Two outputs into one input

[soundguymark]

Hiya Guys

 

Done a quick search but found nothing useful.

 

Just as a point of interest I was wondering how you can route two inputs into one input, for example using two mixing desks and wanting both L+R outputs to go into the same EQ, I have been told that a parrallel of the two outputs would work but is not advised as it can damage the outputs of the desks, is there some form of simple circuit to do this?

 

I know in an ideal world you would never have to do this but if im ever faced with cascading two desks but needing all the inputs I want to know if there is a solution, also if all the auxes and masters had to be routed through the desk channels there is a lot of channels being used up.

 

Hope this all makes sense

 

Thanks for any help guys

 

Mark

[Pete]

Route it through a mix wizard (or similar)?

[london sound]

Reading your profile I would have thought that this was known to you.

 

 

However with most pro desks you can sum buses between desks and some cases even bus up PFL etc.

Simplest method run two desks into third.

 

Ian

[Jivemaster]

This is the use for the small mixer you started in business with. the one that wasnt big enough as business progressed.

[Lamplighter]

Or feed each source through a resistor, commoned at the input. For most unbalanced outputs 4k7 ohms would be a good starting point. If the outputs are balanced then 2k2 in each leg. In both cases this will stop any output from seeing the low impedance of other outputs. Increase the input gain to makeup for the mixing loss.

To make a real job of it mount in a diecast box.

Brian

[soundo26]

hi;

Some desks have an input marked 2 track this input usually accepts a line input and is controlled by a single pot and goes straight to the output buss of the mixer without going through the desks own EQ stage, this will allow you to feed the output from one desk into that input allowing the output from both desks to go the next common input (probably a graphic EQ). Alternatively you could use the tape input. Generally I believe that there is no great harm in commoning two outputs into one input as this has been done for years on various bits of kit certainly for commonising the two channels of a stereo pre-amp to mono, this is in effect commonising two amplifier into one, (but if you are worried you might be able to use diodes to provide a non-return type of thing but I'm not into electronics so I'm not sure of that) This may only be done if both mixers are using the same mains supply.

I can't really see why you would want to commonise these outputs because if you are using two dissimilar desks each would have it's own sound qualities which could be dissimilar.

If all else fails there certainly is nothing wrong with feeding the output of the first desk into any available line inputs of the second desk (not the XLR Mic inputs as they may have phantom power on them), just keep the input gain at unity and the channel EQ flat.

Hope this helps!

[bruce]

(but if you are worried you might be able to use diodes to provide a non-return type of thing but I'm not into electronics so I'm not sure of that)

 

Diodes??

 

No.

 

Brian (Lamplighter)'s suggestion of a couple of resistors was correct.

 

Bruce.

[soundo26]

I stand corrected but did say I wasn't an electronics expert!!

[jayselway]

Maybe an "el cheapo" 1U Line mixer might be of use. (Gently) Shove it in the rack, both desks into it, output into the EQ, and who knows, it might come in handy for other jobs when you're not using two desks!

 

Or the resistor idea would work, and is cheaper! I agree though, make it nice in a die cast box :blink:!

[Bobbsy]

A small four or six input mixer can be extremely useful.

 

From the TV and Film work I used to do, for ages I had a nice AD260 four input field mixer...excellent spec but just four inputs to a single stereo output (plus a headphone out). Over the years I used it for all sorts of applications like the one the OP mentioned and lots of others such as a single channel headphone amp or a simple monitor mixer for a musical director wearing cans (band in one channel, vocals in another, his own keyboard in the third and talkback in the fourth, with him playing with his own balance...).

 

Not doing film stuff any more, I did the sensible thing and sold my field kit last year...and have been regretting it since!

 

Bob

[RustyBrooks]

The words audio and combiners entererd into google produced this

 

http://www.tkk.fi/Misc/Electronics/circuits/linesum.html

 

Looks like it works, have used similar ready made boxes in the past that cost lots, if your handy with an iron, should be very usable

 

Please spot the 10k resistors, which match the impedences of pro audio equipment, unlike 2k2 which is only really only of use for domestic

[Soundie]

So to combine two balanced sources into one would you need a 10K resistor on both the hot and cold legs of each input?

[maeterlinck]

Just buy a line converter or mini-mixer. We got one here that takes two balanced inputs and outputs one. Levels are based on the values of some pots on the front. Works well, off the shelf, won't break anything. Can't remember who makes ours but I'll have a look Monday if you want.

[Ben Langfeld]

Behringer to the rescue! :) But seriously...very versatile tool. A drama group I work with has one in the top of the radio rack which we use to mix radios in rehearsals instead of getting the proper desk out.

[big-ben]

Although the above Behringer product would do the job, it's almost £90. Why not try this (http://www.behringer.com/UB502/index.cfm?lang=ENG). Two inputs, no eq, adjustable gain for each input, then output to your equaliser, and all for £31.

 

PS If your local dealer's prices are higher, tell them the £31 is the price on the Behringer website and they should price match it.