RTZ 9762A User manual

RTZ Professional Audio, LLC
Atlanta, GA USA
http://www.rtzaudio.com
COPYRIGHT © 2014, RTZ PROFESSIONAL AUDIO, LLC REV-A.03
05/12/2014
9762A
LEGENDS 500
MICROPHONE PREAMPLIFIER
Owner’s Manual
RTZ PROFESSIONAL AUDIO

TABLE OF CONTENTS
1WELCOME!............................................................................................................................. 3
2OVERVIEW ............................................................................................................................. 3
3INSTALLATION AND CONNECTIONS.................................................................................. 4
3.1 ENVIRONMENTAL CONSIDERATIONS.................................................................................... 4
3.2 CLEANING THE UNIT........................................................................................................... 4
3.3 MODULE CONNECTIONS..................................................................................................... 5
5FRONT PANEL CONTROLS.................................................................................................. 8
5.1 +48V PHANTOM POWER ENABLE ....................................................................................... 9
5.2 +48V POWER STATUS INDICATOR...................................................................................... 9
5.3 OVERLOAD SIGNAL (OL) INDICATOR................................................................................... 9
5.4 GAIN SELECT SWITCH........................................................................................................ 9
5.5 SIGNAL PRESENT (SP) INDICATOR...................................................................................... 9
5.6 DIRECT INSTRUMENT (DI) SOURCE SELECT........................................................................ 9
5.7 LOW-Z MICROPHONE IMPEDANCE SELECT.......................................................................... 9
5.8 LINE OUTPUT POLARITY INVERT SELECT........................................................................... 10
5.9 100 HZ HIGH PASS FILTER ENABLE.................................................................................. 10
5.10 LINE OUTPUT VU METER INDICATOR................................................................................ 10
5.11 DIRECT INPUT (DI) -UNBALANCED.................................................................................... 10
5.12 OUTPUT LEVEL CONTROL ................................................................................................ 10
6OPERATION ......................................................................................................................... 11
6.1 GAIN AND LEVEL ADJUSTMENTS....................................................................................... 11
6.2 USING THE DI INPUT ........................................................................................................ 11
6.3 POLARITY AND IMPEDANCE SELECTION............................................................................. 12
6.4 USING 48V PHANTOM POWER.......................................................................................... 12
6.5 LINE OUTPUT TRANSFORMER TERMINATION...................................................................... 12
7HARDWARE CONFIGURATION FEATURES..................................................................... 13
7.1 PHANTOM POWER ENABLE SWITCH (S1) .......................................................................... 13
7.2 LINE OUTPUT TRANSFORMER STRAPPING (JP2) ............................................................... 13
7.3 LINE OUTPUT TRANSFORMER TERMINATION (JP1)............................................................ 14
7.4 48V LED CONFIGURATION OPTIONS (JP3)....................................................................... 14
8SPECIFICATIONS ................................................................................................................ 16
9LIMITED WARRANTY.......................................................................................................... 17

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RTZ Professional Audio
1 Welcome!
Thank you for purchasing your new Model 9762A Legends 500 Series
microphone preamplifier! Before operating or installing the unit, please
read this manual thoroughly and retain it for future reference. Additional
copies of this manual are available upon request or from our website at
http://www.rtzaudio.com.
All units are carefully packed to endure the rigors of shipping and
handling. However, please inspect all contents and packaging
immediately upon receipt. Please report any problems to us immediately.
In the event of damage, retain all shipping and packaging materials for
shipper damage claims inspection.
The 9762A is designed to deliver a lifetime of musical pleasure and
trouble free operation. If you experience any problems or difficulties,
please contact us directly. Do not attempt to modify, alter or repair the
unit yourself. Each unit has been carefully tested and calibrated for
proper operation. Any unauthorized modifications may destroy the unit or
severely degrade performance and void the warranty.
2 Overview
The 9762 preamplifier is designed to emulate the vintage 1970s large
format consoles (i.e. Neve 1073 Series) yet provide a more open and
detailed sound by using modern components and transformers. We use
a super high quality input transformer (manufactured by Lars Lundahl of
Sweden) with excellent sonic performance. This transformer is
considered by many to be one of the world’s finest input transformers.
The preamp gain blocks and gain structure have been carefully
optimized to match the input transformer impedance characteristics as
closely as possible. This combination of classic circuitry and a modern
input transformer allows the 9762 to deliver a classic super fat sound
with the benefit of increased high-end openness and clarity.
The standard unit contains a single channel of high gain amplification
capable of providing up to 75 dB of gain. The microphone input and line
output signals are fully transformer balanced and isolated. The (DI)
instrument input is unbalanced. Standard features include +48V
Phantom power, polarity (phase) reverse, DI input source select,
microphone impedance select and HPF (high pass filter) options. The
9762A is a high performance preamplifier designed for the popular 500
Series modular rack style format. It is well suited for professional
recording, sound reinforcement, broadcast or any application where a
high quality preamplifier is required.

