MINI-TUBE
User's Manual
MINI-TUBE
MONO TUBE PREAMP
R
LTO
www.altoproaudio.com
Version 1.0 August 2004
English
SAFETY RELATED SYMBOLS
External Connection
CAUTION
Always use proper ready-made insulated
mains cabling (power cord). Failure to do
so could result in shock/death or fire. If
in doubt, seek advice, from a registered
electrician.
RISK OF ELECTRIC SHOCK
DO NOT OPEN
This symbol, wherever used, alerts
you to the presence of un-insulated
and dangerous voltages within the
product enclosure. These are voltages
that may be sufficient to constitute the
risk of electric shock or death.
Do not Remove any Covers
Within the product are areas where high
voltages may present. To reduce the risk
of electric shock do not remove any
covers unless the AC mains power cord
is removed.
Covers should be removed by qualified
service personnel only.
No user serviceable parts inside.
This symbol, wherever used, alerts
you to important operating and maintenance instructions. Please read.
Protective Ground Terminal
AC mains (Alternating Current)
Hazardous Live Terminal
Fuse
ON: Denotes the product is turned on.
OFF: Denotes the product is turned off.
To prevent fire and damage to the
product, use only the recommended
fuse type as indicated in this manual.
Do not short-circuit the fuse holder.
Before replacing the fuse, make sure
that the product is OFF and disconnected
from the AC outlet.
WARNING
Describes precautions that should be
observed to prevent the possibility of
death or injury to the user.
CAUTION
Protective Ground
Describes precautions that should be
observed to prevent damage to the
product.
Before turning the product ON, make sure
that it is connected to Ground. This is to
prevent the risk of electric shock.
Never cut internal or external Ground wires.
Likewise, never remove Ground wiring
from the Protective Ground Terminal.
WARNING
Power Supply
Ensure that the mains source voltage (AC
outlet) matches the voltage rating of the
product. Failure to do so could result in
damage to the product and possibly the user.
Unplug the product before electrical storms
occur and when unused for long periods of
time to reduce the risk of electric shock or
fire.
Operating Conditions
Always install in accordance with the
manufacturer's instructions.
To avoid the risk of electric shock and
damage, do not subject this product to
any liquid/rain or moisture. Do not use this
product when in close proximity to water.
1
Do not install this product near any direct
heat source.
Do not block areas of ventilation. Failure
to do so could result in fire.
Keep product away from naked flames.
IMPORTANT SAFETY INSTRUCTIONS
Read these instructions
Follow all instructions
Keep these instructions. Do not discard.
Heed all warnings.
Only use attachments/accessories
specified by the manufacturer.
Power Cord and Plug
Do not tamper with the power cord or plug.
These are designed for your safety.
Do not remove Ground connections!
If the plug does not fit your AC outlet seek
advice from a qualified electrician.
Protect the power cord and plug from any
physical stress to avoid risk of electric shock.
Do not place heavy objects on the power
cord. This could cause electric shock or fire.
Cleaning
When required, either blow off dust from
the product or use a dry cloth.
Do not use any solvents such as Benzol
or Alcohol.
For safety, keep product clean and free
from dust.
Servicing
Refer all servicing to qualified service
personnel only.
Do not perform any servicing other than
those instructions contained within the
User's Manual.
2
Preface
Dear Customer,
Thanks for choosing LTO Mini-Tube Mono Preamplifier and thanks for choosing one
of the results of
LTO AUDIO TEAM job and researches.
For our LTO AUDIO TEAM, music and sound are more than a job...are first of all
passion and let us say...our obsession!
We have been designing professional audio products for a number of years in cooperation
with many of the world's major brands in audio field.
The LTO line presents unparalleled analogue and digital products made by Musicians
for Musicians in our R&D centers in Italy, Netherlands, United Kingdom and Taiwan.
We provide you with world -class designs, while our software development teams continue
.to develop and impressive range of audio specific algorithms.
