Pendulum Audio MDP-1 User manual

MDP-1
Vacuum Tube Mic/DI Preamp
Operating Manual
Pendulum Audio, Inc.
PO Box 339, Gillette, NJ 07933
TEL: [phone]
Web: http://www.pendulumaudio.com
email: [e-mail]
Pendulum Audio

INPUT
OUTPUT
2 1 MIC 2 MIC 1
120V/60Hz 30W
MDP-1 Vacuum Tube Mic/DI Preamp
Pendulum Audio, Inc.
Designed By Greg Gualtieri
Serial No.
WARNING: To reduce the risk of fire or electrical shock, DO NOT expose to rain or moisture. DO NOT remove covers. Refer servicing to qualified personnel. For proper operation, be sure to provide adequate ventilation. Made in USA.
Date Code
ON
POWER
DI 2 DI 1
1A
Line: 100kΩ/-20db
Instrument: 1MΩ
MDP-1 Condensed Operating Instructions
An 11 position rotary switch that controls the gain of the tube stage in 3dB steps. The range is: +33 to +63dB for the mic input, +20dB to + 50dB for the DI instrument input, and 0 to + 30dB for the DI line input. A passive attenuator that controls the output level to the XLR and 1/4" (parallel) output connectors. By increasing the Gain (driving the tubes harder) and lowering the Output level, subtle variations in the character of sound are possible. For the 'cleanest' sound, set the OUTPUT control to 10, and adjust the GAIN setting for the proper signal level. In the Output position, the VU meter indicates the signal level at the XLR and 1/4" output connectors (post-Output control). The meter is electronically isolated from the signal path, and is calibrated to 0VU = +4dBu (1.23Vrms). In the Gain position, the VU meter indicates the signal level of the
tube gain stage (pre-Output control). The meter is electronically isolated from the signal path, and is calibrated to 0VU = +20dBu (7.75 Vrms).
GAIN
OUTPUT
METER
The DI input selects between Instrument (with 10 MΩinput impedance at the front 1/4" jack, or 1MΩat the rear jack) and Line (100KΩinput
impedance, with a -20db pad at both inputs). The 1/4" front and rear panel jacks are wired so that the rear jack is disabled when the front jack is used. Selects between the MIC input (via the XLR input connectors on the rear panel) or DI input signals (via the front or rear 1/4" input jacks). Supplies 48 volts to the XLR inputs for condenser microphones requiring phantom power. Do not use with dynamic, ribbon or tube mics. The -20 position inserts a 20 db pad in front of the mic input transformer. Mic phase reverse switch, where ‘+’ is normal phase (input pin 2 hot), and ‘-’ is inverted phase (input pin 3 hot). An 11 position rotary switch that provides a gentle (6db/octave) low frequency rolloff with 10 user-selectable turnover frequencies. The low cut filter does not affect the DI input signal.
DI Input
MIC/DI
+48V
0/-20
+/-
Mic Lo Cut
Pendulum Audio
+
120
40
50 80
30
100
60
20
Off 180
150
MIC
-20
DI INPUT
METER
Hz
GAIN
48V 0
0
MIC LO CUT
OFF
INSTRUMENT
Instrument:
10MΩ
Line:
100KΩ/-20db
OUTPUT
LINE
DI
+
MIC
-20
48V 0
0
DI
DI INPUT
INSTRUMENT
Instrument:
10MΩ
Line:
100KΩ/-20db
LINE
METER
GAIN
OUTPUT
OFF
120
40
50 80
30
100
60
20
Off 180
150
Hz
MIC LO CUT
CHANNEL 1 CHANNEL 2
OUTPUT
48
39 57
42 54
45 5
1 9
4
7
6
3
+20
DI
+50
+33
MIC +63
0 10
51
36 60
8
2
ON
OUTPUT
48
39 57
42 54
45 5
1 9
4
7
6
3
+20
DI
+50
+33
MIC +63
0 10
51
36 60
8
2
MDP-1
Vacuum Tube Mic/DI Preamp
Pure Tube • Class A • High Voltage
GAIN GAIN
10
20
7532 1 012
3
10
20
7532 1 012
3

MDP-1 Vacuum Tube Mic/DI Preamp
Features • All tube, short signal path design
• Pure class A, high voltage circuitry
• Transformerless tube output stage capable of delivering +35dBu
• Low noise, wide bandwidth and superior transient response
• Choice of mic input transformer for 'full' or 'focused' sound
• 30dB gain range in 3dB steps
• Fully transformerless DI with 100kΩ, 1MΩand 10MΩinput impedances
• Ten position mic lo-cut filter (20-180Hz)
• Large illuminated VU meters fully buffered from the signal path for low distortion.
