with a box that has XLR outputs. This one also has an internal power supply which is a great convenience: https://www.allen-heath.com/ahproducts/zedi-8/

[Hugh Robjohns]

Is one of these statements wrong, or could this be an instance of impedance-balanced?

Either or both. I'd be inclined to think the statement on page 7 is correct, and the specs are a cut'n'paste from something else.

For the trivial cost of a 120-ohm resistor, and use of a TRS jack socket in the mixer, this could be a useful feature...

Impedance balancing is a useful facility, but there is a bit more to it than just stuffing a 120 Ohm resistor on the cold leg!

If it's truly not balanced, then I'll have to fudge a cable with resistor externally.

You'd be much better off using a transformer in a line isolation box. At least you'll get true balancing with excellent CMRR across a wide bandwidth that way.

[Alan45]

Thanks for your responses.
I've looked at the Allen-Heath mixer, which looks neat. But I am budget conscious, otherwise I'd probably go for the Yamaha MG10XU.
The 'cold resistor' is a convenient way of creating a pseudo-balanced output. I appreciate it needs to be well-matched to the source output impedance, but why do you say there is more to it than that?
Looks like I'll have to borrow an 802 and run some tests myself, unless someone knows for sure how its Main Out jack is wired.

[Wonks]

I often find the specification values on Behringer spec sheets to be very misleading and at variance with the description. I really don’t know how they get away with it.

In this instance the quick start guide also says the main outs are on unbalanced mono jacks, so I’d also run with unbalanced.

You could make up pseudo-balanced cables if you run into ground loop issues over short distances, but with 100 foot runs I’d be looking for a mixer with balanced outputs.

[Hugh Robjohns]

The 'cold resistor' is a convenient way of creating a pseudo-balanced output. I appreciate it needs to be well-matched to the source output impedance, but why do you say there is more to it than that?

One of the main benefits of a balanced interface is that it provides rejection of external interference — which seems to be your requirement. However, effective rejection requires perfectly matched impedances to ground from the hot and cold legs, and at both ends, and across the entire bandwidth of interest. If that matching is off by a few Ohms the CMRR figure plummets.

Moreover, matching the impedance at DC doesn't guarantee a match in the MHz region where RF interference lurks...

Thats why there's more to it than just bunging in a 120R resistor.

If done correctly, the result is a truly balanced output — not pseudo-balanced. If not done correctly, the CMRR will be low and the interface will have little practical benefit over an unbalanced output in terms of interference rejection.

This impedance-balanced format is badly named because all balanced interfaces are impedance balanced by definition.

The practical difference is that the whole signal is carried on the hot line, instead of half the signal on each of the hot and cold lines (with a polarity inversion on the cold).

Impedance balanced outputs are useful if the destination could be balanced or unbalanced as the same signal level is received in both cases. It's also cheaper and simpler to implement, but few designs are well balanced across the entire spectrum.

Looks like I'll have to borrow an 802 and run some tests myself, unless someone knows for sure how its Main Out jack is wired.
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[Hugh Robjohns]

As if by magic... I have just been supplied with the complete circuit diagrams of the 802 mixer and from them I can confirm that the main outputs, fx sends, and control room outputs are all setup as impedance balanced outputs on TRS sockets.

Problem solved....

[tomas]

I've looked at the Allen-Heath mixer, which looks neat. But I am budget conscious

This is well understood, and it is precisely why I suggest the A&H mixer to be on your shortlist. Unlike the Behringer, this one is still in production. Unlike the Behringer, there is no external power supply that you may lose. Unlike the Behringer, it has balanced outputs without needing any transformer box or specially made cables.

Sometimes, the smarter budget choice is to pay a little bit more upfront to avoid hassles later on.

[Alan45]

As if by magic... I have just been supplied with the complete circuit diagrams of the 802 mixer and from them I can confirm that the main outputs, fx sends, and control room outputs are all setup as impedance balanced outputs on TRS sockets.

Problem solved....

