Locomotive Audio 14B User manual

USER’S MANUAL
MODEL 14B
SINGLE CHANNEL TUBE COMPRESSOR
HANDMADE IN ST. LOUIS, MO USA

INTRODUCTION
Thank you for your purchase of the Locomotive Audio Model
14B! This hand-built vacuum tube compressor is a product
of so much time, research and development. Inspired by
many beautiful pieces of equipment from the 50s and 60s,
we were able to design a circuit with high quality components
and modern features for today’s engineers. With proper
treatment, our products will be able to give you many years
of reliable service, so you can focus on being creative and
making the best recordings possible! We thank you for your
support of Locomotive Audio.

INSTALLATION
Vacuum tube equipment can get very hot, so thought and care should be
taken in how it is installed. The 14B will t in a 19” equipment rack, tak-
ing 2 units of space (2U). The chassis for the 14B has vents punched out
of the top and sides for heat to escape. It is good practice to leave 1U of
space above the unit for better ventilation.
The Locomotive 14B has its tubes and transformers installed on the
outside of the unit. Route audio and power cords in a direction where they
would be least likely to touch these components.
LINE VOLTAGE & FUSE
The unit is powered by 115v or 230v AC sources. The AC Voltage Slide
Switch (page 8) is preset by Locomotive Audio before leaving production.
Before using the 14B for the rst time, please make sure the AC Voltage
Slide Switch on the back of the unit (page 8) is in the correct position
for your mains voltage. If operated set to the incorrect voltage, harm to
the unit may result. With unit turned off, use a at-head screwdriver to
change the voltage selection if necessary.
All Locomotive Audio products contain a fuse in the IEC power entry mod-
ule for protection of both YOU and the unit. In order to check or replace
the fuse, a small at-head screwdriver is needed to open the fuse drawer.
Be sure to unplug the unit before beginning this procedure. Always re-
place the fuse with the same rating and type as specied for your mains
voltage on back of the unit. If replacement fuses of the correct specica-
tions consistently blow, there may be an issue with the unit and qualied
service technician should be contacted. If within warranty period, please
contact Locomotive Audio for instructions.
POWERING UP
Once installed in a secure equipment rack and plugged into the AC mains
power source, the user may then power the unit on by ipping the power
switch on the front of the unit to the up position. At this point, the power
lamp will light, and the unit will need at least 5–10 minutes for the tubes
to warm up for best results.
POWER LAMP & VU BULBS
The power lamp and backlit VU meter will illuminate after the unit is
switched on. If either of these do not light, the bulb may be burned out or
there may be another underlying issue. The rst step would be to replace
the bulb. If replacement is necessary, use a 14V .08A bayonet style bulb
for the power lamp and a 6.3V 1 watt festoon style bulb for the VU meter.
LEGAL NOTICES
©2014 Locomotive Audio, LLC
Manual Revision 14B-1
All information provided in this manual is thought to be accurate and free
of errors at the time of printing. Locomotive Audio, LLC shall not be liable
for any errors or omissions in this manual.
All information in this document is protected by copyright. No part of this
manual may be reproduced without the permission of Locomotive Audio,
LLC. Locomotive Audio, LLC reserves the right to make changes or im-
provements to this product at any time.
WARNINGS & SAFETY
Before powering up your new Locomotive Audio unit for the rst time,
please understand the dangers of vacuum tube electrical equipment.
The extremely high voltages within the chassis and around the tubes can
SERIOUSLY INJURY OR EVEN KILL YOU.
Before plugging your unit into the wall, please make sure all tubes are
properly seated in their sockets and not bent or angled with the tube pins
exposed. The base of the tube should be ush with the tube socket.
Also be sure to mount your unit in a stable, secure rack to reduce the risk
of movement and damage. The unit is grounded through the IEC power
cord supplied in the box. Always use a properly grounded outlet and never
use a ground lift plug adapter for a non-grounded outlet. Do not use unit
near any liquid or excessive moisture. If liquid were to enter the unit,
unplug EIC power cord from wall and wait at least 5 minutes before at-
tempting to touch or clean the unit.
