The ADCOM GFA-565 is a high-current power amplifier designed for high-fidelity audio systems. It is engineered to deliver substantial power into a wide range of loudspeaker loads, including those with very low and reactive impedances, while maintaining extremely low distortion. The amplifier's design emphasizes robust power delivery and sonic purity, avoiding protection circuitry that could degrade the audio signal.
Function Description:
The GFA-565 serves as the final amplification stage in an audio system, taking a low-level audio signal from a preamplifier and boosting it to a high-power level suitable for driving loudspeakers. It can operate in a stereo mode, providing two channels of amplification, or in a bridged mono mode, combining its power into a single, more powerful channel for driving a single loudspeaker. The amplifier is designed to handle demanding loudspeaker loads, including those with complex reactive characteristics, without compromising performance or introducing significant distortion. Its high-current capability allows it to deliver large peak currents, exceeding 70 amperes per channel, which is crucial for dynamic and impactful sound reproduction, especially with challenging speaker designs.
Important Technical Specifications:
- Power Rating (FTC Requirements):
- 250 watts continuous average power into 8 ohms (20Hz-20kHz, <0.04% THD, both channels driven).
- 350 watts continuous average power into 4 ohms (20Hz-20kHz, <0.05% THD, both channels driven).
- 700 watts continuous average power into 8 ohms (20Hz-20kHz, <0.1% THD, bridged).
- IM Distortion (SMPTE):
- 1 watt to 250 watts into 8 ohms: ≤0.009%
- 1 watt to 350 watts into 4 ohms: ≤0.009%
- Bridged (SMPTE) 1 watt to 700 watts into 8 ohms: ≤0.05%
- IM Distortion (CCIF, 4kHz to 20kHz):
- 250 watts into 8 ohms: ≤0.002%
- 350 watts into 4 ohms: ≤0.003%
- Bridged (CCIF) 700 watts into 8 ohms: ≤0.005%
- THD + Noise (at 250 Watts into 8 Ohms):
- 20Hz: 0.008%
- 1kHz: 0.004%
- 10kHz: 0.006%
- 20kHz: 0.010%
- THD + Noise (at 350 Watts into 4 Ohms):
- 20Hz: 0.009%
- 1kHz: 0.004%
- 10kHz: 0.015%
- 20kHz: 0.025%
- THD + Noise (at 400 Watts into 8 Ohms, Bridged):
- 20Hz: 0.001%
- 1kHz: 0.004%
- 10kHz: 0.020%
- 20kHz: 0.040%
- Frequency Response @ 1 Watt into 8 Ohms (10Hz to 20kHz): +0.-0.25dB
- Power Bandwidth (-3dB): 5 Hz to 100kHz
- Dynamic Headroom into 4 Ohms: 2.5dB
- Signal-to-Noise Ratio, "A" Weighted (250 watts into 8 ohms): ≥110dB
- Gain: 27.0dB
- Input Impedance: 100,000 ohms
- Input Sensitivity:
- 250 watts into 8 ohms: 12.1V rms
- 1 watt into 8 ohms: 130mV rms
- Damping Factor (20Hz to 20kHz): >800
- Rise Time (5kHz, 90V peak-to-peak square wave, 20% to 80%): 2.3us
- Semiconductor Complement: 46 transistors, 2 zener diodes, 13 diodes, 2 ICs, 2 diode bridges
- Power Consumption (Continuous, Both Channels Driven):
- Quiescent: 88VA
- Maximum: 1800VA
- 250 watts into 8 ohms: 835VA
- 350 watts into 4 ohms: 1350VA
- 700 watts into 8 ohms, bridged: 1550VA
- General Power: 120VAC/60Hz
- Chassis Dimensions: 6-3/4" (172mm) x 17" (432mm) x 13-7/16" (340mm)
- Maximum Dimensions: 7-1/4" (185mm) x 17" (432mm) x 14-3/16" (360mm)
- Weight: 51lbs (23kgs)
- Weight, Packed: 55lbs (25kgs)
Usage Features:
- High Current Design: Capable of delivering over 70 amperes per channel, ensuring robust performance with low-impedance and reactive loudspeaker loads.
- Triple-Darlington Output Stage: Utilizes ten sets of specially selected TO-3-type, metal-cased bipolar output transistors for efficient power delivery and wide safe operating area.
