Farfisa Compact Service Manual

Page 2

Some explanation on schematics

SE - 1'0: Operating schematics
The schematics show the general principles, which are the following ones;

a) The signals are originated by oscillators G 10. Each one of them produces all the freqUencies of same
name (i. e. G 10 » C produces all Cs, G 10 - A produces all As, etc,).

b) The Vibrato is obtained operating directly on the oscillators of the various notes.

c) Every key has three contacts: the lower one operates on 16 frequencies, the medium one operates on
8' frequencies, the upper one operates on 4' frequencies.

d) All the contacts related to every octave, C~ B, for 16 or B or 4, have common ends for connection to
filters; these ends are represented by common bars and each one them is connected by means of a shielded
cable to a series of switches operated by the MTB ON/OFF tab.

e) The MTB switches are meant to convey the signals to the tone stops when the MTB tab is in OFF
position. in this case, inserting one tone stop (or several stops at the same time), the signals are conveyed to
filter FD 10, where part of the signals is blended and then conveyed to filter FA l0 for the formation of the
sharp tones (oboe, trumpet, strings).

The signals proceeding from filter FA 10 return to the tone stops and through the inserted tab, they are
conveyed to the L.F. preamplifier. At the same time, in the filter FD 10, an attenuation of the higher harmonics,
interesting the signals conveyed to the low pass filter, takes place, giving way to an output of sweet tune
signals, ready to be conveyed, through the special tone stops (bass, flute), to the L. F. preamplifier.

f) When MTB is inserted, the switches convey the signals proceeding from the common bars to filter
FD 10 through MTB stops (lo-8'-4). The total blending of signals in FD 10 is then conveyed directly to the
special in take of MTB, where the filtered signals, available at the outlet No. To of FD 10 (sweet tune) are com
veyed to the outlet of MTB.

The LP, preamplifier is connected only to the outlet of MTB and amplifies therefore only the signals con-
veyed to this device through l6»B-4 stops (Green tabs) with the exclusion of the tone stops (white tabs).

9) When «All Booster» is inserted, the signals proceeding from the common bars are permanently con-
veyed, at constant level, to filter FD-lO through MTB stops 16', 8, 4'.
SE - ll: Simplified keying schematics for Treble and Manual Bass.

it shows the wiring of the various notes, making reference to one note only (A).

SE - l2: Circuit diagram of Treble registers

The drawing reports the connections interesting the tone stops and the connections between the registers
and the filters. -

In the left top corner, framed in a square, it is shown the schematic diagram of MTB device.

SE - 13: Circuit diagram of Pedal registers, Vibrato and Reverb.

The drawing showing the Manual Bass and the Pedalboard stops indicates the potentiometers for the volume
regulation of single notes, while the drawing related to Vibrato and Reverb shows Potentiometer R 536 for the
regulation of the time of Reverberation.

SE -14: Schematics of Master oscillators (G 10), fillers (FD 10), (FA 10), Vibrato circuit and Pedal
amplifier (PS 10).

The schematics show the values of all components assembled in the printed circuits for repair purpose.

SE . 15: Circuit diagram of Power Supply. Preamplifier and Reverb.

Complete electric schematis, showing the voltage rating and the features of electric components. Almost
in the centre of the page it is indicated the Swell Pedal photoresistor operating as volume control.

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