User Guide
Mic-PreEminence
Microphone Preamplifier
Issue 5, April 1994
© 1994 Studio Technologies, Inc.
5520 West Touhy Avenue
Skokie, Illinois 60077 U.S.A.
Telephone (847) 676-9177
Fax (847) 982-0747
www.studio-tech.com
50101-494, Issue 5
Table of Contents
Quick Guide to Using the Mic-PreEminence ............................... 5
Introduction.................................................................................. 6
Installation.................................................................................... 7
Operation..................................................................................... 8
Technical Notes...........................................................................10
Circuit Description........................................................................11
Troubleshooting...........................................................................13
Appendices
Appendix A
Specifications .........................................................................16
Appendix B
Enabling the Output Coupling Capacitors ..............................1 7
Appendix C
Replacing the 0.33uf Coupling Capacitors .............................17
Appendix D
Solutions for RF Problems .....................................................18
Studio Technologies Limited Warranty........................................19
Schematic Diagrams.........................................Not included in PDF
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 3
Quick Guide to Using the
Mic-PreEminence
Connect your selected Mic-Pre-Eminence line outputs to the line inputs of
the next device.
All of us get in a hurry to use a new device.
Studio Technologies, Inc. wants you to fully
understand how best to use the Mic-PreEminence. First we’d like you to read this
long and highly exciting manual. If you’ve
already read the manual and want to refresh your memory, here’s a quick run
through on how to get things going:
1) Check the back panel to see if the AC
mains voltage selected is correct for
you, 115V or 230V. A 0.5A fuse should
be in place for 115V; 0.25A for 230V.
2) Plug in the power cord and turn on the
power switch, located on the front
panel.
3) On front panel: Turn phantom power
switch to the ON position if +48V phantom voltage is required. Set the phase
reverse switch to NORMAL, and set
gain control to MIN gain (fully counterclockwise). Do this for each channel.
4) Using shielded, low capacitance microphone cable, connect a microphone to
the microphone input connector on the
back panel. Do this for each channel.
5) Each channel contains two line outputs,
balanced and unbalanced, which are
located on the back panel. The balanced outputs use 3-pin, XLR-type
connectors with pin 2 high and a nominal output level of +4dBu. The unbalanced outputs use monaural ¼-inch,
2-conductor jacks (tip and sleeve), and
have a nominal output level of –10dBv.
6) Careful! Turning the phantom power
switch on or off, or the power switch
on or off, can produce a large amplitude
spike in the line outputs. Protect your
ears, speakers, and equipment by
being careful while the Mic-Pre-Eminence line output is connected to another piece of equipment.
7) With signal going into the microphone,
adjust the Mic-PreEminence gain control to give the desired output level. The
LED meter can provide assistance in
setting the level. The meter is designed
to have characteristics somewhere
between that of a VU meter and a peak
(PPM) meter. It is strictly a reference
and shouldn’t force you into setting the
gain to give a “standard” reading on the
meter. Even if the red LED is lighting on
peak signals, you are most likely still far
from the Mic-PreEminence’s clipping
point; the red LED lights approximately
18dB below clipping!
8) Watch the gain setting! Most equipment connected to a Mic-PreEminence
line output will clip well before the MicPreEminence will. Example: your tape
recorder may be distorting on peak
signals even though the Mic-Pre-Eminence isn’t. This is because the tape
recorder input is being overloaded with
too much signal. Turn down the MicPreEminence gain control until the
distortion stops.
9) Enjoy the great sound!
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 5
Introduction
General Description
The Mic-PreEminence is a highperformance, two-channel microphone
preamplifier. The Mic-PreEminence, with
its low noise, low distortion, and high
speed design provides a level of technical
and sonic performance that is virtually
unmatched. As a complete, stand-alone
unit, the Mic-PreEminence is applicable
for studio and location recording, digital
sampling, live broadcasts, and sound
reinforcement.
Features
• Two independent preamplifier channels
• +48Vdc phantom power, switchable
on/off
gain, unlike the characteristics of most
console mic preamplifiers. We use superior,
high-performance circuits not found in other
audio equipment. By building a dedicated
microphone preamplifier, we were not
hampered by the cost restrictions that
console manufacturers have. We think that
the result is an incredibly great sound and
excellent specifications.
Additional Note From the Designers
This issue of the Mic-PreEminence instruction manual covers a new and improved
version, the Mic-PreEminence Second
Edition. We are gratified with the response
we’ve received about the original unit over
the past few years. We’ve heard some
fabulous recordings that were made by
excellent engineers, along with assistance
from the Mic-PreEminence. Keep up the
good work!
