Connecting.input-Lines - Crown D-150 Service Manual

Because the output wire gauge and length raises the resultant
source impedance or lowers the Damping Factor by adding series: «
selection. For dynamic moving-coil loudspeakers the valueRy --
should preferably be. that. measured by an ohmmeter across the
voice coil, rather than the manufacturer's rating. For elec
be used for R, -
ff the load (matching. teanstoriner, inductance, or ibe
electrostatic speaker system) appears as a short-circuitatiow freé
quencies, a large non-pélarized: capacitor' (paralleled with a
resistor)-should-be-placed:in series. withthe. jgad.
For electrostatic speakers (if the manufacturer has not provided a
lar Capacitor oF S90- 708 mitdand 4
ohn power resistor should be placed in senes with the plus +)
speaker lead. This. will prevent lerge low-frequency currents from
darnaging 'the: electrostatic" tansfortier 'or from unnecessarily
activating the D-150's protectivé.system. An effective test to
determine if such parts are-needed is to measure the DC re-
sistance between the output-terminals with a
résistarice-is tess than 3 ohms, the parts si
shown schematically in-Figare- Ss 9.
40,200...
FIGURE 3:9.
SCHEMATIC FOR FULL RANGE
ELECTROSTATIC SPEAKER, CONNECTION
should nét be used. A cormmon exariple is the standard 3-
circuit "inch phone jack. and lug awen. wired - for stereo
sound. .
4. Connectors having low-current-carrying capacity are "vers.
5. Connectors having any tendency to short, or having shorted
leads, are unadvisabie. on
Most commercially-available- headphones employ a A-circuit 4%
inch phone plug which violates condition No. 2. This is no handi-
cap if # pad is inserted between'the atip: jack, which is only
sensibie when such a large amp! is coupied to such a small
HE this precaution is not only may the trans-
ducer te-Gairned out but permanent hearing loss 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 foops;"and
feedback from output(s) to input(s). °
in high fidetity audio applications any good vacuun?-tube or solid-
State control center will operate'successfully into the 25K ohm
inputs "of the D-150. Occasionally a high-impedance output of
poorly-designed preamps will be encountered, and/or a larger
_ output coupling capacitor may be required (o prevent excessive
— fow-tr quency rolloff).
For. joudspeaker-driving applications, the vane should-be free of
large sub-audio or undesired low frequencies, as they cause over-
heating and overloading of the loudspeaker. To remove such low
frequencies, a series capacitor may be placed in the input signal
line. (The graph of Figure 3-12 indicates the effectofthe size of the .
capacitor on the frequency response. 1) Only a low-leakage paper,
oF cause general overload
'sewing -tate stage of the amip (which is employed to provide RF
overload protection). The following filters are recommended for
such applications (Figure 3-13),
A second precaution is "ground loops" — electronic jargon for un-
desirable circulating currents flowing in a grounding system. A
commion form of loop (possibly resulting in hurn In heoutpuld is a
pair of input cables whose area is subjected to a magnetic hum