G.R.A.S. 12AU Instruction Manual

www.gras.dk

LI0083 – Revision 22 June 2017

Instruction Manual

12AU 1-Channel Power Module
with Signal Conditioning and Power Amplifier

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LI0083 – Revision 22 June 2017

Revision History

Any feedback or questions about this document are welcome at [e-mail].

Revision Date Description

1 7 November 2012 Tentative version
2 14 December 2012 First publication
3 18 December 2012 Minor corrections to General Description
4 29 November 2016 Correction to page 10, amplifier input impedance
5 22 June 2017 Specs. for power amplifier output voltage swing changed

to ±13.5 V

Copyright Notice

© 2012-17 G.R.A.S. Sound & Vibration A/S

http://www.gras.dk

Any technical documentation that is made available by G.R.A.S. is the copyrighted work of
G.R.A.S. and is owned by G.R.A.S.

The content in this document is subject to change without notice. G.R.A.S. Sound & Vibration A/S
is not liable or responsible for any errors or inaccuracies that may appear in this document.

Trademarks

Product names mentioned in this document may be trademarks or registered trademarks of their
respective companies and are hereby acknowledged.

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LI0083 – Revision 22 June 2017

Contents

General Description ....................................................................... 4

Features ................................................................................................... 4

Microphone Conditioner .............................................................................. 5

Speaker Amplifier ...................................................................................... 6

Monitor Section ......................................................................................... 6

Power Supply ............................................................................................ 6

Physical Interface .......................................................................... 7

Front Panel ............................................................................................... 7

Rear Panel .............................................................................................. 10

The 12AU Behavior and Protocol Specification .................................. 11

Interface and Protocol Specification ............................................................ 11

List of Commands and Responses ............................................................. 12

Installing the USB-driver and Control Software ................................. 18

Installing the USB Driver ........................................................................... 18

Installing the Control Software ................................................................... 19

Preparing the 12AU for Measurements ............................................ 21

Cables and Connections ............................................................................ 21

Multi-channel Measurements .................................................................... 22

Operating the 12AU via its PC Application ....................................... 23

Using the Graphical User Interface ............................................................. 23

The Setup Menu ...................................................................................... 24

The Tools Menu ....................................................................................... 24

The Help Menu ........................................................................................ 28

Operating the 12AU Using Commands ....................................................... 28

Dealing with Overload in a Production Setup..................................... 29

Overload Caused by Handling .................................................................... 29

Minimizing Overload ................................................................................ 29

Appendix ................................................................................... 30

Updating the USB driver ........................................................................... 30

Technical Specifications ................................................................ 33

Warranty and Service ................................................................... 34

Warranty ................................................................................................. 34

Service and Repairs .................................................................................. 34

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General Description

The G.R.A.S. 12AU Power Module is a supply and conditioning amplifier for simultaneously
powering a preamplifier for a condenser microphone and an amplifier for a loudspeaker or any
other sound source using a loudspeaker/earphone/coupler. By design, it avoids system-generated
noise, e.g. from ground loops. In a measurement set-up, the 12AU controls both the paths of the
signal sent out to the loudspeaker and the resulting acoustic signal picked up by the microphone.
In both cases, its set-up for handling these signals independently comes under external control.

The 12AU is remote controlled entirely via its USB interface, and, for this purpose, is delivered with
a control program for Microsoft Windows

®

. Settings on the 12AU can be controlled by the control
software’s graphical user interface and easily confirmed by the LEDs on the front panel. See “Using
the Graphical User Interface” on page 23 for instructions. It is also possible to operate the 12AU
typing commands in its View Log window, see “Operating the 12AU Using Commands” on page

28.

It is optimized for computerized production line testing. Up to six 12AUs can be connected to and
operated from the same PC.

Features

• Single channel conditioning amplifier for microphone preamplifier and speaker amplifier with

measurement of current output

• Controls the paths of the outgoing and received signals at the same time

• Very low inherent noise

• The speaker input and the analogue outputs are floating with respect to common ground to

avoid system-generated noise

• Measurement of loudspeaker impedance without disturbing the speaker

• Fulfils EMC requirements according to EU regulations

• Full remote control via USB interface

• LEMO input with 200 V polarization voltage for externally polarized microphone

• CCP input for prepolarized microphone

• Gain settings for noise and overload control:

– Microphone conditioner: 0 to 50 dB in 10 dB steps
– Speaker amplifier: –20 dB to +10 dB in 10 dB steps
– Current output: 0 dB and +20 dB

• Filters:

– Microphone amplifier: 1 Hz or 20 Hz
– Speaker amplifier: DC or AC coupling (10 Hz)

• Comprehensive status and overload indication

• Rack mountable in 19” rack.

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LI0083 – Revision 22 June 2017

Microphone Conditioner

Input and output

The 12AU has two microphone inputs, a LEMO input for externally polarized microphones and a
CCP input for prepolarized microphones.