• Dual, 5-segment LED level metering
• Output phase reverse switch
• Selectable balanced or unbalanced
outputs
• Adjustable gain range, +12dB to +68dB
• Electronically balanced input and output
circuitry
Note From the Designers
The Mic-PreEminence was designed by
James Cunningham with help from Gordon
Kapes, Mitch Budniak, and Phil Sutterlin.
When designing the Mic-PreEminence, our
goal was to produce a transparent, clean
sound. We were not shooting for specs, but
rather for great sound. We knew that if we
achieved the sound, the specs would be
there. We wanted nothing added to or
subtracted from the original signal besides
Changes were made for three reasons:
improve reliability, enhance unbalanced
operation, and provide better level metering. For reliability, zener diodes were added
to the input circuitry to prevent overvoltage
spikes from damaging the circuitry. These
diodes do not hurt the sound in any way.
They only kick in at very high signal levels,
levels that are not present in any normal
microphone input signal. They are especially helpful in minimizing the spikes that
are created when the phantom power
switch is turned on or off.
To make using the Mic-PreEminence’s line
outputs more convenient when interfacing
with unbalanced “–10” equipment, a separate unbalanced output with nominal signal
level of –10dBv has been added to each
channel. The unbalance switches have
been replaced with output select switches.
Issue 5, April 1994 Mic-PreEminence User Guide
Page 6 Studio Technologies, Inc.
They select if signal will be present on the
balanced outputs (XLR connectors), or on
the unbalanced outputs (¼-inch, 2-conductor
monaural jacks). The nominal level of the
balanced outputs is +4dBu, unbalanced is
–10dBv.
Level monitoring has been improved by
going to 5-segment level meters, instead
of the original signal present and clipping
LEDs. The meter ballistics are designed
to give a combination of VU and peak
performance.
We hope you like the improvements!
Installation
Mounting
The Mic-PreEminence is rack-mountable,
requiring one 1.75-inch (4.5cm) rack space.
It weighs a bit over four pounds (1.9kg),
and operates on AC mains power of either
nominal 115Vac or 230Vac.
Locating the Unit
It is a good idea to keep the
Mic-PreEminence physically separated
from other electronic devices that produce
electrical fields. As a high gain device,
hum and noise pickup is possible through
the chassis and associated cabling. Locating
the unit away from power amplifiers, power
transformers, lighting controls, etc., will
help to avoid pickup of unwanted signals.
If the Mic-PreEminence is mounted in a
rack, be sure that sonic “garbage” is not
being picked up from nearby equipment.
Connecting the Unit to Power
The Mic-PreEminence may be operated
from mains power of either nominal 115Vac
or 230Vac, 50/60Hz. Units shipped to North
America are factory selected for 115V
operation and are supplied with a 0.5A 3AG
fuse and a power cord. Units shipped outside North America are factory selected for
230V operation and are supplied with a
0.25A 5x20mm fuse. No power cord is
supplied with those units. Your dealer or
distributor will provide an AC mains cord.
Before connecting the Mic-PreEminence
to power, determine the actual line voltage
and check to see that the voltage selector
switch (located on the back panel of the
unit) is set to the appropriate voltage.
Please note that an incorrect setting could
seriously damage the unit. Should it be
necessary to change the voltage selection,
ensure that the correct fuse value is used:
0.5A for 115V, 0.25A for 230V.
The Mic-PreEminence uses an IEC
standard connector to mate with the AC
mains cord. The wire colors in the AC mains
cord should conform to the internationally
recognized CEE color code and must be
wired accordingly:
Connection Wire Color
Neutral (N) Light Blue
Live (L) Brown
Protective Earth (E) Green/Yellow
Signal Connections
All signal connections on the
Mic-PreEminence are made via 3-pin,
XLR-type male and female connectors, and
¼-inch, 2-conductor monaural jacks standard to the audio industry. The microphone
input connectors are female, the balanced
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 7
line output connectors are male, and the
unbalanced output connectors are female.
The Mic-PreEminence conforms to the
world standard for 3-pin audio connectors:
pin 1 shield, pin 2 signal high, pin 3 signal
low. This standard is especially applicable
for the Mic-PreEminence as most recording
studio quality microphones conform to this
standard. Pin 1 on the four XLR-type audio
connectors and the sleeves of the two
¼-inch, 2-conductor jacks are connected in
common with power supply common, chassis ground, and power cord ground.
Operation
Using the Controls and Meters
There are five switches and two gain
controls on the front panel of the Mic-PreEminence. There are two switches on the
back panel.