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3 Installation and Connections
The 9762A is designed for standard API™ 500 Series compatible
modular rack systems. Ideally, the rack should be mounted where cool
air flows across the rack and modules. Do not obstruct the flow of air
around and across or through the preamplifier module or rack. In tight
equipment enclosures, consider placing a ventilated rack panel between
racks to allow increased airflow. Do not place the rack or module unit
near strong magnetic fields and noise sources such as power amplifiers,
console power supplies, transformers, motors, florescent lighting,
computers, etc.
3.1 Environmental Considerations
The 9762A is designed to operate reliably over a wide range of ambient
temperatures. Always provide proper ventilation to avoid overheating
conditions. This extends component life and provides maximum
operational stability of the circuits. Ideally, the 500-series mainframe
housing the module should be mounted in a rack where cool air flows
around all sides of the rack and unit.
The 9762A is fully transformer isolated to help reduce interference and
hum from outside sources. However, the unit should not be placed near
strong magnetic fields or noise sources such as power amplifiers, power
supplies, transformers, motors, florescent lighting, computers, etc.
Mount the power supply away from the module rack or other audio gear
to avoid magnetic field radiation. This is especially true of the line output
transformer (or output transformers in any other modules, RTZ or not)
3.2 Cleaning the Unit
The 9762A is painted with a durable epoxy paint, but always use care
not to scratch the finish or metal. Do not use harsh cleaners or chemicals
to clean the unit or knobs. Use alcohol or a mild window glass cleaner
with a cotton ball the clean the control surfaces. Do not spray any
cleaners on the PCB or faceplate to avoid seepage into the unit and or
possible damage to the PCB or components.
WARNING
NEVER INSERT THE 9762A MODULE INTO A RACK WITH POWER
APPLIED; DOING SO WILL LIKELY DAMAGE THE MODULE AND
VOID THE WARRANTY. NONE OF THE 500-SERIES RACKS ARE
DESIGNED TO ALLOW HOT-SWAPPING MODULES. DOING SO
COULD DAMAGE THE MODULE BEING INSTALLED, AND/OR
OTHER MODULES ALREADY INSTALLED, AND/OR THE RACK
ITSELF. TO AVOID DAMAGE, ALWAYS POWER THE RACK DOWN
WHEN INSTALLING ANY MODULE.

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3.3 Module Connections
Install the module in a 500 rack (always with the rack powered down)
and verify that the XLR input and output cables are connected properly.
In some cases you may wish to lift the ground wire from pin 1 of the
output signal XLR cable to “float” the ground and create a “telescopic
shield”. This method provides full ground loop isolation since the 9762A
is fully transformer isolated.
The 9762A is designed for balanced mode operation as typically found in
professional studio installations. While it can be wired for unbalanced
operation, we highly recommend using balanced mode operation for
reduced hum and interference. If you must wire the unit for unbalanced
operation, keep the cables as short as possible. Connect pin-3 of the
rack output signal connector to ground for unbalanced operation. Note:
the transformer coupled output means that you MUST connect pin 3 to
ground for unbalanced operation. It’s best to carry pin-3 all the way to the
unbalanced input and ground it there.
Power up the rack after all the I/O cables and connections are properly
established. The 9762A VU and signal LED’s should illuminate when the
rack is powered up. If the LED’s fail to illuminate, check that your
mainframe has the correct +/- 16V power and that no fuses are blown.
Table 1: Edge Finger Pin Definitions
Pin#
Description
1
CHASSIS GROUND
2
OUTPUT '+' (+4 dBm)
3
N/C
4
OUTPUT -' (+4 dBm)
5
AUDIO GROUND
6
N/C
7
N/C
8
INPUT '-' (+4 dBm)
9
N/C
10
INPUT '+' (+4 dBm)
11
N/C
12
+16 VOLTS DC
13
POWER GROUND
14
-16 VOLTS DC
15
+48 VOLTS DC

