I wish to build a simple audio mixer...

Discussion in 'The Projects Forum' started by mike_crawford, Dec 1, 2010.

  1. mike_crawford

    Thread Starter New Member

    Jan 21, 2010
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    I found info on this site, and loved its simplicity,

    http://www.tkk.fi/Misc/Electronics/circuits/linesum.html

    the author uses 10K resistors in his circuit but I notice the volume level drops significantly vs a normal direct connection (with no resistors of course)

    Was wondering if using lower value resistors in his circuit would be safe all the while allowing volume levels to increase towards that of a direct connection.

    Thanks
     
  2. #12

    Expert

    Nov 30, 2010
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    Need more information.

    If you're mixing low level signals from two small amplifiers, for instance, and they have self protection resistors in them, you can just twist the wires together. If you try that with a good power amplifier, all the magic smoke will escape.

    Better description will get better answers.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The inputs can be tied together as shown, but the output of that should be fed into a buffer amplifier after mixing.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Yes, it would probably be safe to go as low as 1k or so, without knowing anything more about the signal. The resistors make sure the load on the signal's source is not too great. A load of 1k might be too much for a line level source, but isn't likely to ruin it. If the source can power headphones, then it's capable of driving even more load, like down to 100 ohms. A loudspeaker amp goes down to 4 ohms without worry. And simply shorting the two channels together often works because the equipment is designed to protect itself from such things.

    In short, the answer depends on your source.
     
  5. mike_crawford

    Thread Starter New Member

    Jan 21, 2010
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    I want to take 3 portable .mp3 players (running on 1.5V battery each) and simply mix them together into my amplified computer speakers.
     
    Last edited: Dec 1, 2010
  6. wayneh

    Expert

    Sep 9, 2010
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    "them" meaning the headphone outputs? As I said, these can take more load than a line-level source. iPod headphones have a 32Ω impedance, so if you mix through 100Ω resistors, instead of 10K, you should be safe and you'll have plenty of volume. In fact you'll probably be able to overdrive the input to your amp. Keep the mp3 volume low until you find a sweet spot.
     
    mike_crawford likes this.
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    No out put of a power amp shud be mixed.

    The mixing resistor value serves as the load to respective driver.

    To mix audio efficiently and effectively from different sources while maintaining the Audio's bandwidth, an active mixer using op-amps is always preferred rather than a lossy resistor network
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The resistors have identical values so they cut the signal from each source in half no matter what the actual resistance is (depending on the source and load resistances). A real mixer circuit mixes signals with no loss or can have gain if you want.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What is the purpose of mixing two outputs?

    Is this an application where an input selector/pre-amp would serve a better purpose?
     
  10. wayneh

    Expert

    Sep 9, 2010
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    It's also worth mentioning that any decent movie editing or sound processing software, eg. GarageBand or iMovie, would do a very fine job of mixing multiple audio streams while maintaining full fidelity.

    But I understood the OP to mean he wanted to truly MIX (not switch) multiple mp3 player outputs. Maybe in a car, or in a poor-man's DJ situation?
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    As we are talking about .MP3s, computer software can do mixing MUCH better and write out as an MP3 to be played on a single player.
     
  12. mike_crawford

    Thread Starter New Member

    Jan 21, 2010
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    Its actually for a table hockey scoreboard, the three .mp3 players provide various hockey sounds, organ music etc., so a 'real' mixer is not really necessary.

    My current 3-way cable uses 5K resistors (originally was 10K), and sounds pretty good, but I am going to try 1K for even better results.

    PS- this forum is awesome, all of you have been a great help :)
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If the MP3 players are electrically activated, you could use something along the lines of a couple 4066 bilateral switches(2 for stereo, 1 for mono) to select the input.
     
  14. radiohead

    Active Member

    May 28, 2009
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    Why are you using such an old schematic? There are much better schematics out there for simple mike and low level audio mixing. Plus, if you were to actually use that circuit, you would probably need to amplify the signal at the output to get it back up to a useful level.
     
  15. mike_crawford

    Thread Starter New Member

    Jan 21, 2010
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    I gutted some old PC speakers that has a built-in amp....it seems to boost the signal pretty well.
     
    Last edited: Dec 3, 2010
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