Power Switch
The power switch controls the AC mains
to the unit. Power can be applied to the
Mic-PreEminence continuously without
adverse effects. Energy conservation
practices dictate applying power only as
required; think green! When power is
switched on or off, high level audio “pops”
on the output connectors are likely. This is
a function of the DC power sources turning
on or off to the Mic-PreEminence circuitry.
Care must be taken to ensure that these
“pops” do not damage equipment or ears
associated with the Mic-PreEminence
outputs.
Phantom Power Switches
Each channel contains a phantom power
switch. When this switch is in the ON
position, +48Vdc is applied via 6.81k ohm
resistors to pins 2 and 3 of the associated
microphone input connector. This +48Vdc
power should allow virtually all phantom
powered microphones to work correctly.
Microphones that require high start-up
current, such as the Neumann TLM 170,
will operate correctly. When using microphones that do not require phantom power,
the phantom power switch should be left in
the OFF position. When phantom power is
switched on or off, high level audio “pops,”
several seconds of hissing noise, or other
strange sonic gyrations on the line outputs
are possible. Care must be taken to ensure
that these noises do not damage equipment or ears associated with the Mic-PreEminence line outputs. The level meter
LEDs will light for a few seconds when
applying or removing phantom power. This
is due to leakage current coupled through
the input capacitors to the input semiconductors. This is completely normal and does
not indicate any Mic-PreEminence problems. After the current dissipates, the lights
resume their normal function and the normal sonic cleanliness returns.
Output Phase Switches
The output phase switch associated with
each channel reverses the relative phase
(input versus output) of both the balanced
and unbalanced outputs. For the balanced
output the switch reverses the connections
to pins 2 and 3 of the output connector.
For the unbalanced output the switch
changes the point in the circuitry where the
unbalanced output obtains its signal. In the
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NORMAL position, a positive going signal
on microphone input pin 2 will result in a
positive going signal on both pin 2 of the
balanced output connector and the tip of
the unbalanced output. In the REVERSE
position, a negative going signal would be
present on the aforementioned pins. A
small click or pop may be heard over the
line outputs when the output phase switch
is actuated.
Gain Controls
On each channel, a gain control determines
the amount of gain applied to the microphone input signal. In the MIN position
approximately 12dB of gain is added to
the input signal. In the maximum position,
approximately 68dB is added to the input
signal. The two gain controls are completely
independent of each other and cannot be
coupled to track together. The gain control
should be set so that an average input
signal produces the desired balanced or
unbalanced output level. In many situations
the desired average balanced output level
would be +4dBu, and –10dBv for unbalanced operation.
The gain control is not a pad that would
reduce the performance of the Mic-PreEminence; it directly controls the gain of
the Mic-PreEminence input stage. The
headroom available is always the difference
between the maximum output level in the
balanced mode (+30dBu balanced into 10k
ohms) and the sum of the input level and
the gain selected by the gain control. In the
likely case of wanting an average output
level of +4dBu, you would have 26dB of
headroom!
The gain control is really intended to match
the input level with the desired output level.
It is not intended to be used to “ride” the
level sent to the piece of equipment connected to the balanced or unbalanced line
output. The gain control is intended to be
set and left during a particular recording or
broadcast passage.
It is almost impossible to overload the MicPreEminence if the gain control is set to
correctly match the input of the next piece
of equipment in the audio chain. With the
Mic-PreEminence’s wide gain range, even
a +4dBu input signal with the gain control
set for minimum (+12dB) would give 14dB
of headroom before clipping!
Level Meters
The 5-segment LED level meters can provide assistance in setting the gain controls.
The meter circuitry was designed to have
characteristics somewhere between that of
a VU meter and a peak (PPM) meter. They
are provided strictly as a reference and
shouldn’t force you into setting the gain
controls to give “standard” VU-type readings on the meters. Even if the red LED is
lighting on peak signals, you are most likely
still far from the Mic-PreEminence’s clipping
point; the red LED lights approximately
18dB below clipping! When the red LED
lights, it is telling you that you are operating
in what most people consider the headroom
range.
Output Select Switches
The back panel contains two push
button switches that select which outputs,
balanced or unbalanced, are active.
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Studio Technologies, Inc. Page 9
Balanced Operation
Input Capacitors
In many cases, users of the Mic-PreEminence will be connecting the balanced
outputs to the balanced inputs on another
piece of equipment. The output select
switches should be set to the BAL position.
In this case the output stage is capable of
a +30dBu (+29dBu into 600 ohms) signal
level before clipping.
Unbalanced Operation
In some applications, the unbalanced
line outputs will be used to link the
Mic-PreEminence with “–10” unbalanced
inputs on another piece of equipment.
