Audio Technologies HDA400 stereo headphone amplifier Operating and maintenance manual

HDA400
STEREO HEADPHONE AMPLIFIER
OPERATING AND MAINTENANCE MANUAL
© Copyright 1997-2007, Audio Technologies Incorporated - Printed in USA
Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www.
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DESCRIPTION
The HDA400 is a rugged, AC powered headphone amplifier, which will provide
excellent performance driving a wide range of typical stereo headphones. It will
drive the usual 32 to 600 ohm high efficiency stereo headphones to teeth rattling
levels near 120dB SPL with a combination of high output voltage swing (16Vp-p)
for high impedance phones and a protected high current capability (.2Ap-p) for
low impedance phones. It will do the above at distortion levels below .10% and
response flat to .25db both measured over the full frequency range of 20Hz to
20kHz.
The HDA400 has balanced, bridging ¼ inch TRS stereo program inputs with front
panel CLIP indicator, MASTER level control and MONO/STEREO switch. Inputs
are electronically balanced but will operate properly when if an unbalanced ¼
inch TS plug is inserted. An internal input stage gain selector plug (P2) optimizes
the input stage gain for either -10dBu or +4dBu nominal inputs or the program
INPUT CLIP indicator shows input overdrive. A MASTER LEVEL control and
MONO/STEREO switch adjust the program signal fed to all output channels
Four high compliance output channels drive paralleled front and rear ¼ inch TRS
output headphone jacks. The high compliance output circuitry comfortably drives
all phones from 32 to 600 ohms. Although designed to drive either the front or the
rear output jack, the HDA400 will drive two sets of headphones plugged into the
same channel with only slightly reduced drive to each. To minimize major
loudness differences use identical headphones. Individual output channels can
be setup for monaural operation by inserting a jumper wire into the WX02
position of the desired channel. Do not use mono headphones with a Tip- Sleeve
plug with the HDA400. The rear jacks can also feed remote headphone
distribution boxes.
The HDA400 includes an internal bi-polar power supply, which will operate at 115
or 230VAC by changing internal jumpers. The power cord is a standard IEC320
type that you can easily swipe from someone else if you lose it.
CONNECTIONS
Balanced inputs are connected with their HI to TRS -TIP and LO to TRS-RING,
Shields go to TRS-SHLD. Unbalanced input lines should be connected with their
center hot wire to TRS-TIP and with the cable shield to TRS-SHLD. Be careful to
observe HI-LO input polarity to avoid monaural or center stage cancellation
effects The HDA400 is shipped setup for -10dBu nominal input level (+12dBu
peak). An internal jumper plug P2 may be moved to accommodate levels at
+4dBu nominal (+22dBu peak). To change P2, remove the top cover by
removing the four upper Phillips head screws (two on each side). P2 is located
on the right side of the PC board directly behind the volume control and has two
positions; for –10dBu inputs move the plug to the left, for +4dBu inputs move the
plug toward the right. Ensure that no internal wiring is caught or pinched, replace
the cover and screws.
Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www.
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Use only TRS output plugs and stereo headphones. The use of TS plugs on
mono headphones shorts one headphone output to ground. Although this will not
damage the HDA400, it will load down the power supply and reduce maximum
output levels to the other output channels. Output TRS plugs should all be wired
left to TIP, Right to RING and common to SHIELD.
CAUTION
The HDA400 provides a comfortable listening level of 1mW at around 12 o’clock
on the volume control for most headsets. The HDA400 is capable of driving many
headsets to DANGEROUS LEVELS over 120dB SPL. If you can hear distortion,
it’s TOO LOUD! Levels near 120dB SPL can easily cause PERMANENT
HEARING DAMAGE, BE CAREFUL! Treat your ears with tender loving care and
they will follow you anywhere.
PERFORMANCE SPECIFICATIONS
OUTPUTS:
Four high compliance 6V/80mA stereo drivers capable of
over 100mW into 32 to 600 ohm stereo headphones
DYNAMIC RANGE: 110dB Typical at output into 600-ohm headphones
DISTORTION:
.10% THD maximum, 20-20000 Hz, below clipping
RESPONSE:
+0/-.5dB, 20-20000 Hz
GAIN:
26dB maximum
NOISE:
-90dBu E.I.N., 20 – 20000 Hz
SEPARATION:
70dB minimum at 1kHz
INPUTS:
Stereo, 20K balanced, bridging, -10/+4dBu nominal
INDICATORS:
INPUT CLIP - onset of input stage clipping, Yellow LED
POWER – monitors internal DC voltage - Red LED
POWER:
115/230VAC, 50/60Hz, 24VA, and IEC320 3 pin connector
SIZE:
1RU package; 19” (48.3cm) W x 1 ¾” (4.5cm) H x 7.5”
(19.05cm) D 15lbs (6Kg)
Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www.
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