Presonus Audio electronic Stereo Amplifier Single Channel Tube User Manual

DigiTUBE  
Single-Channel Tube Mic-Preamplifier  
with S/PDIF Output  
USER’S MANUAL 1.1  
Copyright © 2001, PreSonus Audio Electronics, Inc.  
ALL RIGHTS RESERVED  
 
OVERVIEW 1  
1.1 INTRODUCTION  
Thank you for purchasing the PreSonus DigiTUBE Single-Channel Tube Mic-  
Preamplifier with S/PDIF Output. This preamp was designed using state of the  
art components to deliver crystal clear audio for an indefinate period of time.  
We believe the DigiTUBE to be an exceptional sounding unit and an exceptional  
value.  
Please contact us at 1-800-750-0323 with your questions or comments regard-  
ing this product. PreSonus Audio Electronics, Inc. is committed to constant  
product improvement and believes the best way to accomplish this task is by  
listening to the experts on our gear, our valued customers. We appreciate the  
support you have shown us through the purchase of this product.  
Please pay close attention to how you connect your DigiTUBE 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 DigiTUBE to familiarize yourself with its features and applications.  
Good luck and enjoy your DigiTUBE!  
1
 
1 OVERVIEW  
1.2 FEATURES  
The following is a summary of your DigiTUBE’s features:  
Dual Servo Gain Stage  
Your DigiTUBE contains a dual servo gain stage (no capacitors). This design  
provides ultra low noise performance and wide dynamic control. The DigiTUBE  
can boost the desirable signal without increasing unwanted background noise.  
Mic/Instrument/Line Input  
The DigiTUBE has a Neutrik™ combo (XLR & ꢀ”) connector. The XLR input can  
be used for microphone signals and phantom power is available for condenser  
mics when the 48V switch is engaged. The XLR will also accept line level signals  
when the PAD/LINE switch is engaged. The ꢀ” input will accept instrument level  
signals, only. The PAD/LINE switch has no effect on the ꢀ” input and it should  
be understood that the ꢀ” input is not designed to accept line level signals.  
Pad/Line  
A switch on the front panel may be used to engage a -20dB pad for mic level  
signals or change the XLR input operating level from mic to line. Using the -  
20dB 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, thereby avoiding distortion.  
48V  
The DigiTUBE has 48V phantom power available. Phantom power assures  
optimum performance from your condenser microphone without the need of  
an external power supply. A 80Hz switch is provided on the front panel of the  
DigiTUBE that enables the user to insert an 80Hz filter. Often referred to as a  
rumble filter, this feature is useful for eliminating bothersome low-end sounds  
such as air conditioning noise without greatly altering the desired audio.  
Parametric Equalizer  
The equalizer section is equipped with three dual concentric potentiometers  
The outer control selects the frequency and the inner control boosts/cuts the  
selected frequency. The EQ controls are LOW, MID, HI from left to right. The  
bandwidths are broad enough and have enough overlap to allow a very effective  
contour of the incoming audio signal.  
2
 
OVERVIEW 1  
Drive  
The DigiTUBE is provided with a DRIVE potentiometer for controlling the amount  
of signal routed through the 12AX7 vacuum tube. This feature lets you control  
how much saturation of the signal occurs. Greater levels of tube saturation give  
the signal greater warmth and a richer sound. This feature works equally well  
on mics and instruments and is just what is needed to tame that ‘brittle’ sound  
encountered with different types of digital media.  
Internal Clock  
An internal clock is provided for 44.1 kHz or 48 kHz operation selectable by way  
of the switch on the back panel. An INTERNAL/EXTRERNAL selector and a BNC  
connector for external clock input can be found on the back panel as well as the  
S/PDIF connector for the DigiTUBE’s digital output.  
3
 
