Academy Audio Hi-End MUSES VCM Manuale d'uso - Pagina 5
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6. Theory of Operation
A potentiometer based volume control, shown at Figure 2, is the most traditional volume control
solution.
J1
C1
VOLUME CONTROL
INPUT
J2
C2
R1
OUTPUT
R2
0
Figure 2. Potentiometer Volume Control
A capacitor C1 blocks any DC current from the input reaching the potentiometer, and capacitor C2
prevents any input DC bias currents from the downstream circuitry passing through the potentiometer.
Both capacitors are needed to avoid cracking noises while adjusting the volume. Resistor R2 represents
a load of the volume control. Both capacitors are in the audio signal path and may affect sound quality.
They have to be of a high quality type, and properly sized to pass low frequency audio signals with
minimum degradation. Capacitor C2 may be omitted if the downstream circuit has a JFET high
impedance input with practically no bias current. The C1 may be removed only if the circuitry feeding
the volume control has no DC output component at all times. Precision of the volume control operation
is affected by the load, and is degraded when the load impedance is less than 10 times higher than the
potentiometer value. Placing a high input impedance buffer or amplifier after the volume control
assures perfect compliance with the regulation curve. So called "passive" volume controls use no active
electronic circuitry and are heavily dependent on the input impedance of the loading audio component.
The MUSES®72320 volume control chip is built on the resistive elements commutated with a high
quality MOSFET switches, and performs like a potentiometer based volume control. Figure 3 is an
excerpt from the official JRC datasheet.
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