Nakamichi OMS-30

Commentary

A CD player that emphasizes reproduction of low-level signals.

A newly developed deglitching system is used between the D/A converter and the analog circuits.
In a typical CD-player, the digital signal is converted by a D/A converter into an analog signal, and sent through a sample-and-hold circuit to an analog low-pass filter. The sample-and-hold circuit removes the glitch noise that is unavoidably attached to the output of the D/A converter. However, since this circuit consists of analog switches and capacitors made of semiconductors, parts are connected in series with the signal line, so that delicate signals tend to be buried in the noise. To this point, Nakamichi uses a newly developed deglitching system to remove the glitch without using a sample-and-hold circuit.
This deglitching system uses a transistor whose switching speed is more than one order of magnitude faster than conventional switches. When the switch is closed, the output of the D/A converter is muted. This eliminates the need for a transistor to be connected in series to the signal line, and only the glitch signal is cut off quickly. Moreover, since the switching time is extremely short, there is no need to store data in a capacitor.
By adopting this deglitching system, we are able to reliably reproduce minute signals as small as -90dB, which were previously buried in noise.

The digital filter uses a 16-bit digital filter, which moves unwanted high-frequency signals (sidebands) away to twice the higher frequency, making it possible to use a relatively low-order, slow analog filter.

The D/A converter uses a 16-bit D/A converter using a highly accurate ladder type IC.

The analog filter is a 5th-order Chebyshev type active filter. Since this filter is of relatively low order in the active type, phase characteristics (especially group delay characteristics) are also good. The cutoff frequency is also set at 30 kHz, and almost flat group delay characteristics are obtained up to 20 kHz.

The power supply section uses a unique multi-regulated power supply and a dedicated master power regulator to provide ideal power supply to the analog section. In addition, each local power regulator and master power regulator have a non-NFB power supply configuration with no feedback loop, so they are not affected by voltage fluctuations and provide clean power supply.
In addition, the ground line uses an isolated ground system. The power line of the analog section incorporates a buffer with transistors. The current flows from + to -, and the ground only regulates the reference potential. Thus, even if noise or contamination is present in the current, it is not affected by the ground potential. This eliminates interference between the ground lines of analog circuits.

The pickup section uses a 3-beam laser pickup with enhanced information pickup capability of the central main beam.
In addition, a newly developed LSI for digital signal processing, which is highly integrated, is used to suppress the generation of digital noise and minimize interference with analog circuits. In addition, the servo section is independent of this LSI to improve the tracking performance to the disk.

It employs a master clock method in which multiple LSIs for signal processing are synchronized by a single crystal oscillator to prevent beat noise due to interference between multiple clocks.

The disk drive mechanism is floated from the main base chassis by a damper composed of spring and rubber, and is structured to be less affected by internal resonance and external vibration.

For the chucking method to fix the disk to the center spindle, a unique method of Nakamichi is adopted. When chucking, a centering mechanism that tapers the spindle with aluminum shavings works to accurately hold the center of the disk on the axis of the spindle, thereby preventing read errors due to disk eccentricity.
In addition, the chucking arm that holds the disk employs a magnet chuck method that uses permanent magnets to fix the disk. In this method, the chucking arm is completely separated from the disk when the disk is mounted, so that it is not affected by vibrations from the chassis, contributing to improved traceability of the laser pickup.

It has a program memory function of up to 15 songs.
In addition to adding and modifying memory programs, you can also display the total time since the first song stored in memory program and memory when called.
In addition, it is equipped with a one touch memory function. If you perform a memory operation during normal playback, the music you are listening to can be stored as it is.

It is equipped with a time counter display function. When a disc is loaded, the service mode displays the total number of tracks and the total playing time. In normal regenerating condition, the time counter display can be switched to one of three types : track / time / remaining time. When playing back a memory, you can make a call to a stored program.

It is equipped with skip search and double speed queuing function.

It uses a direct peration function, and when you press the play button with the disc table open, it is automatically loaded and starts playing.

Equipped with a repeat play function.

Equipped with headphone output terminal with output adjustment volume.

Wireless remote control is included.

Model Rating

Type	CD Player
Reading system	Non-contact optical (semiconductor laser used)
Error correction method	CIRC method
Number of channels	2-channel stereo
Sampling frequency	44.1kHz
Quantization	16-bit straight line
Disk rotational speed	Approx. 200 ~ 500 rpm (Constant Linear Velocity)
Wow and flutter	Below the measurement limit
Frequency characteristic	5 Hz to 20 kHz ± 0.5 dB
Signal-to-noise ratio	97 dB or more (IHF A-WTD)
Dynamic range	92 dB or more
Total harmonic distortion factor	0.006%(1kHz)
Total harmonic distortion factor + noise	0.007%(1kHz)
Channel separation	90 dB or more
Output	Line : 2.5V/600 Ω (1 kHz, 0 dB) Headset : Approximately 35 mW, 40 ohm load (1 kHz, 0 dB)
Pwer	100 VAC, 50Hz/60Hz
Power consumption	16W max.
External dimensions	Width 430x Height 100x Depth 322 mm
Weight	Approx. 6.6 kg
Attachment : Remote Control Unit RM-3CD
Method	Infrared pulse type
Pwer	DC3V(1.5Vx2)
External dimensions	Width 50x Height 19x Depth 162 mm
Weight	Approximately 100g (including dry batteries)