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Topic: Using an External DAC

  1. #1

    Using an External DAC

    I have a Delta 66 and I hear a slight hum through the speakers. It\'s not very loud, but I\'m wondering how quiet they can get. The speakers are Mackie HR824s.
    Will an external DAC get rid of all noise? How quiet should I expect the monitors to be?

    Anthony Lombardi

  2. #2

    Re: Using an External DAC

    As I recall, the Delta outputs are unbalanced. If not, check that you are using balanced cables. If they\'re RCA jacks they\'re unbalanced. If they\'re 1/4\" phone jacks, they might be balanced. The balanced 1/4\" TRS cables have connectors similar to stereo headphone jacks - the big old fashioned ones, not the little modern do-hickeys. Of course XLRs are the other balanced connector option. You can get 1/4\" TRS to XLR cables from a good music shop.

    If you\'re hearing 60 Hz hum, a good quality balanced cable will likely solve it.

    If you can\'t go balanced, get the shortest, highest quality balanced cable that makes sense. You can go with Monster, or even get some of the thicker stuff at Radio Shack. Some of their gold plated stuff isn\'t all that bad these days.

    Other tricks are to plug your audio card into the PCI slot as far away from the other cards as possible. Make sure it\'s plugged in tight, and well bolted to the chassis. Also, ensure that no cables in the PC run near it. Similarly, make sure your external cable is strung far from your power cords.

    If that doesn\'t solve it, try getting an improved power supply. I recommend the Fortrons. They\'re some of the quietest PSs out there, and have a beefy output. The 350W model is all of $38 from directron.com. I use a $27 300W job that proved to put out more than 350W in tests.

    While an external DAC can offer higher quality sound than an internal one, you should be able to use an internal one with no audible hum.

    Good luck, and let us know the results.

  3. #3

    Re: Using an External DAC

    Ooh. I had some other thoughs. Another thing that can cause the problem is if the amp and PC are going through different household circuits. Try plugging them into the same power strip.

    Another trick that lets you get away with plugging into different circuits is to use a \"floating ground\". This only works with balanced cables. You simply disconnect the ground wire from one end. The Mackies may have a switch for \"floating ground\". If not, just open the connector on one end of your audio cable and disconnect the ground wire on that end only.

    That\'s all the audio magic I can think of today...

  4. #4

    Re: Using an External DAC

    Thanks for the tips Jon. I new about the outlet tip. I was on a different outlet than my computer and the hum was much worse. Now they\'re the same outlet, the hum is less but still there.
    The outputs are TRS, but the cable to the breakout box does go right by a power cord. I\'ll mess with it tomorrow and let you know.

    Anthony Lombardi

  5. #5

    Re: Using an External DAC

    Yeah, I\'d be interested in the cable differences.

    How about hiss? and white noise maybe? How do we get rid of this?

  6. #6

    Re: Using an External DAC

    Well I moved a ethernet card further away from the audio card, and also moved the external cable away from the power cable, and now it seems a little quieter. The hum really isn\'t very noticable from normal listening distance. It\'s still there though.
    I\'m still not quite sure how this compares to an external DAC though. For example, if I use an external DAC, can I expect no sound whatsoever from my monitors? Or will there always be some sound?
    By sound I mean anything: hum, hiss, white noise, etc.

    Anthony Lombardi

  7. #7

    Re: Using an External DAC

    Well, you\'ve done the cheap fixes...

    You might test to see if the problem exists without the soundcard. If you turn off the power to the speakers, unplug the cable from the soundcard, short the tip and the ring (but not the sleeve) in a solid way, and then turn on the monitors, you\'ll hear the noise floor with your cables. If you still hear hum, it\'s not your soundcard. It might be the cable, or a power-conditioning problem. Or even a defect in the monitor - but that\'s unlikely if they behave the same.

    Oh wait... another cheap fix. Does the sound card allow multiple output levels? If so, set it to the louder position, and turn down the gain at the monitors. That can do wonders.

    And, of course, the other non-cheap fix is the external DAC. Or better cables. Or power conditioning.

    Good luck with the cash-free solutions!

  8. #8

    Re: Using an External DAC

    I shorted the tip and ring as you mentioned, and the hum completely went away. Actually the hum was gone as soon as they were unplugged from the breakout box, without shorting them. There was still a slight hiss though. I guess this his must be due to the cable then? The cables aren\'t particularly fancy ones. They aren\'t gold plated.
    I suppose if I use an external DAC, the hum should disappear right? Then to get rid of the hiss, I need better cables?

    Anthony Lombardi

  9. #9

    Re: Using an External DAC

    The hiss may be thee cables, but it\'s more likely the amp in the speakers. Can you reduce the gain of the amp?

    It would be interesting to short the tip and ring, and then connect the ground to the PC. If that starts the hum, then you have an isolation problem.

    If the external DAC uses an optical link to the PC, that will isolate it.

    Fun with the black art of audio!

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