2 CONTROLS & OPERATION  
2.1 FRONT PANEL  
The front panel of the DigiTUBE contains:  
POWER  
OUTPUT LEVEL (dBu)  
-42 -36 -30 -24 -18 -12 -6  
-3  
0
3
6
9
12 15 18 24  
TUBE PREAMP  
5
EQUALIZER  
0
120  
0
0
5k  
24  
2k  
PAD/  
LINE  
EQ  
IN  
48V  
80Hz  
0
10  
3
48  
30  
1k  
+12  
900  
5k  
+12  
3k  
-12  
15k  
+12  
-12  
-12  
DRIVE  
GAIN (dB)  
LOW  
MID  
HIGH  
MIC/INSTRUMENT  
LINE  
LEVEL  
FREQ  
The front panel of the DigiTUBE is divided into two sections: the tube preamp  
controls are located on the left hand side of the unit’s front panel and the  
equalizer section is on the right.  
2.1.1 TUBE PREAMP SECTION  
Neutrik™ Combo Microphone (XLR) / Instrument (ꢀ”) Input  
Drive Control  
Pad/Line Switch  
Gain Control (3dB - 48dB)  
+48V Phantom Power Switch  
Mic/Line/Instrument Input  
The DigiTUBE has a Neutrik™ combo connector which provides both an XLR and  
a ꢀ” TS input. The XLR connector can accept microphones or by engaging the  
PAD/LINE switch, line level signals. The ꢀ” input is for instrument level signals  
only. If you wish to adapt a line level device with a ꢀ” connector, An XLR  
connector with pins 1 and 3 tied together for ground and the hot connected to  
pin 2 must be made. This adapts the unbalanced line level cable to input signal  
via the XLR input and the PAD/LINE switch to convert the input to accept a line  
level signal.  
Drive  
The DRIVE potentiometer controls how much signal  
5
is routed through the 12AX7 vacuum 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  
0
10  
effect can be used to compensate for the harsh-  
ness commonly encountered in digital signals with  
4
 
CONTROLS & OPERATION 2  
the resulting sound possessing a ‘richer’ and ‘sweeter’ tone. If an overdriven  
signal is desired, this can be achieved by significantly raising the level of the  
DRIVE control. Overdriving the tube is especially useful for direct electric guitar  
sounds. Setting the DRIVE control is a matter of taste; the amount of saturation  
needed to achieve a desired result depends upon the resulting sound you want  
to hear. Experiment!  
Gain  
This control is used to determine the amount that a  
24  
signal being processed by the pre-amplifier is increased  
in level at output. Dynamic mics and instruments  
without pre-amps may require more gain than con-  
denser mics and instruments that have a built-in  
3
48  
pre-amp (care should be taken with instruments having  
their own built-in pre-amp not to overdrive the ꢀ”  
input of the DigiTUBE). Line level signals can only be processed through the  
XLR input connector with the PAD/LINE switch in the LINE position. Attempt-  
ing to use the ꢀ” input for line level signals exceeds the design parameters of  
the DigiTUBE. The ꢀ” input of the Neutrik™ connector is designed to accept  
instrument level signals and attempting to use the ꢀ” input for line level will  
likely yield an unsatisfactory result. Activating the PAD/LINE switch reduces the  
incoming signal by 30dB. This is a very useful feature for rapidly reducing the  
level coming into the DigiTUBE to prevent the input signal from over-modulat-  
ing (distorting). This may occur due to a high output level from a microphone.  
Padding the mic input serves to provide increased ‘headroom’ for the operator  
and allow greater variance in adjusting the GAIN control. Placing the switch  
to the PAD/LINE position allows the XLR connector to accept line level signals.  
Line level signals can be used in the XLR input without overdriving the input.  
Keyboards and other line level devices can be inserted into the DigiTUBE XLR  
input by selecting the LINE position.  
Note: the PAD/LINE switch does not affect the ꢀ” input of the Neutrik™  
connector. The ꢀ” input is designed to accept instrument level signals ONLY!  
5
 