Placing the output select switches to the
UNBAL position disconnects the output
circuitry from the 3-pin XLR-type connectors
and connects it via “pads” to the ¼-inch,
2-conductor output connectors.
Technical Notes
Capacitors in the Mic-PreEminence
When designing the Mic-PreEminence,
Studio Technologies, Inc. tried to incorporate all sonic improvements that are
practical from a cost and implementation
standpoint. The design we implemented
requires a minimum number of audio
coupling capacitors. An explanation of their
purpose and possible substitution follows.
As the Mic-PreEminence contains two
identical channels, all references will be
made to one of the channels. Please refer
to the schematic diagrams at the end of this
manual while studying this section.
The microphone input is capacitor coupled
to the input stage to block phantom power
that may have been selected. The 100uf
electrolytic capacitors used in this location
are a low leakage type. You could rightfully
say that the capacitors are not required if
phantom power is switched off, but in most
cases (we realize not all) phantom power
will be used. In the case where phantom
power is off, the capacitors still prevent
stray DC from possibly “blowing up” the
input section. There are really no cases
where eliminating or shunting the input
capacitor pairs is recommended.
Interstage Capacitors
As the circuit is for all intents and purposes
balanced throughout, two capacitor pairs
are required to couple the input stage to the
output stage. These capacitors are required
to prevent normal DC in the input stage
from affecting the output DC balance adjustment. The capacitor pairs consist of a 100uf
electrolytic type in parallel with a 0.33uf
stacked, metallized film type. Removing
or shunting these capacitors should not
be performed.
Output Coupling
As shipped from the factory, the line output
circuits are directly coupled to the output
connectors. This has been accomplished
by shunting the output capacitors, which are
the same type and value as the interstage
capacitor pairs, by soldering 0 ohm resistor
jumper wires into the Mic-PreEminence
circuit board. This direct coupling provides
the best sonic performance. A small DC
voltage, typically not exceeding 100 millivolts, may be found on the line outputs due
Issue 5, April 1994 Mic-PreEminence User Guide
Page 10 Studio Technologies, Inc.
to output circuit offset. This should not pose
a problem for most devices connected to
the Mic-PreEminence line outputs. In the
unlikely case that capacitor coupling of
an output stage is required, the two 0 ohm
resistors can easily be removed, placing
the coupling capacitors in the circuit.
Detailed instructions for enabling the output
capacitors can be found in Appendix B.
Replacing the 0.33uf Capacitors
The coupling 100uf electrolytic capacitors,
as previously mentioned, are paralleled with
0.33uf stacked, metallized film type capacitors. We feel that this provides an excellent
coupling characteristic. Other people in
the audio industry feel that polypropylene
capacitors “sound” better than other types,
including the film type we chose for the
Mic-PreEminence. Our egos are not tied
to the parts we chose so we welcome you
to select the parts you feel most confident
about. We have no problem with qualified
technicians replacing the stock film type.
Refer to Appendix C for detailed instructions
on replacing the 0.33uf capacitors.
RF Problems and Solutions
Because the Mic-PreEminence is a wide
bandwidth device, there may be cases
where radio frequency signals can get into
its circuitry via the microphone input. So
as not to penalize the many for the few,
the Mic-PreEminence does not include any
overt RF suppression circuitry. We want as
little done to the input signal as is required.
It is possible to implement a low pass filter
by adding inductors in series with the input
signal. Only if there is an RF problem
should this action be taken. Refer to
Appendix D for detailed instructions.
Level Designators
Studio Technologies, Inc. has opted to use
the dBu designation as it seems to be quite
rational. Using dBm was fine when all audio
line outputs were terminated with 600 ohm
loads. In this way it was easy to say that
0dBm is 1 milliwatt dissipated in the known
load (i.e., 0dBm across 600 ohms will
measure 0.7746V). In contemporary
applications, an output is rarely terminated
in 600 ohms. Generally, 5k ohms or higher
is used. The dBu designation is a better
reference because it refers to dB referenced to 0.7746V, with no reference to load
impedance. This takes into account the
current audio scene with load impedances
varying greatly. When the Mic-PreEminence
specifications refer to the clipping output
level in dBu, this would translate to dBm
only when the output is terminated with
600 ohms.
The unbalanced line output level is
specified in dBv, as is common with “–10”
equipment. The dBv refers to dB referenced to 1V, in contrast with dBu that is
referenced to 0.7746V. So if you measure
+4dBu on the balanced output you will
measure –7.8dBu on the unbalanced output. This –7.8dBu corresponds to –10dBv.
Got it?!
