Crown D-150 - Installation Guide; Unpacking and Inspection; Mounting Options and Ventilation

Because the output wire gauge and length raises the resultant
source impedance or towers the Damping Factor by adding series.
resistance, the nomograph (Figure..3-11) is provided for wire
selection:
For
dynamic
moving-coil
loudspeakers
the
value
Ry:
«
should preferably be. that. measured by an ohmmeter across the
voice coil, rather than the manufacturer's rating. For elect
speakers and such, thenarufactuter' s rated impedance should.
be used for Ry.
if the load (matching, transformer, inductance, or fulbrange
electrostatic speaker system) appears as a short-circuit atlow ire
quencies, a large non-polarized capacitor (paraticled with a
resistor) should be placed:in series with the load.
For electrostatic speakers (if the fnanufacturer has not provided a
capacitor) an external. non: capacitor of 890-708 mid and 4
ohm power resistor should ‘be placed in series with the plus (+)
speaker: lead: “This: will prevent = low-frequency currents from
activating the D-150's protective system. Ari effective test to
determine if such parts are needed is to measure the OC re-
a meter. {f the
resistance is less than 3 ohms, the parts ‘should be added as
shown
schernatically
in
Figure
39,
Z
FIGURE 3-9.
SCHEMATIC FOR FULL RANGE
ELECTROSTATIC. SPEAKER.CONNECTION
“to ba tied coe durine tiated ) 4
should not be used. A commen example is the standard 3-
circuit “inch phone jack. and. Plug: when, wired, Aor stereo.
4. Connectors having low-current-carrying capacity are “ver-
boten.’ .
5. Connectors having any tendency to short, or having shorted
leads, are unadvisable. Es
Most comunercially-availabie headohonee employ a 4-circuit K-
inch phone plug which violates condition No. 2. This is no handi-
cap if d pad is inserted between! @ alvip-and jack, which is only
sensible when such a large amp fer i J
transducer. Hf this precaution is igri ; NOt Only may the trans-
ducerbebdrned out but permanent hearingloss could result. The
recommended pad is shown in Figure 3-10.
"FIGURE 3-10.
SCHEMATIC OF EARPHONE PAD
3.9 CONNECTING INPUT LINES
Connecting the inputs will require observance of three basic pre-
cautions: Undesirable signals to the inputs, “ground loops, ” and
feedback from output(s} to input(s).
In high fidetity audio applications any good vacuum-tube or salid-
state control center will operate successfully into the 25K ohm
inputs-of the B-150. Occasionally a high-impedance output of
poorly-désigned preamps will be encountered, and/or a larger
output coupling Capacitor may be required (to prevent excessive
low. frequency rolloff)..
For cles esosving sulications, the input should be free of
large sub-audio or undesired low frequencies, as they cause over-
heating and-overloading of the loudspeaker. To rermave such low
frequencies, a series capacitor may be placed in the input signal
line.
(The
graph
of
Figure
3-12
indicates
the
effectofthe
sizeof
the
capacitor on the frequency response.) Only a jow-leakage paper,
is employed to provide RF
overload protection). The following filters. are recommended for
such applications (Figure 3-13).
Asecond precaution is “ground loops” — electronic jargon for un-
desirable circulating currents flowing in a grounding system. A
common form of loop (possibly resulting in hum in the output) is a
pair of input cables whose area is subjected to.a magnetic hum
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