Tascam 414MKII How the dbx Works, Cleaning the Pinch Roller, Cleaning the Capstan Shaft

Care and Maintenance

Cleaning the Pinch Roller

Clean the pinch roller at least once each day the deck is used. Use a good rubber cleaner.

1.Clean the pinch roller with a cotton swab moistened with rubber cleaner, until there is no visible residue on the pinch roller.

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

Cleaning the Capstan Shaft

After cleaning the pinch roller, clean the capstan shaft with a cotton swab moistened with head cleaning fluid.

Erase head	Capstan
Record/Play head		Pinch roller

Degaussing the Tape Path

Hold the degausser about 1 m (3 feet) away from the recorder. Turn it on, slowly move into 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.

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.

How the dbx Works

The dbx system 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 system 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.

Input	Á Encoder	Á	Tape deck		Á	Decoder	Output
Dynamic range	Encode					Decode
of	(Compress)	Record		Playback		(Expand)	Á80dB	Saturation
input signal	80dB	Á40dB		Á40dB
	+20dB						+25dB	level
				+15dB			+20dB
		+10dB
	0dB			Á
		Dynamic range of tape
				(65dB)
		–30dB
				Á
				–50dB			–60dB
	–60dB
	dbx encoding/decoding level diagram						–80dB	Noise level

SUBSONICS AND INTERFERENCE

The dbx system 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 system, 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. If 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.

36