Circuit Description
General Information
The following paragraphs describe the
circuitry of the Mic-PreEminence. This
information will help you understand how
the unit works and, if required, help identify
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 11
where a failure may be located. Please
refer to the Mic-PreEminence schematic
diagrams while reading this material.
P ower Supplies
The Mic-PreEminence contains circuitry to
provide the ±18Vdc, +18Vdc, and +48Vdc
required for operation. The audio circuitry
uses the ±18Vdc, the LED level meters use
the separate +18Vdc, and the phantom
power feed uses the +48Vdc. A step down
transformer converts the incoming AC
mains voltage to nominal 40Vac. The primary is tapped for either 115Vac or 230Vac
mains input. A switch on the back panel
selects which tap is connected. The secondary of the transformer has a center tap,
which is connected as the circuit common
and is strapped to the metal chassis and the
ground wire of the line cord. The transformer’s secondary connects to two rectifier/
filter sections: a voltage doubler and a full
wave bridge. The voltage doubler raises
the nominal 40Vac to nominal 85Vdc. This
is then fed to an adjustable high-voltage 3terminal regulator which produces +48Vdc.
A trim potentiometer on the circuit board is
factory adjusted to +48Vdc (±0.1Vdc). The
full wave bridge produces nominal ±30Vdc.
One positive and one negative fixed voltage
3-terminal regulator produces ±18Vdc.
Another, lower power regulator produces
+18Vdc which is used by the levels meters.
Preamplifier Circuit
The input stage is unique because it
achieves very high current gain with
extremely low noise. A transistor array
package feeds two high slew rate operational amplifiers in a non-differential configuration. The input is capacitor coupled to
block the +48Vdc phantom power that may
be present. The output of the two operational amplifiers are capacitor coupled to
the output stages.
The balanced output stage uses highperformance operational amplifiers that
allow the driving of low source impedances
(600 ohms) with a large voltage swing.
Cross feedback provides good stability
in driving balanced or unbalanced loads.
Trim potentiometers in the output stage
permit adjustment of the input common
mode rejection while maintaining a “straight
through” balanced circuit without transformers. The output signal is direct coupled to
provide the best sonic performance. Capacitors installed in the circuit board can
be enabled by removing two 0 ohm resistor
jumper wires if capacitor output coupling is
required.
The unbalanced output is achieved by
disconnecting the XLR-type connector,
“padding” the signal, and connecting it to
a ¼-inch, 2-conductor jack. In keeping with
“–10” equipment, the unbalanced outputs
are not intended to drive low impedances
with a large voltage swing. The source
impedance of the unbalanced output is
approximately 200 ohms and is meant to
connect to loads of 10k ohms or greater.
Meter Circuit
Each channel contains a 5-segment LED
level meter circuit to provide the user with
an indication of the internal operating level
and the corresponding output level. The
ballistics of the meter were selected to be
a cross between those of a mechanical VU
meter, and the very fast display of a PPM
meter. The thresholds are set so that the
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first green LED lights at an internal level of
–12dBu, the second at –5dBu, and the third
at 0dBu. The yellow LED lights at +5dBu.
The red LED lights at +12dBu. Audio enters
the meter circuit via an operational amplifier
configured as a half-wave rectifier. The
audio is picked up at the point at which the
input circuit couples to the line driver circuit.
The rectifier produces a DC voltage which
is representative of the audio level in the
preamplifier circuit. This DC is fed to a
meter driver integrated circuit. This IC
contains circuitry to directly control up to ten
LEDs, although the Mic-PreEminence uses
five. The circuit is configured to operate in
the series mode to reduce current draw;
one LED or all five, the current is the same!
The meter IC and the LEDs are powered
by a separate source of +18Vdc. This
eliminates the chance that clicks will enter
the audio signal via the meter circuit. Note
that since the unbalanced outputs are
simply “padded” versions of the balanced
outputs, the meters display correctly for
both balanced and unbalanced operation.
Equipment Required
• Dual Trace Oscilloscope
• Sound Technology 1710A Distortion
Measurement System
• Digital Voltmeter
• Audio Cables as required
Po wer Supplies
The first step in troubleshooting the
Mic-PreEminence is to remove the top
cover (two Phillips head screws on each
side panel), and check the DC voltages at
the test points listed on the schematic. It is
common for failures associated with contemporary audio equipment to be power
supply related. The components most
likely to fail in the power supply are the four
3-terminal regulators (one each for +18,
+18 (meter power), –18, and +48) and the
large filter capacitors. Check and set the
adjustment potentiometer for the +48V
(±0.1Vdc) supply if the adjustable regulator
is replaced.
Analog Problems
Troubleshooting
The following procedures must be
performed by a qualified technician.