Hi Hugh,
Is this for real? If so, it's good news for me, so thank you! I don't need perfect, but I want pretty good, without spending extra on a more expensive mixer, or adding a line isolator or DI box.
Is there any way I can get to see your circuit diagram? I understand you can't post attachments here.

[Hugh Robjohns]

Its not my intellectual property to share, but they appear to be genuine Behringer circuit diagrams and the outputs are configured exactly as I described.

[James Perrett]

There is an older 802 circuit diagram available online from

https://www.synthxl.com/behringer-kenyx-802/

but I can't find a diagram for the USB version. I understand that Behringer service agents have access to more documentation.

[Alan45]

A Google search has revealed schematics for the '802' (not Q802USB) with two different Main Out configurations: one with a TS jack (so grounded cold), and another with a 120-ohm resistor from ring to ground on a fully-wired TRS jack socket. So the situation for currently supplied Q802USB mixers is unclear.
There is an easy test for this, but would need a little assistance from someone with a recently purchased Q802USB (which wouldn't even need to be switched on for the test). It just needs a TRS jack to XLR cable (fully wired) plugged in to either L or R Main Out. Then it's a matter of measuring the resistance between pins 1 and 3 on the XLR with an ohm-meter. This will either be zero, or something close to 120 ohms.
Is there anyone there who could run this test, and report the result? I'm sure it would help others in the same situation. Grateful for any assistance on this, before I splash the cash.
Behringer documentation is lamentably bad for such respected products. It's crazy that we have to resort to this sort of subterfuge just to work out if their outputs are impedance-balanced or unbalanced!

[Wonks]

The 802 is not the Q802USB, and quite a few modifications would have been necessary to incorporate the USB functionality.

If Hugh says he has the circuit diagrams for the Q802USB and they show balanced outs on TRS jacks, why do you think the situation is unclear?

[Alan45]

Hugh refers to a circuit diagram for an '802'. I have found two sources of schematics, neither of which is the Q802USB. One is '802', the other is 'UB802'. Both show a resistor to ground.

However, the link below shows a schematic said to be 'marked up' for the Q802USB, which shows a hard connection to ground, and using a TS jack rather than TRS.

https://www.scribd.com/document/3846497 ... ck-Diagram

So a degree of uncertainty. Short of getting a clear answer from Behringer themselves, I think a test is the only certain answer.

[Wonks]

I’m pretty sure Hugh was referring to the Q802USB rather than an older version, but hopefully he can confirm.

[Wonks]

I’m sure that block diagram (which is nothing to do with Behringer) was drawn up by someone who posted on here looking for one but couldn’t find one.

I’d assume the general signal flow is correct, but I wouldn’t go by any of the hardware representations for the inputs and outputs.

[Alan45]

Agreed - a block diagram is not the whole story by a country mile. It will be interesting if Hugh comes back on this to confirm what he has received.

[Pippacairn]

Hi Alan,
I can confirm that Hugh has the non USB version of the schematic, rather than getting involved with the forum I sent it to him. I forgot that the 2 versions are different, apologies for the confusion.
I’ve had a couple of Xenyx USB mixers and can confirm that the “unbalanced” outputs are actually “impedance balanced”.
Hopefully someone can confirm this is the case with the Q802usb
John H

[Hugh Robjohns]

The schematics John sent me are marked 802, not 802USB... but I'd be amazed if Behringer changed the output circuitry after adding the USB functions.

[Alan45]

I now have what I think is a definitive answer!

I was able to borrow a 13-year old '802', and check the resistance between ring and sleeve on the Main Outs. Both very close to 120 ohms.

I have now purchased a Q802USB from Gear4music (good service, quick delivery!). This also checks out at 120 ohms ring to sleeve.

So, Behringer, you are underselling yourselves when you say "The MAIN OUT connectors are unbalanced mono jacks."

I can now drive 100+ feet from the side of the stage to the hall's main control desk with a lot more confidence.

A big thank you to all those who helped me along the way on this. Hopefully by reporting back my findings I may help someone else in the same position.

[Hugh Robjohns]