Nakamichi ST-7 ()
A high-performance FM/AM tuner with digital synthesis and Schott NR noise reduction, built for audiophiles seeking precise reception and low distortion.
Overview
The Nakamichi ST-7 is an FM/AM tuner made in Japan, designed for high-fidelity audio systems. It features digital synthesis tuning with a PLL circuit using a 25 kHz reference frequency and a full static control method for stable operation. The tuner includes 16 random preset memories, manual tuning via rotary knob, and a Last One Memory function that recalls the last station before power-off. It can be paired with the CA-70 control amplifier for remote operation.
Specifications
| Receiving frequency (FM) | 76.0 ~ 90.0 MHz (in 100 kHz steps) |
| Practical sensitivity (IHF) (FM) | Mono : 10dBf/1.7 μ V; Stereo : 17dBf/3.9 μ V |
| 50dBS/N sensitivity (FM) | Mono : 16dBf/3.5 μ V; Stereo : 28dBf/14 μ V (Schott NR on); 37dBf/39 μ V (Schott NR off) |
| S/N ratio (65 dBf input) (FM) | 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) (FM) | wide mono: Not more than 0.06%; wide stereo: Not more than 0.08%; narrow mono: Not more than 0.25%; narrow stereo: 0.3% or less |
| Capture ratio | 1.9dB |
| Effective selectivity (FM) | Wide : 70 dB or more (± 400 kHz); Narrow : 75 dB or more (± 300 kHz) |
| Stereo separation (FM) | 100Hz wide: 45dB; 1kHz wide: 50dB; 10kHz wide: 35dB; 100Hz narrow: 45dB; 1kHz narrow: 45dB; 10kHz narrow: 35dB |
| 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 |
| Receiving frequency (AM) | 522 ~ 1,629 kHz (9 kHz step) |
| Sensitivity (AM) | 50 dB μ / m |
| Signal-to-noise ratio (AM) | 48 dB or More (90 dB μ / m Input) |
| Total harmonic distortion factor (AM) | 0.4% or Less (90 dB μ / m Input) |
| Selectivity (AM) | 18 dB or More (± 9 kHz) |
| 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) |
| Power | 100 VAC, 50Hz/60Hz |
| Power consumption | Up to 14W |
| External dimensions | Width 435x Height 63x Depth 289 mm |
| Weight | Approx. 4.7 kg |
Design
The ST-7 uses a twin varicap diode in its 6-train front-end and employs dual-gate MOS FETs in both the RF amplifier and mixer circuits. Its IF section allows two-stage switching between wide and narrow bandwidths, and the limiter amplifier uses an FET input with a 3-stage Darlington differential IC. The AM section features a double-balanced mixer and an automatic gain control (AGC) circuit. The tuner includes a 5-segment signal meter switchable to multi-path mode, an FM muting ON/OFF switch, an FM mode switch (stereo/mono), and an output level adjustment volume. It supports auto-seek tuning at two sensitivity levels (~40 dBf and ~20 dBf) and integrates the Schott NR noise reduction system, which improves stereo sensitivity by 9 dB and expands the stereo reception area by approximately 8 times.
Market
The Nakamichi ST-7 was originally priced at ¥138,000 around 1987. Some units may exhibit preset memory loss or a dim display over time, potentially due to aging capacitors or a failed battery.
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