The user should not attempt to service this product beyond changing
tubes. The 14B has a hinged front panel that allows for easy access of
internal parts if issues were to arise. Only a trained technician should
make modications or adjustments as the voltages within the chassis are
very dangerous!
BOX CONTENTS
Your Locomotive Audio product should have been
shipped with the following contents:
(1) 14B unit
(1) User’s Manual
(1) IEC Power Cord

ABOUT THE 14B
Locomotive Audio’s single channel 14B compressor and limiter is based
on a very old, but still very exciting concept of rebiasing the input tube
with a sidechain control voltage. After all, some of the most famous com-
pressors in history, such as the Fairchild 670, Gates Sta-Level and Collins
26U, employed this very technique. The results are a sound that cannot
be replicated with other ways of gain reduction. The Locomotive Audio
14B and its added modern features allow it to achieve a unique sound
in its own right. Starting with the semi-remote cutoff 6BC8 tube, a 12AY7
then drives two powerful push-pull 6V6 output tubes. The 14B is quite a
versatile unit, with the ability to run soft and gentle or hard and aggres-
sive. A sidechain low cut control offers even more exibility, especially
when used on the mixbus and linked with another 14B. This versatile
unit can be used on all kinds of source material including vocals, drums,
guitars, bass, piano and horns. With its high quality Cinemag input and in-
terstage transformers, the 14B has the ability to dene mid-range clutter
and control the peaks at the same time. The user will notice an enhance-
ment on any material run through this unit, even when not compressing.
14B FRONT PANEL SETTINGS
1. METER ZERO ADJUSTMENT
Loosen the locking nut to adjust the VU meter so that the needle
rests at approximately 0 dB when G.R. is selected on the VU Select
Switch under the meter.
Note: After turning on the 14B, the meter will take about 10–20 seconds
to climb towards the 0 dB mark. Sometimes the meter may take 20–30
minutes to adjust completely. What this means is that the input tube
(6BC8) is nally warmed up properly and has reached its stable current.
2. INPUT
The input knob sets the amount of signal that enters the active circuitry.
By increasing input by turning clockwise, more signal will pass over the
threshold, resulting in higher amounts of compression.
MAIN FEATURES
• Tubes: (1) 6BC8, (1) 12AY7, (2) 6V6s
• Classic feedback tube compression circuit
• Stereo Link switch
• Sidechain Low Cut lter control: Off and 70-350Hz
• Hard-wire bypass switch
• Variable input & output controls
• Variable Attack & release controls
• Compress / Limit switch
• Compression turned off with full counterclockwise attack
position switching to line amplier
• Two position VU meter switch: Gain Reduction - Output
• 6BC8 balance adjustment on interior of unit
• Custom Sifam backlit VU meter
• XLR input and output connections
• Cinemag input and interstage transformers
• High-grade Solen capacitors in signal path
• Hand-built in USA with classic turret board technique
• Heavy 16 gauge steel chassis
• 115v/230v AC mains option on rear
• Backed by 2-year limited warranty parts and labor
14B SPECIFICATIONS
The technical data listed below may change without notice
as we are consistently trying to improve our products
• Input load impedance: 10kΩ
• Output impedance: <800Ω
• Variable Attack: (300µs–5ms)
• Variable Release: (100ms–1sec)
• Compression (up to 6:1 ratio) or Limiting (up to 14:1 ratio)
• Flat frequency response: 20Hz-20kHz
• THD+N: <1%
• S/N ratio: >70dB
• Dimensions: 19”w x 3.5”h x 10”d (2u rackspace)
• Shipping Weight: 20 lbs.
• Power Consumption (120/240VAC): 42 watts
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3. IN/BYPASS SWITCH
This hard-wired bypass switch allows you to quickly listen to the differ-
ences between the original signal and the 14B processed signal.
