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TubePRE
Single-Channel Tube Mic-Preamplifier w/ VU Meter
User's Manual
VERSION 1.0
Limited Warranty Outside of The U.S.
Presonus Audio Electronics products are warranted only in the country where purchased,
through the authorized Presonus distributor in that country, against defects in material and
workmanship. The specific period of this limited warranty shall be that which is described to
the original retail purchaser by the authorized Presonus dealer or distributor at the time of
purchase. Presonus does not, however, warrant its products against any and all defects: 1)
arising Out of materials or workmanship not provided or furnished by Presonus, or 2) resulting
from abnormal use of the product or use in violation of instructions, or 3) in products repaired
or serviced by other than authorized Presonus repair facilities, or 4) in products with removed
or defaced serial numbers, or 5) in components or parts or products expressly warranted by
another manufacturer. Presonus agrees, through the applicable authorized distributor, to
repair or replace defects covered by this limited warranty with parts or products of original or
improved design, at its option in each respect, if the defective product is shipped prior to the
end of the warranty period to the designated authorized Presonus warranty repair facility in
the country where purchased, or to the Presonus factory in the U.S., in the original packaging
or a replacement supplied by Presonus, with all transportation cost and full insurance paid
each way by the purchaser or owner. All remedies and the measure of damages are limited to
the above services. It is possible that economic loss or injury to person or property may result
from the failure of the product; however, even if Presonus has been advised of this possibility,
this limited warranty does not cover any such consequential or incidental damages. Some
states or countries do not allow the limitations or exclusion of incidental or consequential
damages, so the above limitation may not apply to you. Any and all warranties, express or
implied, arising by law, course of dealing, course of performance, usage of trade, or otherwise,
including but not limited to implied warranties of merchantability and fitness for a particular
purpose, are limited to a period of two years from either the date of original retail purchase or,
in the event no proof of purchase date is available, the date of manufacture. Some states or
countries do not allow limitations on how long an implied warranty last, so the above
limitations may not apply to you. This limited warranty gives you specific legal rights, and you
may also have other rights, which vary from state to state, country to country.
Presonus Audio Electronics, Inc.
7257 Florida Blvd.
Baton Rouge, LA 70806
225-216-7887
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Table of Contents
1.1 Introduction........................................................................1
1.2 Features.........................................................................................2
2.1 Controls & Connections .......................................................4
2.2 Front Panel.....................................................................................4
2.3 Preamplifier Section .........................................................................4
2.4 Back Panel......................................................................................6
3.1 Operation............................................................................8
3.2 Dynamic Microphones.......................................................................8
3.3 Phantom-Powered Microphones ..........................................................8
3.4 Instrument Input .............................................................................8
3.5 Some Thoughts on Vacuum Tubes.......................................................8
3.6 Application Guide.............................................................................9
3.7 FAQ/Trouble Shooting.....................................................................10
4.1 Technical Specifications ....................................................13
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1.1 INTRODUCTION
Thank you for purchasing the Presonus TubePRE Single-Channel
Microphone/Instrument Tube Preamplifier. This pre-amp was designed
using state of the art components to deliver crystal clear audio for an
infinite period of time. We feel that we have created a reliable,
versatile and affordable piece of audio equipment. It is designed to
meet a multitude of professional audio applications. If you have any
questions or comments in regards to this or any other piece of
Presonus equipment, please fell free to contact us!
Please pay close attention to how you connect your TubePRE to your
system. Improper grounding is the most common cause of noise
problems found in studio or live sound systems. We urge you to scan
this manual before hooking up your TubePRE to familiarize yourself
with its features and various applications.
Good luck and enjoy your TubePRE!
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1.2 Features
The following is a summary of your TubePRE's features:
Dual-Servo Gain Stage
Your TubePRE contains a dual-servo gain stage (no capacitors).
This provides ultra-low noise performance and wide dynamic
control. This gives the TubePRE the ability to boost the desirable
signal without increasing unwanted background noise.
Phantom Power
When the phantom power switch is engaged, power is supplied at
a constant rate. This assures optimum performance of your
condenser microphone and that the signal will be free of distortion
due to insufficient power.
Phase Reverse
This switch enables the user to invert the phase of a microphone if
phase cancellation is noticed when using identical microphones in
close proximity to one another. The phase reverse switch can also
compensate for different XLR connector hook-ups where pin
connections have been inverted.
-20dB Pad
A -20dB pad is available for reducing the incoming signal level.
This pad provides a more manageable signal from high output
devices giving the operator greater control over the incoming
signal and a much reduced chance of over-driving the input and
thereby avoiding distortion.
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80Hz Rumble Filter
A rumble filter is available to eliminate low frequency noise. This
lets you greatly reduce background noise from things such as air
conditioners or wind noise with the flick of a switch without
affecting the desired frequencies.
Mic/Instrument Input
The TubePRE has a separate XLR and 1/4” connector on the back
of the chassis for signal input from microphones (XLR) or
instruments (1/4”).
