Behringer DJ Equipment SX4882 Manual De Usuario

EURODESK SX4882 User Manual

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PFL (Pre-Fader-Listening) is the way to set a desk level. Setting up the channel 

input gain is discussed in the essential section 13. Optimum master aux send 

levels will be dependent on the sensitivity of the FX device being driven, 

but unity gain is a useful starting point. As the mix progresses, more and more 

channels are likely to be sending to effects via the aux buses, and it’s best to 

PFL all sends (aux, subgroup, MIX-B) just before setting up for the final mix.
Outboard reverbs etc. should all be made to work hard. There’s no point in having 

an 85 dB dynamic range if the input meter of your reverb is barely flickering. 

On the other hand, digital distortion is not one of the nicer noises around. 

Fortunately you can SOLO the FX returns. Here you’ll have to rely on your ears 

to detect digital distortion, since different outboard processors calibrate their 

meters differently, and their dynamic range is not sufficient to allow, say, 15 dB of 

headroom (as is the case with DAT etc.). The PFL/SOLO meter, on the other hand, 

looks only at the desk’s analog aux input level, if you hear distortion, but the 

meter says you’re just hitting 0 dB, then it must be coming from the aux send 

amp or the FX unit. If PFL on the aux send reveals nothing amiss, turn down the 

input on the FX unit, and turn up the desk’s aux return.

Electronic inputs tend to have impedances measured in tens of kiloOhms. 

Outputs, on the other hand, are generally two or three orders of magnitude less. 

This is just as well, otherwise a signal at an output might find that the line of 

least resistance is the limit of the preceding unit.
In the patchbay section we recommended that you parallel the MAIN MIX output 

of the EURODESK SX4882 into all 2-track recording inputs. It would not do any 

harm to buffer each output from the primary one (i.e. that feeding into your most 

expensive DAT recorder or 1/2” mastering machine) with a 470 Ohm resistor. 

Cassette, DAT and reel to reel recorders’ input impedances should be similar, 

but just in case they aren’t, it is better to add a fraction of a dB of thermal noise to 

the inputs of the secondary recorders in the shape of a resistor, rather than 

having an unusually low impedance input grabbing most of the signal. 

Another neat idea is to parallel the Monitor L/R output via a 47 kOhm resistor 

pair. Now you can safely connect e.g. a tuner to either extra hole, without shifting 

the stereo image (this would happen if a low impedance tuner input was 

connected directly across one side of the monitor output). Now, whenever you 

monitor an instrument’s input level with the PFL/SOLO function, you can check 

its tuning also. That should impress the customers. Especially those using old, 

unstable, but very desirable analog synths.

Fig. 11.1: Resistor-buffered parallel wiring for bay 8 (see section 8 “The patchfield”)

Balanced inputs and outputs are offered on most audio connections on the 

EURODESK SX4882 (inserts and direct outs being the major exceptions).
Why? Though all audio cables (except speaker cables) have earthed screens, 

the shielding they afford from the electromagnetic garbage that permeates 

the atmosphere is never perfect. The balanced line is a simple but effective 

mechanism to overcome this problem. Instead of one insulated audio 

conductor, two, usually twisted together, are contained within a single screen. 

One conductor, wired to pin 2 of an XLR-type connector by international 

convention (after decades of total confusion!) carries a signal variously referred to 

as “hot” or “positive”. Pin 3 is wired to the “cold” or “negative” conductor.
What does this mean? Consider an unbalanced line. Now, that’s much easier 

to understand. You have one “hot” or “positive” core, and an earthed screen. 

The “hot” wire’s waveform, if looked at on an oscilloscope, would be directly 

correlated to the audio signal waveform. If you looked closely at the trace, 

you‘d see random noise along the X axis. What you probably wouldn’t see, 

however, is any superposition of 50, 100 Hz, etc. corresponding to mains hum 

interference, since these frequencies would be tangled up in the audio signal 

(to spot them visually you’d need to perform a FOURIER TRANSFORM). AC mains 

frequency and its overtones are picked up by any wire, and some will always leak 

through a cable screen. The question is, when does it become audible?
Well, all other things being equal, the amount of mains hum picked up by a cable 

is independent of the signal level. Speaker lines run 50 or more volts, enough to 

diminish the effect of mains radiation to vanishingly small even with no screen. 

(In fact, at these voltages another effect comes into play: capacitive resistance. 

All output / input pairs normalised!