Academy Audio Hi-End MUSES VCM User manual

© 2014 Academy Audio Inc.
Academy Audio Inc.
discovering the soul of music®
Hi-End MUSES®
Mini Electronic Volume Controls
Cat. No. VCM Ver. 01
User Manual
Rev. 02
MUSES®is a trademark of NJR Corporation. Other trademarks are a property of their respective owners.

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1. Introduction
Thank you for purchasing the VCM, a Hi-End MUSES® Mini Electronic Volume Control from Academy
Audio Inc.
The VCM is a reduced size version of our Hi-End MUSES® Electronic Volume Control board, and is a
complete ready to use two channel volume control unit that requires a +/-15V power supply and control
signals to operate.
The unit is built using a unique NJR MUSES®72320 volume control chip. Unlike other electronic volume
control chips, this chip does not include any active circuitry, and therefore provides vanishingly low level
of noise and distortions.
The VCM can be used with an outboard amplifier/buffer section or without any active amplifier/buffer.
A footprint is provided for a dual JFET opamp for a standalone complete volume control application.
A control signal for an external high quality MUTE relay is provided to eliminate any unwanted noises
from power-up/power-down processes.
2. Mechanical Installation
Total assembly height is 0.300”. All dimensions are in 0.001” unless noted otherwise.
Figure 1. VCM Board Connections (Top View).
Ø0.100”
4 holes
Address
Jumpers
Dual Opamp
Footprint
“R-“ Output
Audio and
Power
Header
Connector
Aux Control
Connector
Control
Connector
“L-“ Output

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Refer to Figure 1 for mechanical dimensions and mounting holes location.
The VCM board offers multiple installation options:
Horizontal. Use four mounting holes provided at the corners of the board. Use spacers to
elevate the board over the mounting surface. Optionally, use a 16-pin dual row 0.100”x0.100”
header installed in J3 position from the bottom to connect to the application board. J3 carries
all required audio and power connection. When used with one of the MCU Control boards from
Academy Audio, control signals may be received through a flat cable connector J2.
Vertical. Use a right angle 16-pin dual row 0.100”x0.100” header installed in J3 position from
the top to connect to the application board. No extra supporting features are needed. J3 carries
all required audio and power connection. When used with one of the MCU Control boards from
Academy Audio, control signals may be received through a flat cable connector J2.
Combo Installation. When used with an MCU-M board, the VCM may be installed as a compact
module at the face plate, similar to a standard potentiometer. For this type of installation, use
spacers to attach the VCM board to the MCU-M board through the matching mounting holes.
Use a 6-pin straight connector inserted in J4 position to receive control signals from the MCU-M
board. Use solder connectors J1 and J5 or a 16-pin header J3 to connect to power and audio
circuitry.
To install multiple Volume Control boards position the VCM boards at least 0.500” from each other.
Control signals shall be shared through the connector J4.
3. Address Selection
Up to eight MUSES Volume Controls may be independently addressed through one MUSES control bus.
The VCM board is supplied with a default address of 000, which may be changed by jumpers A0, A1, and
A2. Any address from “000” to “111” may be selected using jumper resistors in the ADDRESS positions
A0, A1 and A2 on the VCM board.
Please note that the standard Academy Audio MCU control boards for MUSES products are supplied for
a default address of 000, and will not operate other addresses. Consult the factory for other codes
availability.
4. Power Requirements
The VCM board requires a clean analog bi-polar power source of Vcc=+12Vdc to +15Vdc, 10mA and
Vee=-12Vdc to -15Vdc, 5mA. More current will be needed if an on-board opamp is used. Digital power
is generated by an onboard voltage regulator.
5. Connectors Description
The VCM board features several multifunctional connectors that provide all required connectivity for
every application option.

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A universal connector J3 combines all audio, power and control connection points. J3 is arranged as a
16-pin dual row 0.100”x0.100” PCB pattern that can accept a standard straight or right angle header.
With a header installed, the connector J3 may be used as a mechanical mounting feature for the VCM
board. The J3 connector pin assignment is summarized in a Table 1.
Table 1. J3 Pin Assignment
Pin
Ref
Description
Power
1
+15V
+12V to +15V analog power
3
GND
Analog Ground
5
-15V
-12V to -15V analog power
Control*
8
MUTE
Output to Muting relay control. (Active High –Mute Off.)
9
CLOCK
Not Used
11
LATCH
Not Used
13
DATA
Not Used
16
D_GND
Digital Ground
Audio
2
In_L
Left Channel Input
4
Com_L
Left Channel Common
6
L+
Left Channel Potentiometer Output
7
Out_L
Left Channel Opamp Output (with opamp installed)
10
In_R
Right Channel Input
12
Com_R
Right Channel Common
14
R+
Right Channel Potentiometer Output
15
Out_R
Right Channel Opamp Output (with opamp installed)
* Control signal connections may be used as input or output depending on the application.
A control connector J4 is provided for connection with an optional matching MCU-M control board. The
J4 connector pin assignment is summarized in a Table 2.
Table 2. J2 and J4 Pin Assignment
Pin
Ref
Description
1
+5V
Digital Power for MCU-M controller only
2
D_GND
Digital Ground
6
LATCH
LATCH MUSES Control Signal
7
DATA
DATA MUSES Control Signal
5
CLOCK
CLOCK MUSES Control Signal
8
MUTE
Mute Control Input. (Active High –Mute Off.)
If an MCU Control Board or a remotely installed MCU-M control board is used, all control signals are
provided through the flat cable connector J2.

