The TEAC AN-80 is a DOLBY B system noise reduction unit designed primarily for use with a tape deck featuring two magnetic heads. Its circuit composition allows for playback and record mode selection via a changeover switch. While continuous monitoring is not possible with a three-head type deck, the recording check function provides momentary monitoring of the recording process. The unit is noted for its ease of operation and adjustment.
Function Description:
The AN-80's core function is to reduce noise in audio signals using the Dolby B system. This system processes audio during recording to minimize inherent tape hiss and other noise, then reverses the process during playback to restore the original signal dynamics while keeping the noise suppressed. The unit is designed to integrate with existing tape decks, enhancing their audio fidelity.
Important Technical Specifications:
Overall Electrical Characteristics:
- Frequency Response: 30Hz to 13kHz ±2dB.
- Increased SN Ratio (B-weighted measurement, at level below DOLBY reference level):
- 10dB or better at 10kHz
- 5dB or better at 1kHz
- Overall 6dB or better
- Input Sensitivity (Line input, minimum input voltage required for reference level): 30mV±2dB.
- Input Impedance (Line input): 35kΩ or more.
- Output Level (Line output, load resistance 50kΩ or more): 580mV±2dB.
- Maximum Output Voltage (Load resistance 50kΩ or more): 2.3V or more.
- Output Impedance: 6kΩ or more.
- Harmonic Distortion Factor (At monitor terminal reference level): 0.5% or less.
- Multiplex Filter:
- 19kHz: -35dB or less
- 38kHz: -30dB or less
- SN Ratio: 60dB or better.
- Calibration Oscillator:
- Level variation: ±1dB or less
- Oscillation Frequency: 400Hz±15%
Record Mode Characteristics:
- Frequency Response (At reference level):
- 10kHz: +10dB±1dB
- 1kHz: -5.5dB±1dB
- 30Hz to 15kHz: ±1.5dB
- Record Input Sensitivity (Minimum input voltage required for reference output level): 30mV±2dB.
- Input Impedance: 35kΩ or more.
- Record Output Level (Load resistance 50kΩ or more): 580mV±2dB.
- Maximum Record Output Level (Load resistance 50kΩ or more): 2.3V or more.
- Output Impedance: 3kΩ or less.
- Harmonic Distortion Factor (At reference level): 0.5% or less.
- Multiplex Filter:
- 19kHz: -18dB or less
- 38kHz: -13dB or less
- SN Ratio (Input terminal shorted with 4.7kΩ): 60dB or better.
Playback Mode Characteristics:
- Frequency Response:
- 10kHz: -10dB±1dB
- 1kHz: -5.5dB±1dB
- 30Hz to 15kHz: ±1.5dB
- Playback Input Sensitivity (Minimum input voltage required for reference level): 30mV±2dB.
- Input Impedance: 35kΩ or more.
- Playback Output Level (Load resistance 50kΩ or more): 50mV±2dB.
- Maximum Playback Output Level (Load resistance 50kΩ or more): 2.3V or more.
- Playback Output Impedance: 6kΩ or less.
- Harmonic Distortion Factor (At reference level): 0.5% or less.
- Multiplex Filter:
- 19kHz: -20dB or less
- 38kHz: -20dB or less
- SN Ratio (Input terminal shorted with 4.7kΩ): 60dB or better.
General Specifications:
- Power Supply: 100V 50/60Hz (U.S. model: 117V AC 50/60Hz).
- Power Consumption: 4W.
- AC Outlet: 500W maximum (Power switch not interlocked).
- Overall Dimensions: 3.4" x 16.1" x 10.7".
- Weight: 8.8 lbs (4 kg).
Usage Features:
The AN-80 is designed for straightforward operation. Its primary controls include:
- REC LEVEL: Adjusts the recording input level.
- REC CAL: Used for calibrating the recording level.
- MODE SW: Selects between record and playback modes.
- METER SW: Likely selects which channel (Left or Right) or function the Dolby meter displays.
- DOLBY SW: Engages or disengages the Dolby B noise reduction system.
- REC TONE SW: Activates an internal tone for calibration purposes.
- RECORDING CHECK: Allows for momentary monitoring of the signal during recording.
- PLAY CAL: Used for calibrating the playback level.
- POWER SW: Turns the unit on and off.
The unit's ease of operation and adjustment are highlighted, making it user-friendly despite its technical capabilities.
Maintenance Features (Adjustment Procedures):
The service manual provides detailed procedures for adjustment, inspection, and calibration, intended for service engineers. Key adjustments include:
- Level Meter Sensitivity Test (Dolby Level Meter): Involves depressing the REC TONE switch and adjusting VR-106 to ensure the meter pointer is within a specified range, with a target voltage of 100 mV from TP-1 to ground.
- Record Characteristic Test: This involves connecting test equipment (oscillator, oscilloscope, distortion meter) and setting a specified level. The REC CAL resistor is set fully clockwise, MODE to REC, DOLBY to IN, and METER to L. An AF oscillator at 100 Hz is adjusted via ATT until the AN-80 meter indicates the reference level. This point is considered 0 dB for frequency response/SN ratio measurements or 100% for distortion factor.
- SN Ratio Improvement Measurement: This procedure uses a test tape (product No. 69911008-00) and an erased tape. It involves adjusting output levels, setting MODE to PLAY, METER to L, and PLAY CAL to achieve reference level. Noise levels are measured with the DOLBY switch ON and OFF at 1 kHz and 10 kHz using a noise analyzer to determine the improvement.
- AN-80 Built-in Oscillator Level Adjustment: Sets the output level of the internal calibration oscillator. An AC voltmeter is connected between TP-1 and ground (27). With the L channel MODE switch to REC and REC TONE switch depressed, VR-105 is adjusted for a 100 mV reading.
- Playback Amplifier Input-Output Characteristic Adjustment: This is a multi-step process for both L and R channels. It involves setting the PLAY CAL resistor, MODE to PLAY, and adjusting the AF oscillator frequency and output voltage (-20 dB at 100 Hz) to achieve a reference level on the meter. Further adjustments are made at 3 kHz and 5 kHz using attenuated signals, adjusting VR-101 and VR-103 to specific dB readings (-27 dB and -40 dB respectively).
- Multiplex Filter Adjustment: Addresses potential malfunction from FM tuner leak carriers. With MODE set to REC, an AF oscillator at 100 Hz and -20 dB output is used to set the reference level. L-103 (and L-104 for the R channel) is then adjusted for a minimum at 19kHz±1% or less. L-101 and L-102 do not require adjustment.
Precautions for Maintenance:
When adjusting the AN-80, special care must be taken to eliminate induction hum. General precautions for servicing precision equipment should also be observed. When adjusting semi-fixed variable resistors, an insulated screwdriver must be used. The reference level for 0 dB is defined as 0.775 V. All voltage measurements are taken with a VTVM at no signal, and test voltages are average values with a 20% tolerance.
Performance data and specifications are subject to change with future modifications.
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