Dolby HX Pro-Head
Room Extension System
To record good
quality sound, it is necesary to give bias current to the head. The bias current has characteristics as
follows:
Increasing the bias
current reduces the distortion in low-frequency range but lowers the recording
level in high-frequency renge.
Decreasing the bias
current improves the recording level in high-frequency range but increases the
distortion in low-frequency range.
In the case of a
common deck, a specific level of bias current is determined according to the
characteristics of recording head. Therefore, bias current cannot be applied to
the head according to the frequency levels of music signal.
In order to solve
such problems, this unit employs "Dolby HX-Pro". It picks up the high
frequency of music source changing at all times, and controls the bias current
level according to the changing frequency. It serves to make the bias current
level then most suited for the music source.
This system always
operates in recording mode irrespective of the noise reduction system, but the
dynamic range in record/playback can be further increased by using this system
in combination with a noise reduction system. Particularly, combination with the
dbx NR system mounted in this unit will double the MOL (Maximum Output Level)
in high frequency range, whi the record/playback of digital source as in CD.
Record
Calibration/Bias Control Function
There are sometimes
differences in playback output level even in case of same recording level or in
sound quality even in case of same recording source. This is because the
characteristics of the cassette tape used are different with the makers and
brands.
To solve this
problem, RS-B905 is furnished with a record calibration knob and bias control
knob. These knobs can be used to adjust
the sound volume and quality while comparing the music signal (original sounds
of record and tuner) and recorded signal (sound recorded on tape).
Record Calibration
Knob
Used to calibrate
the difference in recording level of music signal and recorded signal.
Bias Control Knob
Used to correct the
high-frequency sound quality of music signal and recorded signal.
In this way, the
record characterisctcs will not be distorted by tape, and the characteristics
can be kept nearly uniform.
The comparison by
hearing can be done by only one monitor switch because this unit is of 3-head
type with record, playback and erase heads.
MPX Filter
If FM stereo
broadcast is recorded by Dolby NR, then the pilot signal included in the
broadcast is also processed by Dolby NR as music signal, causing deterioration
of sound quality and worsening of noise reduction effect.
Pilot Signal
This signal is used
to separate FM broadcast into L and R channels, which is emitted at 19 kHz very
close to the music frequency band.
To solve this
problem, RS-B905 is equipped with MPX filter switch to cut off the pilot
signal. It serves to cut off the 19 kHz
single frequency of the pilot signal, which is different from a high cut filter
installed in an amplifier, etc.
Also, MPX filter
hardly causes change of sound quality in a sense of hearing.
Class AA Circuit
Recording Equalizer Amp
Recording equalizer
amp is an amplifier to supply recording current to the head. Usually, loads
such as recording head and bias trap circuit are added to the amplifier.
Therefore, the current phase and voltage phase are fluctuated causing the
recording signal to be distorted. This unit employs "class AA" amp in
which two types of amplifier circuits (voltage control amp and current supply
amp) different in ampllifying system. This recording equalizer amplifier is not
influenced by the fluctuation of current phase or voltage phase as mentioned
above, and is excellent in waveform response.
Operation Principles
of Noise reduction System
Dolby NR, B type, C
type
The level of hiss
noise generated during playback is constant.
So, it is more offensive to the ear when the music signal level is
lower. Accordingly, raising the signal level during recording and lowering the
level during playback will result in reduction of noise generated by the
tape. Dolby NR B type does it in high
frequency range, and C type, in high and medium frequency range.
Dbx NR
Cassette tape is low
in saturation level (limit of recording level). Therefore, distortion will be
generated if music signal with large dynamic range (ratio of sound volumes of
the weasound and the strongest sound) is recorded as it is.
dbx NR halves the music signal during recording and
doubles it during playback. In this way,
dynamic range as large as 110dB and noise reduction effect as high as 30 dB can
be obtained, and good quality sound can be recorded even in case of music
source with dynamic range as in CD and live performance.
Monitor Switch
In order to avoid
faulty recording such as low sound level or distortion, it is very important to
monitor the state of recording. In the case of a common deck (2-head type), the
sound that can be monitored during recording is always the sound before recording.
So, when checking the state of actual recording, you have to rewind the tape
and play it back.
Technics RS-B905 is
of 3-head type, and the record head is independent of the playback head. Also,
the sound before recording can be compared with the recorded sound by use of
the monitor switch, therefore the state of recording can be easily checked.
Specifications
Deck System: Stereo cassette deck
Track Sysstem: 4-track, 2-channel
Heads
Rec/Play :
Combination head
Erasing : Double-gap
ferrite head
Motors
Capstan :
Electronically controlled DC motor
Rell Table Drive :
Electronically controlled Dc motor
Recording
System: AC bias
Bias Frequency: 85 kHz
Erasing System: AC erase
Tape Speed: 4,8
cm/sec. (1-7/8 ips)
Frequency Response
Metal : 20 - 22,000
Hz (±15 dB); 30 Hz - 21 kHz (DIN)
CrO₂ : 20 - 21,000
Hz (±15 dB); 30 Hz - 20 kHz (DIN)
Normal : 20 - 20,000
Hz (±15 dB); 30 Hz - 19 kHz (DIN)
Dynamic Range (with
dbx on): 110 dB (1 kHz)
Max. Input level
Improvement (with dbx on): 10 dB
Signal-to-Noise
Ratio (signal level = max recording level, CrO₂ type tape)
dbx on : 92 dB (A
weighted)
Dolby C NR on : 75
dB (CCIR)
Dolby B NR on : 67
dB (CCIR)
NR off : 57 dB (A
weighted)
Wow and
Flutter: 0,04% (WRMS) ±0,12% (DIN)
Fast Forward and
Rewind Time: Approx. 95 sec.
Input
Sensiblity/Impedance
Line :
60 mV/47 kΩ
Output Voltage /
Impedance
Line :
400 mV/2,2 kΩ
Headphones
; 125 mV/8Ω
General
Power
Consumption: 25 W
Power Supply: 110 / 120/ 220/240 V AC 50/60 Hz
Dimensions (W x H x
D): 430 x 25 x 110 mm (16-15/16" x
11-7/32" x 4-5/16")
Weight: 5 kg (11 lbs)
