CIRCUITS
Q1 is an integrated circuit voltage regulator and Q2 is the pass transistor,
forming a regulated power supply with current foldback to protect both
the supply and the load. Resistor R2 establishes current limiting at approximately
300 milliamps. Output voltage
is set by the ratio of R3:R4. R3 is adjusted by paralleling two resistors
(if required) to obtain an output voltage between 39 volts minimum and
41 volts maximum.
STUDIO B utilizes a bridge typepower supply design and Q3 is a unity
gain operational amplifier supplying current for the center tap and providing
a +20 volt reference for the unit. CR7, CR8, CR2l, CR22, CR41 and CR42
are voltage dropping zener diodes to reduce the supply voltage to within
the voltage rating required for their associated operational amplifiers.
The Sound Column driver circuit consists of OpAmp Q21 which drives Q22
and Q23. Resistor R27 establishes the sensitivity level for optimum operation
and its value will depend upon nominal input level to the unit. At the
normal +4 dBm input, R27 is 4700 ohms.
The Program/Line Amplifier circuit includes OpAmp Q41 which drives Q42
and Q43. Input is switchable by means of S22 to provide an internal mix
of program and reverberation signal, or to function as a reverb line amplifier
only (in conjunction with a console having an echo send and return system
for mixing). Resistor R43 determines the sensitivity level and is normally
27K ohms for a +8 dBm output level. By changing R43, output levels up
to a nominal +16 dBm are possible.
CAUTION: If +8 dBm is too 'hot' a level
,
use an external pad on the output. Do not change R43 for a level
below +8 dBm.
R49 establishe8 the quiescent current for Q42 and Q43 to eliminate crossover
distortion. Meter M41 is a settable damped VU meter and is normally factory
set for a zero VU reading at +8 dBm. R54 can be adjusted to set the meter
for zero readings up to +16 dBm.
Reverb gain is controlled through Q81, an OTA device whose voltage gain
can be controlled from cutoff to a closed loop gain determined by the
ratio of R88 and R89. The control signal is a current which varies from
zero to approximately 30 microamperes as controlled by the setting of
R70, R71 and the signal generated by Q61's circuitry.
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