This document describes the Panasonic SU-373 Stereo Integrated Amplifier, a component of the SC-3730 system.
Function Description
The Panasonic SU-373 is a stereo integrated amplifier designed to process and amplify audio signals from various sources, delivering them to speakers or headphones. It features multiple input selectors for different audio components, tone controls for sound adjustment, and a power amplifier section. The amplifier also incorporates a protection circuitry to prevent damage from short circuits or incorrect speaker impedance. A remote control transmitter is included for convenient operation.
Important Technical Specifications
Amplifier Section:
- Rated Minimum Sine Wave RMS Power Output: 100W per channel (8 ohms) at 20 Hz - 20 kHz, both channels driven, with 0.09% total harmonic distortion.
- 1 kHz Continuous Power Output: 105W per channel (8 ohms), both channels driven, with 0.09% total harmonic distortion.
- Dynamic Headroom: 1.1 dB (8 ohms).
- Total Harmonic Distortion (half power at 1 kHz): 0.09% (8 ohms).
- SMPTE Intermodulation Distortion: 0.09% (8 ohms).
- Frequency Response:
- PHONO: RIAA standard curve ±0.8 dB.
- TUNER, CD/AUX, TAPE 1, TAPE 2/EQ: 10 Hz ~ 70 kHz, -3 dB.
- Input Sensitivity:
- PHONO: 0.4 mV (2.5 mV, IHF '66).
- TUNER, CD/AUX, TAPE 1, TAPE 2/EQ: 15 mV (150 mV, IHF '66).
- S/N (IHF, A):
- PHONO: 71 dB (73 dB, IHF '66).
- TUNER, CD/AUX, TAPE 1, TAPE 2/EQ: 75 dB (94 dB, IHF '66).
- Maximum Input Voltage (PHONO): 128 mV (135 mV, 1 kHz).
- Input Impedance:
- PHONO: 47 kilohms.
- TUNER, CD/AUX, TAPE 1, TAPE 2/EQ: 20 kilohms.
- Tone Controls:
- BASS: 50 Hz, +10 dB ~ -10 dB.
- TREBLE: 20 kHz, +10 dB ~ -10 dB.
- Loudness Control (volume at -30 dB): 50 Hz, +9 dB.
- Output Voltage (TAPE 1, TAPE 2/EQ REC OUT): 150 mV.
- Low Frequency Damping Factor: 50 (8 ohms).
- Load Impedance:
- MAIN or REMOTE: 8 ~ 16 ohms.
- MAIN and REMOTE: 8 ~ 16 ohms.
General:
- Power Consumption: 360W, 470 VA.
- Power Supply: AC 120V, 60 Hz.
- Dimensions (W x H x D): 430 x 119 x 240 mm (16-15/16" x 4-11/16" x 9-7/16").
- Weight: 7.0 kg (15.4 lb.).
- Color: Black Type (K).
- Area: U.S.A. (M).
Usage Features
The SU-373 amplifier offers a range of controls and connections for versatile audio setup.
- Input Selectors: Dedicated buttons for PHONO, TUNER, CD/AUX, TAPE 1, and TAPE 2/EQ allow users to switch between different audio sources. Indicators show the currently selected input.
- Tape Monitor Function: TAPE 1 and TAPE 2/EQ inputs/outputs enable connection of tape decks for recording and playback, with a monitor selector to listen to the source or the recorded signal.
- Tone Controls: Separate BASS and TREBLE knobs provide adjustment of low and high frequencies, respectively, to tailor the sound to personal preference.
- Loudness Switch: Engages a loudness contour to boost bass and treble frequencies at low volume levels, compensating for the ear's reduced sensitivity to these frequencies.
- Volume and Balance Controls: A large volume knob adjusts the overall output level, while a balance control allows fine-tuning of the left and right channel output. Volume/balance level indicators provide visual feedback.
- Peak-Power Meters: LED power level meters display the output power, helping users monitor signal levels.
- Headphones Jack: A front-panel jack allows private listening through headphones.
- Speaker Selectors: Buttons to select MAIN, REMOTE, or both sets of speakers.
- Remote Control: The amplifier is compatible with a remote control transmitter (EUR64196) for convenient operation from a distance. A flat cable (SWKUV96KM) is provided for remote control operation.
- AC Outlets: Two unswitched AC outlets are provided on the rear panel for connecting other audio components, allowing them to be powered on/off with the amplifier.
- Ground Terminal: A GND PHONO TUNER terminal is available for connecting the ground wire of a turntable, though it is noted that for some turntables (e.g., SL-H309U), a ground wire connection is not required.
- Pre Out/Main In: These terminals allow the amplifier's preamplifier and power amplifier sections to be used independently or to connect external audio processors like graphic equalizers.
Maintenance Features
The manual provides detailed instructions and precautions for servicing and maintenance:
- Safety Precaution: Emphasizes unplugging the power cord before servicing, using manufacturer-recommended components for replacement parts, checking the power cord condition, restoring insulation barriers, and performing an insulation resistance test before returning the equipment to the customer.
- Insulation Resistance Test: A specific procedure is outlined to measure insulation resistance between the AC plug and exposed metal parts to ensure safety against electric shock.
- Protection Circuitry: The amplifier includes a protection circuit that activates if conditions like shorted speaker wires or incorrect speaker impedance are detected. If activated, the unit will not operate until the power is turned off and then on again after the problem is corrected.
- Before Repair: Instructions include disconnecting AC power, discharging power supply capacitors through a 10Ω, 5W resistor to prevent damage to solid-state devices, and gradually restoring power with a variac to avoid overcurrent. Normal current consumption at 120V, 60Hz in NO SIGNAL mode should be 250~500mA.
- Disassembly Instructions: Step-by-step guides with diagrams are provided for removing the front panel, P.C.B.s (Printed Circuit Boards), power amplifier IC, and bottom board.
- Thermal Compound Application: When mounting the power IC, it is specified to apply silicon thermal compound (SZZ0L15 or equivalent) to the rear of the power IC for proper heat dissipation.
- Terminal Guide: A guide for transistors, diodes, and ICs is included to aid in component identification during servicing.
- Replacement Parts List: Comprehensive lists of resistors, capacitors, integrated circuits, transistors, diodes, lamps, fuses, switches, accessories, and cabinet and chassis parts are provided with part numbers and descriptions for easy replacement.
- Caution for Micro-Computer: Specific warnings are given regarding the IC203 micro-computer, noting that it is sensitive to static electricity and that new ICs are shipped in conductive foam boxes. It advises against touching the IC or LSI with fingers directly.
- Schematic and Connection Diagrams: Detailed circuit diagrams and wiring connection diagrams are included to assist technicians in troubleshooting and repair.
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