CIRCUIT DESCRIPTION
REMOTE RECEIVER and
CONTROL LOGIC
AUDIO LINE
LEVEL INPUT
SELECTOR
SYSTEM
JFET BUFFER AND RECORD OUTPUT DRIVER
VIDEO
SWITCHING
TAPE MONlTOR
SWITCHING
LINE AMPLIFIER
TONE CONTROL SYSTEM
MUTING SYSTEM
The | Remote | Receiver | circuitry | decodes | the | infrared | pulses | received | from | the | Remote |
| Control |
| via | the | |||||||||||||||||
front | panel | Infrared | Receiver. This decoded information is sent to | the | Control | Logic, | which | controls all | |||||||||||||||||||||||||
internal | signal | routing and Front Panel indicators. The Control | Logic | also | receives | input | commands | from | |||||||||||||||||||||||||
the |
| Front Panel buttons. |
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The | Control | Logic | creates digital codes fed to a | electronic | selector | switch. | This |
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besides allowing convenient remote operation, eliminates | signal | degradation | due | to | mechanical | switch | |||||||||||||||||||||||||||
contacts, | and | allows the electronic switches to be | located close | to the’rear | panel | inputs | for | minimum | |||||||||||||||||||||||||
signal path lengths and reduced interchannel crosstalk. |
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The | output | of | the | audio | Selector | System | is | followed by | a | very | high | JFET | buffer | pair | |||||||||||||||||||
to | establish | negligible | CMOS |
| switch loading | (for | low | distortion) | and | to | provide | a | source | ||||||||||||||||||||
for |
| the | Tape | Outputs and the Volume and Balance controls. |
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The | Control | Logic | creates digital codes fed to a | electronic | selector | switch. | These | inputs | are | ||||||||||||||||||||||||
selected simultaneously with the corresponding audio | inputs. | The | selected | video | input |
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| fed |
| through | ||||||||||||||||||||||
separate | wide | bandwidth | +6 | dB amplifiers | for each | of | the | Video | Monitor | and | Video |
| Record | Outputs. | |||||||||||||||||||
Only | Video | 1 | and | Video | 2 | signals | are | available | at | both | the | Video | Monitor | and Record | Outputs. | Video | |||||||||||||||||
3 | is blocked | from | the Video Record Output to prevent | feedback | from | occurring. |
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The | Tape | Monitor | buttons drive | to break the line input path | to | insert | tape | ||||||||||||||||||||||||||
input | signals. | This | switching |
| arrangement |
| allows | optimum | signal | routing | by | placing the | switches | close | |||||||||||||||||||
to | the | Tape | Input | jacks | and | the | Input | Selector | System. |
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The 945 Line Amplifier is a
complementary high gain output stage, | symmetrically | driven | for balanced | low | harmonic |
distortion. This topology uses only four | active devices | per | channel and extremely short | loop | feedback, |
yielding high bandwidth and excellent | stability. |
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The feedback loop contains two user selectable paths: one conventional path for flat response, and another path allowing insertion of a tone control network. This arrangement allows maximally flat response and the shortest, cleanest signal path when tone control action is not required.
The output of the Line Amplifier is capacitor coupled to the output of the preamplifier.
The | Tone | In/Out | button | allows complete removal | of | the | tone controls from the signal | path. | This switching | ||||
is | accomplished | with | the same | type | of | Input | Selector. | This | |||||
switching | arrangement | eliminates | signal | degradation | due | to mechanical switch contacts, and allows | the | ||||||
electronic | switch | to | be | located | very close to | the | Line | Amplifier circuitry. |
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The Bass Control is of a moving inflection, variable turnover type, and the Treble Control is of a shelving, variable turnover type. These types of tone controls offer the best “tools” for modifying tonal balance without introducing unwanted side effects. See Operation Section for further information.
The Muting System monitors the power supply voltage. During the
The muting is accomplished by grounding the Line Output jacks and disconnecting the output of the Line Amplifier, using a relay with gold contacts.