• Soft-start warm-up with output muting
• Gold-plated switch contacts, I/O connectors and tube sockets
• Fully regulated high voltage (300V) and filament dc power supplies
• Custom toroidal power transformer with shield for minimum hum
• Polypropylene capacitors and metal film resistors (pairs matched to 0.1%)
• Single-sided pc boards to minimize capacitive interaction
Introduction
Thank you for purchasing the Pendulum MDP-1, a modern two channel vacuum tube Mic/DI
preamp designed to be the ultimate way to get your mic or source directly to tape or hard disk. Unlike
vintage or hybrid designs, the MDP-1 uses a pure tube, class A high voltage circuit topology with a
transformerless output stage to deliver an open, intimate sound with a level of detail that meets the
requirements of the most demanding recording applications. Our short signal path design excels in
audio performance, delivering extremely wide bandwidth, low noise, and high headroom. The MDP-1
has all the things you'd expect in a full-featured mic preamp, including phantom power, phase reverse,
input pad, a mic lo cut filter with 10 frequencies and large, illuminated VU meters. In addition, the
full-featured DI input on each channel is has an entirely transformerless signal path, and accepts line
and instrument level signals at a variety of input load impedances.
Since a key component of the sound of any tube mic preamp is the input transformer, a choice of
two low turns-ratio transformers is available. The MDP-1A is equipped with two Jensen 13K7
transformers for a ‘full’, open sound with plenty of sparkle in the high end and a deep low end -
perfect for recording all sources, especially instrumental music. The MDP-1B is equipped with two
custom-wound transformers for a more 'focused' sound for extra presence and clarity in the midrange -
ideal for a vocal sound that easily distinguishes itself in a mix. The MDP-1C is configured with a
Jensen 13K7 in channel 1, and a custom transformer in channel 2.
Unpacking The unit was carefully packed at the factory to protect against damage in transit. Nevertheless, be
sure to inspect the unit and shipping carton for any signs of damage that may have occurred during
shipment. If there is any damage, notify us immediately for further instructions. It’s also a good idea
to save the carton and packing materials should you ever need to return the unit for repair. The
shipping carton should contain the following items: the MDP-1 Mic/DI Preamp, an IEC 3 prong
power cord, and this operating manual.
Mounting The MDP-1 uses two EIA-standard rack spaces, and can be mounted in any standard 19 inch
(483mm) equipment rack. If the MDP-1 is mounted in a mobile rack or road case, it is important that
the rear of the chassis is supported to prevent possible damage from mechanical shock and vibration.
Excessive shock and vibration can cause damage or premature failure of the vacuum tubes, or cause
them to shaken loose from their sockets. Please avoid rough handling.

Ventilation For proper operation, it is very important that adequate ventilation is provided. Vacuum tubes
produce a significant amount of heat that must be removed from inside the chassis. The side panel
vent holes and top panel slit vents should never be blocked in any way. Never mount the MDP-1
below a rack unit with a depth greater than 7 inches (178mm). Do not mount the MDP-1 near other
heat-producing equipment such as power amplifiers or other vacuum tube products. If possible, leave
open at least one rack space above the unit, and use a rack spacer with a ventilation grille. Never
operate the MDP-1 inside a road case where the side panels are cushioned in foam.
Preventing Ground Loop Hum
One of the reasons the MDP-1 sounds so good is that unlike many other vacuum tube products, it
operates single-ended, Class A without an output transformer. However, it does not benefit from the
galvanic isolation provided by an output transformer. For this reason, a few precautions are necessary
to insure hum-free operation:
• Isolate the front panel from the rack rails. Use plastic shoulder washers to prevent electrical contact
between the rack ears of the MDP-1 and the metal rails of the equipment rack.