The LEMO input has a 7-pin LEMO 1B socket for a microphone preamplifier such as the
G.R.A.S. Preamplifiers 26AM, 26AC, and 26AK. Fig. 1 shows the wiring diagram of this input
socket which is also compatible with a range of microphone preamplifiers from other suppliers

such as Norsonic, L&D and Brüel & Kjær. The input impedance is 100

kΩ.

Fig. 1. 7-pin LEMO female socket 1B (external view).

The CCP input has a standard BNC socket.

The Microphone Output is a standard BNC socket for direct use with analyzers, voltmeters, oscil­loscopes etc. The output is floating (2 kΩ//100 nF to common ground). The output impedance is
100 Ω.

Input for Externally Polarized Microphone or Pre-polarized Microphone (CCP)

The 12AU has a 7 pin LEMO socket for a microphone with a LEMO type preamplifier and a BNC
socket for a CCP microphone set.

The polarization voltage can be set to 200 V or 0 V, a green LED on the front indicates the
currently selected polarization voltage.

The preamplifier voltage supply is ±15 V DC. The CCP supply is 4 mA.

Bandwidth, Filters and Noise

The bandwidth of the Microphone Conditioner is from 1 Hz to 100 kHz (–3 dB). A 20 Hz
(Butterworth 3. order) high-pass filter can be selected remotely. A front-panel LED lights up when
the filter is switched on.

The noise floor relative to input, with the input shorted, is (≥20 dB gain) <1.5 μVrms
(20 Hz - 20 kHz). With the input loaded with a 20 pF dummy microphone, the noise is less than
5 μVrms (20 Hz – 20 kHz).

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Gain

The gain can be set to one of the following: 0 dB, +10 dB, +20 dB, +30 dB, +40 dB or +50 dB
(± 0.2 dB). One of a series of front-panel LEDs lights up to indicate the current gain setting.

Overload Detection

If either of the conditioning amplifier stages goes into overload, this is indicated by a red LED.
Gain and filter settings can be optimized to improve headroom/reduce overloads.

Speaker Amplifier

The speaker amplifier has a bandwidth (-3 dB) from DC to 80 kHz (DC coupled) and from
10 Hz – 80 kHz (AC coupled). AC or DC coupling is set remotely.

Phase shift (input to output) is ≤

±1° (DC to 20 kHz). The maximum output voltage is ±13.5 V,

the maximum output current

±1.4 A. The current output (voltage/current ratio) can be set to

1 V/1 A or 10 V/1 A (remote controlled).

Input and output

The input connector is a standard BNC socket, floating with 10 kΩ//100 nF to common ground.
The input impedance is 10 kΩ.

The speaker amplifier has two outputs, a voltage output and a current output. The voltage output
connector is a 2 pin LEMO (pin 1 is output, pin 2 is return). The current output connector (remote
controlled) is a BNC socket, floating with 2 kΩ//100 nF to common ground.

Gain

The gain can be set in steps of 10 dB (±0.2 dB), from –20 dB to +10dB. One of a series of front
panel LEDs lights up to indicate the current gain setting.

Overload

Voltage and current overload detection are indicated by separate LEDs on the front panel (remote
controlled reading and reset).

Monitor Section

The signals that are fed to and taken out of the 12AU can be monitored via the monitor BNC
output socket. Front panel LEDS indicate the actual selection: Mic Out, Amp In., Amp Out,

Current Out.

Power Supply

The 12AU can be powered from a mains/line supply of either 115 V AC or 230 V AC ,
selected with a switch on the rear panel.

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Physical Interface

Front Panel

The 12 AU is designed for mounting in a 19” rack.

Mic Out

Amp In

Amp Out

Cu

r

rent Out

+20dB

+30dB

+40dB

+50dB

Monitor

Microphone Conditioner

Overload

High

P

ass

200Volt

CCP

-20dB

-

10dB

0dB

+10dB

Overload

AC Coupled

Mute

Amplier

Overload

0dB

+20dB

Current

G.R.A.S. Sound &Vibration

Power Module Type 12AU

Gain

Gain

Gain

Output

0dB

+10dB

Power On

I

O

Fig. 2. Green LEDs show the operational status and red LEDs warn about overload.

When the 12AU is switched on, the default settings will be applied. All LEDs are lit for a few
seconds to show that the 12AU is working properly. After approximately 10 seconds, it switches
to operational mode.

Selections are made via the USB connection on the rear panel using the accompanying control
software.

The Monitor Section

The Monitor function of the 12AU makes it possible to monitor the input and output signals via
separate sockets, one on the front and another on the back.

Mic Out

Amp In

Amp Out

Cu

rrent Out

+20dB

+30dB

+40dB

+50dB

Monitor

Microphone Conditioner

Overload

High

P

ass

200

V

olt

CCP

-20dB

-10dB

Gain

Gain

Output

0dB

+10dB

Current Out LED. Lit when the
amplifier current output is selected.

Amp Out LED. Lit when the
amplifier output signal is selected.

Amp In LED. Lit when the amplifier
intput signal is selected.

Mic Out LED. Lit when the micro­phone output signal is selected.

Output. BNC socket for monitor­ing the output signal.

