Academy Audio Hi-End MUSES VCM User Manual - Page 7
Browse online or download pdf User Manual for Control Unit Academy Audio Hi-End MUSES VCM. Academy Audio Hi-End MUSES VCM 12 pages. Mini electronic volume controls
Print Page
A single ended Volume control arrangement is presented at Figure 4.
J4
+15V
J5
GND
J7
+15V
J9
IN_L
J10
COM_L
J12
IN_R
J14
COM_R
Figure 4. VCM with JFET Opamp. Single Ended Volume Control Application.
Capacitors C3 and C5 block DC input signals. Resistors R2 and R4 isolate the opamps' outputs from
capacitive load and improve stability. Optional DC blocking networks C2R3 and C4R5 prevent a DC bios
voltage of up to 10mV from opamps' outputs from reaching the downstream audio circuits. If this
voltage is not a problem for the downstream circuitry, the optional networks can be omitted. The value
of C2 and C4 capacitors may be greatly reduced, (and quality film capacitors may be used), if the input
impedance of the downstream circuitry is high. E.g. for input impedance of 47kOhm, 1uF 63V
polypropylene capacitors would provide a low frequency -3dB point of about 3.4Hz.
A muting relay RL1 controlled by a switch R8R7Q1 provides quiet startup and turn-off of the circuit. The
MUTE control signal received from the control board is output at pin 8 of the VCM board.
Figure 5 presents a balanced version of the Volume control that features two VCM boards with JFET
opamps installed.
VCM Board
with JFET
Opamp
Installed
J3
CON16
C3
47uFx35V NP
C5
47uFx35V NP
J1
OPTIONAL
(SEE TEXT)
C2
R2
47
47uFx35V NP
R3
100K
RL1
C4
R4
47
47uFx35V NP
R5
100K
R6
MUTE
6.8K
Page 7 of 11
GND
+5V
J2
+5V
R1
22
C1
J6
0.1uF
OUT_L
J8
COM_L
D1
ZENER 5.6V 500mW
J11
OUT_R
J13
COM_R
Q1
2N2222A
R7
22K