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6. Theory of Operation
A potentiometer based volume control, shown at Figure 2, is the most traditional volume control
solution.
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.
J2
C1
0
C2
OUTPUT
J1
INPUT
R2
R1
VOLUME CONTROL

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Figure 3. MUSES®72320 Volume Control Chip Recommended Application.
Capacitors Cin connected to input pins 23 –In_R and 26 –In_L perform the function of the capacitor C1
of Fig. 2. Capacitors equivalent to the capacitor C2 of Figure 2 are omitted due to external J-FET opamps
used at the potentiometers’ outputs.
Two 10kΩ internal potentiometers connected to pins 5, 7, and 8 for the Left channel, and pins 9, 10, and
12 for the Right channel allow to add up to +31.5dB gain to each channel if desired. When these pots
are configured for a 0dB gain, the opamps act as buffers introducing minimum distortion and noise to
the signal.
7. Application Information
7.1. Power and Audio Connections
The VCM board features separate connections for the Left (Com_L) and Right (Com_R) analog grounds.
These grounds are connected on the board to minimize cross talk. It is recommended to use isolated
ground audio connectors to ensure the lowest cross talk and noise pick-up. Make sure the input signals
do not exceed 9Vrms at +/-15V analog power.
The VCM board features a footprint U2 for a dual JFET opamp in a DIP-8 case. A high quality dual opamp
such as MUSES01, MUSES8920, OPA2604, or similar installed in a position of U2 provides the most
compact and efficient Volume control solution.
L+
L-
R+
R-

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A single ended Volume control arrangement is presented at Figure 4.
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.
R4
47
COM_L
C4
47uFx35V NP
J14
OPTIONAL
(SEE TEXT)
+15V
J9
J8
R1
22
J4
OUT_R
+5V
J13
C2
47uFx35V NP
OUT_L
C3
47uFx35V NP
J12
C1
0.1uF
GND
J10
COM_R
R2
47
COM_L
J3
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
C5
47uFx35V NP
R6
6.8K
R5
100K
+5V
R3
100K
-
+
RL1
VCM Board
with JFET
Opamp
Installed
R7
22K
J5
Q1
2N2222A
+15V
MUTE
J1
GND
J7
D1
ZENER 5.6V 500mW
IN_L
J2
IN_R
J11
J6
COM_R

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Figure 5. VCM with JFET Opamp. Balanced Volume Control Application.
The VCM board may be used as a classic potentiometer Volume control. In this case the U2 footprint
should not be populated. Figure 6 depicts a single ended Volume control solution shown with an
optional Muting relay control circuit R6R7Q1, and optional DC blocking networks C2R3 and C4R5. The
outputs are taken from Pin 6 L+ and Pin 14 R+ of the 16 pin application connector.
J9
OUT_R
HOT
R9
47
J2
J6 OUT_L
HOT
R1
10
-
+
RL2
OPTIONAL
(SEE TEXT)
C6 47uFx35V NP
-
+
RL1
R4
100K
OUT_R
COLD
J5
C5
47uFx35V NP
J16
C8 47uFx35V NP
+15V
J7
R5
100K
D1
ZENER 5.6V 500mW
IN_L
COLD
J4
J12
J11 COM_L
R7
22K
J15
J8 OUT_L
COLD
R8
47
R6
100K
C1
47uFx35V NP
COM_R
C1
0.1uF
J2
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
IN_R
COLD
J1
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
J17
Q1
2N2222A
COM_L
MUTE
C4 47uFx35V NP
GND
C3
47uFx35V NP
+5V
R3
100K
J1
IN_L
HOT
C2 47uFx35V NP
COM_R
R6
6.8K
VCM Board 2
with JFET
Opamp
Installed
C7
47uFx35V NP
IN_R
HOT
J13
J10
VCM Board 1
with JFET
Opamp
Installed
J3
+15V
J14