Operating the Mic-PreEminence with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 13
If the power supplies are not at fault, use
standard troubleshooting procedures to
locate the problem. A simple technique is
to connect an audio signal to the input and
trace the signal (again, using the schematics) until the source of the problem is found.
Troubleshooting the Mic-PreEminence can
require a bit of patience, as it is a balanced
device; AC
checked.
and
DC voltages must be
Alignment
Alignment is required after any repair not
involving the power supply or level meters.
The following paragraphs will aid in aligning
the Mic-PreEminence circuits, thus restoring
proper operation. It is important to perform
the alignment procedures whenever you
have replaced any of the audio-related
components. Alignment can be tricky and,
if at all possible, factory repair and realignment is recommended.
Caution: DO NOT attempt to adjust any
of the common mode reject/output balance
trim pots inside the unit before you understand the entire alignment procedure and
are equipped to go through the entire
process.
All signal measurements are to made in
reference to circuit common test point. This
point is common for the +18, +18 (meter),
+48, and –18V power supplies; pin 1 of the
four XLR-type connectors; sleeve of the
¼-inch, 2-conductor jacks; chassis ground;
and earth ground via the mains power cord.
The common test point is located on the
right side of the circuit board, near the
power supplies, and is labeled COM.
Mic-PreEminence to ignore signals to
input XLR pins 2 and 3 that are common in
phase and amplitude. The output balance
relates to the output circuitry producing
equal amplitude excursions in the positive
and negative direction (in the case of the
balanced output, when measuring with
respect to pin 1, if pin 2 is 2V, then pin 3
should be –2V).
The widely used 1710A Distortion
Measurement System from Sound
Technologies is an excellent, although
somewhat older, audio test set. This instrument, along with an oscilloscope, will allow
easy CMR adjustment. The following test
procedure refers directly to settings on the
1710A and the oscilloscope.
1) On Mic-PreEminence: front panel gain
control at MIN, phantom power OFF,
phase reverse NORMAL, output to BAL,
and power to ON.
2) On 1710A: generator at –10dBm,
oscillator set to low distortion, frequency
1kHz, source impedance 150 ohms,
noise filter on at 30kHz, hum filter on,
analyzer mode to volts power, analyzer
input range switch to +10.
Common Mode Reject/Output
Balance
Any repair of the Mic-PreEminence audio
circuitry requires adjustment of the two trim
potentiometers associated with the repaired
channel. These trim pots serve a dual
function: setting the input common mode
rejection and the output circuit level balance. From now on we will refer to this
procedure as setting the CMR (common
mode rejection). Input common mode
rejection relates to the ability of the
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3) Connect 1710A generator output to
Mic-PreEminence mic input: one terminal of balanced output to pin 2
and
3, the CT (center tap) terminal to pin 1.
The other balanced output terminal is
not used. This puts a common mode
signal on the Mic-PreEminence mic
input.
pin
4) Connect Mic-PreEminence balanced
line output to scope: pin 1 to scope
common, pin 2 to scope input channel
1, pin 3 to scope input channel 2. In this
way the two traces will show both sides
of the balanced line output.
5) On scope: both input channels set for
AC, sensitivity to 5 millivolt scale.
6) On Mic-PreEminence: set the two CMR
trim pots of the channel under test to
12-o’clock (when looking from the front
of the unit).
7) While watching both traces on scope:
in tandem, adjust the trim pots slowly
clockwise to give minimum but equal
levels for both traces.
8) On scope: adjust input sensitivity to
0.5V scale.
9) Change 1710A generator output
connection to Mic-PreEminence mic
input: one terminal of balanced output
to pin 2, the other balanced output
terminal to pin 3, CT terminal to pin 1.
This puts a differential mode signal on
the Mic-PreEminence input.
12) Connect the Mic-PreEminence
balanced line output to the 1710A
analyzer input (balanced): pin 2 to one
side of balanced input, pin 3 to the
other side.
13) On 1710A: analyzer mode to set level,
set adjust pot to get 0 reading on meter.
14) Connect the 1710A generator output to
the Mic-PreEminence mic input in the
CMR mode configuration as previously
described in step 3.
15) On 1710A: mode switch to dB volts, it
should measure –64dB minimum. (The
–64dB reading relates to an actual CMR
measurement of 70dB when the test
setup is taken into account.) After
measurement is taken, change mode
switch back to set level.
16) If CMR measurement is not –64dB or
better (e.g., –70dB, –80dB, etc.), go
back and start CMR adjustment procedure again.
17) If any repairs have been performed
on the other channel, repeat the entire
procedure for that channel.
