Adcom GFA 5503 Service Manual

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SERVICE MANUAL

ADCOM®

details you can hear

3 CHANNEL
POWER AMPLIFIER

GFA-5503

TABLE OF CONTENTS

Introduction ................ 1
Test Procedures ............. 1
Parts List .................. 2
Voltage Conversion ............ 5
Specifications ............... 7
Schematic ................. 8

8551 East Anderson Drive, Suite 105
Scottsdale, Arizona 85260
USA
Tel: 480-607-2277
Fax: 480-348-9876

Web: http://www.adcom.com

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INTRODUCTION

This service manual is intended to assist trained and qualified technical personnel in verifying the
performance of, adjusting, and repairing the ADCOM GFA-5503 amplifier. The procedures described
here are not intended for persons unfamiliar with the appropriate safety and test procedures.

XII WARNING NJ"

THERE ARE POTENTIALLY LETHAL VOLTAGES WITHIN THE GFA»5503 AMPLIFIER WHICH WILL
BE ACCESSIBLE ONCE ITS TOP COVER IS REMOVED. DO NOT ATTEMPT FAMILIARIZATION,
INSPECTION, OR ANY PROCEDURE WHATSOEVER UNLESS You HAVE DISCONNECTED THE
GFA-5503 FROM THE WALL AC OUTLET OR OTHER SOURCE OF AC POWER AND THE POWER-
SUPPLY CAPACITORS ARE COMPLETELY DISCHARGED. THESE INSTRUCTIONS ARE
PROVIDED FOR USE ONLY BY COMPETENT TECHNICAL PERSONNEL. Do NOT UNDERTAKE
ANY SERVICE PROCEDURES IN THE GFA-5503 UNLESS YOU ARE TECHNICALLY QUALIFIED
TO DO so.

TEST PROCEDURES

. All tests are performed with a 115V, low-distortion (less than 2% THD), AC-power source, 8-ohm
resistive load (except slew rate), and a signal source of not more than 600 ohms.

An 80kHz low-pass filter is employed during THD distortion measurements.

Signal-to»noise measurements are A" weighted.

Damping factor is measured by comparing the 1 watt output voltage with and without an 8 ohm load.
Slew rate is measured with an inductive load, and is derived with a dual-time-based oscilloscope
reading the slope of a full power 5kHz square wave. DO NOT OPERATE THE AMPLIFIER AT
FULL-POWER SINE WAVE ABOVE 22kHz OR FULL-POWER SQUARE WAVE ABOVE 5kHz.

IMPORTANT
BEFORE PROCEEDING WITH ADJUSTMENTS, MAKE SURE AMPLIFIER IS AT ROOM
TEMPERATURE.

CORRECT BIAS ADJUSTMENT IS CRITICAL TO THE PERFORMANCE OF THIS AMPLIFIER.
MAXIMUM OUTPUT POWER, MINIMUM THD AND HEAT DISSIPATION ARE AFFECTED BY THE
BIAS SETTING AND MUST BE CORRECT TO MAINTAIN THE SONIC QUALITY AND LONGEVITY
OF THE AMPLIFIER.

BIAS ALIGNMENT

Prior to performing BIAS ALIGNMENT turn unit on and allow to idle for approximately 5 MINUTES before
attempting adjustments.

1. Connect millivoltmeter across emitter resistor R52 for left channel (R52 for center channel, R51 for
right channel)
2. Adjust bias pot P2 until meter reads 50mV +/» 5mV

DC OFFSET ADJUSTMENT
Connect millivoltmeter across speaker output
Adjust DC offset pot P1 until meter reads OmV +/- 10mV

N-A

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GFA-5503 SPECIFICATIONS

Power Rating (To FTC Requirements)
200 watts continuous average power per channel into 8 ohms at any frequency between 20Hz to 20kHz with
all channels driven at less than 0.18% THD
350 watts continuous average power per channel into 4 ohms at any frequency between 20Hz to 20kHz with
all channels driven at less than 0.18% THD

IM Distortion (SMPTE)
1 watt to 200 watts into 8 ohms
1 watt to 350 watts into 4 ohms

S 0.05%
.. S 0.05%

IM Distortion (CCIF, Any Combination trom 4kHz to 20kHz)
200 watts into 8 ohms .. g 0.04%
350 watts into 4 ohms .. s 0.04%

THD + Noise at 200 watts into 8 ohms (Typical)

20HZ ..... 0.018%
1kHZ ..... 0.02%
10kHZ... 0.07%
20kHZ ..... 0.13%

THD + Noise at 350 watts into 4 ohms (Typical)

20Hz.. . 0.018%

1kHz.. 0.02%

10kHZ... 0.08%

20kHz... .. 0.16%
Frequency Response @ 1 Watt into 8 ohms (10Hz to 20kHz) ... +0, -0.25dB
Power Bandwidth (-3dB) ... 3H2 to 130kHz
Dynamic Headroom into 4 ohms ... 1.7 dB
Signal to Noise Ratio, A Weighted (200 watts into 8 ohms) . 2 100dB
Gain .... 29dB
Input Sensitivity

for 1 Watt ..... .. 0.1 volts

.. 1.4 volts

for 200 Watts..

Input Impedance .. 49.9kQ
Damping Factor (20Hz to 20kHz) .... 2 700
Rise Time (5kHz, 90V, peak-to-peak square wave, 20% to 80%) .. 1.5pS
Power Consumption (Continuous, All Channels Driven)
Quiescent. .. 199VA
Maximum.. .. 855VA
80 watts into 8 ohms. 1440VA
125 watts into 4 ohms.. ..... 720VA
Power (Available in 230VAC on special order) ..... 115VAC - 50/60Hz
Chassis Dimensions . 7 (178mm) x 17 (432mm) x 16 (406mm)
Maximum Dimensions. 7 1/4 (184mm) x 17 (432mm) x 16 (406mm)
Weight .. .. 57 lb. (20 kg)

Weight, Packed .. . 63 lb. (23 kg)