• Isolate the MDP-1 from units mounted above or below it in the rack. Make sure the front panels are
not in electrical contact and that the top or bottom cover screws of the MDP-1 are not touching those
of any other units.
• Connect the 3 prong IEC power cord to the single-point star grounded electrical source for your
facility.
The idea here is to make sure the MDP-1 seeks ground at only one point. For safety reasons, do
not lift the ground at the IEC power cord. Keep in mind that in a properly grounded hookup, the
MDP-1 does not hum. Please, take the time to do this right, and you will be rewarded with hum-free
operation. Call us if you have any questions. Please note that pin 2 is hot.
Power Requirements
The MDP-1 is equipped with a 3-prong IEC power connector and detachable cord. Never operate
the MDP-1 with the ground on the power cord defeated. Unless otherwise stated, this unit operates
from 120V/60 Hz at 30W. The ac fuse is accessible from the rear panel and is rated at 1A/250V (3AG)
SLO-BLO. To check or replace the fuse, make sure the unit is unplugged. Operation at 240V/50Hz is
available as an option. Please contact us for more information.
Servicing Other than changing the tubes, the user should not attempt to service the MDP-1 beyond that
described in this manual. Never remove the covers or attempt to replace the tubes until the unit has
been disconnected from the ac power source, and all circuits inside have been allowed to discharge for a
period of at least 30 minutes. The vacuum tubes become very hot once the unit has been turned on,
and they should not be touched until they have cooled to room temperature. To reduce the risk of fire
or electrical shock, do not expose to rain or moisture, or operate it where it is exposed to water. Since
potentially lethal voltages are present inside the unit, it should only be opened by qualified service
personnel. Refer all servicing, or any questions about servicing, to Pendulum Audio, Inc.
Operation
While the operation of the MDP-1 may appear to be rather straightforward, there are a few features
which may differ from what you’re accustomed to seeing on other stand-alone mic preamps. You may
find it useful to refer to the Condensed Operating Instructions at the beginning of this manual to
quickly identify the operation of the front panel controls. However, we suggest you read through this
section to take advantage of all its features, and to make sure you are operating the MDP-1 in the way
most appropriate for the type of recording you’re doing.

Hookup Please refer to the rear panel layout (see the Condensed Operating Instructions) for the location of
the inputs, outputs, ac power inlet and power switch. Make all connections to the MDP-1 before
applying power.
Inputs• On the right hand side of the rear panel are the input jacks for channels 1 and 2. The female XLR
connectors on top are the transformer-balanced mic inputs. Connect microphones to these inputs
using standard balanced XLR mic cables. Pin 1 = ground. Pin 2 = + (positive phase), pin 3 = -
(negative phase). Note: these inputs may be +48v phantom powered, as selected by the ‘+48’ switches
on the front panel. Do not use phantom power on a microphone that does not require it! (e.g.
dynamic, ribbon, or tube microphones). Make all mic connections before applying phantom power!
• The two 1/4” jacks below the XLR connectors are the unbalanced DI input connectors for channels 1
and 2. The input impedance of these jacks is 1MΩwhen the DI input switch on the front panel set to
Instrument, or 100KΩwith a 20dB pad when the DI input switch set to Line. These inputs can be
used for connecting an instrument directly to the rear panel, or for connecting the MDP-1 to an
unbalanced patch bay. The two 1/4” inputs on the front panel can be used for either instrument
(10MΩ) or line level (100kΩ/-20dB) signals.
Outputs
• To the left of the input jacks are the output jacks for channels 1 and 2. The male XLR connectors on
top are 3 pin unbalanced outputs, with Pin 1 + Pin 3 = ground, and Pin 2 = output. Connect these
outputs to 3 pin balanced console, converter, or tape inputs. If you encounter ground loop hum when
connecting to active-balanced inputs, lift the shield from Pin 1 on the input end of the cable. When
connecting to a balanced patch bay, be sure that Pin 2 = Tip. For connection to transformer-balanced
inputs, do not lift the ground at either end of the cable.
