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Music Media Hardware

Building Your Own KVM Switch...With Audio Connectors? 80

Posted by Cliff from the adding-your-own-twist-to-now-common-hardware dept.
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?
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Building Your Own KVM Switch...With Audio Connectors? More

Building Your Own KVM Switch...With Audio Connectors?

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  • cheaper solution (Score:5, Informative)

    by rumpledstiltskin ( 528544 ) on Friday May 09, 2003 @08:28PM (#5923272) Homepage Journal
    instead of spending $500 or spending all your time building your own switch, just buy a tuner with multiple inputs. you get to have your switch (at the cost of having to push one more button, although if you use the remote it shouldn't be all that strenuous) and you could hook up some advanced (dolby, dts, whatever) audio to it if you'd like.

    • Re:cheaper solution (Score:5, Informative)

      by TimeTrip ( 254631 ) on Friday May 09, 2003 @08:46PM (#5923366) Homepage
      It also allows you to separate the audio from the video/keyboard/mouse. Often times at work, i switch between machines on my KVM switch, but keep my headphones connected to just one machine because its playing my mp3's :). If the audio was run throught the KVM switch i would probably go insane.
      • It also allows you to separate the audio from the video/keyboard/mouse. Often times at work, i switch between machines on my KVM switch, but keep my headphones connected to just one machine because its playing my mp3's :). If the audio was run throught the KVM switch i would probably go insane.
        heh - that's why I have a box running a shoutcast server on my lan ;)
    • "(at the cost of having to push one more button..."

      The added benefit here is that you can keep the audio going on one machine while switching to the other. If you're listening to MP3s this is nice. Or, if you're waiting for a really long process to finish and it has a sound queue, then you can leave that audio channel open.

      I agree with parent poster, this'd likely be a better option for ya.

    • Re:cheaper solution (Score:4, Insightful)

      by grammar nazi ( 197303 ) on Friday May 09, 2003 @09:19PM (#5923503) Journal
      A tuner is a nice idea. I was thinking that one of those $30 radio shack sound mixers would also be nice. You can run all the audio through it and adjust levels depending upon what you choose to concentrate on.
    • Personally I use a mixer, that way I can keep playing mp3s on one computer and listen to the sound effects from another, and still use one set of speakers. Ok it does not auto switch like a kvm would dpo from one computer to another, but there again I don;t want it to because I want to hear the sounds from more than one machine.

      James

      PS for really cheap people with 2 computers use that input on your sound card ;-)
  • buy a manual select printer switch and put in audio jacks. vwala. how tough could that be? not being an electronical switch though i imagine you could get some nasty "pops" when changing between devices.

  • Mix instead? (Score:5, Interesting)

    by Piquan ( 49943 ) on Friday May 09, 2003 @08:57PM (#5923408)
    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.
    • Actually, I did just this. I have two machines connected on a LCD display, one uses the DVI input, the other the analog input. I bought a simple USB switch and built a simple mixer using four resistors. It works perfectly.
  • Take Switch #1 - Plug in 4 computers. Take Switch #2, plug in 3 computers and the output from switch#1. Now you have a 7 Computer Switch with all the features of your 4 port switch, at twice the cost of course.

    • I tried this before with a 4 port kvm and 2 port kvm with horrible results...

      Although it looks like some of the higher end kvm's can be daisy chained through a special connector i don't think even the highest end ones will work as suggested in parent.

  • Here's an idea (Score:5, Informative)

    by HotNeedleOfInquiry ( 598897 ) on Friday May 09, 2003 @09:06PM (#5923445)
    If your 8-port switch has led select lights for the port that is active, bring out a wire from each of the signals that drives the leds and wire each of them to a simple buffer transistor and relay.

    Each of the relays would gate the respective sound signals onto a common bus. Use a double pole relay for stereo. 2N2222 (npn) and 2N2907 (pnp) are available from Fairchild through Digikey in TO-92 packages and would be a good choice for a relay driver.

