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Gear / Technical Help => Microphones & Setup => Topic started by: perks on September 01, 2015, 04:31:51 PM
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Can you run XLR cables between the preamp supplying 48V and the PFA? My Nbob active cables are too short for what need to use them and I don't have enough time to get another Nbox extension cable built.
So what I want to know if this would work?
Schoeps caps > Nbox collettes/cables > Naiant PFA > 10' XLR cable > 48V Preamp > interconnects > recorder.
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Should work fine.. assuming the PFAs are properly configured to power the Schoeps.
Might be marginally better to make the longer XLR run between the preamp and recorder, but probably not as convenient for powering and may not be practical in your intended setup. Shouldn't matter anyway given that the balanced mic-level run from PFA to preamp is only 10', PFA should be able to drive a cable run of far longer without problems. Jon will likely post with specifics.
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Don't know about Schoeps specifically but you can run 200' from pre/phantom to mics if you use decent cable.
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Schoeps or other make of mic isn't the run length concern, but one of PFA powering specifics- the PFA is often specific to the powering requirement of the particular mic manufacturer.
Concerning run length, an active cable run and/or an unbalanced run are what need to be kept as short as possible. Doesn't matter nearly as much with a balanced run. However, in general its less interference-prone to make a long run at line-level rather than mic-level. At 10' it won't matter, that's not a long run. At 200' I'd make more effort to put the preamp near the mics and make the long run from the preamp to recorder at line-level, rather than a long mic-level run to the preamp.
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I was thinking quality balanced cable with a good shield. Both a line signal and a mic signal are prone to the same amount of noise from external sources using the same cable, you just would notice it much more on a mic signal. Unbalanced - 10 foot I think is supposed to be the max (my memory is suspect) though I have done more with no noticeable extra noise. It depends on where you are running it but you are definitely opening yourself up for more trouble the longer you go.
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"Both a line signal and a mic signal are prone to the same amount of noise from external sources using the same cable, you just would notice it much more on a mic signal."
You amplify noise along with the signal. Start with a higher signal level relative to the noise level and retain a greater signal to noise ratio.
Same cable, same run, line verses mic level signal- the common mode interference noise will be at the same level in both cases. But the line-level signal has a higher RMS voltage than the mic-level signal, so the difference between the noise level and signal level is greater with the line-level signal. When the mic-level signal is amplified to the same level as the line-level signal, the noise is also amplified by the same amount. So noise increases by the same amount as the level difference between the mic-level and line-level signals. Good balanced cables allow you to start with a lower noise level, but regardless of what that beginning noise level actually is, it is going to be amplified as much as the signal is amplified. Starting with a higher level signal means the noise needn't be amplified as much.
Unbalanced mic cables need to be kept short to avoid HF rolloffs for impedance reasons, and 10' is typically a good general limit there. I've run line-level unbalanced signals 40' without problems using two 20' RCA's plugged together for soundboard feeds. I was somewhat concerned about interference, but haven't had problems doing it. Again, a the strong line-level signal helps there.
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Thanks for the info! much appreciated.