10) On scope: observe both traces. The
two AC voltage levels should be equal
within ±20 percent of each other. This
step confirms that the output is balanced. If not go back to step 3 and
again perform the CMR adjustment.
11) Connect the 1710A generator output
to the Mic-PreEminence mic input in
the differential mode configuration as
previously described in step 9.
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 15
Appendices
Appendix A
Specifications
Mounting
One space in a standard 19-inch (48.3cm) rack
AC Mains Requirements
115Vac or 230Vac, ±10%, switch selectable,
50/60Hz, 10 watts
Fuse
0.5A 115V, 0.25A 230V; units shipped to North
America use 3AG type, units shipped outside North
America use 5x20mm type
Number of Preamplifier Channels
2
Connectors
Microphone Inputs: XLR-type female, pin 2 high
Gain Range
+12 to +68dB, related to balanced output
Slew Rate
20V/usec
Distortion (THD)
0.0020%, 20Hz to 20kHz, 30dB Gain
Input to Output Phase Shift
9 degrees maximum, 20Hz to 20kHz
Input Common Mode Rejection
70dB, 20Hz to 20kHz, 30dB Gain
Balanced Outputs Type
Electronically balanced
Output Impedance: approximately 100 ohms
Output Level at Clipping (0dBu=0.7746V):
+30dBu into 10k ohms Balanced
+29dBu into 600 ohms Balanced
Unbalanced Outputs Type
Electronic
Balanced Outputs: XLR-type male, pin 2 high
Unbalanced Outputs: ¼-inch, 2-conductor phone
jack
AC Mains: standard 3-blade plug, meets IEC 320
specifications
Microphone Inputs Type
Electronically balanced, capacitor coupled
Phantom Power
48±0.1Vdc, current limited via 6.81k ohm feed
resistors, on/off individually switchable for each
channel
Input Impedance
7.8k ohms
Noise
–69.5dB at 60dB Gain (i.e. –129.5dB EIN, which is
one dB above theoretical minimum) –103dB at 30dB
Gain (20Hz to 20kHz bandwidth, 150 ohm resistor
on input)
Frequency Response
+0/–1.5dB, 20Hz to 60kHz, 40dB Gain
+0/–0.5dB, 10Hz to 90kHz, 68dB Gain
Nominal Output Level (0dBv=1V): –10dBv (technically the unbalanced output is set to be 11.8dBu
below the nominal balanced output of +4dBu)
Output Impedance: approximately 200 ohms
Output Level at Clipping (0dBv=1V): 16dBv into
10k ohms
Intended Load to Unbalanced Output: the
unbalanced outputs are intended to be connected
to loads of 10k ohms or greater
Dimensions (Overall)
19.00 inches wide (48.3cm)
1.75 inches high (4.5cm)
7.00 inches deep (17.78cm)
Weight
4.2 pounds (1.9kg)
Specifications and information contained in this user
guide subject to change without notice.
Issue 5, April 1994 Mic-PreEminence User Guide
Page 16 Studio Technologies, Inc.
Appendix B
Enabling the Output Coupling Capacitors
5) Return the top and bottom cover to
their correct location and put the
screws back in.
As shipped from the factory, the Mic-PreEminence balanced and unbalanced output
circuits are directly coupled to the output
connectors. In rare instances, capacitor
coupling of the outputs may be required.
With this in mind, output capacitor pairs
(100uf in parallel with 0.33uf) have been
installed in the circuit board. The Mic-PreEminence is shipped from the factory to
achieve direct coupling, and these capacitor
pairs have been shunted with 0 ohm resistor
jumper wires. To put the capacitors in the
circuit, carefully remove the 0 ohm resistor
jumper wires. Later, the shunts can easily
be added to return the Mic-PreEminence
to the stock configuration.
The following procedures must be
performed by a qualified technician.
Operating the Mic-PreEminence with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
1) Ensure that the AC mains cord is re-
moved from the Mic-PreEminence AC
mains input connector on the back panel.
2) Remove the top and bottom cover (four
Phillips head screws for each cover).
3) Refer to the schematic at the back of
this manual for the part ID numbers of
the 0 ohm resistor jumper wire(s). The
ID numbers will start with the letter R
followed by a number. Two ID numbers
are found for each output channel.
4) Carefully cut out the appropriate 0 ohm
resistor jumper wire(s) with diagonal
cutting pliers.
6) Check the Mic-PreEminence for correct
operation.
Appendix C
Replacing the 0.33uf Coupling
Capacitors
This procedure involves removing the existing 0.33uf coupling capacitors and replacing
them with ones of your choice. Physically,
polypropylene capacitors are much larger
than film types and may be tricky to install.