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LI0083 – Revision 22 June 2017

Microphone Conditioner Section

These LEDs indicate the current preamplifier-input status which is controlled via the USB inter­face connection on the rear panel.

+20dB

+30dB

+40dB

+50dB

Microphone Conditioner

Overload

High

P

ass

2

0

0Volt

CCP

-20dB

-1

0dB

0dB

+

1

0dB

Overload

A

C Coupled

Mute

Amplier

Overload

0dB

+20dB

Current

Gain

Gain

Gain

0dB

+1

0dB

Gain LEDs. Indicates current gain setting.
Gain settings are from 0 dB to + 50 dB in
10 dB steps.

Input Overload LED. Lit when
microphone signal overloads the 12AU.

Overloads can be latched and read via
the USB interface, in which case they are
cleared when read. Alternatively, overload
messages can be signalled to remote con­trol, displayed briefly and cleared automati­cally.

High Pass (20 Hz) LED. Lit when high-pass
filter is active. Otherwise, full-bandwidth
conditions apply, i.e. 1 Hz to 100 kHz
(– 3 dB). When fast settling is enabled, the
High Pass LED will flash during settling.

200 V LED Lit when then 200 V Polariza­tion is enabled.

CCP LED. Lit when the CCP input is ena­bled.

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Amplifier Section

These LEDs indicate the status of the amplifier which is controlled via the USB interface connec­tion on the rear panel. The amplifier can be set to voltage or current amplification, with separate
gain and overload settings for each mode.

-20dB

-1

0dB

0dB

+10dB

Overload

A

C Coupled

Mute

Amplier

Overload

0dB

+20dB

Current

G.R.A.S. Sound & V

ibration

Power Module T

ype 12 AU

Gain

Gain

Power On

I

O

Gain LEDs. Indicates the actual gain set­ting. Gain settings are from –20 dB to +
10 dB in 10 dB steps.

AC-Coupled Lit when output is
AC-coupled. When not lit the output is
DC-coupled.

Current Gain LED. The LED indicates the
actual current gain setting, 0 dB or +20 dB.

Current overload LED. Lit when current
output goes into overload. Overloads can
be latched and read via the USB inter­face, in which case they are cleared when
read. Alternatively, overload messages can
be signalled to remote control, displayed
briefly and cleared automatically.

Overload LED. Overloads can be latched
and read via the USB interface, in which

case they are cleared when read. Alterna­tively, overload messages can be signalled
to remote control, displayed briefly and
cleared automatically.

Mute LED. Lit when output is muted.

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Rear Panel

Mains Input and Voltage Setting

Amplier

Output

Current

Output

Amplier

Input

Monitor

Output

USB

Control

Serial No.
XXXXXX

230

Voltage Setting Switch for either 115 VAC or 230 VAC.

Mains Input and Fuse Holder. Input socket for either 115 VAC or 230 VAC

mains supply. Fuse holder for 1 A slow fuse.

Monitor and Amplifier Sockets

Amplier

Output

Current

Output

Amplier

Input

Monitor

Output

USB

Control

Microphone

Output

Microphone

Input

CCP

Input

Monitor Output. BNC output socket for monitoring the
currently selected signal. Output impedance is 100 Ω.
Also repeated on the front panel.

Amplifier Input. BNC input socket for signal to the speaker amplifier,
for example from a signal generator. Input impedance is 10

kΩ.

Current Output. BNC output socket for a voltage signal proportional to the current
through the output circuit of the speaker amplifier.

Amplifier Output. 2-pin LEMO connector for a loudspeaker with an impedance of 2 Ω or more.

USB and Microphone Sockets

Amplier

Output

Current

Output

Amplier

Input

Monitor

Output

USB

Control

Microphone

Output

Microphone

Input

CCP

Input

USB Control. USB socket for connection to a USB
computer port.

Microphone Output. BNC output socket for the microphone signal.

Microphone Input. 7-pin LEMO input connector for microphone preamplifier.

The wiring diagram is shown in Fig. 1.

CCP Input. BNC Input connector for Constant Current Powered transducers.

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The 12AU Behavior and Protocol Specification

Interface and Protocol Specification

Compatibility

The 12AU protocol specification complies with the 12AP specification version 1.2, where appli­cable. (The Floating command is omitted).

USB Interface

There is no flow control/handshaking; therefore commands must be sent one by one, waiting for
the response.

The input buffer is 64 bytes, in case of overflow a response: “Buffer overflow” will be submitted.
This will not happen under normal conditions.

12AU Startup Sequence

After power on or restart, the 12AU immediately initializes the settings of 12AU to current
default settings and turns on all LEDs.

If connected to PC, the OVL leds will be turned off when then USB connection is established,
typically after 4 seconds from power on.

Appoximate after 8 seconds the IRQ and overload system is enabled, the LED will reflect the
setting and a Reset<crlf> is submitted.

Behavior

A watchdog is enabled. It will restart 12AU if the processor stops working – this will send the
string Reset<crlf> to the host. In this case the host knows that the fault has occurred and will
be able to reinitialise 12AU.

Commands

Note: <LF> in input will be ignored, and commands are in uppercase.