SoundDevices MixPre manual

SoundDevices MixPre manual
Sound Devices, LLC
300 Wengel Drive
Reedsburg, WI 53959 USA
Voice 608.524.0625
Fax 608 524.0655
MixPre Microphone Preamplifier
User Guide and Technical Information
General Description
The MixPre from Sound Devices is a studio-quality
two-channel, portable, stereo microphone
preamplifier/mixer. With its pan switches, built in
slate microphone, 1 kHz tone oscillator, and
headphone monitoring, the MixPre is a flexible,
portable mixer. The MixPre has impressive audio
performance and comprehensive features, making
it ideal for the front end of any studio or field
High Performance Microphone Inputs
Maximum of 66 dB of gain per input.
Premium Lundahl input transformers provide
superior sonic quality and freedom from
interference problems.
Sealed, conductive plastic potentiometers for
long-life, reliable gain adjustment.
Phantom power, selectable between 48-volts
and 15-volts.
High-pass filters with 80 or 160 Hz corner
frequencies, 6 dB per octave. Filters are
inserted prior to any active circuitry for extra
high headroom.
Input panning to Left, Center, or Right outputs.
Audio Performance
Dynamic range exceeding 110 dB.
10 Hz to 50 kHz audio bandwidth.
Exceptionally low distortion characteristics.
Discrete 6-transistor balanced output drivers
provide robust drive for long cable runs.
Headphone Monitoring
High current headphone monitor circuit enables
monitoring of program audio or external stereo
tape return audio.
Headphone level control and peak-indicator.
P/N 388.004
Printed in U.S.A
production system. Radio, television, and film
production engineers value the compact size and
ability to withstand extremes in the field. The
MixPre combines rugged mechanical and electrical
construction, compact size, and high-quality
components. The MixPre allows no-compromise
performance for any application.
Level Metering
Sunlight-readable, seven segment GaN LED
output meters.
3 position LED brightness switch.
Two-color LEDs per input channel indicate
clipping and limiter activity.
Audio Limiters
“Unclippable” input peak limiters via two-stage
opto-isolator circuit with adjustable limiter
threshold (per input).
Dual mono or linked stereo limiter operation.
Flexible Powering
Internal battery-power from two AA batteries
with easy access battery compartment.
Chassis-isolated external 5 to 18 VDC input on
4-pin Hirose connector.
Power LED indicates low battery power.
Trouble Free Design
High strength, extruded aluminum chassis with
protective metal end panels withstands
punishing field conditions.
All-metal connectors solidly mounted to the
chassis for durability and RF immunity.
Free from “Pin 1” grounding problems.
RF filtering on all inputs and outputs.
Phistersvej 31, 2900 Hellerup, Danmark
Telefon 3946 0000, fax 3946 0040
- pro audio with a smile
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
Mic Input to Output, per channel, continuously variable
Gain Range
-∞ – 66 dB
-∞ – 56 dB
-∞ – 56 dB
-∞ – 46 dB
Frequency Response (see graph below):
20 Hz – 30 kHz, +0.2, -0.5 dB
-1 dB at 5 Hz, 50 kHz
(relative to 1 kHz level with 150 ohm source, gain controls
set at 50%)
Equivalent Input Noise:
-126 dBu (-128 dBV) minimum
(150 ohm source, flat weighting, 22 – 22 kHz bandwidth,
gain control set at 50% or higher, phantom power off)
Input Clipping Level:
–10 dBu minimum, phantom off
0 dBu minimum, phantom on
Output Clipping Level:
+22 dBu minimum with 100k ohm load
+20 dBu minimum with 600 ohm load
+11 dBu (2.75 V RMS) minimum with 100k ohm load
Dynamic Range:
110 dB minimum
THD + Noise:
0.05% maximum
(from 50 Hz to 22 kHz @ +4 dBu output level, 22 Hz - 22
kHz filter bandwidth, gain control at 50%, phantom off)
Common Mode Rejection Ratio:
100 dB minimum at 80 Hz
60 dB minimum at 10 kHz
Channel Separation:
