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  1. #1
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    Running stereo audio to single XLR inout amp

    Hi there, I want to know whats the right way to connect stereo to out to XLR line in on an amp. If I do it wiring 2 so tip, 3 to ring and 1 to sleave using an adapter be it RCA to stereo to XLR (using 1/4 " stereo jack terminology...) I hear a watery, reverberating out of phase type of sound. I'm guessing the left (cold) signal might be cancelling some part of the right signal (hot)on the input of amp.I saw the connection suggestion on this site. How do i fix this without cutting losing the left or the right on such a connection? How do I get a decent mono signal from a stereo output?

  2. #2
    Are you talking about a stereo output on a single 1/4" jack? If so, wiring one channel to XLR pin 3 inverts the signal, so any sound that appears in both channels (that is, centrally panned) will cancel out.

    The right way is to combine both channels and connect to pin 2. This brings up another problem, in that two outputs don't usually like to be shorted together. I like to put a 1K ohm resistor in series with each output and join the "downstream" ends of the two resistors, so the channels are a bit isolated from each other. The fact that nobody seems to make a Y-cord with resistors built in is perhaps the greatest continuing strangeness in all of audio.

  3. #3
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    Thanks, makes sense.
    I am curious though, wont the resistors drop the signal level and if so to what extent?

  4. #4
    The usual input impedance of a power amp is 5k- 10k ohms. A 1k resistor in series with that will drop the signal 1/10th to 2/10ths of a decibel. The smallest drop a trained ear can actually hear, with a continuous sinewave tone, is 1dB. With music, 3dB.

    A more serious issue, potentially, is that if you have more than 100 feet downstream from the resistor, you could lose high frequencies. I assume the cable isn't that long.

  5. #5
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    Thank you for that explanation. The theory behind these things is really interesting. Could you suggest any good sites/books/resource for study on these matters? The cable's we use exceeds 150ft to over 300ft sometimes. In the situation above we didnt have 2 cables (for stereo) to do the job so we had to use one (the stereo to mono with the amp bridged) and over the distance the unbalanced cable also lose a lot of its signal so it seems using the 2 cables gives the easiest solution. I definitly want to look into your suggestion, so if u could direct me to some resources i would really appreciate it.

  6. #6
    Unfortunately, there aren't many.

    Sound Reinforcement Handbook, by Gary Davis and Ralph Jones - written for Yamaha and published (I think) by Hal Leonard. Oriented toward live performance reinforcement in a clear style intelligible to laymen.

    Sound System Engineering by Don Davis (no relation to Gary, I think) and Patronis - this is the book used by Syn-Aud-Com seminars, founded by Davis. Highly technical and thorough. Syn-Aud-Com has long been the "gold standard" in pro audio technology training.

    Audio Cyclopedia by Howard Tremaine - as its name implies. Dated but a valuable compendium of traditional audio techniques. Good bedtime reading and eventually you'll know a great deal.

    Handbook for Audio Engineers, a new audio cyclopedia by Glen Ballou - updated from Tremaine's book.

    NSCA (National Systems Contractors Association, USA) - many study guides and newly published books.

    I've been asked to write a book but I'm not sure printed textbooks are even relevant any more. Don't hold your breath.

    Many of the above are extremely expensive, but can be found used on Ebay. For example, Ballou's book is nearly $250 new but as low as $35 used.

    Think about what part audio is going to play in your life. Do you want to master it and use it professionally, or will it just be an avocation? If the latter, the Yamaha book is probably your best bet.

  7. #7
    (Smack head) I should have mentioned this... have you made a thorough search of the instructional material on this website? Click the blue "audio" link at the top of the page. Lots there.

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