• The two 1/4” jacks below the XLR connectors are unbalanced output connectors, wired in parallel to
the XLR outputs, with Tip = Pin 2, Ring = Pin 1. Use them for connecting the MDP-1 to
unbalanced inputs.
AC Power
• On the left side of the rear panel is the IEC input socket. Connect to a 120V/60Hz receptacle with the
3 prong IEC power cable supplied with the MDP-1. For safety reasons, do not lift the ground on the
power plug by using a 3-to-2 ground lift adapter.
• Turn on the power to the unit using the ac power switch located above the power inlet socket.
Although it might seem a bit awkward to put the ac power switch on the rear panel of the MDP-1,
there is a very good reason for it. By keeping the ac away from the front panel, hum induced by the ac
line into the front panel circuitry can be virtually eliminated. This is especially important with the
MDP-1, since the DI instrument input jacks on the front panel operate at 10MΩ, and are very
susceptible to ac hum.
• If necessary, replace the 1A/250v 3AG SLO-BLO fuse only with the same type and rating.
Power-up Sequence
• To prolong tube life, the MDP-1 goes through a soft-start sequence for gently applying power to the
tubes and stabilizing the circuit before engaging the outputs. When the power switch is turned on, the
outputs are relay-muted to ground and the dc voltage on the tube filaments is ramped up to 12.6Vdc.
Next, the high voltage supply is slowly increased to 300V and the circuit is allowed to stabilize for
about 2 minutes. Finally, the relays lift the outputs from ground and the blue ‘on’ led on the front
panel is illuminated. For best results, please allow the MDP-1 to warm up for at 10 minutes or
longer before using.

Using the MDP-1 as a Mic Preamp
Please refer to the front panel layout (see the Condensed Operating Instructions) for the location of
all switches and controls discussed below. The operation of both channels is identical. All switch
contacts that pass audio are gold-plated for high reliability.
Input Mode: MIC
With the input switch in the ‘MIC’ position, the MDP-1 is configured as a mic preamp, with the
XLR input connectors enabled and the DI inputs on both the front and rear panels disabled. In this
mode the signal path consists of the input transformer followed by a Class A tube gain stage with a
transformerless output. The nominal source impedance is 150Ω. When the MDP-1 is used with a
transformerless microphone with a very low output impedance (50Ωor less), an external impedance-
matching network (available from us) may be necessary to improve transient response.
Phantom Power: +48V/0
In the +48V position, 48 volts is supplied to pins 2 and 3 of the XLR input. The phantom
voltage is applied via two 6.81kΩmetal-film resistors that are hand-matched to better than 0.1%.
Mic Input Pad: 0/-20
In the -20 position, a 20dB impedance-matched resistive pad is inserted in front of the input
transformer to prevent overload. To optimize common-mode rejection, the metal-film resistors are
hand-matched to better than 0.1%. Use this position when recording with mics placed on sources with
high sound pressure levels such as drums, guitar amps, or when close-micing a singer with a high
output mic. Use if distortion is heard, or if the output level of the preamp is too high with the GAIN
selector switch at its lowest setting (+33dB). For the best noise performance, use only when
necessary.
Phase: +/- In the - position, the phase of the mic signal is inverted at the secondary of the input transformer.
Configured this way, the phase of the mic can be switched without interrupting the dc voltage to a
mic requiring phantom power. Positive phase is Pin 2 hot.
Mic Lo Cut: Off to 180Hz
The MIC LO CUT is an 11 position rotary switch that provides a 6dB per octave rolloff with 10
user-selectable turnover frequencies: 20, 30, 40, 50, 60, 80, 100, 120, 150 and 180Hz. It offers a
greater selection of frequencies and gentler low frequency contouring than the low cut filters on most
mics or mixers. In the ‘Off’ position, the filter circuit is removed from the signal path. Note that the
Mic Lo Cut filter affects only the mic input, and not the DI input.
GAIN: +33 to +66dB
The GAIN Control is an 11 position rotary switch that adjusts the gain of the tube stage from
+33dB to +66dB in precise 3dB increments. The 1% metal-film resistors that determine gain are
selected for precise matching between the two channels. At low gain settings, there is more global
feedback in the tube circuit, which offers a more ‘accurate’ and ‘controlled’ sound. At higher gain
settings, the sound is a little more ‘open’ and ‘harmonically rich’. Used in conjunction with the
OUTPUT control (discussed below), subtle variations in the character of sound can be achieved.
