On Sat, 15 Nov 2003 18:04:01 +1300, Gregory Parker wrote:
> On Sat, 15 Nov 2003 17:50:22 +1300, harry <> wrote:
>
>>On Sat, 15 Nov 2003 16:10:20 +1300, Murray Symon wrote:
>>
>>> On Sat, 15 Nov 2003 15:19:48 +1300, Nicholas Sherlock wrote:
>>>
>>>> Chris wrote:
>>>>> Hi there all,
>>>>>
>>>>> I want to know if there's a way I can connect 3 sound cards (on three
>>>>> separate PC's) to a single set of speakers.
>>>>>
>>>>> I know this can be done by using an expensive KVM switch that handles
>>>>> sound, but I already use a cheapie KVM that works well for me and I
>>>>> don't really want to go and buy another one.
>>>>
>>>> Yes, of course, just buy a Y-shaped audio cable that can do this for you.
>>>> Inside will be a transistor that combines the signals.
>>>>
>>>> Cheers,
>>>> Nicholas Sherlock
>>>
>>> A Y shaped cable will only give you 2 inputs into 1 output.
>>> A transistor is not used for combining signals, that will be
>>> done (if you are lucky) by resistors.
>>> However, most Y leads seem to not even bother with resistors.
>>>
>>> Using a many-into-one cable will combine the outputs from all
>>> the PC soundcards all of the time. You may not want this.
>>>
>>> Seeing as you mentioned using a KVM switch, you might be best
>>> to get an audio switching box (such as sold by Dick Smith).
>>> These allow you to manually select which input goes to the
>>> output.
>>>
>>> Murray.
>>
>>If he does want to have the six signals on all the time he could passively
>>combine the three lefts with ~4k7 series resistors to the input of
>>one powered speaker and the rights the same to the other input.
>>There will be an insertion loss but there's plenty of gain on powered PC
>>speakers.
>>
>
>
>
> Useless if the powered spwkers have a 8 ohm input, and yes they do as I have
> some..
It will work even better, nice low impedance at the summing point, all the
resistors are doing is stopping the sound card outputs from loading each
other. An even better solution is to use a dual op amp as a virtual earth
mixer.
http://www.all-electric.com/schematic/simp_mix.htm
There are plenty of project boards that will do the trick, but the passive
combiner is the cheapest.