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4 Design Features
The 9762A has been designed and built with great attention to detail. In
particular, the input transformer and gain switching network have been
painstakingly matched and optimized to present the proper load
impedance to the microphone transformer (and hence, the microphone)
at all gain settings. This refinement, combined with a super high quality
input transformer, gives the 9762A a more detailed sound when
compared to vintage units.
The module’s PCB carrier and faceplate are made of heavy gauge steel
for extra strength and maximum magnetic shielding. The PCB is a four
layer design with full ground plane shielding to serve as a signal
reference plane internally for maximum signal isolation and ground
shielding.
4.1 Input Stages
The input transformers are optimized for 200-Ohm impedance
microphones or other devices having 200-Ohm source impedance. The
LO-Z impedance select switch configures the transformer input for either
50-Ohm (LO-Z) or 200-Ohm source impedance. Keep in mind that the
impedance select switching is accomplished by configuring the input
transformer primary wiring as either a series or parallel circuit, which
affects the transformer’s turns ratio. By nature, the impedance switching
affects the signal level by roughly 6 dB when switching impedances.
Miniature sealed gold contact relays are used for all audio switching
functions and maximum reliability.
A separate high impedance FET buffer stage is used in the instrument
direct input (DI) stage. The FET input buffer stage serves as a high
impedance conversion stage designed to prevent loading of the
instrument pickups. The DI switch allows manual selection of the DI or
microphone input source. Additionally, the DI select switch may also
serve as a channel mute switch when the DI or microphone input is not
in use.
4.2 Phantom Power
The phantom power switching circuitry uses a smooth power ramping
design to help reduce pops and clicks during switching. The phantom
voltage ramps up quickly when enabled and ramps down quickly when
disabled. Phantom power may also be completely disabled via DIP
switch S1 located on the lower PCB near the edge fingers. Phantom
power is fully protected against continuous shorting via each channel’s
current limiting resistors.
4.3 Gain Blocks and Metering
The 9762 provides up to 75 dB maximum gain using a dual gain block
type design. Gain is selectable from –20 dB to -75 dB in 5 dB increments
via the twelve position rotary switch. At higher gain settings (above -50
dB), a second gain block is inserted into the signal path for additional
gain and increased headroom. The input signal stages are designed for
maximum headroom throughout the audio path at any gain setting.

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The SP (signal present) and OL (overload) LED’s provide input stage
signal monitoring. In normal use the OL should not light to prevent signal
distortion. The signal quality degrades rather quickly once the OL
threshold is reached. The SP and OL LED’s monitor channel activity and
clipping for the signal source currently selected by the DI switch.
The eight LED VU meter monitors the master output level from the line
amplifier stage. The first LED lights at around –20 dB with subsequent
steps at –10 dB, –6 dB, –3 dB, 0 dB, +3 dB, +10 dB and +18 dB. The
master LEVEL control is used to trim the output level using the VU meter
as a level reference.
4.4 Line Amplifier Stage
The line amplifier stage input level is controlled by the master LEVEL
control. The LEVEL control acts as a channel fader to trim the line
amplifier output as needed. In general, the LEVEL control should be set
to the maximum position (fully CW) and the input GAIN control is then
adjusted to obtain the desired output signal level. If the output signal is
slightly “hot”, use the LEVEL control to trim the output level back to
obtain the desired output signal level.
In situations where distortion or warmth is desired, the input GAIN setting
may be set “hot” and the output LEVEL control is used to trim the output
back to a suitable level. Use care with this technique to avoid overdriving
the input stage excessively as the signal becomes very ugly sounding at
extremes. Also, keep in mind the line amplifier stage is capable of
delivering very large output level swings (around 40V peak-to-peak!);
excessive signal levels could damage the input stages of gear being
driven by the 9762.