2 CONTROLS & OPERATION  
Input  
Phantom power is available through the XLR input of the  
DigiTUBE. This 48V of phantom power is for condensor mics  
and/or any other devices that may require it via XLR inputs.  
1
2
3
PIN 1 = GND  
PIN 2 = + (+48V)  
PIN 3 = - (+48V)  
2.1.2 EQUALIZER SECTION  
Low (30Hz - 1kHz) +/- 12dB  
Mid (900Hz - 5kHz) +/-12dB  
High (3kHz - 15kHz) +/-12dB  
80Hz Switch  
EQ IN Switch  
Low  
0
The LOW control is a dual concentric potentiometer  
120  
with the outer ring allowing the selected frequency to  
be boost or cut by as much as twelve decibels. The  
straight up, twelve o’clock, position is labeled zero  
(0). When the outer control knob is in this position,  
no effect is exerted on the signal, regardless of what  
30  
1k  
+12  
-12  
frequency is selected with the inner controller. Rotating the outer control knob  
to the left or counter-clockwise reduces the selected frequency. Rotating the  
outer controller to the right or clockwise increases the selected frequency. The  
inner control knob selects the frequency. The LOW EQ control goes from 30Hz  
to 1kHz. The control frequency is narrower to the fully counter-clockwise or left  
side. As the inner control is rotated clockwise, the frequency bandwidth is much  
more broadly defined.  
For example, from the fully counter-clockwise position of 30Hz to the first mark  
represents a difference of 10Hz - 15Hz whereas from fully clockwise or 1kHz to  
the first marked position back represents as much as a 100Hz difference. The  
significance of this to the operator is that a movement of the frequency selector  
from a fully counter-clockwise position to approximately the twelve o’clock  
position represents smaller incremental frequency changes compared to the fre-  
quency changes that occur when the selector travels clockwise past the twelve  
o’clock position and beyond.  
6
 
CONTROLS & OPERATION 2  
Mid  
0
The dual concentric potentiometer labeled MID controls  
the frequencies from 900Hz to 5kHz. The outer ring  
provides boost or cut at the frequency selected by the  
inner knob by plus or minus twelve decibels with the  
straight-up noon position equal to zero or no boost or  
cut. The inner control knob begins at 900Hz in the left  
2k  
900  
5k  
+12  
-12  
or fully counter-clockwise position and continues to 5kHz in the right or fully  
clockwise position. This control behaves in the same manner as the LOW control  
with the frequency widths delineated by the knob’s markings becoming wider as  
the knob travels to the right or the clockwise direction.  
High  
0
The Equalizer dual concentric control labeled HIGH  
5k  
operates in the same manner as the LOW and MID  
controller. The inner HIGH control knob is used to  
boost or cut frequencies ranging from 3kHz to 15kHz  
3k  
15k  
+12  
by as much as 12dB by adjusting the outer ring of the  
controller.  
-12  
80Hz Switch  
The DigiTUBE equalizer section contains a switch labeled 80Hz. Engaging this  
switch activates an 80Hz filter (often referred to as a rumble filter). This filter is  
useful for eliminating extraneous low-end sounds from the signal being ampli-  
fied. Frequencies from 80Hz and below are cut from the incoming signal. This  
will eliminate low-frequency noises such as air-conditioning hum or the sounds  
of nearby traffic or other vibrations that may be transmitted through the micro-  
phone stand into the microphone. It can also be useful for reducing the effect of  
electrical hum that may be the result of grounding problems.  
EQ In  
The EQ IN switch provides the ability to audition the effect that the equalizer is  
having on the signal being processed. Pushing the switch to the latched position  
inserts the equalizer into the signal path. Releasing the switch takes the EQ out  
of the signal path. You can quickly judge the effect your efforts at adjusting the  
equalization of the incoming signal are achieving and rapidly compare it to the  
un-equalized signal.  
7
 
2 CONTROLS & OPERATION  
OUTPUT LEVEL (dBu)  
-42 -36 -30 -24 -18 -12 -6  
Metering  
-3  
0
3
6
9
12 15 18 24  
The DigiTUBE has a 16 step LED meter to observe output level. The meter  
begins at -42dbu and goes to +24dbu (clip). A red LED is also provided on the  
front panel to indicate when the unit has power and is ready for operation.  
8
 
