Presonus Audio electronic Microphone TubePre User Manual

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  
ii  
 
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  
iii  
 
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.  
2
 
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.  
3
 
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).  
4
 
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  
5
 
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  
6
 
1/4” phone plug wiring input and output  
TIP High (+)  
SLEEVE GND (-)  
The output 1/4” phone plug is unbalanced  
7
 
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.  
9
 
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  
10  
 
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  
11  
 
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  
13  
 
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  
14  
 

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