Nakamichi ST-7 ()
An FM/AM tuner with digital synthesis and Schott NR noise reduction, built for audiophiles who want precise reception and low distortion.
Overview
The Nakamichi ST-7 is an FM/AM tuner made in Japan for high-fidelity systems. It uses digital synthesis tuning with a PLL circuit on a 25 kHz reference frequency, and a full static control method for stable operation. It has 16 random preset memories, manual tuning by 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 front-end is a 6-train design with a twin varicap diode, and dual-gate MOS FETs handle both the RF amplifier and the mixer. The IF section switches between wide and narrow bandwidths in two stages. The limiter amplifier has an FET input and a 3-stage Darlington differential IC. The AM section has a double-balanced mixer and an automatic gain control (AGC) circuit. Controls include a 5-segment signal meter that switches to multi-path mode, an FM muting ON/OFF switch, an FM mode switch (stereo/mono), and an output level adjustment volume. Auto-seek tuning works at two sensitivity levels (~40 dBf and ~20 dBf). The Schott NR noise reduction system 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 show preset memory loss or a dim display over time, potentially due to aging capacitors or a failed battery.
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