The Technics ST-9600 is a high-performance FM/AM stereo tuner designed for exceptional audio fidelity and versatile operation. This device is engineered to provide clear, low-noise reception of both FM and AM broadcasts, making it a central component for any high-quality audio system.
Function Description
The ST-9600 serves as a tuner, receiving radio signals and converting them into audio signals that can be amplified and played through speakers. Its primary function is to provide high-quality FM and AM stereo reception. The unit incorporates advanced circuitry to minimize noise and distortion, ensuring a clean and accurate audio output.
A key feature of the ST-9600 is its sophisticated recording and playback capability. When connected to a tape deck, the tuner allows users to record broadcast programs. The device includes a "Rec/Playback" switch with multiple positions ("AMP," "SOURCE," and "TAPE (LOW NOISE)") to optimize the signal path for different recording and playback scenarios.
- "AMP" Position: In this mode, the signal from the FM MPX (multiplex) or AM section is routed directly to the amplifier's input. The recording output (REC OUT) is taken from the signal after de-emphasis, allowing for direct recording of the broadcast signal. Playback from a tape deck is also routed through the amplifier.
- "SOURCE" Position: This setting is designed for recording the direct tuner output. The signal from the FM MPX or AM section is sent to the recording output before being processed by the amplifier's input. This allows for a clean recording of the source signal. Playback from the tape deck is then routed to the amplifier.
- "TAPE (LOW NOISE)" Position: This specialized mode is crucial for achieving high-quality recordings with minimal noise. When recording an FM broadcast, the tuner output is transmitted to the amplifier, and the signal taken from the recording terminals of the amplifier is recorded and played back. This method introduces noise generated within the tuner, as well as FM noise, into the recording. To counteract this, the "TAPE (LOW NOISE)" position incorporates a special recording and playback circuitry. This circuitry applies de-emphasis to the FM signal before it is sent to the tape deck for recording. During playback, the signal from the tape deck is re-emphasized. This process effectively reduces the high-frequency noise that would otherwise be audible in the recording, resulting in a cleaner, more faithful reproduction. The frequency response of the FM signal is intentionally modified in this mode: the high-frequency signal is boosted prior to recording and then attenuated during playback. This ensures that the signal recorded on the tape deck has a higher level, reducing the impact of tape hiss and other noise. The de-emphasis time constant for recording can be reduced by approximately 10 dB/10 kHz lower than when recording in the usual way.
The tuner also features a muting circuit, which suppresses inter-station noise and other unwanted sounds when tuning between stations or when the signal strength is weak. This circuit is designed to reduce noise in FM stereo broadcasts, especially noise heard during reception of weak signals. The muting circuit operates automatically if the input signal is below a certain specified level, controlled by an electronic switch.
Another important function is the "Pink Noise" circuitry. This circuit is designed to generate a discrete output in the high-frequency range. It can be used for determining the recording level when recording an FM broadcast, or for making the frequency response flat.
The ST-9600 also includes a servo tuning system. This system ensures accurate tuning to the desired frequency by automatically correcting any drift or errors. It uses a discriminator error voltage to adjust the local oscillator frequency, maintaining precise tuning.
Important Technical Specifications
The ST-9600 boasts impressive technical specifications that underscore its high-fidelity design.
FM TUNER SECTION:
- Frequency range: 88 – 108 MHz
- Antenna terminals: 75Ω (unbalanced), 300Ω (balanced)
- Sensitivity:
- IHF (usable sensitivity): 1.9 µV (10.8 dBf)
- 50 dB quieting sensitivity:
- Mono: 3.0 µV (14.8 dBf)
- Stereo: 30 µV (34.8 dBf)
- S/N (Signal-to-Noise Ratio):
- Mono: 80 dB
- Stereo: 75 dB
- Total harmonic distortion (400 Hz, 100% modulation):
- Frequency response: 20 Hz – 18 kHz (+0.2 dB, -0.8 dB)
- Capture ratio: 1.0 dB
- Alternate channel selectivity: 90 dB
- Stereo separation (at 1 kHz): 50 dB
- Image rejection (at 98 MHz): 105 dB
- IF rejection (at 98 MHz): 100 dB
- Spurious response rejection (at 98 MHz): 100 dB
- AM suppression: 60 dB
- Subcarrier product rejection: 45 dB (at 1 kHz, 35 dB at 10 kHz)
- Leak carrier (19 kHz, 38 kHz): -65 dB
AM TUNER SECTION:
- Frequency range: 525 – 1605 kHz
- Sensitivity: 30 µV
- S/N: 50 dB
- Image rejection (at 1000 kHz): 80 dB
- IF rejection (at 1000 kHz): 80 dB
GENERAL:
- Output voltage: 0.77 – 1.55V
- Power supply: AC 110V/120V/220V/240V (50/60 Hz)
- Power consumption: 25W
- Dimensions (W x H x D): 450 x 173 x 362 mm (17-3/4" x 6-13/16" x 14-1/4")
- Weight: 8.7 kg (19.2 lbs)
These specifications highlight the tuner's ability to deliver exceptionally clean and accurate audio, particularly in FM stereo, with very low distortion and high signal-to-noise ratios. The high selectivity and rejection figures ensure that only the desired station is received, free from interference.
