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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: John Michaels. on December 11, 2015, 10:49:08 AM
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Hi all,
I have an Allen & Heath Zed14 mixer, and recently had to take it into a space in which I had to patch its output into a basic Mackie's input, to connect to the existing installed system. Given the installation it was impossible for me to steal the outs directly. Anyway - we've used this same procedure multiple times with this and other boards with no significant issues. On this occasion, however, we were getting an excessive amount of noise, and a hum that both seemed to get louder at times. (Power for the entire system was coming off of the same circuit). And furthermore, upon using a Roland m200i thereafter in the same fashion, it sounded clean.
Anyway, this led me to check to measure the voltage of the outputs of the console (my intent was to see if I had dropped a shield pin... though I'm not certain that this is at a ll a valid way to diagnose this). What was interesting was, when measuring voltage across pins 2 and 3, with a 400hz sine wave, with channel and main outs at unity (panned center), and the gain boosted until the output meter read zero, I got a voltage of something like 2.2V on the left chanel and about 1.7 on the right. I also measured across pins 1 & 2 on each out, and got roughly the same difference between them. Is this an indication of a logical problem (either with the above situation or something else)?
I know that whole thing is very wordy - my apologies. Let me know if there is anything I can clear up for anyone.
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Let me know if there is anything I can clear up for anyone.
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Mac
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Did you use the Mackie's XLR input(s)? If so, its phantom power was on and this damaged the output stage of your mixer (hopefully just the output coupling caps).
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Did you use the Mackie's XLR input(s)? If so, its phantom power was on and this damaged the output stage of your mixer (hopefully just the output coupling caps).
Very valid (and fairly probable) consideration, Tim. What would the direct symptoms of this be? Also, to diagnose this, would the caps be noticeably swollen/ damaged?
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Very valid (and fairly probable) consideration, Tim. What would the direct symptoms of this be? Also, to diagnose this, would the caps be noticeably swollen/ damaged?
direct symptoms could be low level, erratic level changes, audible distortion...it basically sounds like the tone has been sucked out of the signal and you need to boost the snot out of it to obtain any usable level.
- Jordan Wolf
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Assuming your voltages are correct-that is a 2.2ish dB difference.
Not enough to indicate an electronic failure of some sort.
I would consider that either the panning was not exactly center, or there was some other routing going on.
Remember that parts have tolerances, but that seem.
s a little bit out of tolerance.
I suggest doing some more testing by routing the signal to other places and measuring
But in then end a 2dB difference between console outputs is not enough to get really concerned about.
You could also take it to a repair center and see what they find.