Tascam 424MKIII How the dbx Works, Cleaning the Pinch Roller, Cleaning the Capstan Shaft

Cleaning the Pinch Roller

1.Press a cotton swab that has been moistened with rubber cleaner to the pinch roller on the right hand side of the capstan shaft (or, on the left hand side if REW is pressed). This will prevent the swab from becoming tangled in the mechanism.

2.Clean it until there is no visible residue coming off onto the swab.

3.Using a clean cotton swab, wipe off all the excess rubber cleaner from the pinch roller. Make certain that there is no foreign matter remaining on either the pinch roller or the capstan shaft.

Cleaning the Capstan Shaft

1.Clean the capstan shaft by lightly pressing a cotton swab moistened with head cleaning fluid onto the shaft. Clean thoroughly and wipe off excess fluid.

Degaussing the Tape Path

How the dbx Works

The dbx is a wide-band compression-expansion system which provides a net noise reduction (broadband, not just hiss) of a little more than 30 dB. In addition, the compression during recording permits a net gain in tape headroom of about 10 dB.

A compression factor of 2:1 is used before recording; then, 1:2 expansion on reproduce. These compression and expansion factors are linear in decibels and allow the system to produce tape recordings with over a 90 dB dynamic range – an important feature, especially when you're making live recordings. The dbx employs RMS level sensors to eliminate compressor-expander tracking errors due to phase shifts in the tape recorder, and provides excellent transient tracking capabilities.

To achieve a large reduction in audible tape hiss, without danger of overload or high-frequency self-erasure on the tape, frequency pre-emphasis and de-emphasis are added to the signal and RMS level sensors.

1.	Hold the degausser about 1 m (3 feet) away
	from the recorder. Turn it on, slowly move in to
	the tape path. Move the degausser slowly back
	and forth, touching lightly all metal parts in the
	tape path. Slowly move it away again to at
	least 1 m (3 feet) from the recorder before
	turning it off.
2.	To complete the cleaning and demagnetizing
	procedure, press STOP. The head block will

Input	ç￿ Encoder	ç￿ Tape deck			ç￿ Decoder
Dynamic range	Encode				Decode
of	(Compress)	Record		Playback	(Expand)
input signal	80dB	ç￿40dB			ç￿40dB
	+20dB			+15dB
		+10dB	ç￿
	0dB
		Dynamic range of tape
				(65dB)
		–30dB
			ç￿	–50dB
	–60dB

Output

￿

80dBç￿ Saturation +25dB level

+20dB

–60dB

retract. Then hold STOP and press COUNTER

RESET to cancel the cleaning mode.

CAUTION

If the surface of the unit gets dirty, wipe the surface with a soft cloth or use a diluted neutral cleaning fluid. Clean off thoroughly. Do not use thinner, benzine, or alcohol, as they may damage the surface of the unit.

dbx encoding/decoding level diagram –80dBNoise level

SUBSONICS AND INTERFERENCE

The dbx incorporates an effective bandpass filter. This filter suppresses undesirable subsonic frequencies to keep them from introducing errors into the encode or decode process. However, if rumble from trains or trucks is picked up by your microphone and fed to the dbx, modulation of the program material during low level passages may occur. This low-frequency component will not itself be passed through the recorder and so, will not be present at reproduce for proper decoding. It this low-level decoding error is encountered, and subsonics are suspected, we suggest the addition of a suitable high-pass filter in the microphone line.

49