OUTPUT: 0 to 10
The OUTPUT Control is a passive attenuator positioned between the final tube stage and the
output connectors. It can be used in conjunction with the GAIN control to adjust the level that is sent
to a tape machine or hard disk recorder. For the cleanest sound, set the OUTPUT control fully
clockwise (completely out of the signal path) and use the GAIN control to set the overall signal level.
To add more ‘harmonic content’ by driving the tubes at a higher signal level, set the GAIN control to

a higher gain setting and use the OUTPUT attenuator to bring the output level down to a more
useable range. Or, use the OUTPUT control to make fine adjustments (within the 3dB range of the
GAIN switch settings) to the level sent to a tape machine. Use the VU meter GAIN setting (discussed
below) to monitor how hard the tubes are being driven. Used sparingly, this gentle tube ‘overdrive’
can create subtle changes in the harmonic balance of the source. Used to excess, it will cause audible
distortion. Proceed with caution. With the OUTPUT attenuator set to mid-range, the level of
attenuation is 20dB for load impedances greater than 10kΩ.
Note: Our use of a resistive output attenuator after a low impedance tube output stage is sure to raise
an eyebrow. First, the output impedance is increased from 600Ωup to as much as 5kΩat the 3:00
position of the output potentiometer. Second, a higher output impedance may in principle cause
problems when attempting to drive a long run of high-capacitance cable.
If this moderate increase in output impedance troubles you, keep the output control turned all the
way up, use the GAIN control exclusively and the MDP-1 will deliver a true 600Ωoutput impedance
with high output drive capability and good stability. In practice however, when the preamp is use in a
typical control room and connected by a reasonable length of cable to a tape or A to D converter
input, the OUTPUT control offers a very convenient way to make minor level adjustments, or to
create subtle variations in the character of sound. Try it, and you may like it.
METER: OUTPUT/GAIN
The illuminated ANSI VU meters are electronically isolated from the signal path, and can be
switched to measure levels at two points in the signal path. Keep in mind that a VU meter is a
mechanical device, designed in accordance with a with a well-accepted ballistic standard, to indicate an
average loudness level. On the other hand, the led meters on your digital recorder are reading a peak
program level, and faithfully register all those short transient spikes that add little to the perceived
loudness of the program material. The ratio of the peak to average levels can be 20dB or greater
depending on the source (e.g. drums). So, if you’re wondering why the led meters on your recorder are
dancing around zero, but the VU meters on the MDP-1 are hovering at or below -10, you’re simply
seeing the difference between the peak and average program level.
OUTPUT
When the METER switch is in the OUTPUT position, the VU meter indicates the signal level at
the XLR and 1/4” output connectors (post - OUTPUT attenuator). The meter is calibrated to 0VU =
+4dBu (1.23vrms). Use this setting to monitor the average program level sent to a tape machine or
console input.
GAIN When the METER switch is in the GAIN position, the VU meter indicates the signal of the tube
stage (pre - OUTPUT attenuator). The meter is calibrated to 0VU = +20dBu (7.75vrms). Use this
setting to monitor how hard the tube stage is being driven, and to gauge the onset of audible
distortion.
OFF The center position of the METER switch turns off the VU meter.
Using the Mic Preamp Without the Input Transformer
Here’s another tip that may raise an eyebrow. The MDP-1 can be used with high output tube
microphones as a fully transformerless mic preamp. Simply connect the mic to the rear panel DI
input using an XLR to 1/4” adapter, and switch the input mode to DI. Increase the GAIN about 20dB
to compensate for the lack of transformer gain and the 6dB loss when running the mic unbalanced.
The noise performance suffers a bit, but when used for recording vocals with a high output
microphone (e.g. Neumann M149), the results are superb. Keep the mic cable as short as possible.

Using the MDP-1 as a DI Preamp
The MDP-1 features a full-function DI with a signal path that is entirely transformerless. Please
refer to the front panel layout (see the Condensed Operating Instructions) for the location of the
switches and inputs discussed below. The operation of both channels is identical. All switch contacts
that pass audio are gold-plated for high reliability.
