Sound Devices MixPre Bedienungsanleitung
©2001-2004 Sound Devices, LLC
Sound Devices, LLC
300 Wengel Drive
Reedsburg, WI 53959 USA
Ph: +1 (608) 524-0625
Fax: +1 (608) 524-0655
www.sounddevices.com
MixPre
Microphone Preamplifier
User Guide and Technical Information
MixPre Compact Mixer
2
WELCOME
The MixPre 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 com-
prehensive features, making it ideal for the front end of any studio or field
production system. Radio, television, and film production engineers value
its compact size and ability to withstand environmental extremes. The
MixPre combines rugged mechanical and electrical construction, compact
size, and high-quality components for no-compromise performance for any
application.
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User Guide and Technical Documentation
KEY FEATURES
High Performance Microphone Inputs
• Maximum of 66 dB of gain per input
• Premium Lundahl input transformers
• Sealed, conductive plastic potentiometers
• Phantom power, selectable between 48-volts and 15-volts
• High-pass filters with 80 or 160 Hz corner, 6 dB per octave
• 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
Headphone Monitoring
• High current headphone monitor circuit
• Headphone level control and peak-indicator
Level Metering
• Sunlight-readable, seven segment GaN LED output meters
• 3 position LED brightness switch
• Two-color clip/limiter activity LEDs per input channel
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
• Chassis-isolated 5 to 18 VDC external power input
• Power LED indicates low battery power
MixPre Compact Mixer
4
FRONT PANEL
2
L C R L C R TAPE RTNSLATE
1kHz METER
L
R
-30 -15 0 +4 +8 +12 +16
INT EXTPHONES
POWER
MIC
MIC INPUTS
1 2
12V
48V 80
160
LIMITER
L R
LR
TAPE OUT
PHANTOM
LINK
ON THRESHOLD
TAPE RTN
LEVEL
1(L) 2(R)
LINE OUTPUTS
5-18 VDC
+
-
TAPE RTN
2
3
4
51
6
13
2
7 8 9 10
13
12
11
1. Gain Controls
Adjusts the input gain via sealed, conductive plastic rotary potentiom-
eters.
2. Input Peak/Limiter LED
Two-color LED illuminates red at 3 dB below clipping; illuminates amber
to indicate limiter activity.
3. Pan Switches (Input Assignment)
Three-position switch pans inputs to Left, Center (both left and right) or
Right outputs.
4. Slate Microphone
Condenser microphone with AGC controlled by momentary Slate Micro-
phone Switch. Slate Microphone output appears at all outputs.
5. Tone Oscillator/Slate Microphone Switch
Toggle switch activates a 1 kHz tone oscillator when switched to the
left position and activates the slate microphone when in the right (mo-
mentary) position. Microphone inputs are muted when tone or slate are
activated.
6. Output Level Meter
Indicates peak output level in dBu appearing at the left and right out-
puts.
7. Meter Brightness Control
Three-position switch adjusts the intensity of illumination of the output
meter; low illumination, normal illumination, or super-bright illumina-
tion.
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 posi-
tion is momentary.
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User Guide and Technical Documentation
9. Headphone Connector
Accepts stereo and mono headphones with 1/4-inch connectors.
10. Headphone Volume Control
Adjusts the level in the headphones.
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.
13. POWER LED
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.
MixPre Compact Mixer
6
INPUT PANEL CONNECTORS AND CONTROLS
2
L C R L C R TAPE RTNSLATE
1kHz METER
L
R
-30 -15 0 +4 +8 +12 +16
INT EXTPHONES
POWER
MIC
MIC INPUTS
1 2
12V
48V 80
160
LIMITER
L R
LR
TAPE OUT
PHANTOM
LINK
ON THRESHOLD
TAPE RTN
LEVEL
1(L) 2(R)
LINE OUTPUTS
5-18 VDC
+
-
TAPE RTN
2019
1817
1614 15
14. MIC INPUTS
Transformer-balanced XLR inputs accepts microphone level signals. Pin
2 = hot, pin 3 = cold, pin 1 = ground.
15. PHANTOM Power
Three-position switch selects either 48-volt or 15-volt phantom power for
both inputs. Center position turns phantom power off. Phantom posi-
tions 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 re-
moves 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.
18. Tape Return Level Control
Recessed potentiometers adjust Tape Return level feeding the Head-
phone Monitor.
19. Limiter Switch
Activates input peak limiter. ON position functions as a dual mono lim-
iter, 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.
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User Guide and Technical Documentation
OUTPUT PANEL CONNECTORS
2
L C R L C R TAPE RTNSLATE
1kHz METER
L
R
-30 -15 0 +4 +8 +12 +16
INT EXTPHONES
POWER
MIC
MIC INPUTS
1 2
12V
48V 80
160
LIMITER
L R
LR
TAPE OUT
PHANTOM
LINK
ON THRESHOLD
TAPE RTN
LEVEL
1(L) 2(R)
LINE OUTPUTS
5-18 VDC
+
-
TAPE RTN
21 25242322
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 = cold, pin-1 = ground. To unbalance, use pin-2 as signal and
pin-1 as ground, pin-3 should not be grounded.
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 trans-
former) from 5–18 VDC. Locking, 4-pin Hirose pin-4 (+), pin-1 (–).
MixPre Compact Mixer
8
OPERATIONAL NOTES
Input Circuitry
The isolation characteristics of transformers are superior to other balanc-
ing 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 re-
sponse 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 rejection.
Output Circuitry and Tape Output
Each line level XLR output of the MixPre uses an active-balanced output
stage. The circuit provides robust line driving capability. To drive unbal-
anced inputs, pin-3 should not be connected. When unbalancing the con-
nection the output level will be reduced by 6 dB.
The Tape Output is designed to feed consumer level devices, such as com-
puter 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 pream-
plifier and as a simple mixer. As a mixer, many applications are possible,
such as:
• Quickly reversing the stereo image of a recording without reconnecting
inputs or outputs.
• 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 postproduction processing of input 1 audio.
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User Guide and Technical Documentation
Phantom Power
Microphones requiring phantom power should use the lowest voltage ac-
ceptable 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 oper-
ate 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 connect-
ed 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 phan-
tom power, therefore, consult the wireless receiver documentation.
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, vibration, unidi-
rectional 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 micro-
phones 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 Mix-
Pre enables monitoring of program (mixer) audio or a second audio source.
In normal operation the headphones monitor the output bus directly. Using
MixPre Compact Mixer
10
the Tape Return input, a second audio source can be monitored in the head-
phones. This is useful to verify that signal is reaching cameras and tape ma-
chines. 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.
Limiters
The MixPre has two built-in peak responding limiters, one for each input
channel. The three-position 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 virtually “unclippable”, but does
not change the input impedance as other “at the mic” limiters do. The cir-
cuit 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) al-
lows 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 channel.
Tone Oscillator and Slate Microphone
The switch labeled 1 kHz/SLATE controls two functions. The 1 kHz posi-
tion (left - locking) activates a 0 dBu level 1 kHz sine wave calibration
tone - sent to both 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 docu-
ment “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.
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