Because we are convinced you are the most important member of LTO AUDIO TEAM
and the one confirming the quality of our job, we would like to share with you our work
and our dreams, pay attention to your suggestions and your comments. Following this
idea we create our products and we will create the new ones! From our side, we guarantee you and we will supply you also in future the best quality, and the best fruits of
our continuous researches and the best prices.
Our Mini-Tube Mono Preamplifier is the result of many hours of listening and tests
involving common people, area experts, musicians and technicians. The result of this
effort is a half rack space unit, the heart of which is an extremely low-noise microphone
pre-amp circuit that uses discrete components to produce a highly transparent sound.
Nothing else to add, but that we would like to thank all the people that made the LTO
Mini-Tube Preamplifier a reality available to our customers, thank our designers and
all the LTO staff, there to make possible the realization of products containing our
idea of music and sound and there to support you, our customers, in the best way, conscious that you are our best richness.
Thank you very much.
LTO AUDIO TEAM
3
TABLE OF CONTENT
1. INTRODUCTION ............................................................................................5
2. FEATURE LIST ..............................................................................................5
3. CONTROL ELEMENTS .................................................................................5
3.1 The Front Panel
a. Guidepost of The Front Panel
b. Supplementary Descriptions
3.2 The Rear Panel
a. Power Supply Connection
b. Analogue Inputs/Outputs
4. INSTALLATION & CONNECTION..................................................................8
4.1 Mains Connection
4.2 Audio Connection
a. Wiring Configuration
b. In Line Connection
4.3 Rack Mounting
5. APPLICATIONS..............................................................................................9
5.1 The Mini-Tube as A Microphone Preamplifier
5.2 The Mini-Tube as A Direct-Injection Box (DI Box)
5.3 The Mini-Tube as A Level Translator
6. TECHNICAL SPECIFICATIONS .................................................................11
6.1 Block Diagram
6.2 Specifications
7. WARRANTY .................................................................................................13
4
1. INTRODUCTION
Thank you very much for expressing your confidence in LTO products by purchasing
our Mini-Tube Mono Preamplifier. With the Mini-Tube you have acquired an extremely
musical and flexible Mono Microphone Preamplifier which is based on many years of
experience and findings in amplifier technology and is used through the world in renowned
studios, sound reinforcement systems as well as in broadcast and television studios.
The LTO Mini-Tube meets highest and no-compromise requirements in terms of operation,
sound, specifications and workmanship.
The LTO Mini-Tube is a half rack space unit, the heart of the MINI-TUBE is an extremely
low-noise microphone pre-amp circuit that uses discrete components such as 12AX7WA
Tube and NJM4580 Quad Operational Amplifier IC to produce a highly transparent sound!
The switchable +48V Phantom Power supply allows you to operate your condenser microphone more conveniently.
2. FEATURE LIST
Half rack space
Robust and compact design
Servo microphone preamplifier
20dB pad
+48V phantom power
Phase reverse
VU meter
Clip LED
12AX7WA low-noise tube
XLR and 1/4" connectors for both input and output
High quality and fidelity components
SMD technology for top performance
Manufactured under QS9000, VDA6.1 certified management system
3. CONTROL ELEMENTS
3.1 The Front Panel:
(2)
MINI-TUBE
LTO
20
3
10
6
50
100
VU
0
(4)
(6)
3
TM
MONO TUBE PREAMP
5
PAD
LTO
POWER OUTPUT
PHASE
+48V
40
0
GAIN
(1)
(3)
5
80HZ
LOW CUT
(5)
20
0
DRIVE
CLIP
(7) (8)
a. Guidepost of the front panel
(1) VU Meter (volume indicator for output signal)
(2) 20dB PAD
(3) Phase Reverse Switch
(4) +48V Phantom Power Switch
(5) 80Hz Low Cut Switch (filter low frequencies below 80Hz)
(6) Gain Control (0 to +40 dB)
(7) Drive Control (0 to +20 dB)
(8) CLIP Indicator (indicating for clipped signal over +20dBu)
b. Supplementary Descriptions
- Phantom Power Switch (4):
This switch activates the +48 volts phantom power to supply condenser mics and
any other devices requiring continuous power by means of the XLR cable. The +48V
is applied both to the positive (pin2) and negative inputs (pin3) of the XLR connector:
Phantom
Power Supply
XLR Connector
PIN1 ( Ground )
PIN2 ( Positive )
PIN3 ( Negative )
GND
+48V
+48V
Caution: Please make sure that you are using an appropriate microphone before
you activate this switch to supply the +48V phantom power. Read the operating
instructions accompanying the microphone. Some condenser mics might need
another type of power supply, old dynamic microphones could be damaged by
the +48V voltage, and unbalanced microphones should never be operated in
combination with a +48V power supply.