    Likewise, an Omron TX2-5V is a reasonably priced DPDT telecom relay with a 5v coil, also available from Digikey.

    • Re:Here's an idea (Score:3, Informative)

      by Kz ( 4332 )
      Instead of mechanical relays, use electroinc analog switches, like the easily found 4066. cleaner, less power, no need of buffer transistors. maybe you'd have to use a transistor to match the LED output to the CMOS logic, but that's easier than driving a relay.
  • If you're just trying to get sound (alerts, alarms , whatnot...) why not just buy some cheap speakers? You can pick up something that'll put out sound for under $10 per set.
    If you're looking for higher end sound (music, et all) then you're probably better off dropping the $5C.
  • Forget about what I just typed, Do what I am thinking about damn it!

  • USB KVM (Score:4, Insightful)

    by MrResistor ( 120588 ) <peterahoff.gmail@com> on Friday May 09, 2003 @09:14PM (#5923482) Homepage
    Maybe if you used a USB audio output device and a USB KVM?

    I haven't tried this myself, but it seems like it should work.

    • Re:USB KVM (Score:3, Informative)

      by jmorris42 ( 1458 )
      Haven't actually tried it either, but I doubt you can do that. KVMs have to have smarts so as to fake out each PC to think it always has the keyboard/mouse. Some are even bright enough to hold the state of the keyboard LEDS and restore the correct pattern when you switch machines. Unless you got one that was also smart enough to handle audio in a similar way (at which point it would probably BE the audio device) you would run into trouble. You see, if the KVM isn't faking things for a device each time y

      • Re:USB KVM (Score:3, Informative)

        by MrResistor ( 120588 )
        I think Linux would be just fine. I have 2 USB mice, an Intellimouse Explorer and a little IBM optical travel mouse (for my 3 year old, the MS mouse is huge and the side buttons are positioned so that she can't grip it and reach buttons 1 and 2 without hitting the side buttons, the other one is the perfect size for her hand). I hotplug them all the time with no problems, on SuSE 8.1 Pro with the default kernel, if you care.

        I know how KVMs work, or at least how they are supposed to work ;-) but I don't thi

      • Re:USB KVM (Score:1, Interesting)

        by Anonymous Coward
        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.)
        • "In theory, theory and practice are the same. In practice they aren't."

          Not much you could expect the system to do if the sound device disappears while sound is playing other than to abort. So much for flipping to another machine for a moment and expecting the MP3 to still be playing when you flip back.
  • Another option might be just getting a 16 point patch bay... You could either do it with 1/4" mono or stereo jacks and you'd only need one or two patch cables.

  • KVM (Score:3, Funny)

    by Naikrovek ( 667 ) <jjohnson@ps g . com> on Friday May 09, 2003 @09:44PM (#5923607)
    Keyboard, Video, Mouse. are you surprised that there is no audio?

    get a mixer. there is probably little reason you'd want to play music on more than one computer at a time, so just get a mixer and put them all into the mixer and out the speakers right in front of you.

  • Don't switch audio -- mix it. (Score:3, Informative)

    by -dsr- ( 6188 ) on Friday May 09, 2003 @09:51PM (#5923623) Homepage Journal
    Buy a cheap audio mixer and control all your sound inputs individually.
    • I've been looking at this for a while and can't find anything that does what I want at a reasonable price.
      I want to be able to have stereo inputs 1 to 6 and mix those into either of stereo outputs A or B, output C might be useful too. If anyone has any suggestions.....?
      I'm quite happy to build my own, I just don't have the knowledge to design it or the time to acquire that knwledge, but I can probably build it.
      • To summarize:

        You can build mixers pretty easily using op-amps, and Forrest Mims' "Engineer's Notebook" has quite a few useful designs.

        Where to get it? Rat Shack, although these days it's often not stocked (just like their 150-2160 UHF-only TV antennna grumble grumble)... RS is going downhill.

