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Building Your Own KVM Switch...With Audio Connectors?
Michael B asks: "I recently bought an 8 port KVM to switch between various workstations and servers at home, and I'm realizing what I can't switch is audio! I've seen 4 port audio/video type switches (for things like switching between video console systems) but this doesn't address more than 4 ports and having the adding RCA/S-Video is a waste. I've thought of building one from scratch using Radio Shack parts, but can't find any info, such as a schematic, online. Does anyone have any ideas or sources of info for this one? Belkin seems to make a 4 port KVM with audio, which would be nice, but I need more than 4 ports. Thanks for any help!" After a bit of digging, I found this monster, which does 8-port KVM and audio, but that weighs in at a hefty $500USD, which is rather expensive. Has anyone managed to find schematics to such switchers so that folks, who aren't afraid of soldering irons, can build their own?
How about just building an audio mixer? IIRC, Forrest Mims's "Engineers Notebook" (the one on op-amps, I think) has a multi-channel mixer that allows for an arbitrary number of inputs. This way, your MP3s don't stop when you go to work on your laptop, etc.
I built a 2X2 for switching two computers to either earphones or speakers. Two DPDT switches, one controls input, one controls output. i1 i1 i2 i2 1 2 1 2 o1 o1 o2 o2 1 and 2 are connected together, i and o are inputs and outputs, left and right. Tie all grounds together, switch L+R. I guess doing that could cause a ground loop hum, but it hasn't caused a problem for me. There isn't really a pop or anything when you switch mine, even with the speakers on. You need reasonably good quality switches though, if the switch feels loose or wiggly, it will probably cause a lot of static when you switch it. I found a lot of my surplus switches were not up to audio use. I eventually settled on push-on push-off switches I scavenged from an old set of speakers, they were power and bass boost switches. This concept is the same way one would build a switch with many more inputs or outputs, you just need rotary switches, DP#T where # is the number of things to switch. Here are some switches The 2 pole 5 position and 2 pole 6 position from there is probably what you want. You can cascade a DPDT and two 5 position rotary switches for 10 outputs with one input or vice versa. Scavaging from manual computer switch boxes is probably not a good idea, since most of those are low numbers of positions, with high number of poles.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
I've seen several recomendations for just using standard audio gear to mix the inputs (and was looking for something like that lastnight). Any recomendations for a nice low end mixer with 4-8 inputs and 2+ outputs, bonuses for rack mountable.
You could daisy-chain the soundcards - i.e., the LINE-OUT from one to the LINE IN of the next one. The last PC will have its speakers playing all signals mixed and the cost will be very low (just stereo cables).
I mean, you said you have a mix of servers and workstations at home. Do you really need to hear the Windows bell or chime sounds on your servers (or if you're running linux servers...why do you have them configured to make sounds?)?
It just doesn't seem worth the effort to try to find a solution to this "problem" when it doesn't even seem to be much of a problem. But you're certainly free to spend your free time doing whatever you want, including trying to hack together your own KVM switch.
Good luck.
In theory, you should be able to arbitrarily disconnect and reconnect USB devices, with none of that crazy 'fake out' logic needed for PS/2.
(I say "in theory" because I just had to reboot windows to see a new mouse.)