CONTROLS & OPERATION 2  
2.2 BACK PANEL  
The back panel of the DigiTUBE contains:  
Ext. Clock Input  
Sleeve = GND  
Ring = Input  
Tip = Output  
POWER  
18 VAC  
Clock  
Sync  
DIGITUBE  
Created, Designed and  
48  
44.1  
ext.  
int.  
Manufactured In The USA  
by PreSonus Audio Electronics, Inc.  
S/PDIF  
Insert  
Balanced Output  
The back panel of the DigiTUBE is divided into a digital and an analog section.  
2.2.1 DIGITAL SECTION  
S/PDIF Digital Output (RCA)  
External Clock Input (BNC)  
Clock switch (44.1k and 48k)  
Sync switch (Internal and External)  
2.2.2 ANALOG SECTION  
TRS Insert  
The ꢀ” TRS Insert connector operates at line level.  
Tip  
Sleeve  
Sleeve  
Ring  
Tip  
TIP = Output  
RING = Input  
SLEEVE = GND  
Ring  
Cable Wiring Diagram for ꢀ” TRS Insert  
XLR Output Jack  
The output XLR connector is servo balanced and operates  
at 0 = 0dB. It should be noted that the output signal  
available on Channel 1 and Channel 2 are identical mono  
outputs, not stereo.  
1
2
3
PIN 1 = GND  
PIN 2 = High (+)  
PIN 3 = Low (-)  
9
 
2 CONTROLS & OPERATION  
2.3 VACUUM TUBES  
The DigiTUBE comes supplied with a 12AX7 vacuum tube that provides excel-  
lent performance characteristics. We encourage owners of the DigiTUBE to try  
different brands of 12AX7 vacuum tubes to investigate the various performance  
possibilities they might provide.  
2.3.1 REPLACING THE VACUUM TUBE  
1. Disconnect the DigiTUBE from it’s electrical outlet.  
2. Remove the six screws that attach the top of the unit’s chassis. The vacuum  
tube is mounted in a horizontal fashion in the middle of the DigiTUBE’s body.  
3. Carefully remove the vacuum tube from it’s receptacle. Be sure to hold the  
socket in place while gently wiggling the vacuum tube out.  
4. Insert the replacement vacuum tube into the receptacle. Care should be  
taken to properly align the pins on the vacuum tube to the corresponding holes  
in the receptacle. (Caution should also be taken to not break the circuitboard.)  
5. Replace the top of the DigiTUBE.  
6. Restore power to the unit and resume operation.  
Remember, tube life and performance are affected by how often a tube is  
used and by 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 interval for tube  
replacement may vary greatly. If you notice deterioration in sound quality then  
it’s probably time to change the vacuum tube.  
2.4 POWER SUPPLY  
This unit is supplied with an external power supply designed to operate at the  
required voltage of the country where the retail sale occurred. Use of a power  
supply other than one supplied with the unit constitutes an infringement of the  
warranty and effectively voids it. Use of an improper power supply may damage  
the unit and could pose serious danger of electrical shock or fire.  
10  
 
CONTROLS & OPERATION 2  
11  
 
4 TECHNICAL SPECIFICATIONS  
Number of Channels ............................................................................ One  
Performance  
THD + Noise (Unweighted) ......................................................0.05% @ 0dB  
Tube Drive..............................................................................10% @ 30dB  
Noise Floor .....................................................................................-94dBu  
Signal to Noise................................................................................ >90dB  
Power Supply Rejection.................................................................... >98dB  
Amplifier Type............................................................................Dual Servo  
Input  
Connectors....................................................................... Neutrik™ Combo  
Input Impedance, XLR .................................................................. 5k Ohms  
Input Impedance, High Z ꢀ”...................................................... 1Meg Ohms  
Output  
Output Impedance, XLR Balanced................................................... 51 Ohms  
Output Impedance, ꢀ” TRS Insert..................................................Tip = Out  
Ring = In  
Sleeve = GND  
Digital...................................................................... S/PDIF RCA Connector  
Front Panel Controls  
Tube Drive............................................................................ 0dB to +30dB  
Gain .......................................................................... 0dB to +40dB - 20dB  
Pad...........................................................................+ 48V Phantom Power  
EQ..................................................................................... In/Out Selector  
Low........................................................................................30Hz - 1kHz  
Mid.......................................................................................900Hz - 5kHz  
High ..................................................................................... 3kHz - 15kHz  
Metering  
8 Segment LED...............................................................-28dBu to +18dBu  
Power Indicator................................................................................... LED  
Back Panel Controls  
Sample Rate Selector..........................................................44.1kHz / 48kHz  
Internal / External Clock...............................................44.1kHz / 48kHz only  
12  
 