Greater than 80 dB at 1 kHz (gain controls set to 50%)
Transformer-balanced, 2k ohm input impedance
Active, impedance-balanced, 120 ohm output
Tape (3.5 mm)
Unbalanced, tip-left, ring-right, sleeve-ground, 2.4k
ohm output impedance
High Pass Filters:
80 Hz or 160 Hz (switch selectable), 6 dB per octave
Phantom Power:
15 V through 680 ohm resistors or 48 V through 6.8k
resistors (switch selectable)
Thresholds independently adjustable from
+6 dBu to +18 dBu
10:1 limiting ratio
5 mS attack time, 100 mS release time
Amber/Red LED indicates limiting/clipping
Dual mono or stereo linked
Internal Voltage Rails:
+15 V and –15 V, regulated
Peak responding 7 segment GaN (Gallium Nitride) meter
with 3 brightness levels
2 AA alkaline batteries, 6 hours life typical with +4
dBu signal into 600 ohms, no phantom power
Isolated external DC input jack, 5-18 V on locking 4pin Hirose connector, pin-4 = (+), pin-1 = (-),
Use gold Hirose #HR10A-7P-4P or silver Hirose
#HR10-7P-4P for locking mating DC connector.
Voltages above 18 VDC cause no damage to unit, but
will open an internal poly fuse. Poly fuse will reset
when voltage is removed.
Power LED:
Green indicates power and good battery.
Red indicates power and low battery. LED turns red when
approximately 1 hour of battery life remain (phantom off).
Green with external DC power.
All inputs to all outputs, non-inverting. Pin 2 of XLRs “hot”
to unbalanced inputs and outputs.
Operating Temperature Range:
0 to 70 degrees C (32 to 160 degrees F)
43 mm x 94 mm x 140 mm (h x w x d)
(1.7” x 3.7” x 5.5”)
Weight (unit only):
0.8 kg
2.0 lbs.
Weight (packaged):
1.2 kg
3.0 lbs.
Meets FCC Part 15 Class B
Eligible to bear CE mark (see conformance statement)
Page 2
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
Front Panel Controls, Connectors, and Indicators
+4 +8 +12 +16
1. Gain Controls
Adjusts the input gain via sealed, conductive
plastic rotary potentiometers.
2. Input Peak/Limiter LED
Two-color LED illuminates red at 3 dB below
clipping; illuminates amber to indicate limiter
8. Tape Return Switch
Toggle switch allows external audio to be
monitored in the headphones. The center
position is MixPre program audio. The left and
right positions monitor tape return audio; the
left position is locking, and the right position is
3. Pan Switches (Input Assignment)
Three-position switch pans inputs to Left,
Center (both left and right) or Right outputs.
9. Headphone Connector
Accepts stereo and mono headphones with ¼”
4. Slate Microphone
Condenser microphone with AGC controlled by
momentary Slate Microphone Switch. Slate
Microphone output appears at all outputs.
10. Headphone Volume Control
Adjusts the level in the headphones.
5. Tone Oscillator/Slate Microphone Switch
Toggle switch activates 1 kHz tone oscillator
when switched to the left position and
activates the slate microphone when
momentarily moved to the right position.
Microphone inputs are muted when Tone
Oscillator or Slate Microphone are activated.
6. Output Meter
Indicates peak output level in dBu appearing at
the left and right outputs.
7. Meter Brightness Control
Three-position switch adjusts the intensity of
illumination of the output meter; low
illumination, normal illumination, or superbright illumination.
Page 3
11. Headphone Peak LED
Illuminates 3 dB before clipping of either
channel of the headphone circuit. Also
illuminates 3 dB before clipping of either
channel of Tape Return audio.
12. POWER Switch
Three-position switch selects the power
source. The unit is powered from internal
batteries when in the left position; powered
from external DC source when in the right
position. Center position is off.
Two-color LED illuminates green when the unit
is powered and changes to red when batteries
require changing. For external DC, the power
LED is always green.