Usage Features
The ST-9600 is designed for user-friendly operation with several features that enhance its usability.
- Front Panel Controls: The front panel includes controls for tuning, band selection (FM/AM), muting, and the recording/playback switch. A large tuning knob provides smooth and precise station selection.
- Signal Strength Meter: A signal strength meter helps users optimize antenna positioning for the best reception.
- Stereo Eye: A stereo indicator light (often referred to as a "stereo eye") illuminates when a stereo FM broadcast is being received, confirming stereo reception.
- Output Terminals: The rear panel provides various output terminals, including REC OUT, PLAYBACK, LINE IN, and LINE OUT, allowing for flexible connection to amplifiers, tape decks, and other audio components.
- Antenna Connections: Both 75Ω (unbalanced) and 300Ω (balanced) antenna terminals are provided for FM, accommodating different antenna types. An AM antenna terminal is also included.
- Voltage Selector Switch: A voltage selector switch allows the unit to be adapted for different power supply voltages (110V, 120V, 220V, 240V), making it suitable for international use.
Maintenance Features
Maintenance of the ST-9600 primarily involves calibration and occasional component replacement, as detailed in the service manual.
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Alignment Instructions: The manual provides comprehensive alignment instructions for both FM and AM sections. These procedures are crucial for maintaining optimal performance and include:
- FM MPX Alignment: This involves adjusting various circuits, such as the pilot signal, separation, and distortion, to ensure accurate stereo decoding and low distortion.
- Stereo Separation Alignment: Specific adjustments are made to maximize stereo separation, ensuring a clear distinction between left and right channels.
- Output Terminal Stereo Separation Alignment: This ensures that the stereo separation is maintained at the output terminals.
- Leak Carrier Alignment: Adjustments are made to minimize the leakage of the 19 kHz and 38 kHz subcarrier signals into the audio output.
- Pink Noise Alignment: This procedure involves adjusting the pink noise output level for accurate recording level determination.
- AM Alignment: This includes aligning the RF amplifier, oscillator, and IF amplifier for optimal AM reception.
- FM IF Alignment: Adjustments are made to the IF amplifier and detector circuits to ensure maximum sensitivity and linearity.
- FM Muting Alignment: This involves setting the muting threshold to effectively suppress inter-station noise without cutting off weak but listenable signals.
- Signal Meter Alignment: Calibration of the signal strength meter ensures accurate indication of signal strength.
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Block Diagram: The block diagram provides a detailed overview of the tuner's internal circuitry, aiding technicians in troubleshooting and understanding signal flow. It illustrates the various stages, including the RF amplifier, IF amplifier, detector, MPX decoder, and audio output stages.
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Schematic Diagram: A comprehensive schematic diagram is provided, showing all components and their interconnections. This is essential for detailed circuit analysis and repair.
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Printed Circuit Board Wiring View: Diagrams illustrating the component layout on the printed circuit boards are included, facilitating component identification and replacement.
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Replacement Parts List: A detailed list of all replaceable components, including transistors, integrated circuits, resistors, capacitors, and other parts, is provided with their part numbers. This ensures that correct replacement parts can be ordered for repairs.
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Dial Cord Installation Guide: Instructions for replacing the dial cord are included, which is a common maintenance item for tuners with mechanical tuning mechanisms.
The ST-9600's robust design and comprehensive service documentation ensure that it can be maintained and repaired effectively, extending its lifespan and preserving its high-performance audio capabilities. Its combination of advanced features, precise engineering, and detailed maintenance information makes it a valuable and enduring piece of audio equipment.
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