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Preamp Frying Mixing Board Channels?

Discussion in 'Preamps & Processing' started by AnalogAndyNYC, Dec 20, 2013.

  1. AnalogAndyNYC

    AnalogAndyNYC Active Member

    Apr 1, 2011
    I'm a DJ, well more like mp3J, and recently I tried using the USB out on my laptop to send the signal instead of the 1/8" soundblaster headphone jack. I bought a ART USB Dual Preamp so that I can go out of my laptop's USB out, into the USB in on the preamp, and then the preamp has two 1/4" outs, and then I have 1/4" to RCA cables that go from the preamp into my Pioneer DJM 600 board which has RCA inputs. I was using a Presonus StudioLive board before and I think this preamp might have burned up one of the channels on that board because it worked brilliantly for the first week or two that I had the new USB preamp, then the channel that I had it plugged into stopped working. I hooked the preamp up to the Pioneer board last night, worked brilliantly, then tonight I noticed sound was only coming out of the right speaker. So I switched channels and BAM both speakers worked perfectly. Could my preamp be burning up the channels on my boards? If so, can you help me to understand exactly why? Is it the wrong application? Wrong cables? Too much gain on the pre? Please help!!!
  2. Boswell

    Boswell Distinguished Moderator Resource Member

    Apr 19, 2006
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    Without your going through all the cases in detail, it's difficult to say what may be wrong. However, what I can say is that the 1/4" line outputs of the ART USB pre-amp are balanced (TRS) and you are probably using unbalanced (TS) phone plug - RCA cables. This may be causing overheating problems in the ART box due to the -ve outputs being short-circuited by the mono TS plugs.

    One thing you could try is using the headphone jack output of the ART box instead of the two line outputs. The headphone jack carries left and right unbalanced signals and would better match unbalanced inputs. To use the headphone jack to feed RCA inputs you would need a splitter cable like this one. The plug marked "tip" is the left channel and "ring" the right channel.
  3. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Nov 21, 2005
    Pioneer DJM 600 states that it has two XLR/Phone mic inputs. Whether the "Phone" input is balanced TRS, or not, is not clear. You should have gone from the ART balanced outs to the XLR ins, using TRS-to-XLR cables, if necessary. You would have then set gain by setting the Pioneer levels to their optimum, adjusting the computer program levels that go to the ART, and then adjust the ART to send signal to the Pioneer to just below clipping. this may take some juggling of Pioneer input levels, computer output levels to the ART, and ART output levels. What you'll be looking for is the cleanest signal with the best level. If you had done this, than nothing should have gone wrong on that situation.

    On the Presonus board, if you were using balanced cables to channel inputs, the same thing should apply. If you had done it properly, there should have been no problem.

    Running the ART 1/4" outputs into RCA jacks IS a problem. Those inputs weren't designed to handle that much signal. Normally, RCA jacks take a much smaller signal level than a 1/4" TS or TRS jack, and even an XLR jack with input level controls. You can run an RCA jack into a 1/4" jack, and boost the signal, though it may add noise...but you'll rarely have success running a more-powerful signal of a 1/4" output into an RCA input, unless it is specifically designed in some way, like input levels, switching, etc.

    When you say you "switched channels", do you mean you plugged them into a different set of channels, or you just swapped, say, left and right, and it suddenly worked? If it's the former, I'd back off that before you blow up another set of channels. If it's the latter, then it's not in the mixer, because the channels now work, so that couldn't have been the problem.

    My advice is to unplug EVERYTHING, and test all your equipment, using proper input devices for all the inputs. Test all input channels, and test headphone outputs, and any other outputs. You can still use your computer soundcard to test RCA inputs. if you have a mic, test any mic inputs. Get some proper TRS-TRS or TRS-XLR cables and test a mic from your ART to the proper inputs of your mixers.
    You just need to step back and test everything, and figure out how to connect everything properly.

    One other possibility is bad cabling, so test all those, also.

    It's possible that you've fried some channels, if you were running a high level from the ART into RCA inputs.

    You also need to see if that ART is self-balancing/unbalancing on the outputs. Some gear will automatically allow an unbalanced 1/4" TS jack to be used to connect to other unbalanced equipment, and also to use a balanced TRS jack to connect balanced equipment. If the ART doesn't do that, then Boswell's theory may also have some merit.

    Good luck,


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