- Phase Reverse Switch (3):
This Phase Reverse Switch reverses the audio signal's phase by 180 , Normally,
you won't need this switch, however, in some cases, it might be necessary, for
example: the inversion of the pins of the XLR connector may be necessary to
alter the audio phase of linked microphone 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 (2):
A 20dB Pad is designed to attenuate the incoming signal level to provide increased
"headroom" for the operator.
- Gain Control (6):
This control sets the amount of boost to the signal being processed by this preamplifier. Use this control to adapt the Mini-Tube to either home recording level
6
-10dBV ) or professional level (+4dbu). When the gain is too low, the tube effect
becomes less audible and the S/N (Signal to Noise) ratio deteriorates. Generally,
Dynamic mics and instruments without preamps will require more gain than condenser mics and instruments that have a built-in preamp. If you should require more
signal out of the preamp for a hotter recording level, cranking up the gain should
provide all the signal that you'll need.
To obtain the best possible S/N (Signal to Noise) ratio and subsequently the best
transparent sound, keep an eye on the VU Meter.
- Drive Control (7):
The effect achieved by this control can be subtle to extreme, depending on the
settings 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 infinitely richer and sweeter.
An over-driven signal can be achieved by significantly raising the level of the Drive
control. This over-driven tube effect is extremely useful in providing cool guitar
sounds and way cool for use with harmonicas for that authentic "Blues harp" vibe.
The limits on the possibilities of the Drive control are up to you, your application
and your imagination.
3.2 The Rear Panel
OUTPUT
18VAC~
POWER
INPUT
MODEL
SERIAL
BALANCED
UNBALANCED
BALANCED
UNBALANCED
a. Power Supply Connection
Please use the 18VAC AC/AC Adaptor provided by
Tube. Detail your can follow the illustration.
18VAC~
POWER
LTO to connect your Mini-
MODEL
SERIAL
IN
18VAC
b. Analogue Inputs / Outputs
The output XLR connector is servo balanced and operates at +4dBu. The output
1/4" Phone jack is unbalanced and operates at -10dBv.
7
4. INSTALLATION & CONNECTION
4.1 Mains Connection
- Please ensure that the LTO Mini-Tube Preamplifier is connected to the correct supply
voltage before operating this unit.
- Only use the 18VAC AC/AC Adaptor provided by LTO.
4.2 Audio Connection
The LTO Mini-Tube Preamp presents with balanced XLR connectors and 1/4" TRS
phone jack and it can be interfaced by several ways to support a variety of applications without any signal loss.
a. Wiring Configuration
Either the 1/4" TRS (Tip-Ring-Sleeve) phone jack or the XLR servo connector can
be wired in balanced and unbalanced modes, which will be determined by the
actual application status, Please wire your systems as the following examples:
For 1/4" Phone jack
+
-
+
Tip
Ring
Tip
+
Tip
Ring
Sleeve
Sleeve
TS Type Unbalanced
Sleeve
TRS Type Balanced
TRS Type Unbalanced
For XLR connector
Pin2 (+)
Pin3 (-)
(Linked to Pin1 manually,
Pin1 ( )
Pin2 (+)
Pin3 (-)
)
Pin1 ( )
XLR Type Unbalanced
XLR Type Balanced
b. In Line Connection
For these applications, the Mini-Tube Preamp provides XLR connector and
1/4" TRS phone jack to easily interface with most professional audio devices. Follow
the configuration examples below for your particular connection.