Drive
The TubePRE provides a Drive potentiometer for controlling the
amount of signal routed to the 12AX7 vacuum tube. This feature
lets you control the amount of tube saturation. Greater levels of
tube saturation give the signal greater warmth and a richer sound.
This works equally well on mics and instruments.
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2.1 CONTROLS & CONNECTIONS
2.2 Front Panel
The TubePRE front panel has the following features:
Phantom Power Switch (+48v)
Phase Reverse Switch
Drive Control (0 to 20dB)
-20db Pad
Gain Control (0 to 40dB)
80Hz filter
Backlit VU meter
2.3 Preamplifier Section
Phantom power is available for the input of the TubePRE. The 48 volts
are supplied through the XLR connector for condenser mics and any
other devices requiring continuous power (through the XLR input).
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XLR wiring for phantom power
PIN 1
PIN 2
PIN 3
GND
+48v
+48v
Phase Reverse Switch
Allows the user to invert the polarity of the XLR connector by switching
pins two and three. The inversion of the pins of the XLR connector may
be necessary to alter the audio phase of two like microphones to
compensate for phase cancellation. It may be required that the wiring
of a cable’s XLR connector be switched to successfully utilize phantom
power.
-20dB Pad
Provides -20 decibels of attenuation with the push of a button. This is
a very useful feature for rapidly reducing the level coming into the
TUBEPRE and thus preventing the input signal from distorting the
input. This may occur due to a high output level from a microphone or
line device. Padding the input provides increased “headroom” for the
operator.
Drive
The TubePRE drive control increases the amount of signal routed
through the 12AX7 vacuum tube. (The gain controls overall volume,
whereas the drive controls volume routed through the tube.) The
effect achieved by this procedure can be subtle to extreme, depending
on the setting being used. A “warming up” of the sound can be noticed
at lower settings. This desirable effect is especially good for
microphones and on an electric bass and the resulting sound is
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infinitely richer and sweeter. An overdriven signal can be achieved by
significantly raising the level of the drive control. This overdriven tube
effect is extremely useful in providing distorted guitar and for creating
that authentic “blues harp” vibe (harmonica). The possibilities of the
drive control are limited only to your application and your imagination.
Gain
This control governs the amount of boost to the signal being processed
by the preamplifier. Dynamic mics and instruments without preamps
normally require more gain than condenser mics and instruments that
have a built-in preamp (care should be taken with instruments having
their own built-in preamp not to overdrive the input of the TubePRE).
Increasing the gain should provide the signal that is needed from the
preamp for a hotter (louder) recording level.
2.4 Back Panel
XLR wiring for input and output
PIN 1
PIN 2
PIN 3
GND
High
Low
(+)
(-)
The output XLR is balanced
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1/4” phone plug wiring input and output
TIP High (+)
SLEEVE GND (-)
The output 1/4” phone plug is unbalanced
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3.1 OPERATION
3.2 Dynamic Microphones
Lower output levels characterize dynamic microphones, so more gain
is needed to achieve sufficient operating levels. Occasionally it is
necessary to add the -20dB pad to the microphone to avoid distortion
(e.g. when recording percussion). Do not use phantom power when
using dynamic microphones.
3.3 Phantom Powered Microphones
Phantom powered microphones such as condenser and some ribbon
microphones require external power to preamplify the microphone.
These microphones typically have much higher output than dynamic
microphones. Therefore the -20dB pad is almost always necessary
when close mic-ing to avoid clipping (overdriving) the preamplifier.
3.4 Instrument Input
The instrument input is designed to handle 1/4” plugs from
instruments such as guitars and basses. This instrument input is an
ultra high impedance amplifier designed to allow the full audio
potential of an acoustic or electric instrument pickup. Plugging a
preamplified signal (line level) into the TubePRE is not recommended.
3.5 Some Thoughts on Vacuum Tubes
The TubePRE comes supplied with a 12AX7 vacuum tube that meets or
exceeds the stated performance criteria for the unit. We expect some
owners of the TubePRE will try different tubes to investigate the
various performance possibilities they might provide. Remember, tube
life and performance are affected by how often a tube is used and by
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how hard the tube is driven when in use. Signs of wear may be
exhibited by poor performance or by the tube becoming “microphonic”.
Periodic replacement of the vacuum tube is recommended. The time
between the suggested replacements varies greatly with use. If you
notice deterioration in sound quality then it’s time to change the tube.
Replacing the tube in the TubePRE
1. Unplug the unit. Proceed with caution, as the tube could be hot.
Remove the two screws from the top and the two screws from the
bottom of the unit. Also remove the two screws that surround each of
the XLR plugs.
2. Carefully remove the plastic hex nut that is on the unbalanced
output and the instrument input.
3. Remove the left side panel.
4. Remove the black chassis.
5. Place your thumb on the backside of the card that holds the tube
and carefully unplug the tube.
6. Align the pins of the new tube and place it in the socket with your
thumb again on the back of the tube socket card. Make sure that the
tube is completely seated in the receptacle.
