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My question is simple: If I open up a guitar cable, or use the jacks from a guitar/pedal (I have a few lying around) and connect the hot outputs and grounds together, could I connect that to another cable, therefore get a 2 inputs connected to one output? I have a loop pedal that does this, but I want 3 inputs to one output in total.

My idea is this:

=======cable 1 hot====(to hot output) == == == cable 2 hot == == ==
-------cable 1 gnd----(to gnd output) -- -- -- cable 2 gnd -- -- --

(sorry for bad diagram; markdown is mean >:0 )

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    It might be better to ask this on the electronics stack exchange. I am slightly puzzled whether you are connecting two outputs together or two inputs. I would certainly not connect two outputs together. I would not suggest doing either unless you know what you are doing. – badjohn Feb 24 at 17:09
  • btw, stack exchange doesn't use HTML, it uses Markdown. There's a quick guide at the top of the question/answer space when you're editing, or a full guide here - meta.stackoverflow.com/editing-help – Tetsujin Feb 24 at 17:16
  • they are similar, but okay; I will edit – Komali Feb 24 at 17:19
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    No. Get a mixer to do this. – Legorhin Feb 24 at 19:09
5

Edit: there seems to be some confusion here.

Based on the description in the question, I'm assuming you have two devices that output a line-level signal, and you want to connect those to a device that only has one input available.

If this is the case: don't wire the cables together directly. This may damage your devices: the output voltage from one device ends up in the output stage of the other device, which isn't designed to handle that.

There are several ways to do this safely:

  1. use a switch, to connect one output at a time to the input. Simple, but requires you to turn down the output volume because a simple switch isn't guaranteed to make the switch silently.
  2. use a mixer.
  3. use a passive summing mixer. In its simplest form, this is just two resistors wired into the cable. This will result in a 6 dB signal loss.
  INPUT 1 -------\/\/\/\---+
            ---+   R1  10K   +------------ OUTPUT
               |             |       +----
    INPUT 2 -------\/\/\/\---+       |
            ---+   R2  10K           |
               |           (shields) |
               +---------------------+

The other way round: splitting the output of one device to feed 2 devices, is described in danmcb's answer.

| improve this answer | |
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    This as exact as an answer can be. – ojs Feb 25 at 10:55
  • Where is the confusion? "could ... get (a) 2 inputs connected to one output? ... I want 3 inputs to one output in total." The OP is perhaps not a native English speaker, but this is completely clear in what is being asked. Also - in 30 years as an electronics and audio engineer, I have never heard of line outputs (as in mixer/FX pedal line out) being damaged by being connected together. They invariably have resistors to protect them, and even the op amps that generally driver them could handle this without. This is a myth. – danmcb Feb 26 at 15:56
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It absolutely depends on the type of output.

What you want to do is called "distributing" the output to a number of inputs. Some types of output are actually designed to be distributed, some are not. Some can, but only with a bit of care and technical consideration.

(To know how and how many you need to know a bit of electronics, there is something called "impedance matching". I am going to try to not get into that.)

Some examples:

  1. A "line level output" from a mixer (like the MIX outputs or an insert send point) can be distributed to a reasonable number of outputs in parallel (i.e. hot to hot, gnd to gnd ...) - how many is "reasonable" depends on impedances but 3 or 4 should be no problem.

  2. A microphone or guitar output generally cannot be distributed - they are not designed to be. You should first amplify the signal through an appropriate pre-amp which has a line level output, and distribute that instead.

  3. The speaker out from an amplifier is not line level - it is "hotter" (i.e. more volts and also ability to supply current). You can connect an amp to more than one speaker - but with care. Consideration must be given to the impedances of the speaker, the rating of the amp, and parallel/series configuration.

  4. A headphone output can sometimes drive more than one pair of headphones - but again with some care about impedances, and the results may be unsatisfactory as the headphones may differ a lot in volume, and there would usually be no means of adjusting them individually.

So - the answer to your question is - "it depends". Your case sounds like case 2, so what you propose is not recommended.

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  • why is this the accepted answer? Its informative but doesn't actually answer the question that was asked. Hobbes' response is about connecting multiple inputs to one output and this covers the inverse. – Legorhin Feb 25 at 20:43
  • @Legorhin No, connecting multiple inputs to one output is the same as connecting one output to multiple inputs, i.e. distributing a signal. – danmcb Feb 25 at 21:43
  • @Legorhin I misclicked – Komali Feb 26 at 17:12
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You can use a passive "AB Y" pedal to accomplish this. It's probably more common to want to split one source to two destinations, but you can also operate them in the opposite way.

Overall though, a (small) mixer is probably a better solution in that it will give you the ability to control the sources independently.

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