DENON DR-M4

Commentary

A cassette deck developed as the highest quality model of the M series.

The mechanism uses a two capstan system, in which two sets of capstan are installed around the head, and the rotational speed of each of the two sets of capstan is slightly changed to achieve appropriate tape tension near the head and stable tape travel.
In addition, both capstans and pinch rollers cut off tape vibrations caused by the movement of the hub in the cassette half and the sliding of the tape with the slip sheet before they affect the head surface, thus achieving clear sound quality with less modulation noise.

The capstan drive motor uses a direct-drive motor with a flat-faced design to obtain strong rotational torque and eliminate uneven torque. In addition, since it is brushless, it generates no electrical noise and improves durability.
In addition, the wow flutter has been improved by directly driving the capstan and directly servoing it in combination with the speed detection mechanism attached to the flywheel surface. This servo circuit also employs an all-round integrated sample-and-hold type FG servo, providing high gain and extremely high stability.
The DR-M4 uses a quartz lock system to control the rotational speed, and the phase control circuit using an accurate and stable crystal oscillator makes the FG servo operation more reliable.

A silent mechanism has been adopted for the running system.
In this mechanism, a motor-cam drive is adopted without using a large mechanical noise such as a plunger. In addition, a microcomputer is placed between an optical detection counter, a unique position detection encoder, and a mechanical control motor (for cam drive), and a computer controls searching for tape points and checking the drive mode.

Non-slip reel drive system has been adopted to achieve uniform winding tension.
This system takes advantage of the characteristics of the relationship between the rotational speed and torque of the reel motor. It eliminates changes in the take-up force due to changes in temperature and moisture, which are problems with general mechanical slip mechanisms, and improves the drop-out, wow flutter, phase characteristics, etc., as well as the durability of the mechanism.

Uses SF (Super Frequency) combination head for recording and reproducing head.
Super Permalloy with high saturation magnetic flux density is used for the core of the recording head, and it is compatible with high-level recording tapes such as metal tapes. Moreover, by using Sendust for the dummy core, abrasion resistance is greatly improved.
In addition, a high-density ferrite core with low high-frequency loss and excellent abrasion resistance was adopted for the reproducing head for the first time as a combination head. Moreover, by reducing the size of magnetic particles to less than 1/2 of the conventional size, fluctuation of magnetic characteristics due to sliding noise and temperature change, which cause modulation noise, is improved.
The SF head is a combination of these heads. In particular, the recording gap and the playback gap, which are indispensable for maintaining high frequency and phase characteristics, are kept within 1/20 degree of parallel deviation, and wide and flat frequency characteristics are obtained. In addition, oxygen-free copper wire is used for the coil to improve sound quality.

The power supply circuit completely separates the amplifier circuit from the logic circuit to eliminate mutual interference. The amplifier circuit uses an independent power supply system called an independent power supply to stabilize the circuit.

A low-noise differential input push-pull DC amplifier circuit is used for both the recording amplifier and the playback amplifier. A ± 2 power supply system supplies a high-voltage power supply to further expand the dynamic range and prevent clipping distortion in the signal transmission system. In addition, the capacitor between the playback head and the first stage amplifier is removed, and a DC amplifier is used up to the last stage to improve sound quality.
The bias circuit employs a highly stable transformer and push-pull configuration to improve bias waveform distortion and reduce erase noise.

A wide-range peak meter using a fluorescent bar graph method is used for the display.
In the FL meter, Dolby B & C, monitor, tape position, etc. are displayed centrally. In addition, the peak meter is equipped with a peak hold function which Oatley set every 1.5 seconds.

A one touch rec-pause mechanism is adopted, and recording standby can be performed just by pressing the REC button.

Uses Dolby B Type and Dolby C Type as noise reduction systems.
The DR-M4 has a double-Dolby configuration so that Dolby playback is possible even during simultaneous recording and monitoring.

Built-in MPX filter allows cutting of 19 kHz pilot signal of FM source.

A computer counter is used, and by switching the switch, not only the normal 4-digit electronic counter but also the driving time can be displayed in minutes and seconds.

Equipped with a computer tuning function.
This function automatically finds the best position for a tape among 100,000 adjustments, adjusts the sensitivity for any tape, and sets the frequency response to be flat.

It is equipped with a computer search function that can find the beginning of 20 songs before and after.
This function operates by detecting the unrecorded portion of 3 to 4 seconds or more between songs.

Equipped with a memory stop mechanism.

It is equipped with output level control which is linked with volume control of headphone.

Equipped with timer play / rec mechanism. By connecting a timer sold separately, it is possible to record your absence and play an alarm.

The Pause/Mute mechanism is used to combine the Rec Mute and Pause to improve operability.
When recording, press and hold the Rec button to mute, release it to pause, and press the Play button again to record.

Equipped with a follow-up recording mechanism, you can change from a regenerating condition with the tape running to a recording state with one touch operation.

Equipped with remote control terminal and separately sold remote control unit RC-57 can be used.

Model Rating

Type	Cassette deck
Track system	4-track 2-channel stereo
Tape selector	3-Level Auto Tape Selector (Normal, CrO2, Metal)
Heads	Recording : SF Combination Head Erasing : double-gap ferrite heads
Motor	For Capstan : FG Servo Quartz Lock DD Motor For Reel : DC Motor For mechanical control : DC motor
Wow and flutter	± 0.04% (W. Peak) 0.027%(WRMS)
Early winding time	Approximately 90 seconds (C-60)
Overall frequency response (input -20VU)	Metal tape : 20 Hz to 23 kHz (25 Hz to 21 kHz ± 3 dB)
Overall signal-to-noise ratio	Dolby CNRon : 73 dB or more (CCIR/ARM measurement method for 3% THD level)
Input terminal	Mic : 0.35mV/10k Ω Unbalanced (suitable for microphones of 10k Ω or less) Line : 77.5mV/50k Ω Unbalanced
Output Terminal (Vol. max)	Line : 775mV/10k Ω Unbalanced Headphone : 1.2 mW (8 Ω load, suitable for 8 Ω ~ 2k Ω headphones)
Pwer	100 VAC, 50Hz/60Hz
Power consumption	22W
External dimensions	Width 464x Height 115x Depth 286 mm
Weight	6.5kg
Sold separately : Remote Control Unit RC-57 (¥ 6,000)
Cord length	5m
External dimensions	38 mm wide x 17 mm high x 120 mm deep
Weight	Approx. 160g (including cord)