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
Input Panel Connectors and Controls
Transformer-balanced XLR inputs accepts
microphone level signals. Pin 2 = hot, pin 3 =
cold, pin 1 = ground.
15. PHANTOM Power / Input Gain Switch
Three-position switch selects either 48-volt or
15-volt phantom power for both inputs. Center
position turns phantom power off. Phantom
positions reduce input sensitivity by 10 dB.
16. High-Pass Filter Switch
Three-position switch selects 80 Hz or 160 Hz
corner frequency filters, 6 dB per octave.
Filters affect both inputs. Center position of
switch removes filters from the signal path.
17. Tape Output
3.5 mm TRS stereo output (unbalanced) can
be used to feed consumer level DAT, MiniDisc,
and CD recorders. Tip = left, ring = right,
sleeve = ground.
Output Panel Connectors
18. Tape Return Level Control
Recessed potentiometers adjust Tape Return
level feeding the Headphone Monitor.
19. Limiter Switch
Activates input peak limiter. ON position
functions as a dual mono limiter, with each
input signal controlling its own limiter. LINK
functions as a stereo limiter, with both left and
right inputs controlled simultaneously. Center
position of switch turns limiter off.
20. Limiter Threshold Level Control
Recessed potentiometers adjust peak level of
limiter activation. Can be independently
controlled for each input.
21. Strap Slot
Attachment point for camera straps.
22. Tape Return Input Connector
3.5 mm TRS stereo (unbalanced) connector
allows external audio sources to be monitored
in the MixPre Headphone circuit. Tip = left,
ring = right, sleeve = ground.
23. Left and Right Line Level Outputs
Active-balanced XLR line-level outputs. +22
dBu peak output level. Pin 2 = hot, pin 3 =
Page 4
cold, pin 1 = ground. Pin 3 can be grounded
or ungrounded to drive unbalanced inputs.
24. BATTERY Compartment
MixPre operates on two AA batteries. Insert
positive (+) end of batteries first.
25. External DC Power Input
Accepts external DC power source (battery
supply or AC to DC transformer) from 5 - 18
VDC. Locking, 4-pin Hirose pin-4 (+), pin-1 (-).
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
Operational Notes
Input Circuitry
The isolation characteristics of transformers are
superior to other balancing techniques for the
adverse and uncontrolled environments of field
production. Input transformers provide complete
galvanic isolation from the source, meaning there
is no direct electrical connection. Signals are
“transformed” magnetically. The MixPre features
expensive Lundahl input transformers, which are
unparalleled in sound quality. Lundahl input
transformers use premium magnetic core material
and advanced winding techniques to achieve high
signal handling capability and flat frequency
response while keeping distortion to a minimum.
Because of their inherently high common mode
impedance, transformers are unrivaled by any
other type of input for common-mode noise
Output Circuitry and Tape Output
Each line level XLR output of the MixPre uses a
discrete, six-transistor, “impedance balanced”
output stage. The circuit uses oversized, high
speed transistors to achieve low-distortion, robust
line driving capability. Pin 2 is driven with signal,
and pin 3 is not. [A common misunderstanding is
that a “balanced” output refers to equal and
opposite signals on pins 2 and 3. Correctly,
“balanced” refers to equal impedances from each
signal (pin 2 and pin 3) to ground, not the signal
voltage.] To drive unbalanced inputs, pin 3 can be
grounded or left unconnected. There is no change
in signal level driving balanced or unbalanced
The Tape Output is designed to feed consumer
level devices, such as computer sound cards, DAT
or MiniDisc recorders, and cassette recorders. A
cable wired with 3.5 mm TRS to 3.5 mm TRS or,
3.5 mm TRS to Left/Right phono (RCA) connectors,
is useful when directly connecting the MixPre to
portable consumer audio electronics.
