Audio Database

681ZX
Commentary

The second generation of the 680 ZX was announced at the same time as the 682 ZX. This is a standard speed single speed stereo cassette deck.
Unlike the 682 zx, the Dolby NR processor and its peripheral circuit are used for both recording and playback, and simultaneous recording and playback monitoring is not possible.

The mechanism uses a frequency-distributed double capstan system to achieve stable tape travel and uniform head touch. At the same time, the two capstan diameters and the fly-wheel diameters are changed to avoid overlapping of the flutter cycle. This reduces rotation unevenness and modulation noise. In addition, the tape pad lifter prevents adverse effects due to uneven pad pressure and slight vibration of the pad spring material.
In addition, vibrations from motors and other rotating bodies are transmitted to the tape, which can increase flutter. To reduce this, we use aluminum alloy, which has a higher damping property than iron, as a chassis material. Resin is out-plated on aluminum alloy to absorb small vibrations and prevent resonance.

When the control button is pressed, the logic circuit is activated and the control motor is used to operate the mechanism.
By driving the cam with a motor instead of using a solenoid plunger, the sound at the time of operation is reduced, damage to tape and transport is reduced, temperature rise is lowered, and power consumption is reduced.
The main motor uses a PLL servo motor to detect rotational speed fluctuations, compare the phase with the reference signal the reference signal oscillator, and control the rotational speed to an accurate value, thereby achieving high-precision rotation.

The head uses a discrete three head system in which a recording head, a reproducing head and an erasing head are completely separated from each other.
The P-8L type read head is used. By using a laminated core made of crystalline material, the narrow gap of 0.6 microns prevents loss during playback. The frequency response extends to 22 kHz. In addition, the shape is designed to eliminate the low-frequency waviness (contour effect), resulting in flat playback down to the ultra-low-frequency range. By using a special shape to eliminate the core deflection phenomenon, the read head is durable for more than 10,000 hours.
The recording head uses an R-8L type. Like the read head, the gap is 3.5 microns with a laminated core made of crystalline material. As with the read head, this head also uses a special shape to ensure more than 10,000 hours of durability.
E-8L type is used for the erasing head. It is a double gap type using ferrite core with excellent high frequency characteristics and Sendust core with high magnetic flux density at the tip.

The recording EQ circuit, playback EQ circuit and output-line amplifier circuit use a double NF circuit that applies negative feedback to the electrolytic capacitor. This reduces distortion caused by the capacitor and stabilizes direct current.
In addition, the recording equalizer and the recording head, and the reproducing head and the reproducing equalizer amplifier are directly connected to each other and the coupling capacitor is removed to improve the characteristics. For example, distortion during recording and reproduction is reduced, and phase shift in low frequencies is prevented.

Equipped with an auto-calibration function, you can adjust the azimuth and recording / playback level simultaneously and automatically with one calibration operation.
The azimuth adjustment is started by pressing the Auto Cal and Play buttons from the recording pose. First, a 400 Hz test tone is recorded and played back, and the phase difference between the left and right channels is detected. The signal is sent to the operational amplifier to control the motor, which moves the lever connected via the belt and gear to adjust the tilt angle of the recording head. When the azimuth deviation is eliminated, the phase difference disappears, the motor stops and the adjustment is completed.
When the azimuth adjustment is started, the level adjustment is also started at the same time. The signal reproduced with the 400 Hz test tone is detected through the buffer amplifier and applied to the comparator. The comparator compares the signal with the reference signal. The voltage difference causes the motor to rotate, the connected slide volume for calibration is operated, and the signal current (recording level) of the recording head is changed. This causes the playback output level to change, and when it becomes equal to the reference level, the motor stops and the adjustment is completed.
The adjustment time, including the azimuth adjustment, is approximately 6 seconds and the error is within ± 0.5 dB. The adjustment range is ± 2.5 dB from the reference value, which is sufficient to cover normal music tapes.

Equipped with a bias adjustment function that can adjust the bias current to a value suitable for the tape being used.
This adjustment is performed by recording and playing back a 15 Hz (-20dB) test tone while observing the reading on the level meter, which is enlarged by 20 dB for easy adjustment.
The adjustment volume is provided for each tape selector and each left / right channel. The adjustment range is ± 4.5 dB for the EX position (normal type), ± 3 dB for the SX position (CrO2 type), and ± 6 dB for the ZX position (metal tape).

In addition to Dolby B Type NR for noise reduction, Dolby C Type NR with higher noise reduction effect is equipped.
Dolby C Type NR basically has the same operation principle as B type NR. By receiving 10 db each from two noise reduction processors of high level stage and low level stage, the noise reduction of 20 db in total is realized.
In addition, the C-type employs a sliding band method in which the frequency at which the operation starts is variable according to the input level and the frequency component, thus suppressing a bleeding phenomenon called noise breathing.
With the Dolby NR switch, switching between C type / B type / off is possible.

It is equipped with a wide range peak level meter of FL display which displays -40dB to + 10 db in 24 segments.

It is equipped with a RAMM function that allows you to select and cue your favorite song from the songs recorded on the tape.

It is equipped with an easy queuing function. If you press the pause button during FF/Rew, the speed is reduced to about 1/3 and you can listen to the recorded content. If you press the FF/Rew button continuously, the speed is reduced to about 1/5 and you can easily start the track.

The Rec Mute function is built-in. If you press the Rec button during recording, the input signal is cut as long as you keep it pressed, creating a silent recording section.

Built-in MPX filter.

By using the audio timer, timer recording and playback are possible.

Remote control unit sold separately can be used to operate from a remote location.

Model Rating
Type Stereo cassette deck
Heads Recording head : R-8L
Playhead : P-8L
Erasing Head : E-8L
Tape speed 4.8cm/s
Wow and flutter Not more than 0.04% Wtd rms
Not more than 0.08% Wtd peak
Frequency response (recording level -20dB) 20 Hz ~ 22 kHz ± 3 dB (ZX Tape)
20 Hz ~ 20 kHz ± 3 dB (SX, EXII tape)
Overall S/N ratio
(IHF A-Wtd rms, 400 Hz, 3%)
Dolby C on : 72 dB or more (70 μ s, ZX Tape)
Dolby B on : 66 dB or more (70 μ s, ZX Tape)
Total Distortion Factor (400 Hz, 0 dB) 0.8% or Less (ZX Tape)
1.0% or Less (SX, EXII tape)
Erasure rate 60 dB or More (1 kHz, 0 dB)
Channel separation 37 dB or More (1 kHz, 0 dB)
Crosstalk 60 dB or More (1 kHz, 0 dB)
Bias frequency 105kHz
Input Sensitivity / Impedance 50mV/50k Ω
Output Level / Impedance
(maximum output level)
Line : 1 V (400 Hz, 0 dB) / 2.2k Ω
Headphone : 45 mW (400 Hz, 0 dB) / 8 Ω load
Dedicated DC output for black box series ± 10 V, 125 mA max.
Pwer 100 VAC, 50Hz/60Hz
Power consumption 36W max.
External dimensions Width 482x Height 143x Depth 340 mm
Weight Approximately 9 kg
Sold Separately Wired Remote Controller RM-200 (¥ 2,000)