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APPLICATIONS
The HPA Jr headphone amplifier is a compact, battery/external Vdc powered amplifier designed to interface your
favorite full-sized professional headphone to a variety of audio input sources. Now you won't be limited to small,
poor quality in-ear or "walkman" type headphones for your monitoring or listening needs. The HPA Jr will allow
you to drive headphones of many impedances to more than adequate listening levels with a full, rich sound not
obtainable at low output levels or with lightweight personal earpiece / headphones. You can use the HPA Jr for
such professional purposes as increased monitor levels from: mixers, portable VCR's, tape recorders or R-DAT's,
personal listening to keyboards and synthesizers or monitoring of home studio gear. You can have fun using an
HPA Jr to produce "concert hall" sound from your "walkman" type player, VCR, CD player or tape deck or from
any source with a headphone or line out signal.
FEATURES
Stereo/Mono Selector Switch:
allows you to hear a monaural source in both ears or to "mono-up" a stereo (or two
channel) source.
Input Sensitivity Switch:
allows selection of either -10dBm or-30dBm input levels so you can match the HPA Jr
to your input source.
Battery/External DC Operation:
you can power the HPA Jr with either two 9 volt transistor radio type batteries
or with any 12-18 Volt dc source through the "EXT +12Vdc" 3.5mm jack.
Standard ¼" Tip/Ring/Sleeve (stereo) I/O Connectors:
Both input and output connectors are the commonly
available ¼" TRS type... NO ADAPTERS NEEDED for most headphones!
Power Switch With LED Indicator:
a convenient pushbutton switch for power on/off, along with a red LED
power on indicator.
Belt Clip:
for convenient hands-free operation.
INSTRUCTIONS FOR USE
Battery Power:
Install two 9 Volt batteries (Duracell MN1604 or equal) in the battery clips provided, using the
two polarized connectors. Access to the battery compartment is gained by removing the four phillips head screws
(two on the sides, two on the bottom) on the unit and sliding off the back cover. When the power switch is pressed,
the red LED will glow showing correct battery installation. Fresh battery life is approximately six hours of
continuous operation.
External DC Power:
Connect a tip/sleeve (mono) 3.5mm plug to the "EXT +12Vdc" jack on the bottom of the
unit. IMPORTANT NOTE: Please observe proper polarity when using external power - the TIP of the plug should
be "+" and the SLEEVE "-". 12-18Vdc may be applied, either from external batteries or via an ac/dc converter like
the GOLD LINE model BE1. A switch in the jack disconnects the internal batteries when external Vdc is applied.
Input/Output Connectors And Gain Setting:
Always begin with the HPA Jr sensitivity set to its lowest (-10dBm)
gain setting. (The sensitivity switch positioned AWAY from the red dot.) The sensitivity switch is located inside
the HPA Jr. For access to the sensitivity switch, see Battery Power above. Connect the input source to the INPUT
jack using a ¼" tip/ring/sleeve plug: TIP is left channel in, RING is right channel in and SLEEVE is
common/shield. Connect the headphones to the OUTPUT jack, again using a standard ¼" TRS plug (usually found
on most headphones). A slight rushing sound in the headphones when the power switch is depressed (with no input
signal applied) will indicate that the HPA Jr is functioning. With the level controls at their fullest counter-
clockwise positions (off), apply the input signal. Adjust the level controls for a comfortable listening/monitoring
level. If it is not possible to produce enough gain from the input source being used, turn the power off and reset the
sensitivity switch to -30dBm (red dot) position. Apply power and repeat adjustment of the level controls, always
beginning at the off (counter-clockwise) position to protect the headphones and your ears. The HPA Jr's high input
impedance allows you to connect it to a variety of sources without loading them, thus you can plug into the
headphone jack of most consumer equipment as well as the line out of tape decks, synths., and home studio
recording equipment. HELPFUL HINT: If your input source has its own output level or volume control, you can
use it to fine tune the resolution of the HPA Jr's level controls. Set the source's level/volume control to the point
where you can obtain the most comfortable control range (resolution) with the HPA Jr's
level controls. Also use
any source level/volume control to trim the input to the HPA Jr to prevent overload distortion, especially if the
input signal exceeds -10dBm.