        RS is definately not the optimum place to get electronic components, but when you need something fast and you aren't buying that much, it's quick. Digi-Key is far better, but keep in mind that DK sucks for small o
  • Skip the KVM switch. If you have 8 machines at home (assuming you aren't running a business from your home), just start consolodating machines. In the end, you'll probably save on your energy bill.
  • They sell A/B audio switchers and A/B/C/D audio switchers... use the A/B to select which one of the two ABCD switch to use, then select one of those. Total cost: about 70 dollars max. I think they come in RCA only, so YMMV. Good luck.

  • Seperate switch (Score:2, Interesting)

    by GigsVT ( 208848 ) *
    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 qua
    • Note to self, PREVIEW! (Slashdot doesn't seem to do the TT tag the way one would expect!)

      I built a 2X2 for switching two computers to either earphones or speakers.

      Two DPDT switches, one controls input, one controls output.

      (ASCII art deleted because Slashdot can't deal with it.)

      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'
  • You don't want to change the audio every time you switch to a new computer. It interrupts the program.
  • 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.

  • Not too hard... (Score:3, Informative)

    by Tom7 ( 102298 ) on Friday May 09, 2003 @11:26PM (#5923995) Homepage Journal
    This is pretty trivial to build; you shouldn't need schematics. Audio signals are pure analog, so all you really need to do is get a switch with multiple throws (3 for stereo) and wire it up to jacks and mount it in some kind of box. If you get a rotary switch you could have a pretty much arbitrary number of computers hooked up to it.

    If you care about sound quality or having the device look nice, just get a desktop mixer. That's perfect for having multiple computers driving a single stereo.
  • Run your audio through an amp. You can then switch the inputs using the remote control, or the big knob on the front. I don't know how many computers you are going to connect, but there's a chance you don't need a KVM switch at all. Most non-cheap monitors come with at least two inputs. I bought two TFTs over the last four months, and both of them had two inputs, one analog, one digital, switchable with an extra button on the front. The Sony X72 even has three inputs: one digital, two analog, and it's a goo

  • Belkin SOHO (Score:2, Informative)

    by Sleepyguy ( 12339 )
    buy a belkin soho .. they are cheap and they support audio and usb.

    _
    • Belkin soho's may sell at a lower price than other kvms, but that does not make them cheap. ~$120 USD according to pricewatch.com. Their kvm cables are ridiculously overpriced. (And you'll need at least two sets of cables to be minimally useful.)

      Worse, they are riddled with mouse control bugs, and its noticably annoying when using Linux. You need to use the mouse while switching, or you'll lose mouse scroll or any mouse control, or freak out the xwindows session. (In which case, you need to do an ctrl-
      • Comment removed based on user account deletion

        • Its not the motherboard or the power supply. It has to do with the fact that the SOHO is overpriced but cheap assed in quality. Instead of storing and maintaining every mouse setting before hopping to the next machine, it feeds a mouse reset code when it hops back to the old machine. This freaks out any Xwindows version besides the latest, and as one AC said, its no good for wheel mice. I'll sooner chuck the SOHO than my wheelmouse.
  • Buy 2 KVMs and use one for the keyboard-video-monitor. Open up the second one and buy some panel mount 1/8" audio jacks or whatever will match your cables. Cut off the mini-DIN and DB-15 jacks, LABEL THE WIRES, then solder in the new jacks.

  • mixer (Score:4, Informative)

    by g4dget ( 579145 ) on Saturday May 10, 2003 @03:21AM (#5924677)
    Why do you want to switch? Why not put the audio into an analog mixer and have all of them active simultaneously?
  • try google CCTV.

    seporate audio switch, who knows

    just an idea

  • Audio, Video, Keyboard and Mouse Switching (Score:2, Informative)

    by Anonymous Coward
    What you are trying to switch is the red, green and blue video signals, which are analogue and have several MHz bandwidth; the horizontal and vertical scan timing signals, which are lowish-speed digital (a few kHz and a few Hz respectively); the keyboard and mouse clock and data, which are low-speed digital (c.1200 baud) but two-way; and the left and right hand audio, which are analogue without much bandwidth (20kHz tops).