Input Mode: DI
With the input switch in the ‘DI’ position, the MDP-1 is configured as a line-level DI preamp,
with the DI inputs on both the front and rear panels enabled and the XLR mic input connectors
disabled. In this mode the signal path consists of a Class A tube line stage with a transformerless
output. The input impedance is 100kΩfor line level inputs, or 1MΩand 10MΩfor instrument
inputs. The front and rear panel jacks are wired so that the rear jack is disabled when a 1/4” plug is
inserted into the front jack.
DI Input: Instrument
With the DI INPUT switch on the front panel in the INSTRUMENT position, the 1/4” input
jacks on the front and rear panels are configured to accept unbalanced high impedance sources. The
GAIN range is +20 to +50dB in 3dB increments.
• The front panel jack has an input impedance of 10MΩ, which ideal for very high impedance sources
such as piezo transducers. Use this input when minimum loading of the source is desired.
• The rear panel jack has an input impedance of 1MΩ, which is ideal for moderate impedance sources
such as passive magnetic guitar or bass pickups. Use this input when light loading of the source is
desired. Loading the magnetic coil of a bass guitar pickup with 1MΩcan sometimes tighten up the
low end, adding definition. Since this effect depends on the inductance any given pickup, try it both
ways and see which sounds the best.
DI Input: Line
With the DI INPUT switch on the front panel in the LINE position, the 1/4” input jacks on the
front and rear panels are configured to accept unbalanced high level sources.
• The input impedance is 100kΩfor both front and rear input jacks, with a -20dB resistive pad inserted
between the input and the tube line stage.
• The range of the GAIN control is 0 to +30dB, which is ideal for line-level sources such as -10dBV
unbalanced consumer audio equipment or keyboard outputs.
• Use the rear panel jacks to connect the DI inputs to an unbalanced patch bay.
Gain and Output Controls
See ‘Using the MDP-1 as a Mic Preamp’ for a discussion of how to use the GAIN and OUTPUT
controls to achieve subtle changes in the character of the sound of the DI. Note that while the MDP-1
can in principle be softly ‘overdriven’ like an guitar preamp, it doesn’t have the same tone-shaping
EQ. However, the MDP-1 can be used to overdrive the front end of a tube guitar amp.

Replacing the Tubes
All vacuum tubes have a limited life due to reduced electron emission from the oxide
coating on the cathode and/or a buildup of impurity gases is the bulb. The life of the preamp
tubes in the MDP-1 is estimated to be several years. If you notice the sound quality
deteriorating - higher distortion, muddiness, or microphonic behavior - it’s time to change
the tubes. We recommend changing all the tubes at once. If you are uncomfortable with
replacing the tubes yourself, please have it done by qualified service personnel. Replacement
tubes are available directly from us.
1. Unplug the MDP-1 and wait at least 30 minutes for the high voltage in the unit to
discharge and for the tubes to cool to room temperature.
2. Remove the top cover by removing the nine #6-32 Phillips-head screws.
DO NOT remove the bottom cover.
3. Note the position of the four tubes (V1-V4) in the porcelain sockets.
• The input tubes are ECC83/12AX7A (V1 and V3)
• The output tubes are 6922/6DJ8 (V2 and V4)
4. Remove each tube and replace with the same type removed from the each socket.
DO NOT install the tubes in the wrong positions!
5. Reinstall the top cover and screws.
There are a large variety of ECC83/12AX7s available. Each type has slightly different
internal structure and design. Consequently, each type has its own sonic signature.
Sometimes the differences are subtle - sometime not. You are encouraged to sample the
different varieties and pick the one that sounds the best to you.
The 6922 is a rugged, military style 6DJ8. Since it is used as a high current output
driver, we recommend replacing it with the same type and rating. The 6922 used in this
fashion has much less influence on the sound of the MDP-1 than the 12AX7A input tube.

