Nakamichi ST-70
¥ 138,000 (around 1987)
¥ 130,000 (around 1989)
Commentary
FM/AM tuner equipped with Schott NR system.
In order to improve reception performance in weak electric fields, a unique Schutz NR system is installed.
In FM broadcasting, there is usually a kind of masking effect. When the volume of the high-frequency component in the broadcast content is larger than the noise, the noise is masked and cannot be heard. When the high-frequency component is less than the noise, the noise can be heard. The Schutz NR system takes full advantage of this masking effect, reducing the noise by changing the amount of blending according to the amount of the high-frequency component in the broadcast content. When there is enough high-frequency energy to mask the noise during the broadcast, there is no blending operation and the channel separation is widened to maintain an accurate stereo image.
This circuit operates between 19 dBf and 53 dBf in signal strength, passes the circuit to maximize channel separation at a signal strength of 53 dBf or higher, and performs normal high-blend operation when signal strength is less than 19 dBf.
The Shotts NR system improves the effective stereo sensitivity by 9 dB while maintaining the stereo image as much as possible, and expands the stereo reception area by approximately 8 times (approximately 2.8 times in distance).
The front-end section uses a twin varicap diode for 6-train front-end to improve RF intermodulation characteristics and achieve high interference rejection capability. The RF amplifier circuit and mixer circuit use a dual-gate MOS FET to ensure excellent linearity, S/N and distortion factor.
The PLL circuit, which is important in the quartz synthesizer method, employs a pulse swallow method in which the reference oscillation frequency is set to 25 kHz outside the audible band, eliminating the problem of residual noise at the reference frequency.
In addition, the digital control signal transmission of the synthesizer employs a full static control method in which only one signal is carried on one signal line, thereby suppressing the deterioration of the S/N ratio.
The IF section supports two stage switching of the IF band.
In the wide position, a four stage linear phase ceramic filter with excellent group delay characteristics is used. In addition, when there is a large amount of interference from neighboring stations, it to the narrow position provides sharp selectivity with three stages of narrow band + two stages of linear phase.
The limiter amplifier section consists of an FET input and a 3-stage Darlington differential IC, which provides high gain, wide dynamic range and high S/N ratio.
In the AM tuner section, the mixer circuit of the RF-amplifier section is double-balanced so that good reception can be obtained when Tsutomu Dainyu is in use.
In addition, we have adopted an automatic gain control (AGC) circuit that lowers the sensitivity of the RF amplifier section to keep the gain constant when the input radio wave exceeds a certain level, improving the RF intermodulation characteristics.
A total of 16 FM/AM random preset memories are installed.
Equipped with a 5-segment signal meter.
This meter can be switched to a multi-path meter.
The auto-seek (auto-tuning) level can be switched between approximately 40 dBf and approximately 20 dBf.
Manual tuning is possible using the rotary knob.
In addition, it is equipped with an FM muting ON/OFF switch and an FM mode (stereo / mono) switch so that it can receive broadcasting stations with extremely weak radio waves.
Equipped with an output level adjustment volume.
Equipped with Last One Memory which stores the broadcasting station just before turning off the power.
When combined with the CA-70 control amplifier, the ST-70 can be operated with the CA-70 remote controller.
Model Rating
| Type | FM/AM Tuner | ||||||||
| FM Tuner Section | |||||||||
| Receiving frequency | 76.0 ~ 90.0 MHz (in 100 kHz steps) | ||||||||
| Practical sensitivity (IHF) | Mono : 10dBf/1.7 μ V Stereo : 17dBf/3.9 μ V |
||||||||
| 50dBS/N sensitivity | Mono : 16dBf/3.5 μ V Stereo : 28dBf/14 μ V (Schott NRon) 37dBf/39 μ V (Schott NR off) |
||||||||
| S/N ratio (65 dBf input) | Mono : 80 dB or more Stereo : 74 dB or higher |
||||||||
| Improvement in Schott NR S/N ratio | 6dB | ||||||||
| Schottz NR operation input level | 19 ~ 53 dBf (5 ~ 250 μ V) | ||||||||
| High Blend Threshold | 19dBf/5 μ V | ||||||||
| Muting threshold | 20dBf/5.5 μ V | ||||||||
| Frequency characteristic | 20 Hz to 15 kHz ± 1 dB | ||||||||
| Total harmonic distortion rate (1 kHz) |
|
||||||||
| Capture ratio | 1.9dB | ||||||||
| Effective selectivity | Wide : 70 dB or more (± 400 kHz) Narrow : 75 dB or more (± 300 kHz) |
||||||||
| Stereo separation |
|
||||||||
| Spurious interference ratio | 100 dB or more | ||||||||
| Image interference ratio | 100 dB or more | ||||||||
| IF interference ratio | 100 dB or more | ||||||||
| AM suppression ratio | 60 dB or more | ||||||||
| <AM Tuner Section> | |||||||||
| Receiving frequency | 522 ~ 1,629 kHz (9 kHz step) | ||||||||
| Sensitivity | 50 dB μ / m | ||||||||
| Signal-to-noise ratio | 48 dB or More (90 dB μ / m Input) | ||||||||
| Total harmonic distortion factor | 0.4% or Less (90 dB μ / m Input) | ||||||||
| Selectivity | 18 dB or More (± 9 kHz) | ||||||||
| <General> | |||||||||
| Output Level / Impedance | FM : 0.5 V ~ 2.0 V (Variable) / 1.5k Ω (1 kHz, mono, 100% modulation) AM : 0.2 V ~ 0.7 V (Variable) / 1.5k Ω (400 Hz, 30% Modulation) |
||||||||
| FM antenna input | 75 Ω (unbalanced) 300 Ω (balanced) |
||||||||
| Pwer | 100 VAC, 50Hz/60Hz | ||||||||
| Power consumption | Up to 14W | ||||||||
| External dimensions | Width 435x Height 63x Depth 289 mm | ||||||||
| Weight | Approx. 4.7 kg | ||||||||
.jpg)