7. Replace the chassis, side, hex nuts and screws.
3.6 Application Guide
Direct Box
The 1/4” and XLR outputs can always be used simultaneously. The
instrument should be plugged into the 1/4” instrument input. The 1/4”
output can be connected to an amplifier on stage and the XLR output
could be connected to the PA system or monitoring mixer.
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With a compressor/EQ/dynamics processor
When running the Tube Pre in conjunction with other processors it is
recommended that the TubePRE be the first unit in the chain. The
other units should be connected to the output (either XLR or 1/4”) of
the TubePRE. Most compressors require that the signal be preamplified
before they are connected. This simply means that the signal is loud
enough for the compressor to process it. In most cases (and there are
exceptions) if you were to plug a microphone/guitar directly into a
compressor the signal will be too low (essentially too quiet) for the
device to process it.
On Recording
When using the TubePRE as a front end for a recording device (such as
the Presonus FIREstation), it is important to watch your output levels.
For example, using the TubePRE for distortion (turning up the gain and
tube drive REAL HIGH) could overload the inputs of the recording
device. In this scenario it is necessary to limit the output level of the
TubePRE. This can be accomplished by using a compressor/limiter
(such as the Presonus BlueMAX).
3.6 FAQ/Troubleshooting
Can I switch the tube?
The TubePRE’s tube can be switched as long as it is a 12AX7. Proper
caution must be taken when switching the tube. Please refer to Section
3.5 of this manual for further directions on changing the tube or check
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If the voltage on the back of my TubePRE does not match the
voltage listed on the power supply what do I do?
The voltage on the TubePRE’s external power supply may change. If
the power supply came factory sealed with the unit, then it is the right
power supply. If the power supply did not come with the unit it is
recommended that it not be used. If your power supply is damaged or
missing, please consult your salesperson or call Presonus.
Can I use a higher/lower/alternate voltage power supply that
was not supplied with my TubePRE?
Use of any power supply that was not included with the unit voids the
warranty of the TubePRE and may cause damage to the unit or the
user. It is strongly recommended that you refer any service issues to
Presonus.
Can the TubePRE be rack mounted?
for rack mounting instructions and to locate the appropriate rack
mount adaptor.
Can I use a different size/style tube in the TubePRE?
The only tube that can be used in the TubePRE is a 12AX7. Any
variation can cause damage to the unit/user and voids the warranty.
Please refer to Section 3.5 of this manual for further directions on
changing the tube. It is strongly recommended that you refer any
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Can I plug my keyboard/CD player/etc into the TubePRE?
It is not recommended that any LINE LEVEL items be plugged into the
TubePRE. This scenario will not cause damage to the unit. However, it
may cause the signal to distort or sound unpleasant. The reason is
that the signal being fed into the unit is too loud for the TubePRE. This
may cause the unit to distort (In some cases this may be the desired
effect).
Whenever I turn up the tube drive all the way my signal sounds
distorted. Why is this?
The tube drive feeds the signal into the tube. The more signal that is
applied to the tube, the greater the chances of distortion. However, to
some this sounds nice on guitar or other instruments. In certain
applications the tube drive is not needed (for example, while recording
books on tape). In other applications, the tube drive can be mixed with
the gain to create desirable effects (think of the tube drive as extra
gain with added equalization).
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9.1 TECHNICIAL SPECIFICATIONS
Preamp Bandwidth..................................................... 10Hz to 50kHz
Number of Channels .................................................................One
Performance
THD + Noise (Unweighted) ......................... 0.05% @ 0dB Tube Drive
................................................................. 10% @ 20dB Tube Drive
Noise Floor ......................................................................... -94dBu
Signal to Noise..................................................................... >90dB
Power Supply Rejection......................................................... >98dB
Amplifier Type................................................................ Dual Servo
Input
Connectors................................................................. XLR and 1/4”
Input Impedance, XLR .................................................... 1.3k Ohms
Input Impedance, High Z 1/4”......................................... 1Meg Ohms
Output
Output Impedance, XLR Balanced........................................51 Ohms
Output Impedance, 1/4”TRS Unbalanced ..............................51 Ohms
Panel Controls
Tube Drive ................................................................ 0dB to +20dB
Gain ......................................................................... 0dB to +40dB
Phase Reversal
- 20dB Pad
+ 48V Phantom Power
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Metering
VU Meter.............................................................. -20dBu to +3dBu
Clip LED............................................................................ +20dBu
Power Supply
Type..................................................... Linear/External Transformer
Input.....................................................................16 VAC/1000mA
Power ............................................................................ 16 WATTS
Physical
Weight...................................................................................4lbs.
Size.............................................................................. 1/3 U Rack
Dimensions.........................................................5.5” X 5.5” X 1.75”
Mounting..................................................Universal Rack Tray Insert
Chassis ..................................................................................Steel
Front Panel......................................................... Brushed Aluminum
Side Panels.................................................... Ribbed Cast Aluminum
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