Fisher CA-890 - Page 5

CIRCUT DESCRIPTION
The CA-890 has the following features:
Full Remote Control/Auto Function Selection
_ AV-Compatible
High Output Power Amplifier (150W x 2)
Built-in Parametric Equalizer
Multi-Protection circuit
aos
1. Full Remote Control/Auto Function Selection
The infrared remote control can be used for control of 46
different audio system functions — that is, practically ail
functions.
Also, auto function selection and synchronized recording are
possible not only with manual operation but also by remote
control.
In order to make this possible, two types of microprocessors
have been developed; a main microprocessor {4k-byte ROM
capacity) and a sub microprocessor (1k-byte).
The main microprocessor is built into the amplifier, and sub
microprocessor are mounted in the components (tuner, CD
player, turntable, cassette deck).
These microprocessors exchange data mutually.
As shown below, the main and sub microprocessors are
connected by two-way data buses.
When the remote contro! is used and auto function selection is
performed, the function indicator flashes (CD player, cassette
deck, turntable).
Directly before access is completed and sound is output, the
indicator stops flashing and remains lit, thus allowing safe
remote control even at a distance.
DaTa
CLock
ReaDY —
REQuest
GND.
Main Sub
Microprocessor Microprocessor
Data is transferred in serial by clock synchronization, and the
READY and REQ lines are used for control of interruption in
order to assure proper operation.
2. AV-Compatible
The CA-890 is equipped with TV and VCR input jacks and
output jacks for VCR recording, making it possible to use the
CA-890 to construct a full AV system.
There are also DIN terminals for extracting information on the
status of the audio components, which when used permit the
display of the status on the TV screen.
3. High Output Power Amplifier (1 50W x 2)
A triple cascode is used in the first stage, preventing
deterioration of the THD due to changes in the signal source
impedance, that is in the volume position.
Also, as each of the three cascodes uses a 1-chip dual
transistor, the structure is electrically and thermal well balanced
and stable.
For the final stage, a large PC200W epitaxial planar transistor is
operated by single push, obtaining 150W at 20 ~ 20kHz with
THD of below 0.02%.
Current mirror chip
OUT
Vi converter chip
Differential amp chip
+IN —IN
Triple cascode
4. Parametric Equalizer
The CA-890 uses the same highly successful parametric
equalizer as was used on the CA-276.
Any two frequencies can be varied independently by +12 dB.
The frequency range is from 20 ~ 800Hz in the low band, and
from 600 ~ 20kHz for the high band. Q is fixed at 1.2.
5. Protection Circuits
The CA-890 is equipped with three different protection circuits,
protecting against a variety of problems.
® DC detection (speaker protection)
The speaker jacks are cut off at the relay if a DC voltage of
3V or greater is generated.
@ Temperature dectection (amplifier protection)
If the temperature of the radiator reaches 120°C (equivalent
to power transistor junction temperature of 150°C), this is
detected by a posistor and the speaker jacks are cut off at
the relay.
@ Load/short-circuit protection (amplifier protection)
If the speaker jacks are short-circuited or they are
connected to a low impedance load, the ASO limiter is
activated and the power transistor is protected.
If certain conditions in the relation of the power transistor
current and load impedance are fulfilled, this ASO limiter
interrupts the input signals using the muting circuit.
+Va +e
Volt Amp.
7—a- OUT