Combining 2 XLR outputs of preamp to 1 xlr

[John Suitcase]

Someone with more knowledge than me can probably give you a better answer, but generally, when combining signals, you want some resistors. You're making a little summing buss, and you want something to keep the preamps from 'seeing' each other, and causing impedance issues. I'd probably try a 5k resistor on each leg, and see how that sounds.

I'm no EE, though, hopefully someone can do the math to get you the right values!

[Matt Syson]

Hi
5K resistors would be fine but since the units you refer to are capable of providing signal into 600 Ohms happily, I would probably use more like 1K or 2K on each conductor (total of 4 resistors). You don't have to provide a 'load' as often used in a 'mix' sense as you will not get 'crosstalk'. Basically you will 'lose' around 6dB from each unit, which you then recover by turning up the gain of the following gear, or drive the preamps a touch harder.
The resistors mentioned prevent the output of one unit from attempting to 'force' signal current up the other unit's output.
Matt S

[wave rider]

Awesome! Thanks for the replies guys. I actually just tried this with 10k resistors as they were all I had and it sounded just fine to me. Does using 10k just mean that the signal is attenuated more then if I used, say, 1k?

[John Suitcase]

Yeah, it'll reduce the level a bit more. You can run resistors in parallel to divide the resistance, if you have a bunch of 10k's sitting around. So, two 10k's running in parallel is 5k. But if it sounds fine, go with it. Someone else might be able to give more info, it seems to me that you might lose some frequency response if the resistor value gets too high, but don't quote me on that...

[Matt Syson]

Hi
If you are running into a 10K INPUT then you will 'lose' a couple more dB when using 10K resistors as opposed to 1 or 2 K. The drop in HF resonse may be noticeable if the cable with the COMBINED signal is long.
Matt S