4. ATTACK
The attack knob sets the time that it takes for the 14B to react and start
to compress a signal that has gone over the threshold. The 14B has
great exibility in its range of attack timing circuitry allowing for a large
palette of tone shaping possibilities. Set near “0” or “Fast”, the engineer
can use the 14B for aggressive peak control nearly as fast as a FET stlyle
limiter, but can also be adjusted to allow transients through unaffected
much like slower optical compressors when set near “100” or “Slow”.
Having the exible range of attack timing will allow for the engineer to use
the 14B on a wide range of material. The attack knob my also be turned
to its maximum counterclockwise position to switch compression off,
making the 14B a line level amplier.
5. LINK/MONO SWITCH
Two 14B compressors may be linked by a 1/4” cable on the back of
each unit, allowing them to work together in tandem. If both units are set
to “Link” mode, they will share sidechain control voltages with each other,
preserving the center image on a stereo track.
For example, if using the units on your master mixbus, dynamic elements
from left and right channels will likely be different. You may have a guitar
panned fully to the left channel, unpanned vocals in the center and and
a banjo panned fully to the right channel. If using the two 14Bs in dual
mono (unlinked), the banjo’s dynamics will cause compression on only
the right channel and therefore the vocal coming out of the right channel
will also be compressed, leaving the vocal coming out of the left channel
unaffected. This will cause the centered vocal to move in the stereo
image. Not good... unless that is what you are going for! Having both
units switched to “Link” mode will tell both compressors to react the
same when either is forced to compress. So, if the right compressor
reacts to the banjo and is forced to compress, the left channel will
compress as well. This will allow for elements such as the vocal to
stay centered in the mix.
6. VU SELECT SWITCH
This switch allows the engineer to meter how much gain reduction is
taking place or how much signal is leaving the output of the 14B. When
set to “Output” and the needle is deected to 0dB on the meter, a +4dBu
signal (1.228v) is leaving the 14B and into the next device.
7. RELEASE
The release knob sets how long the 14B takes to return to unity gain
after the input signal has fallen below threshold of compression. Set near
“0” or “Fast” will allow for the compression to release quickly and allow
for sounds to be more in up front and in your face. Slower release times
will sound more gentle and will allow for more of the original dynamics in
the source material.
8. COMPRESS/LIMIT SWITCH
This switch does two things: rst, it sets the xed threshold that the “In-
put” knob works hand-in-hand with it and also sets the ratio of gain reduc-
tio. On a tube compressor like the 14B, the compression ratio continues
to increase as the input signal level passes over the xed threshold.
When switched to “Compress” the initial compression is 1.2:1 increasing
to 6:1 at 15dB compression. In “Limit” the compression ratio also starts
low and increases up to approximately 14:1 at 15dB of gain reduction.
9.OUTPUT
The output level knob allows the engineer to match the output level with
the input level.
10. SIDECHAIN LOW CUT
Sets the frequencies that activate gain reduction. Turned and switched to
its maximum counterclockwise position, this knob allows all frequencies
to enter the sidechain and begin the gain reduction process. Switched on,
the 14B will start to roll off reaction to frequencies under the selected 70-
350Hz. For example, when using 14B for drum overheads, try sweeping
through frequencies over 110Hz and listen to the less compressed kick
drum come forward as the snare and cymbals continue to activate com-
pression and move further back in the mix. This is an extremely effective
tool for mixbus work as well. It will help to eliminate pumping caused by
low frequency material.
11. POWER SWITCH
Switches unit on. Illumination of the power lamp and VU meter will result.
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BACK PANEL
1. AC POWER ENTRY MODULE
Accepts standard IEC power cord (included) for 115v or 230v AC mains
supply. A fuse is included with each unit for the voltage/current expected
at the location being shipped to. Only use a fuse with the same rating
and voltage as marked on back of chassis.
2. AC VOLTAGE SLIDE SWITCH
Each unit is factory set to the voltage expected at the location being
shipped to. If voltage does not match mains voltage at your location,
switch to reveal the appropriate voltage. Do not operate unit set to incor-
rect voltage. Harm to the unit may result.
