Onkyo TA-2058 User Manual

CIRCUIT DESCRIPTIONS
1. DOLBY HX PRO CIRCUIT
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BIAS SIGNAL
{From O5C,)
| [VOLTAGE
| JREGULATOR
VCA
i
+12¥
| (When Recording)
REFERENCE
VOLTAGE
Hx SW
OIA AUTO ACCUBIAS ON
OUT VOLTAGE CONTROL
RECORDING
HEAQ
In this circuit, the bias oscillates only when recording. The
size of the bias current is controlled by the bias control
voltage. When the HX PRO is OFF, by means of the
recording signal, a non-modulating oscillator voltage is
applied to the absolute value detection circuit. When the
HX PRO is ON, by means of the recording signal coming
from the recording head, a modulating oscillator voltage
is applied to the absolute value detection circuit, and by
means of the recording signal level peak detection value,
the bias current is instantaneously controlled. At such
time, by means of the CR integrated circuit, the frequency
characteristic is maintained. (Approx. 8 KHz)
2. PRESET ACCU BIAS OPERATION
Dia CONVERTER $,% 400H2
(~)
REC AMP
i)
$452 12 KHz
REC. HEAD
HX PRO
CIRCUIT
25 30 PLAY BACK HEAD
AGRM ACCU < <|
| TAPE
Fig. 1 Block diagram
With the LEVEL SELECT, the 12KHz level is set in $
stages. With regard to 400Hz, the 12KHz level is set in 5
stages.
When the ACCU BIAS operation is started, a 400Hz/12kHz
mixed signal is recorded, the bias current in this case being
controlled by a signal from the microcomputer. The play-
back signal is separated by filter into the original 400Hz
and 12kHz signals, and after being rectified these signals
are passed to a comparator where a comparison check is
made to see if one of the signals is greater than the other.
A HIGH comparator output indicates that the 12kHz
signal is greater than the 400QHz signal, and a LOW output
indicates that the 400Hz is lower than the 1 2kHz.
TA2058
®
Smaller 28 = Jn 6
u—— a
_ @
20 ——
*— -
= 0 —~+ Time (t)
2—
‘—
i
Larger _
0
Fig. 2 Bias adjustment method
First the bias is set to step 16 which is in the center of the
bias range shown in Figure 2. Then the 400Hz/12kHz
mixed signal is subjected to a comparison operation to see
which component is larger. If the 12kHz signal is larger,
then the bias level is too small. If the 400Hz signal is larger,
on the other hand, the bias level is too large. In the example
shown in Figure 2, the bias level at step 16 is too large, so
the bias is reduced by % of the total range (8 steps) to
position (2) where the 400Hz and 12kHz components are
again compared. If the 400Hz signal is still larger than the
12kHz signal, the bias level is further reduced by % of the
total (4 steps) (3) and the components then compared
again. This procedure is used for rough adjustment of the
optimum bias. If at this stage, the 12kHz signal is now
found to be greater than the 400Hz signal, the optimum
bias is known to exist between steps 24 and 28. The ope-
ration is now switched to fine adjustment — the bias is
increased by % and then reduced one step at a time from
step 24. The step where the component signal size rela-
tionship is switched from 400 > 12k to 12k > 400 is taken
as the optimum bias (5), and the bias is set at this level.
This fine adjustment operation proceeds only from greater
to lower bias levels in order to avoid misoperation due to
possible drop outs. The effects of a drop out on the bias
adjustment when the bias is changed from a smaller to a
larger level is indicated in Figure 3, while the reverse
case is indicated in Figure 4.
IZKHz Drop out
/ 400Hz
400Hz
T2KHig ~~ Drop out
Read as equal levels
Fig. 3 Example of misoperation
caused by drop out
Fig. 4 Example where effect
of drop out is avoided

Onkyo TA-2058 Specifications

General

Brand	Onkyo
Model	TA-2058
Category	Cassette Player
Language	English