8
Balanced
Tip
Ring
Sleeve
SLEEVE RING TIP
TIP RING SLEEVE
3
3
1
1
2
2
1
3
2
TIP RING SLEEVE
Tip
Ring
Sleeve
1
2
1
2
3
3
Tip
Ring
1
2
3
Sleeve
Unbalanced
1
Tip
Ring
3
2
1
2
3
Sleeve
TIP RING SLEEVE
Tip
1
1
2
3
3
2
Sleeve
1
TIP SLEEVE
2
3
1
2
3
Cent r e
Screen
Tip
TIP SLEEVE
Tip
Sleeve
SLEEVE TIP
Sleeve
Tip
Ring
TIP RING SLEEVE
SLEEVE RING TIP
Tip
Ring
Sleeve
Sleeve
Tip
Cent r e
Sleeve
Screen
Tip
Ring
Centre
Sleeve
Screen
TIP SLEEVE
TIP RING SLEEVE
3
3
1
1
1
2
2
2
1
2
3
3
4.3 Rack Mounting
The most secure mounting is on a "universal" rack shelf, available from various
rack manufacturers or your music dealer. The Mini-Tube Preamplifier's height conforms
to single-space mounting, and up to two Mini-Tube Preamplifier may be mounted
side-by-side in a standard universal EIA 19" equipment rack.
MINI-TUBE
LTO
20
3
10
6
50
100
VU
0
3
TM
MONO TUBE PREAMP
PAD
LTO
POWER OUTPUT
PHASE
+48V
40
0
GAIN
80HZ
LOW CUT
DRIVE
3
10
6
50
100
VU
0
3
CLIP
TM
MONO TUBE PREAMP
5
PAD
LTO
20
0
MINI-TUBE
LTO
20
5
POWER OUTPUT
PHASE
+48V
40
0
GAIN
80HZ
LOW CUT
20
0
DRIVE
CLIP
5. APPLICATIONS
This section presents some typical applications of our LTO Mini-Tube Preamplifier.
Please reserve your time to well understand the application examples, so as to be able
to fully exploit this unit and its versatile features.
5.1 The Mini-Tube as A Microphone Preamplifier
It is the basic application for Mini-Tube.
Before you can use the LTO Mini-Tube as a Mono Microphone Preamplifier,
we recommend that you study the various functions of the unit first. The high gain
factors (+30dB) provided by the microphone preamplifier can produce extreme levels
9
on the output side, which may damage subsequent devices, so you should turn
down all the level controls beforehand, or you can press the 20dB PAD (2) to
attenuate the incoming signal level about 20dB, then hook up a microphone to the
XLR or 1/4" TRS Input connector, and use either the 1/4" jack or XLR output connector
to connect the audio system.
Now, power up the entire equipment, if you wish to use a condenser mic requiring
+48V phantom power, please press the Phantom Power Switch (4) (to avoid electric
damage, please read Control Elements "Phantom Power Switch" carefully). After
that, please adjust your Input Gain Control and Drive Control to get the best result.
5.2 The Mini-Tube as A Direct-Injection Box (DI Box)
When audio signals produced by instruments such as guitars, keyboards, etc. are
transported over long unbalanced lines, the transmission quality may be affected by
Hum or other interference signals included in the cable. So called DI Box are used to
solve this issue: the DI Box converts the unbalanced signal coming from the instrument
into a balanced signal that is sent over the line. Interference included in balanced
cables is then eliminated by a subsequent balanced input stage.
Using the LTO Mini-Tube as a Mono Microphone Preamplifier for this application is
very easy. Simply connect the line output of your instrument to the XLR or 1/4" TRS
Input jack on the rear panel of Mini-Tube, then use the Mini-Tube's balanced output
to send the signal to the next stage.
5.3 The Mini-Tube as A Level Translator
Semi-professional appliances in home recording system are normally operated with a
nominal level of 10dBV, while the level used in studios and other professional application
is 0dBu or +4dBu. So, when you connect devices of both types to each other, you
should consider some kind of level translators of course.
