Akai GX-225D Manual page 23

FL1; HIGH PASS FILTER
FL2; LOW PASS FILTER
Fig. 33
A.N.R. AMP. BLOCK DIAGRAM
—_—Pr- INPUT LEVEL dB
10OHz
lOOOHz
10,000Hz
——eeeem FREQUENCY Hz
Fig. 34. AUTOMATIC NOISE REDUCTION AMP. CHARACTERISTICS
2. A.N.R. OPERATION AND CHARACTERIS-
TICS (Refer to Fig. 33 & 34)
1) The TR1 output signal passes the high pass filter
and the low pass filter and is supplied to TR2 and
TR4 respectively.
2) The TR2 output passes diodes D1 and D2 as well
as condenser C7 and is supplied to TR3. In case
the input signal is high, D1 and D2 decreases the
impedance and the signal supplied to TR3 is
unchanged. Also the signal which passed FL2 is
amplified at TR4 and the TR3 and TR4 signals
merge at the input side of TRS and become a
composite signal.
3) In case the level of the signal which passed High
Pass Filter FL1 is small, diodes D1 and D2
increases the impedance relative to this signal level
and the signal supplied to TR3 is even smaller. The
signal which passes Low Pass Filter FL2, because
there are no variable impedance components such
as D1 and D2, is supplied to TR4 unchanged.
Consequently, both signals merge, becoming a
composite signal and the output becomes a high
frequency reduced signal in relation to a low level
input.
4) The characteristics of diodes D1 and D2 increases
the impedance of low level signals (the lower the
level, the more the impedance is increased) so that
the signal supplied to TR3 is close to Zero.
Consequently, the purpose of condenser C7 is to
prevent decrease below a certain level.
23°