- No Current-Limiting Circuitry: Avoids protection circuits that could degrade the audio signal, relying instead on DC rail fuses for protection.
- Massive Power Supply: Features an extremely large toroidal transformer and 72,000uF of filter capacitance for enormous reserve power capability and stable voltages.
- Direct-Coupled Circuitry: Minimizes sonic deterioration caused by capacitors between amplification stages, allowing amplification of DC and unlimited low-frequency energy delivery.
- OFC Internal Wiring: All internal point-to-point wiring is made of Oxygen-Free Copper (OFC) for optimal signal transfer.
- High-Quality Components: Employs highest-grade parts, including precision non-polarized film capacitors in critical circuits.
- Servo Circuit: Minimizes DC-offset voltage at loudspeaker outputs, preventing woofer "biasing" and low-frequency distortion.
- Dual Heatsinks: Larger outside double heatsinks per channel for greater heat dissipation, better temperature, and dynamic bias tracking, ensuring thermal stability.
- Enhanced Cooling: More cooling vents on the top cover and chassis for greater cooling efficiency, allowing cooler operation into lower impedances.
- Gold-Plated RCA Input Jacks: High-quality, gold-plated brass RCA input jacks with Teflon insulators for minimal high-frequency losses and noise.
- Balanced XLR Inputs: Two high-quality balanced XLR jacks for professional connections, minimizing high-frequency losses and noise.
- 5-Way Binding Post Speaker Terminals: High-grade, gold-plated brass terminals accommodate bare wire, tinned wire, terminal pins, spade lugs, and single or dual banana plugs.
- Stereo/Bridged Mono Operation: A switch allows selection between stereo mode and a more powerful bridged mono mode for single-channel amplification. In bridged mono, input is via the LEFT INPUT RCA jack, and output connections are specific to this mode (LEFT RED output binding post for positive, RIGHT RED output binding post for negative).
- INSTANTANEOUS DISTORTION ALERT LEDs: Unique ADCOM distortion-detection system that lights when non-linear distortion (THD, IM, slew-induced, clipping) reaches 1%, warning of amplifier overdrive.
- THERMAL PROTECTION LED: Indicates when the thermal protection circuit has shut down the amplifier due to heatsink temperatures exceeding 85°C. The amplifier automatically resumes operation once temperatures drop to a safe level.
- AC ON/OFF Switch: Rocker switch on the front panel to energize/de-energize the amplifier.
- POWER LED: Glows when the amplifier is energized, indicating AC voltage is supplied.
- Rack-Mountable: Optional rack-mount adaptors are available for professional installations in standard 19-inch racks.
Maintenance Features:
- Ventilation Requirements: Requires adequate air circulation with four inches of clearance on the top and all sides to ensure proper heat dissipation and long-term, trouble-free operation. Avoid placing near external heat sources or in enclosed cabinets without free airflow.
- Dust and Moisture Protection: Recommend protection from excessive dust and moisture. Occasional vacuuming of accumulated dust on chassis, panels, and heatsinks is advised.
- DC RAIL FUSES: Provides protection for output stages and power supply. Replacement fuses are supplied, and only specific types listed in the manual should be used to avoid damage and voiding the warranty. The power supply capacitors can take more than five minutes to discharge after turning off the amplifier, so caution is advised when replacing fuses or connecting/disconnecting loudspeakers.
- AC LINE FUSE: Protects the electronic circuits of the amplifier. Only specific types listed in the manual should be used for replacement. If the fuse blows immediately after replacement, internal malfunction is suspected, and professional service is required.
- Transformer Thermostat: An internal thermostat interrupts power if the transformer temperature exceeds 125°C, resetting automatically once the temperature decreases.
- Cleaning: The front panel, chassis, top cover, and rear panel can be cleaned with a soft, lintless cloth slightly dampened with a mild detergent solution or non-ammonia glass cleaner. Avoid spraying liquids directly onto the amplifier.
- Warranty and Service: ADCOM offers a Limited Warranty and provides a Technical Service Department for support. Online warranty registration is available. When returning for service, prior authorization and original packaging are required. Shipping must be prepaid via approved carriers (UPS, FDX, etc.).
Need help?
To Next Page
General