The LTO Mini-Tube Mono Microphone Preamplifier is pretty suited for this application.
The Input Gain control allows you to raise or lower your input signal level by as much
as 30dB. The functions Phase Inversion is also enabled in this mode.
10
6. TECHNICAL SPECIFICATIONS
A
A
3
2
1
1
2
2
4
Block Diagram
3
2
4
4
B
C
C
B
D
D
6.1 Block Diagram
11
6.2 Specifications
General
Performance
Preamp Bandwidth
Number of Channels
20Hz ~ 50KHz / 2dB
one
THD+Noise
0.05% @ GAIN +0dBu (A-Weighting)
Output Level (MAX)
+22dBu
-88dBu( 2dBu)
Noise Floor
Signal to Noise
Input
>108dBu
XLR and 1/4"
Connectors
Input Impedance, XLR
1.3K Ohms
Input Impedance, Hight Z 1/4 1Meg Ohms
Output
Output Impedance,
XLR Balanced
51 Ohms
Output Impedance, Hight
Z 1/4" TRS Unbalanced
51 Ohms
Panel Controls Tube Drive
0dB ~ +20dB
0dB ~ +40dB
Gain
Phase Reversal
-20dB Pad
+48V Phantom Power
Metering
Power Supply
Physical
VU Meter
-20dBu ~ +5dBu
Clip Led
+20dBu
Input
18VAC/1000mA
Power
12WATT
Weight
Size
0.7Kg
1U Rack
Dimension (W D H)
210mm 93mm 44mm
12
7. WARRANTY
7.1 Warranty registration card
To obtain Warranty Service, the buyer should first fill out and return the enclosed
Warranty Registration Card within 10 days of the Purchase Date.
All the information presented in this Warranty Registration Card gives the manufacturer a better understanding of the sales status, so as to purport a more effective
and efficient after-sales warranty service.
Please fill out all the information carefully and genuinely, miswriting or absence of
this card will void any of your warranty service.
7.2 Return notice
a. In case of return for any warranty service, please make sure that the product is
well packed in its original shipping carton, and it can protect your unit from any
other extra damage.
b. Please provide a copy of your sales receipt or other proof of purchase with the
returned machine, and give detail information about your return address and
contact telephone number.
c. A brief description of the defect will be appreciated.
d. Please prepay all the costs involved in the return shipping, handling and insurance.
7.3 Terms and conditions
a.
LTO warrants that this product will be free from any defects in materials and/or
workmanship for a period of 1 year from the purchase date if you have completed
the Warranty Registration Card in time.
b. The warranty service is only available to the original consumer, who purchased
this product directly from the retail dealer, and it can not be transferred.
c. During the warranty service, LTO may repair or replace this product at its own
option at no charge to you for parts or for labor in accordance with the right side
of this limited warranty.
d. This warranty does not apply to the damages to this product that occurred as the
following conditions:
Instead of operating in accordance with the user's manual thoroughly, any
abuse or misuse of this product.
Normal tear and wear
The product has been altered or modified in any way .
Damage which may have been caused either directly or indirectly by another
product/force/etc.
Abnormal service or repairing by anyone other than the qualified personnel or
technician. And in such cases, all the expenses will be charged to the buyer.
13
e. In no event shall LTO be liable for any incidental or consequential damages.
Some states do not allow the exclusion or limitation of incidental or consequential
damages, so the above exclusion or limitation may not apply to you.
f. This warranty gives you the specific rights, and these rights are compatible with
the state laws, you may also have other statutory rights that may vary from state
to state.
14
SEKAKU ELECTRON INDUSTRY (H.K.) CO. LTD
No. 1, Lane 17, Sec. 2, Han Shi West Road, Taichung, 401 Taiwan
http://www.altoproaudio.com Tel: 886-4-22313737
email: alto@altoproaudio.com Fax: 886-4-22346757
All rights reserved to ALTO. All features and content might be changed
without prior notice. Any photocopy, translation, or reproduction of part of this
manual without written permission is forbidden. Copyright c 2004 Sekaku Electron
NF01861-1.0
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