Mixing acoustic guitar signals

[wcampagner]

Hello,
Please, can you help me with my question?
I want to mix 4 acoustic guitar signals so that i'll have just one output which will be send to the mixing console through a DI box.
What i want to know is if i can just connect all 4 output wires together or do i need any kind of buffer before it.
All 4 acoustic guitar have active pre-amps on the guitar body.
Thanks,
Wagner.

[armdnrdy]

I would use a small sub mixer.

You can control each guitar max volume and tone before it gets mixed down to one signal in the main mixer.

[wcampagner]

ok, thanks for the answers.
I want to use the minimum equipment possible.
Because all acoustic guitar already have volume and tone controls, so i don't need another controls for these.
I just want to know if is it possible or not.
If i connect all the wires toghether will it make any harm?
Will it damage anything?
Will the tone suffer?
I think it should be fine as all the acoustic guitar already have an active preamp.
But i don't know for sure.
Thanks again,
Wagner.

[PBE6]

It may work fine to just connect all the signals together, then again it might not. Take a look at Section 2.0, especially Fig. 2 and Fig. 3 here:
http://sound.westhost.com/articles/audio-mixing.htm
Good explanations there regarding the positives and (mostly) negatives of passive mixing.

[Keppy]

Active outputs will generally fight each other if connected directly. You can mix them through a resistive load, but this reduces the volume of each source considerably as it creates a voltage divider between the outputs.

About the minimum that's likely to work reasonably well is connecting each input through a separate resistor to the combined output. Better is connecting all those resistors to a summing amp. You can use a single opamp in inverting configuration to sum all four signals without loss. This is not significantly more complicated than a buffer.

[wcampagner]

Ok... thanks for the answers Keppy and PBE6,

Now i know that make a passive mixer is not a good ideal.
I think i'll need an active mixe.

Please, can you send me some suggestions about some good projects??
I saw the GGG Mini Mixer (http://www.generalguitargadgets.com/effects-projects/boosters/mini-mixer/).
Would this be a better approach??

I think i'll do some simplification... as i don't need the volume POTS in the schematics.

Thanks again,
Wagner.

[Keppy]

The GGG design should give you great results with any buffered or active signal. If your guitars are passive (no battery) then R5-R9 should be 1M. Good luck!

[PRR]

I say "passive mixer". Four 10K resistors in a jack-box.

The active preamps will drive 10K easy.

The combined 2.5K output impedance will drive the PA system fine.

While *each* guitar is cut to 1/4, four guitars together sum to "4", so the mix output level for four is *similar* to the output level of one. (This assumption fails if you only play the four guitars one-at-a-time; then a switch-box may be sweeter.)

The cost of trying a 4-resistor mix is almost zero. (Don't cut the leads short, don't glob the jacks with solder, everything can be re-used in another project.) You could lose 15 minutes, or you could gain much simplicity over any active solution.

[ashcat_lt]

I say "passive mixer". Four 10K resistors in a jack-box.

I agree wholeheartedly.

OP mentioned "DI".  I think that is a bad idea.  An active DI might work ok here, but a passive DI is going to step down the whole thing even further, and is completely unnecessary for  "impedance matching".  The value of balancing the run is questionable (yes, best practice, but...), so the only good a DI is going to do is maybe as a very lossy TS>XLR adapter for interface with a stage snake.  Put an XLR jack in this passive mixing box, maybe pseudo-balanced, maybe with a "ground lift", and I think you'll be much better off.

[Jdansti]

For the price, I'd go with something like this:

http://www.amazon.com/Nady-MM-141-4-Channel-Mini-Mixer/dp/B0009X9H9I

http://www.sweetwater.com/store/detail/MX400

These should work fine for active pickups.

[ashcat_lt]

For the price, I'd go with something like this:

http://www.amazon.com/Nady-MM-141-4-Channel-Mini-Mixer/dp/B0009X9H9I

http://www.sweetwater.com/store/detail/MX400

These should work fine for active pickups.

Yeah, that's kind of hard to beat.  If you actually have to buy decent jacks and a box or value your time at all...

I'd probably just go dig up my old DOD resistance mixer.