The Mic-PreEminence circuit board should
not be drilled, or otherwise cut up to fit in
the new capacitors. The leads of the new
capacitors should be bent and adjusted to
fit into the existing printed circuit board holes.
The following procedures must be
performed by a qualified technician.
Operating the Mic-PreEminence with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
1) Ensure that the AC mains cord is re-
moved from the Mic-PreEminence AC
mains input connector on the back panel.
2) Remove the top and bottom cover (four
Phillips head screws for each cover).
3) Refer to the schematic diagrams at the
end of this manual for the part ID of the
coupling capacitors that are to be replaced. The ID will start with the letter
C followed by a number. There are four
0.33uf coupling capacitors in each channel (six if the output coupling capacitors
have been enabled).
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 17
4) Carefully remove the selected capacitors. Use correct desoldering technique
for double sided boards. Do not use
force as that will ruin the plated-through
holes.
5) Install and solder the replacement
capacitors into the board.
6) Return the top and bottom cover to
their correct location and put the screws
back in.
7) Check the Mic-PreEminence for correct
operation.
Appendix D
Solutions for RF Problems
The Mic-PreEminence’s circuit board
contains four locations (two per channel)
where chokes (inductors) may be installed.
These chokes, along with existing Mic-PreEminence circuitry, create low pass filters.
From the factory 51 ohm resistors are
inserted in locations R6 and R7 for channel
1, and R11 and R12 for channel 2. If RF
problems occur chokes should be installed
in series with these resistors. The first thing
to do is to obtain four 100uH chokes. A
good source to obtain these parts is DigiKey Corporation, P.O. Box 677, Thief River
Falls, MN 56701 U.S.A., telephone U.S.A
1-800-344-4539. They are well-equipped to
handle small orders and have a wonderful
catalog. The recommended part is the
8230-68 (Digi-Key part number M8037) or
9230-68 (Digi-Key M9101) made by J.W.
Miller division of Bell Industries. These
devices are about the size of ¼-watt resistors; they are very easy to handle and
install.
The following procedures must be
performed by a qualified technician.
Operating the Mic-PreEminence with
the top and/or bottom cover removed exposes the technician to points in the power
input section with hazardous voltages.
1) Ensure that the AC mains cord is re-
moved from the Mic-PreEminence AC
mains input connector on the back panel.
2) Remove the top and bottom cover (four
Phillips head screws for each cover).
3) You will be installing four chokes in
series with four resistors. They should
be installed to form what circuit board
assembly people refer to as a “teepee”
arrangement. Using a soldering iron,
carefully lift one end of resistors R6, R7,
R11, and R12 (51 ohms) from their
solder pads. Use a solder “sucker” or
“solder wick” to open the holes in solder
pads. Don’t hurt the printed circuit board
with excessive force or heat.
4) Insert and solder one end of a 100uH
choke into one of the empty solder pads.
Cut the excess choke lead on the underside of the circuit board. Solder the other
choke lead to the free end of the 51 ohm
resistor that was removed from the
solder pad. Cut the excess choke lead
from the newly formed junction of the
choke and the 51 ohm resistor. The two
components should neatly stick up from
the circuit board, forming an inverted “V”
or the “teepee.” Repeat this procedure
for the other three chokes.
5) Return the top and bottom cover to
their correct location and put the
screws back in.
Issue 5, April 1994 Mic-PreEminence User Guide
Page 18 Studio Technologies, Inc.
6) Test for elimination of RF problem. If
the problem is not solved contact the
factory for additional suggestions.
Studio T echnologies
Limited W arranty
The Studio Technologies, Inc. product
which you have purchased is guaranteed
against defects in material and workmanship under normal use and service for a
period of three (3) years from date of
manufacture.
During this warranty period any components of the product that prove to be defective will be repaired (or, at the discretion of
Studio Technologies, Inc., replaced) at no
charge provided that the product is returned, shipping prepaid, to the manufacturer.
Information on obtaining service is available
by contacting the dealer from whom the
product was purchased, or by contacting
Studio Technologies, Inc.
This warranty does not apply if, in the opinion of Studio Technologies, Inc., the product
has been damaged due to abuse, misuse,
misapplication, accident or as a result of
service or modification by other than an
authorized dealer service center.
No other warranties are expressed or
implied, including, but not limited to, any
implied warranties of merchantability
and fitness for a particular purpose.
Studio Technologies, Inc. shall not be
held responsible for any consequential
damages or losses arising from the use
of this product.
Mic-PreEminence User Guide Issue 5, April 1994
Studio Technologies, Inc. Page 19
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