    Just how much bandwidth is in a video signal? Well, if you have a screen of 1024x7
    • 1600 x 1200 resolution at 75 Hertz refresh rate is: 1600*1200*75 = 144 MegaHertz. The video system bandwidth must be much greater than that to avoid ruining the video quality. That's why even the $30 nVidia video adapters have a 300 MegaHertz RAMDAC (digital to analog converter).

      19 inch CRT monitors with a 1600 x 1200 resolution cost as little as $225, so that resolution is becoming a standard.

      It is a big technical achievement to switch 1600 x 1200 resolution without video degradation. IO Gear [iogear.com] does
      • Note that IO Gear (at least sometimes) plays games with the supplied cables. A four port KVM will be supplied with 2 ten foot cables and 2 six foot cables. The shorter ones are too short to use in some installations. That isn't mentioned on their web site, that I can see, or in the manual, available online.

        Also, the keyboard controls for switching may not be well considered.

        IO Gear does seem to be the best for video quality.
    • Don't even *think* about using any kind of mechanical switch or relay. Moving parts suck bigtime and will distort any analogue signal you try to pass through them.

      With regards to relays, this statement is simply wrong. A good quality relay is infinitely superior to any electronic switch. For instance, reed relays are available which will switch from DC up to microwave frequencys at useable power levels and have 'on' resistance values which are magnitudes better than an elctronic switch. Bear in mind that
  • 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).

  • Found a 2-port KVM switch with audio!! (Score:4, Informative)

    by shdragon ( 1797 ) * on Sunday May 11, 2003 @01:38AM (#5929383) Homepage Journal
    I found this [newegg.com] at newegg.com

    It's 2 ports, supports audio & is only about 90$.

  • Do it in software (Score:4, Informative)

    by Anonymous Coward on Sunday May 11, 2003 @02:32AM (#5929519)
    How about that:

    Machine you work on:
    cat /dev/audio | nc 192.168.100.1 48050

    Machine you plug your speakers in:
    nc -l -p 48050 > /dev/audio

  • You don't need 8 port audio switching (Score:3, Interesting)

    by donutz ( 195717 ) on Sunday May 11, 2003 @02:55AM (#5929576) Homepage Journal
    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.

    • 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?)?

      Did you read the question? He said that he wanted the audio to run through the KVM switch too. This would imply that the only sounds that he'd be hearing would be coming from the one machine that he's switched to currently--just like the only video that he sees is the video
  • PC Speakers are reasonably inexpensive. Just get a second set for the second comp for $9.97 at Radio Shack. [radioshack.com]

  • 3x female 1/8" stereo jacks

    4x female RCA mono jacks

    4x SP/DT slide switches (3/16" x 1/2")

    2' jumper wire

    1x plastic electrical junction box

    1x clear plastic picture cover from picture frame. (3"X5")

    First 4 parts are available from RadioShack for a total less than $10. The junction box is available at Lowe's for $1.66. The picture cover you can get with any cheap picture frame.

    step 1: lay the junction box upside down on a piece of paper and trace. Cut out the outline.

    step 2: lay out the jack

  • A passive mixer is easy to make, requires no power and can be less redundant. You already have mixers built into each machine (software), so don't waste cash on a mixer. You won't have to throw two switches. Unless you're trying to monitor live feeds, mixing the audio might be a good end result - play MP3s on one machine, while playing a game on another. You can find plans and more by searching [google.com].

    I actually just daisy chain the inputs of my PCs. Take the line out of one. Plug it into the line in of the

  • I have a set up were I like to watch movies on one machine, have my mp3 database on another, and e-mail on another. Yes i do like to here my mail application make a faint beep so I know i have new mail. So i used a 5 channel mixer, obviously for your purposes an 8 channel would be a better solution. One of these can be easily found at a pawn shop for less than 100$. But to be elegent one day I plan to convert my KVM to having 1/8" heaphone jacks for each machine and wire them altogether to one master. That

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