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Shorting any input connector pin
to the case may form a ground
loop and cause hum.
Standard audio cables with
XLR-type connectors may be used
for balanced signal sources. Unbal-
anced sources will require an in-
line adapter.
Operation
In normal operation, the front-
panel LED will glow green.
At high listening levels, the LED
may flash red on program peaks.
This indicates the onset of over-
load, where the loudspeaker
protection limiters are activated.
If the LED is continuously red
for an extended period (8 hrs.),
thermal damage may result.
Calibration Port
The calibration port is for factory
use only. Do not apply external
voltages to any of the connector
pins.
Input Connection
The HD-1 presents a 10 kohm
input impedance at a three-pin
XLR-type receptacle wired as
follows:
Pin 1 Audio common
Pin 2 Signal low (-)
Pin 3 Signal high (+)
Case Earth (AC) ground
Sensitivity Switch
• For professional balanced
equipment, use the +4 dBu
setting.
• For semiprofessional and
consumer unbalanced equip-
ment, use the -10 dBV setting.
Note that the -10 dBV setting is
more sensitive (designed for lower
signal levels) than the +4 dBu
setting:
• +4 dBu position:
1.23 VRMS = 114 dB SPL RMS
• -10 dBV position:
0.316 VRMS = 114 dB SPL RMS
Troubleshooting
Problem Symptom Possible Cause Action
Check AC outlet and power
cord.
Replace fuse. Check voltage
selector and AC line.
Check input cables, connec-
tots and signal source.
Bad AC connectionPower switch on but switch
not lit
Power switch on and lit, LED
out
Power switch on and lit, LED
lit
No sound
Blown fuse
Signal source disconnected
Distorted sound with hum
AC voltage selector incor-
rectly set
Turn off HD-1. Check AC
outlet voltage and selector
switch setting.
Turn off HD-1. Check AC
outlet voltage; if low, contact
power company.
Power brownout
Low sound levels Insufficient drive from signal
source
Input sensitivity incorrectly set
Increase source equipment
output level.
Set input sensitivity switch to
-10 dBV
Selector switch setting correct
Hiss Input sensitivity incorrectly set
Distorted or intermittent
sound
Input cables OK
Bad input connection
Defect in signal source
equipment
Check input cables
Substitute known good signal
source. If problem stops,
replace signal source
equipment.
Driving the HD-1 from a +4 dBu
source with the switch set to -10
dBV will result in increased noise.
Sensitivity setting correct
Check sensitivity switch and
source equipment output.
Stop playback. If hiss
disappears, check program.
Unplug input connector. If
hiss disappears, check
source equipment.
Program material
Source equipment malfunc-
tion
Program material OK