The “Mix” in MixPre
The MixPre pan switches assign each input channel
to an output bus. With this feature, the MixPre can
be used as a two-channel microphone preamplifier
and as a simple mixer. As a mixer, many
applications are possible, such as:
Page 5
Quickly reversing the stereo image of a
recording without reconnecting inputs or
During set up, checking for mono compatibility
by assigning both inputs to the same output.
Recording dialog in mono.
By routing input 1 to Center and input 2 to Right, a
summed mono signal of both inputs appears at the
Right output while only input 1 appears at the Left
output. This is useful for post production
processing of input 1 audio.
Phantom Power / Input Gain Switch
Microphones requiring phantom power should use
the lowest voltage acceptable to maximize MixPre
battery life. Condenser microphones that can
operate on phantom voltages from 11-52 volts will
not have a performance benefit with 48-volt
phantom; therefore 15-volt phantom is
appropriate. The 15-volt setting will increase
battery life versus the 48-volt setting.
Microphones requiring 48-volt phantom will not
operate, or may operate with lower headroom and
increased distortion at the 15-volt setting;
therefore use 48-volt phantom for these mics.
Consult your microphone documentation.
Dynamic microphones do not require phantom
power. A properly connected balanced, dynamic
microphone will not be affected by the presence of
phantom power nor will it draw any current.
However, it is good practice to turn phantom
power off when not needed. Poor or incorrectly
wired microphone cable can cause audible artifacts
in microphone signals. Some wireless receivers
outputs are adversely affected by the presence of
phantom power, therefore, consult the wireless
receiver documentation.
The MixPre phantom power switch reduces the
input circuit gain by 10 dB when switched to either
phantom power setting. As condenser mics are
typically 10 dB or more sensitive than dynamic
mics, the 10 dB pad keeps the input stage from
clipping and helps normalize front panel gain
High-Pass Filter
The two-position high pass (low cut) filter in the
MixPre is useful for removing excess low frequency
energy in audio signals. This excess energy can be
caused by multiple sources, including wind noise,
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
vibration, unidirectional proximity effect, or high
ambient noise levels. The 80 Hz position is
appropriate when recording general speech, music,
and ambient sound. The 160 Hz position is useful
to enhance speech clarity. The MixPre high pass
circuit topology is unique in that the filters are
placed immediately after the input transformer,
before any active gain circuitry. This gives the
MixPre higher headroom with low frequency
signals, as the low frequency signals are not
amplified before they are removed, as in most
other designs. The high pass filter is a single pole
design (slope of 6 dB per octave) and uses high
quality film capacitors for very low distortion. The
high pass filter switch controls both inputs. The
center position of the switch removes the filter
from both audio paths.
When possible, attempt to equalize at the sound
source with microphone selection, use of
windscreens, shock mounts, microphone
placement, and onboard microphone filtering.
Multiple high pass filters (filters on microphones
and on the MixPre) will give an additive effect,
increasing the slope of the filter.
Headphone Monitoring and Tape Return
Headphone monitoring is an essential need in
production audio. The MixPre enables monitoring
of program (mixer) audio or a second audio
source. In normal operation the headphones
monitor the output bus directly. Using the Tape
Return input, a second audio source can be
monitored in the headphones. This is useful to
verify that signal is reaching cameras and tape
machines. The three position Tape Return switch
on the front panel selects the audio source being
monitored. The left and right positions monitor the
tape return audio. Left is locking, and right is
momentary. The center position monitors the Left
and Right outputs of the MixPre. As the MixPre can
drive headphones to very high levels, care should
be exercised when monitoring.
The MixPre has two built in peak responding
limiters, one for each input channel. The threeposition LIMITER switch on the input panel
activates both channels limiters. Each limiter in the
MixPre is a two-stage circuit; the first stage keeps
the input gain stage from clipping; the second
stage limits the variable gain stage to the level set
by the Limiter Threshold control. This unique two
stage topology limits the gain stage directly after
the mic input transformer, to make the front end
Page 6
virtually “unclippable”, but does not change the
input impedance as other “at the mic” limiters do.
The circuit enables the MixPre to limit, when
necessary, in excess of 50 dB, making it very
difficult to clip the unit no matter the gain setting.
