Nakamichi 430

Commentary

400 series FM stereo tuner.

With an emphasis on the selection characteristics of the tuning circuit, we have adopted a frequency straight-line 5-row variable capacitor.
The spurious interference ratio is increased to 100 dB by two RF stages and multi-stage tuning.

A low-noise dual-gate MOS FET is used for the high-frequency amplifier stage. The 3-stage configuration improves quieting sensitivity by 50 dB and reduces distortion. This suppresses high-order harmonic distortion and enhances the ability to eliminate cross-modulation interference and intermodulation interference.

In the IF stage of a common tuner, two or three stage ceramic filters are used to improve the selectivity characteristics. However, although the selectivity characteristics are improved, the group delay time characteristics become rippled and distortion increases. Even if the filter is selected well, the distortion cannot be prevented from increasing at low modulation levels, and the characteristics cannot be prevented from deteriorating at low sound volumes. In addition, the temperature characteristics of each filter stage vary.
For these reasons, only one stage of 4-element one wafer concentrated ceramic filter specially selected for 430 is used, and it is composed of two stages including one stage of LC linear phase filter.
As a result, the advantages of two filters, ceramic and LC, are fully utilized, and both selectivity characteristics and group delay characteristics, which are mutually contradictory, are compatible with excellent numerical values.

Equipped with a 2-stage bandwidth switching mechanism, two stages of normal and narrow can be selected.

It is equipped with SLT (self-lock tuning) circuit to eliminate tuning deviation.
In the local oscillator circuit, a high frequency of 10.7 MHz lower than the receiving frequency is generated and sent to the mixing circuit. Then, by subtracting the local oscillation frequency from the receiving frequency in the mixing circuit, an intermediate frequency of 10.7 MHz is obtained. When the local oscillation frequency drifts due to temperature or other effects, the tuning point itself deviates.
The SLT detects the DC component of the detection output and forcibly corrects the drift of the local oscillation frequency when the tuning error occurs. This is effective enough that the tuning indicator does not turn off even if the dial knob is artificially moved by 200 kHz once the tuning is done.

A PLL circuit is used for the MPX circuit.
When the MPX signal generated in the tuner is out of phase due to heat or humidity, the PLL circuit detects this phase shift and corrects it so that it is always in phase, thus obtaining stable separation characteristics.

The muting circuit uses a unique noise level detection method muting circuit.
In conventional muting circuits, the muting operating point was determined by the antenna input level, but with this method, even relatively weak broadcast signal input tended to be muted.
By detecting the noise level, even a very small amount of broadcast signal input can be reliably received as long as the SN ratio is guaranteed.

Equipped with a high blend switch.
This function eliminates noise by adding the high frequencies of the left and right channels, which have noticeable noise components, and reduces the noise of the weak electric field input.

Dolby FM decode circuit can be mounted.

Digital tuning method is adopted.
If both the left and right tuning indicators of the dial indicator light up, the correct tuning point and the reception frequency are locked by SLT.
The signal indicator shows an input signal and lights up at approximately 55 dBf (300 μ V, 300 Ω), indicating that S/N and distortion factor are sufficient.

There was a wood cabinet for the 400 series as an option sold separately.

Model Rating

Type	FM tuner
Receiving frequency	76 MHz to 90 MHz
Practical sensitivity	1.8 μ V (10.5 dBf)
Distortion Factor (1 kHz or less at 100% modulation)	mono stereo normal: narrow: Not more than 0.06% Not more than 0.2% Not more than 0.09% Not more than 0.4%
Signal-to-noise ratio (IHF)	Mono : 70 dB or higher Stereo : 68 dB or higher
Frequency characteristic	30 Hz ~ 15 kHz + 0.5 -1.5 dB
Effective selectivity (IHF)	Normal : 60 dB or more Narrow : 90 dB or more
Stereo separation	100Hz 1kHz 10kHz normal: narrow: 35 dB or more 30 dB or more 50 dB or more 30 dB or more 35 dB or more 30 dB or more
Capture ratio	normal:1.5dB narrow:4.0dB
Image interference ratio	100 dB or more
IF interference ratio	100 dB or more
Spurious interference ratio	100 dB or more
SCA suppression	75 dB or more
AM suppression	60dB
MPX Filter	19kHz -70dB
Antenna terminal	300 Ω balance 75 Ω unbalance
Output terminal level	500 mv (maximum output at 50% modulation)
Power supply voltage	100 V, 50Hz/60Hz
Power consumption	11VA
External dimensions	Width 400x Height 80x Depth 222 mm
Weight	4.9kg
Sold Separately	400 Series Wood Cabinet (¥ 7,000)