TECHNICAL SPECIFICATIONS 4  
Power Supply  
Type .....................................................................................Linear Supply  
Input................................................................................18 VAC/1000mA  
Power ..........................................................................................15 Watts  
Physical  
Weight.............................................................................................. 8lbs.  
Size............................................................................................ Ω U Rack  
Dimensions..........................................................................8” X 5” X 1.75”  
Mounting..............................................................Universal Rack Tray Insert  
Chassis .............................................................................................Steel  
Front Panel.....................................................................Brushed Aluminum  
As a commitment to constant improvement, PreSonus reserves the right to change any  
specification stated herein at any time in the future without prior notification.  
13  
 
5 PRESONUS LIMITED WARRANTY  
IN THE UNITED STATES  
PreSonus Audio Electronics Inc. warrants this product to be free of defects in material  
and workmanship for a period of one year from the date of original retail purchase.  
This warranty is enforceable only by the original retail purchaser. To be protected by this  
warranty, the purchaser must complete and return the enclosed warranty card within 14  
days of purchase. During the warranty period PreSonus shall, at its sole and absolute  
option, to either repair or replace, free of charge, any product that proves to be defective  
on inspection by PreSonus or its authorized service representative. To obtain warranty  
service, the purchaser must first call or write PreSonus at the address and telephone  
number printed below to obtain a Return Authorization Number and instructions of where  
to return the unit for service. All inquiries must be accompanied by a description of  
the problem. All authorized returns must be sent to the PreSonus repair facility postage  
prepaid, insured and properly packaged. PreSonus reserves the right to update any unit  
returned for repair. PreSonus reserves the right to change or improve the design of the  
product at any time without prior notice. This warranty does not cover claims for damage  
due to abuse, neglect, alteration or attempted repair by unauthorized personnel, and is  
limited to failures arising during normal use that are due to defects in material or workman-  
ship in the product. Any implied warranties, including implied warranties of merchantability  
and fitness for a particular purpose, are limited in duration to the length of this limited  
warranty. Some states do not allow limitations on how long an implied warranty lasts,  
so the above limitation may not apply to you. In no event will PreSonus be liable for  
incidental, consequential or other damages resulting from the breach of any express or  
implied warranty, including, among other things, damage to property, damage based on  
inconvenience or on loss of use of the product, and, to the extent permitted by law,  
damages for personal injury. Some states do not allow the exclusion of limitation of  
incidental or consequential damages, so the above limitation or exclusion may not apply  
to you. This warranty gives you specific legal rights, and you may also have other rights,  
which vary form state to state. This warranty only applies to products sold and used in  
the United States of America. For warranty information in all other countries please refer  
to your local distributor.  
PreSonus Audio Electronics, Inc.  
7257 Florida Blvd.  
Baton Rouge, LA 70806  
(225) 216-7887  
Copyright © 2001, PreSonus Audio Electronics, Incorporated. All rights reserved.  
14  
 
PRESONUS LIMITED WARRANTY 5  
OUTSIDE OF THE UNITED STATES  
PreSonus Audio Electronics products are warranted only in the country where originally  
purchased, through the authorized PreSonus distributor in the country of original purchase,  
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 in the country of original  
retail purchase, 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 St.  
Baton Rouge, LA 70806  
(225) 216-7887  
Copyright © 2001, PreSonus Audio Electronics, Incorporated. All rights reserved.  
15  
 

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