3. MODEL/SERIAL # TAG
When registering your product for your 2-year warranty, please see
the hand stamped tag to obtain the serial number.
4. BALANCED XLR LINE INPUTS
5. BALANCED XLR LINE OUTPUTS
6. STEREO LINK
Connect two separate 14B units with a 1/4” cable (balanced or unbal-
anced) to make use of the “Link/Mono” switch on the front panel.
CHANGING TUBES
Each Model 14B will leave Locomotive Audio with a new set of tubes that
should last for several years. We encourage you to utilize these tubes,
but also experiment with with other brands of New Old Stock tubes to
acheive your sounds! There are no rules with brands or age of tubes. But,
be sure to use only 6BC8 or 6BZ8, balanced 12AY7 and matched 6V6
tubes in the appropriate tube sockets. This will prevent any issue with the
performance of the 14B and damage to the unit.
VU METER CALIBRATION
The VU meters in our units have been pre-calibrated. When needle is de-
ected to 0dB on the VU meter, a signal voltage of +4dBu will be present
on the output of the unit. Turning the small calibration screw on the rear
of the VU meter will allow a qualied technician to adjust display levels.
INTERNAL ADJUSTMENTS
CAUTION: Interior adjustments must be made by a qualied technician.
The voltages inside of the 14B are very high and can be lethal. You may
contact Locomotive Audio to have this procedure done free of charge. It
is also advised to use a nonconductive adjustment tool to avoid shock
when the 14B is open.
The adjustments located on the inside of the 14B deal directly with gain
reduction 6BC8 input tube. This push-pull gain stage requires a strong
balance, otherwise the engineer may hear strange artifacts such as
thumping, uncontrolled oscillation or rippling apparent on the compres-
sion attack. Each 14B will leave Locomotive Audio fully calibrated. As your
6BC8 ages or with the installation of another 6BC8 tube, the following
procedure must be made as no two tubes are the same.
Plate Balance: This potentiometer feeds both halves of the 6BC8 tube
the high voltage B+ power.
Cathode Balance: This potentiometer places a resistance on each of the
two 6BC8 cathodes and can change cathode current, directly inuencing
the voltages on the 6BC8 plates. The plate and cathodes work hand-in-
hand to change bias points, current and gain within the tube.
Test/Operate Switch: This switch sends a 50/60Hz signal to the input of
each half of the 6BC8 tube which can be helpful in balancing.
USE ONLY WITH 250V FUSE
MODEL No.
DESIGNED & MANUFACTURED
IN SAINT LOUIS,MISSOURI
SERIAL No.
LOCOMOTIVE AUDIO
PLATE
BALANCE
6BC8 BALANCE ADJUSTMENT
TEST OPER.
CATHODE
BALANCE
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PROCEDURE FOR
A GOOD BALANCE
There are no rules on how to make
the adjustment, so we will give you a
couple options that work well for us
here at Locomotive! The rst involves
using the “TEST/OPER.” switch and the
second will utilize a snare drum loop
available at www.locomotiveaudio.com
TEST/OPERATE SWITCH PROCEDURE
1. Remove any signal entering the 14B.
2. Set attack and release to the approximate “50” settings
3. Turn both the “Input” and “Output” knobs fully counterclockwise
4. Set “Meter Select” switch to “Output.”
5. On the “6BC8 BALANCE ADJUSTMENT PANEL” set the “TEST/OPER.
switch to the “TEST” position.

WARRANTY
Each Locomotive Audio unit will be given a 60-day warranty from date
of purchase covering parts and labor, excluding tubes purchased with
unit. A 2-year warranty from date of purchase will be offered to original
owners who register their product within the rst 30 days of ownership.
Warranty is void if the product serial number has been removed or if the
product has been damaged due to misuse, accident, unauthorized modi-
cation or repair. Locomotive Audio, LLC. reserves the right to determine
when a problem or issue is eligible for warranty. Warranty is non-transfer-
able and applies only to the original purchaser.