MDP-1 Specifications
Circuit Type: Class A vacuum tube signal path with transformerless output
Mic Preamp
Input Gain: +33 to +63dB in 3dB steps
Input Impedance: 1500Ωtransformer balanced and floating
Frequency Response: -1.0dB 6Hz and 65kHz with 10KΩload, +45dB gain
-1.0dB 20Hz and 65kHz with 600Ωload, +45dB gain
Noise: EIN less than -125dBu with 150Ωinput load, unweighted (Jensen 13K7)
EIN less than -118dBu with 150Ωinput load, unweighted (Custom Transformer)
Distortion: THD+N less than 0.03% from 100Hz-10kHz,
less than 0.07% at 20Hz, measured with -20dBu input,
+10dBu output, +45dB gain
DI Preamp
Input Gain: +20 to +50dB (Instrument), 0 to +20dB (Line) in 3dB steps
Input Impedance: 10MΩor 1MΩ(Instrument), 100kΩwith 20dB pad (Line)
Frequency Response: -1.0dB 5Hz and 250kHz with 10KΩload, +20dB gain
-1.0dB 20Hz and 300kHz with 600Ωload, +20dB gain
Noise: EIN less than -116dBu with input shorted, unweighted
Distortion: THD+N less than 0.04% from 20Hz-10kHz
measured with +10dBu output, +40dB gain
Output Level: +35dBu into 10kΩload, Output control at maximum
+25dBu into 600Ωload, Output control at maximum
Meter: selection of output level (0VU = +4dBu)
or tube gain (0VU = +20dBu)
Phantom Power: +48Vdc applied to pins 2 and 3
MicPad: -20dB pad at the primary of the mic input transformer
MicPhase: inverts the phase at the secondary of the mic input transformer
Mic Lo Cut: 6 dB/octave rolloff from 20-180Hz in 10 steps
Polarity: input and output XLR connectors are pin 2 hot
VacuumTubes: (2) ECC83/12AX7A, (2) 6922
Power: 120Vac, 30W (240Vac optional)
Power Supplies: +300Vdc and +12.6Vdc, fully regulated
with soft-start warm-up and output muting
Dimensions: 2U enclosure, 19" x 3.5" x 12.5" (48.2 x 8.8 x 31.8 cm)
Weight: 14lbs (6.4kg)

Limited Warranty
Pendulum Audio, Inc. warrants to the first purchaser of a new Pendulum MDP-1 Vacuum
Tube Mic/DI Preamp that the unit is free of manufacturing defects in materials and
workmanship for a period of one (1) year from the date of purchase. Pendulum Audio, Inc.'s
sole obligation under this warranty shall be to provide, without charge, parts and labor
necessary to remedy defects, if any, which appear within one (1) year from the date of
purchase. All warranties expressed or implied made by Pendulum Audio, Inc., including
warranties of merchantability and fitness, are limited to the period of this warranty.
Pendulum Audio, Inc. is not responsible for indirect, incidental or consequential damages
arising from the use or failure of this product, including injury to persons or property.
This warranty does not cover damage due to: misuse, abuse, modification, accident or
negligence. The warranty does not apply if the unit is repaired or altered by persons
unauthorized by Pendulum Audio, Inc. in such a manner as to injure, in Pendulum's sole
judgment, the performance, stability or reliability of the unit. The warranty does not apply if
the unit is connected, installed or used otherwise than in accordance with the instructions
furnished by Pendulum Audio, Inc. There is no warranty on vacuum tubes.
If the equipment requires warranty repair, return authorization must be obtained from
Pendulum Audio, Inc. prior to shipment. Equipment should not be shipped to Pendulum
Audio, Inc. until return authorization and the proper shipping address is obtained from us.
The equipment (with all its components parts and connecting cables) must be suitably
packaged, including a note with the owner's name, address, telephone number and a
description of the reason for return. The owner pays two-way shipping (we recommend
UPS), and we suggest that the shipment be insured for its full value.
This limited warranty is in lieu of all other warranties, expressed or implied, and no
representative or person is authorized to represent or assume for us any liability in
connection with the sale of our products than set forth herein. This limited warranty gives
you specific legal rights, and you may also have other rights which vary from state to state.
Pendulum Audio, Inc.• P.O. Box 339, Gillette, NJ 07933.• [phone] • www.pendulumaudio.com