ATI HDA400 User Manual

HDA400

STEREO HEADPHONE AMPLIFIER

OPERATING AND MAINTENANCE MANUAL

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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.

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