Hook-Up Cables And Hum Avoidance - Yamaha MQ802 Operating Manual

Ө AUX INPUTS (1 and 2).
These standard 1/4" (6.3 mm) phone jacks are unbalanced
inputs that apply signal to the Left and/or Right Program
mixing busses via the respective Aux 1 & 2 Level controls
and Pan Pots. Actual input impedance is 25КО, and nominal
level is —20dB (78mV rms), although the Aux Level control
can be adjusted for nominal levels as low as —32dB or as high
аз +4dB. The inputs are intended for nominal 60062 or higher
impedance sources, such as the return from echo or reverb
devices, the output of a tape recorder, or the line output of
another mixer.
Ө SUB IN JACKS (PGM L, РСМ В, FB, ECHO)
NOTE: While the Sub Inputs feed different busses (PGM L,
PGM R, FB, and ECHO), the functions are essential-
ly identical for all Sub In jacks.
These standard 1/4" (6.3 mm) phone jacks are unbalanced
inputs that apply a nominal +4dB (1.23V rms) signal to the
respective Program, Foldback and Echo mix busses via
internal isolation/attenuation pads. Actual input impedance
is 1k, and the inputs are intended for nominal 6000
sources. |
Sub inputs may be used for linking the program, foldback
and/or echo outputs of another mixer to this MO mixer for
expansion of the mixing system, or for applying any suitable
line-level source(s) to the mixer subject only to the mixer's
Master Faders. A common use of the PGM Sub Inputs, for
example, is to play back a stereo program from a tape
recorder (for set up or during intermission) without "using
up" input channels.
© AC POWER CORD
This AC power cord (grounded type) connects to suitable 50
or 60Hz AC mains. Refer to the mixer specifications (page
13), or the label on the mixer's rear panel, for specific line
voltage and power requirements.
The mixer should be AC grounded for safety and for opti-
mum shielding against noise; a 3-conductor power cable is
provided for this purpose. If a 3-wire AC outlet is not avail-
able, or if there is any chance the AC outlet may not be
grounded, a separate jumper wire must be connected from
the mixer chassis to an earth ground. Cold water pipes
generally provide good grounds unless they are insulated by a
length of PVC (plastic) pipe or a water meter. (An electrical -
wire bypasses some water meters, supplying ground continui-
ty for the cold water pipes.) Avoid hot water pipes and gas
pipes. When in doubt, use a length of copper pipe driven into
moist, salted earth, burying at least 1.5 meters (b feet) of
pipe; alternately, use a chemical type ground rod.
© MULTI-PIN "SNAKE" CONNECTOR
This connector (available only on the MQ1602) permits
convenient input of multiple microphone and line sources
from the stage via a "snake": a compound cable that carriés
multiple transmission lines from a multi-input junction box
on stage. This capability eliminates the mess and inconveni-
ence of having to run individual lines from each source to the
mixer inputs.
Hook-up Cables and Hum Avoidance
The mixer's primary input and output circuits are equipped
with transformer-isolated XLR-type connectors and phone
jacks. When the XLR-type connectors are used with the
appropriate 2-conductor shielded cables (e.g., standard
microphone cables), these circuits afford the optimum pro-
tection against hum, buzz, and other noise pick-up.
The XLR-type connectors are wired with pin 2 as. "audio
high" and pin 3 as "audio low", in accordance with DIN and
JIS standards. Some professional equipment and micro-
phones are wired with pins 2 and 3 reversed; generally this
will cause no problem, other than a polarity reversal.
However, if such a piece of equipment uses an XLR-type
connector for an unbalanced input, or if an МО-бегіеѕ
mixer's XLR-type connector is connected, via an adapter
cable to an unbalanced phone jack, the "high" side of the
audio circuit could be grounded. In this case, invert the
wiring of pins 2 and 3 in one XLR-type connector of the
interconnecting cable (or use a suitable polarity-reversal
adapter). Regardless of XLR-type connector polarity, if hum
is encountered try cutting the shield connection at one end
of the cable.
All phone jacks (except the stereo headphone jack) are
intended for use with standard tip/sleeve 1/4" (6.3 mm)
phone plugs and single-conductor shielded cable. Hum reduc-
tion should not be attempted by cutting the shield on these
cables. Instead, restrict unbalanced cables to about 10 feet
(3 meters), and try to set up the system so that either (a) the
equipment involved is all connected to the same AC circuit,
or (b) the third-wire AC mains ground is used on only one
piece of equipment, typically the mixer. Remember, break-
ing a ground path can create a shock hazard.
When routing any cables, especially unbalanced cables, avoid
strong sources of electro-magnetic interference (EMI) or
radio frequency interference (RFI) such as electric motors,
fluorescent lights, dimmer panels, and so forth. To avoid
crosstalk-induced feedback, never bundle microphone input
cables with mixer output cables; these cables should cross at
right angles where practical.
NETTEN TTE RST ҮТЕНҮ a a OC "P([rQOÓ——————————— ——— — — M MÀ M —— [Uti LATINA A ST RR шашин