In no event will Locomotive Audio, LLC. be liable for any incidental or
consequential damages resulting from any defect in the product, including
lost prots, damage to property and, to the extent permitted by law, dam-
age for personal injury, even if Locomotive Audio, LLC. has been advised
of the possibilities of such damages.
REGISTRATION
Email suppor[email protected] the following info within 30 days of
purchase to receive the full 2-year warranty from date of purchase.
• Purchaser Name, phone number, email and mailing address
• Legible scan or photograph of the original sales receipt
• Serial # from stamped metal plate on back of unit
SUPPORT & SERVICE
In the unlikely situation that something would go wrong with your unit, we
would be happy to x it up for you! Please visit our support page to gain
further instructions on how to contact us.
If it is determined your product requires repair, we’ll let you know where to
ship it and we’ll also issue a Return Merchandise Authorization number
(RMA). This number must be displayed on the outside of your shipping
box. Most repairs take approximately 1 week. We will match the shipping
method you used to get it to us. (If you shipped it to us UPS ground, we
will ship it back to you UPS ground; if you overnight it to us, we will ship it
back to you overnight). You pay the shipping costs to us; we ship it back
to you free of charge.
CONTACT INFORMATION
LOCOMOTIVE AUDIO, LLC
P.O. BOX 21751
St. Louis, MO 63109
suppor[email protected]
314.282.0133
6. Rotate the “Output” knob on the front panel until the needle moves
close to the 0dB mark. Being precise is not necessary.
7. Adjust both the “Plate Balance” and “Cathode Balance” while watch-
ing the VU meter for a drop in decibels. The idea is to go back and forth
between the “Plate Balance” and “Cathode Balance” until you get the
lowest reading on the VU meter. It may be necessary to raise the “Out-
put” knob if the needle has dropped so low that you cannot see any more
progress from adjustments.
8. After the lowest meter indication has been obtained, set the
“TEST/OPER. switch back to the “OPER.” position.
SNARE DRUM LOOP PROCEDURE
While the method above does a relatively good job at balancing the
6BC8 for low gain reduction, it doesn’t necessarily mean that the tube
is balanced at mid/deep gain reduction, where the 6BC8 is more prone
to thumping artifacts. We use the method below in conjunction with the
previous method to achieve very good balancing.
1. Set a fast attack “0” and slow release “100.”
2. Set “Meter Select” switch to “GAIN RED.”
3. Using your DAW, set up a snare drum loop (available at
locomotiveaudio.com) so that the snare drum hits every two seconds.
4. Send the snare drum loop to the 14B from your DAW.
5. Turn the “Input” knob clockwise until you can see about 10dB of gain
reduction on the 14B VU meter with each snare hit.
6. Now, set the 14B to a fast release “0.”
7. Record the processed signal back into your DAW on a different channel
and view the resulting snare hits.
8. Adjust both the “Plate Balance” and “Cathode Balance” while watch-
ing each new snare hit until you get a balanced (or close to balanced)
compressed waveform. This will be easy to spot. See the images below.
Again, just like in the Test/Operate Switch procedure above, you may
need to go back an forth between “Plate Balance” and “Cathode Bal-
ance” adjusting in small increments to get it just right. Take your time.
Imbalance. Imbalance. Perfect!

DECLARATION OF CONFORMITY
MANUFACTURED BY:
Locomotive Audio, LLC.
ADDRESS:
P.O. Box 21751
Saint Louis, Missouri 63109
PRODUCT:
14B Single Channel Tube Compressor
CONFORMITY:
Low Voltage Directive 2006/95/EC
(EN 60065:2002/A1:2006 + A11:2008 + A2:2010 + A12:2011)
EMC DIRECTIVE 2004/108/EC
(EN 55103-1:2009 & EN 55103-2:2009)
Year of Afxing CE marking: 2014
The undersigned does hereby declare that the equipment
complies with the above directives.
Eric Strouth
President
Locomotive Audio, LLC.
November 1, 2014

©2014 Locomotive Audio, LLC