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MicMix STUDIO B Master-Room spring reverb

 


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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