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Figure 6. Potentiometer Type Single Ended Volume Control Application.
Unlike previous examples, this circuit is heavily dependent on the loading of the downstream audio
circuitry. The table of Figure 7 shows an error magnitude depending on the value of the loading
impedance.
R_load,
kOhm
Volume Control Position
0dB to -32dB
-32dB to -112dB
Error, dB
Error, dB
10
-4.08
-2.28
20
-2.28
-1.21
47
-1.04
-0.54
100
-0.51
-0.26
200
-0.26
-0.13
1000
-0.05
-0.03
Figure 7. Volume Control Error.
It is obvious that higher impedance loads provide lower volume control errors. It is recommended to
use a buffer or a high input impedance amplifier at the output of the volume control. For buffers and
amplifiers having a bipolar input, resistors R3 and R5 provide a current pass for their input bias currents,
and capacitors C2 and C4 block DC current from reaching resistive elements of the MUSES chip. Resistor
values shall be selected between 100kOhm and 470kOhm for optimal performance. Capacitors’ values
shall be high enough to pass low frequencies of the audio band. For JFET based buffers and amplifiers,
or when the circuit is used as a passive outboard Volume control feeding a power amplifier with a DC
insensitive input, the DC blocking networks C2R3 and C4R5 may be omitted.
Figure 8 demonstrates a balanced application of the potentiometer type volume control.
J10
J12
OPTIONAL
(SEE TEXT)
COM_R
J13
GND
+15V
COM_R
C3
47uFx35V NP
J9
COM_L
J6
C5
47uFx35V NP
+15V
R5
R7
22K
VCM Board
J4
COM_L
Q1
2N2222A
J5
J11
J8
R3
IN_L
MUTE
OUT_R
J14
IN_R
J3
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
R6
6.8K
TO MUTING RELAY
OUT_L
C2
C4
J7

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Figure 8. Potentiometer Type Balanced Volume Control Application.
8. Control Signals
Control signals from any of the dedicated Academy Audio MUSES® controllers may be applied though a
J2 flat cable connector. The connecting cable is provided with the controller board. For balanced
applications, the second VCM board receives control signals from the first board connected to the
controller. J4 connectors of the two VCM board shall have lines GND, LTH, DAT, and CLK connected with
short wires or pins as shown at Figure 5 and Figure 8.
When VCM board is used with a MCU_M board installed on top, no flat connection cable is needed. The
control signals are provided through a receptacle header installed in a J4 position.
9. Muting Relay
According to the MUSES®72320 volume control chip datasheet, the chip is sensitive to the audio signal
applied to the inputs before the power is supplied. In this case a distorted audio may be fed through the
J15
J4
R3
+15V
J13
COM_L
J2
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
R4
COM_L
J3
R1
6.8K
+15V
IN_L
COLD
J8
J1
CON16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
TO MUTING RELAY
R6
C8 47uFx35V NP J14
GND
IN_R
COLD
J7 OUT_L
HOT
IN_R
HOT
R2
22K
R5
IN_L
HOT
VCM Board 1
C5
J10
J6
J9
COM_R
VCM Board 2
C3
OUT_R
COLD
C4 47uFx35V NP
J11
C7
OUT_R
HOT
J17
Q1
2N2222A
C6 47uFx35V NP
COM_R
J16
MUTE
C1
C2 47uFx35V NP
OPTIONAL
(SEE TEXT)
J5
J12
OUT_L
COLD

Page 11 of 11
chip to the outputs. Some power-up pops and clicks are also possible. Therefore, using a muting relay is
highly recommended. Note, that the relay should be activated after about 1 sec of delay upon power-
up, and released immediately at power down. The Academy Audio MCU control boards for MUSES®
products provide the required muting relay control signal. Due to a very low noise of the VCM the
muting relay does not change its status while MUTE mode is activated.
10. Capacitors Selection
It is well known in the High End audio enthusiasts circles that the best DC blocking capacitor in the audio
path is “no capacitor”. However, as discussed in Section 6 of the Manual, presence of the DC voltage
on the input or output of the MUSES® chip may adversely affect the circuit operation and create extra
noise and distortions. Use direct input connection only when it is assured that no DC voltage will be
applied to the inputs. Use direct output connection only when no DC voltage will be applied to the
inputs AND outputs of the chip. In all other cases high quality DC blocking capacitors shall be used.
High quality polypropylene capacitors present the best choice for the output DC blocking when the
control is feeding high impedance loads. They get pricey at higher than 10uF values.
High quality non-polar electrolytic capacitors of 47uf to 100uF provide good results when bypassed with
10nF to 100nF film or C0G (NP0) ceramic capacitors.
The MUSES®72320 volume control chip datasheet shows polar electrolytic capacitors connected with
positive terminals facing the chip inputs. Outstanding results were achieved with ELNA Silmic II polar
capacitors of 100uF at the inputs and 47uF at the outputs, all caps bypassed with 10nF C0G ceramic
capacitors.
11. Using Volume Control
Use the VCM Volume Control as a regular dual channel potentiometer based volume control. Use two
boards for balanced operation. Note that Balance control and Mute functions are also available when
used with Academy Audio MCU control boards for MUSES products.
Please refer to the MUSES®72320 volume control chip datasheet for detailed operation description.
12. Break-in Period
High-End audio enthusiasts are familiar with the “break-in” phenomenon: the sound gets better with
time. In engineering terms that refers to reduced distortions of the audio signal. This distortion
reduction may be attributed to priming of the capacitors and all the contacts in the audio path. A
noticeable sound improvement is expected after about 100 hours of listening.
13. Technical Support
For any questions regarding operation of the VCM board and for the latest documentation please visit
our forum at www.academyaudio.com.
Happy listening!