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5 Front Panel Controls
1. +48V Phantom Power Enable
2. +48V Power Status Indicator
3. Signal Overload (OL) Indicator
4. Gain Select Switch
5. Signal Present (SP) Indicator
6. Direct Input (DI) Source Select
7. Low-Z Microphone Impedance Select
8. Line Output Polarity Invert Select
9. 100 Hz High Pass Filter Enable
10. Line Output VU Meter Indicator
11.Direct Input - Unbalanced
12. Output Level Control

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5.1 +48V Phantom Power Enable
This switch enables +48V phantom microphone power on the rear
microphone input connector. The LED next to the switch lights when
phantom power is active. The +48V switch controls circuitry that ramps
the 48V power up or down gradually to reduce unwanted bangs or pops
in the audio signal.
5.2 +48V Power Status Indicator
This LED indicates when phantom power is active. Note that the
hardware switch S1 on the lower PCB near the edge fingers can be used
to completely disable phantom power to the microphone; this feature is
useful to protect ribbon microphones when used with the 9762A.
5.3 Overload Signal (OL) Indicator
This LED indicates signal overload/clipping conditions at the input gain
block stages. In normal use the LED should not light or flicker. Reduce
the input GAIN switch to lower the input gain and avoid clipping.
5.4 Gain Select Switch
The rotary gain switch has twelve positions that select the input
sensitivity in 5 dB increments from -20 dB to –75 dB for a maximum gain
of 75 dB. The unit is set to maximum gain in the fully CW position.
Always start at the lowest gain setting and increase the gain to obtain the
desired output level.
5.5 Signal Present (SP) Indicator
The SP LED indicates signal activity on the microphone input. The
detector is sourced from the gain blocks prior to the line amplifier and
output LEVEL control. This LED lights at around -30 dBu (referenced to
775 mV) to indicate activity.
5.6 Direct Instrument (DI) Source Select
The DI switch selects the preamp input signal from either the unbalanced
DI input jack or the balanced Microphone Input connector on the rear
panel. The DI input jack is selected in the depressed position; otherwise
the balanced XLR microphone input connector is selected. Note that the
DI switch may also serve as a “MUTE” switch when only one input
source is being used.
5.7 Low-Z Microphone Impedance Select
This switch configures the input transformer for Low-Z impedance mode.
The input transformer and circuitry is optimized for 50-Ohm microphones
or other devices having 50-Ohm source impedance. In the non-
depressed state the input transformer is configured for 200-Ohm source
impedance. Note that the input signal level varies by approximately 6 dB
when the switch is operated. Adjust the gain switch to compensate for
the level change and to avoid masking the tonal differences between
impedance settings when changing impedances.

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5.8 Line Output Polarity Invert Select
This switch inverts the line output polarity (phase) in the depressed
position. Normally the unit will be used with polarity in the non-inverted
state, however you may use this switch to reverse the polarity if needed.
5.9 100 Hz High Pass Filter Enable
This switch enables the 100 Hz high pass filter (HPF). The HPF is 3dB
down at 100 Hz and attenuates signals below this at a rate of 12 dB per
octave. The HPF is useful to cut unwanted low frequency signals when
less low frequency content is desired.
5.10 Line Output VU Meter Indicator
The eight LED’s provide output VU Meter level indication sourced from
the line output amplifier at +18, +10, +3, 0, -3, -6, -10 and –20 dB. The
“0” LED indicates 0 dB output level referenced to +4 dBm.
5.11 Direct Input (DI) - Unbalanced
The Direct Input is designed for use with instrument sources and is
buffered by a Hi-Z FET stage to avoid instrument pickup loading. The
input connector accepts standard ¼“ Phone Plugs in either TS (Mono –
TIP, SLEEVE) or TRS (Stereo –TIP, RING, SLEEVE). Note that when
TRS connectors are used, the RING and SLEEVE are both referenced to
ground internally. The DI input may also be used as an unbalanced
direct input, however, line level +4 dBu signal levels will most likely result
in distortion. In this case, the signal level should be reduced from the
source.
5.12 Output Level Control
The output level control acts as a master fader to facilitate fine trimming
of the output signal level from –90 to 0 dB as required. In normal
operation this control should be set to maximum level (fully CW position)
and then trimmed back as needed to obtain the desired output signal
level.