The three-position Limiter switch can be set to
operate in either dual mono or stereo linked
operation. Dual mono operation (ON switch
position) allows each input to limit independently,
responding only to its input signal. Stereo linked
operation (LINK switch position) connects both
limiters, ensuring that the limiters control both
channels identically. This linking is important for
stereo operation to maintain a proper stereo
image. When the limiters activate, the Peak/Limiter
LED on the front panel illuminates amber in
proportion to the amount of limiting for each
Tone Oscillator and Slate Microphone
Two functions are controlled by the single switch
labeled 1 kHz/SLATE. The 1 kHz position (left locking) activates a 1 kHz sine wave calibration
tone at a +4 dBu output - sent to all outputs.
Inputs are muted when the tone oscillator is
activated. The tone oscillator is useful during setup
to verify connections and to set nominal levels to
recording and transmission equipment. The SLATE
position (right – momentary) of the switch
activates the built in slate microphone (located
behind the front panel). The Slate Mic circuit
contains an AGC (automatic gain control) to keep
the slate level relatively constant regardless of the
acoustic level. Slate microphones are convenient to
document “takes” right at the mixer location when
microphones are “on talent” or away from the
production mixer. Slate microphone audio is
present at all outputs, and inputs are muted while
the slate mic is active.
Above each input gain control is a two-color LED
that illuminates red when the input approaches
clipping (3 dB before clipping). This clip circuit
monitors both the front end gain stage and the
variable gain stage. If the audio signal clips
anywhere, this LED will show it. Above the
headphone level control, the headphone clip LED
shows when either channel of the headphone
circuit is nearing clipping level. The headphone clip
LED also shows when either channel of the tape
return audio is nearing clipping level. Between
these three clip indicators, any clipping, anywhere
in the mixer will be seen before it is heard.
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
When the limiter is activated, the input LED’s
illuminate amber in proportion to limiting action.
The MixPre has a highly visible, seven segment
LED output meter. The meter is peak responding,
showing the instantaneous output level in dBu.
Peak readings are essential when the outputs feed
digital devices. The meter uses expensive Gallium
Nitride (GaN) LED’s which allow for excellent
viewing (with minimal current draw) under all
lighting conditions, including direct sunlight. The
front panel Meter Brightness switch controls the
meter brightness (low, normal, or super-bright).
The meter indicates a signal range of 46 dB. From
left to right the first three LED’s are separated by
15 dB and the next four LED’s are separated by 4
dB. This calibration provides a large dynamic range
with good resolution in the critical signal level
Power Sources
The MixPre is designed to operate from two
internal AA alkaline cells for approximately 6 hours
with typical signal levels (without phantom power).
External DC sources such as AC to DC transformers
and external battery supplies can also power the
MixPre. Because of its regulated power supply
circuitry, audio performance does not change
depending on battery or external DC voltage.
The external DC input supply is galvanically
isolated (floating) from the chassis and the rest of
the circuitry. The isolation provides trouble free
interconnection to other pieces of equipment
sharing the same DC power source. The pin-2 of
the locking Hirose DC connector is positive, and
pin-1 is negative. As the external DC supply is
floating, the positive or the negative can be
connected to the chassis with no adverse effects.
Battery Life
Two factors determine battery life - battery power
and current draw.
Battery Power
For internal power the MixPre uses two AA sized
1.5-volt batteries. Different batteries have different
power capacities depending on their battery
chemistry, age, operational temperature, and
amount of current being drawn. Alkaline cells are a
popular and cost-effective battery type. Lithium
cells have higher power per cell with higher current
draws and yield significantly longer battery life, at
a cost premium. AA carbon cells and AA nickelcadmium cells are not recommended internal
battery types in the MixPre since these batteries
Page 7
have lower power capacity than other types and
will result in very short service life. Temperature
has a significant effect on the life of batteries.
Lithium batteries are significantly better than
alkaline batteries at lower temperatures.
Current Draw
The MixPre can vary significantly in the amount of
current it draws. Several functions of the MixPre
directly affect current draw in different ways. The
following list highlights the larger current drawing
functions. (listed from highest to lowest current
1. Phantom power– the main source of extra
MixPre current draw. (See Phantom Power)
48V Phantom can draw copious amounts of
current out of the batteries depending on what
model microphone is used. Two phantom
powered microphones draw twice as much
current as one. Microphones vary widely in
their current draw depending on type and
phantom voltage applied.
2. Headphone output circuit – high headphone
output levels increase current draw.
3. Meter illumination intensity – higher meter
brightness increases current draw. The meter
can be switched to low for battery
4. Output drive level – higher output drive levels
into low impedance inputs increases current
Experimentation is recommended to determine
battery life for each individual setup and
application. The chart below can be used as a
starting point to estimate battery life.
Eveready AA
No. L91
Duracell AA
MN 1500
Duracell AA
MN 1500
Duracell AA
MN 1500
2 dynamic handheld
microphones, low meter, no
2 dynamic handheld
microphones, low meter, low
2 condenser, 12-volt phantom
powered microphones,
normal meter intensity,
normal headphone drive level
2 studio condenser, 48-volt
phantom powered
microphones, super bright
meter intensity, cranking
11 hrs.
6 hrs.
4 hrs.
2 hrs.
(Test conditions: 70 degrees F, 42 dB of gain with an acoustic
music source, 600 ohm load, +4 dBu output)
©1999-2002 Sound Devices, LLC
MixPre Microphone Preamplifier
User Guide and Technical Information
FCC Statement
This device has been tested and found to comply with the limits for a class B digital device, pursuant to part 15 of the FCC rules. These
limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates,
uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful
interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation.
CE Conformity Statement
Declaration of Conformity
According to ISO/IEC Guide 22
Manufacturer’s Name:
Sound Devices, LLC
Manufacturer’s Address:
Sound Devices, LLC
300 Wengel Drive
Reedsburg, WI 53959 USA
declares that the product:
MixPre Professional Microphone Preamplifier
is in conformity with:
Document No.
EN55103-1 (1997)
Emissions standard for product family audio devices for professional use
EN55103-2 (1997)
Immunity standard for product family audio devices for professional use
EN55022 (1995)/
CISPR 22 (1997)
Radiated and Conducted emissions, Class B
EN61000-4-2 (1995)/
IEC1000-4-2 (1995)
ESD – 6kV contact, 8kV air-discharge
EN61000-4-3 (1995)/
IEC1000-4-3 (1995)
Radiated RF Immunity, 10 V/m, 80% 1 kHz amplitude
EN61000-4-4 (1995)/
IEC1000-4-4 (1995)
EFT/Burst, I/O lines, +/- .25 kV to +/- 1.0 kV
EN61000-4-6 (1996)/
IEC1000-4-6 (1996)
Conducted RF Immunity, 10 V, 80% 1 kHz amplitude modulation
Tested by:
L. S. Compliance, Inc. Cedarburg, Wisconsin
December 16, 1999
Matthew Anderson
Director of Engineering
Sound Devices, LLC warrants the MixPre Microphone Preamplier against defects in materials and workmanship for a period of ONE (1)
year from date of original retail purchase. This is a non-transferable warranty that extends only to the original purchaser. Sound Devices,
LLC will repair or replace the product at its discretion at no charge. Warranty claims due to severe service conditions will be addressed on
OF WARRANTY OR UNDER ANY OTHER LEGAL THEORY. Because some jurisdictions do not permit the exclusion or limitations set forth
above, they may not apply in all cases.
For all service, including warranty repair, please send the MixPre, along with proof of purchase date to:
Sound Devices, LLC
Service Repair
300 Wengel Drive
Reedsburg, WI 53959 USA
Phistersvej 31, 2900 Hellerup, Danmark
Telefon 3946 0000, fax 3946 0040
- pro audio with a smile
Page 8
©1999-2002 Sound Devices, LLC
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