LaChapell Audio 983M User manual

1266 Park Road
Chanhassen, MN 55317
952-401-7700
suppor[email protected]
www.digitalaudio.com
LACHAPELL AUDIO 983M
USER GUIDE
Single Channel Half Rack Vacuum Tube
Preamplifier for Microphones and Instruments
Version 1
February 2019

LACHAPELL AUDIO MODEL 983M
SAFETY INSTRUCTIONS
TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE COVER. CONTACT DIGITAL AUDIO LABS
FOR SERVICING.
The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to alert the user
to the presence of uninsulated and/or potentially dangerous voltage within the products enclosure
that may be of sufficient magnitude to constitute a risk of electric shock to persons.
The exclamation point within an equilateral triangle is intended to alert the user to the presence of
important operating and maintenance (servicing) instructions in the literature accompanying the
appliance.
POWER CORD NOTICE FOR INTERNATIONAL OPERATION
Please call Digital Audio Labs Support at 952-401-7700.
IMPORTANT SAFETY INSTRUCTIONS
1. Read and understand this entire manual.
2. Keep this manual available for reference.
3. Heed all warnings and precautions in this manual and notices marked on the product.
4. Do not use this product near water or damp environments.
5. Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.
6. Provide for proper airflow around product. Do not install near products that produce high levels
of heat. Do not expose the unit to direct sun light or heating units as the internal components
temperature may rise and shorten the life of the components.
7. Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two
blades with one wider than the other. A grounding type plug has two blades and a third grounding
prong.
8. Protect the power cord from being walked on or pinched particularly at plugs, convenience
receptacles, and the point where they connect to the product. Do not use the unit if the electrical
power cord is frayed or broken.
9. Only use attachments/accessories specified by the manufacturer.
10. Unplug this product during lightning storms or when unused for long periods of time.
11. Refer all servicing to qualified service personnel.
12. The product shall not be exposed to moisture. Do not touch the unit with wet hands. Do not handle
the unit or power cord when your hands are wet or damp.
13. The product should be connected to a power supply only of the type described in the operating
instructions or as marked on the product.
CARE
• From time to time you should wipe off the front and side panels and the cabinet with a dry soft
cloth. Do not use rough material, thinners, alcohol or other chemical solvents or cloths since this may
damage the finish or remove the panel lettering.
• The manufacturer cannot be held responsible for damages caused to persons, personal possessions,
or data due to an improper use of product.

LACHAPELL AUDIO MODEL 983M 1
DIGITAL AUDIO LABS LIMITED WARRANTY
Digital Audio Labs warrants their products against defects in material and workmanship for a period of two years
from date of purchase. During this period, Digital Audio Labs will, at its option, repair the defective unit or replace
it with a new or rebuilt one.
The warranty does NOT cover:
• Damage due to abuse, misuse, or accident.
• Damage due to operation contrary to the instructions in the product instruction manual.
• Units on which the product serial number has been removed or altered.
• Units that have been serviced by unauthorized personnel.
All implied warranties, including warranties on merchantability and fitness, are limited in time to the length of
this warranty. Some states do not allow time limitations on implied warranties, so this limitation may not apply
to you. Digital Audio Labs’ liability is limited to the repair or replacement of its product. Digital Audio Labs shall
in no way be held liable for incidental or consequential damages resulting from the use of their product or
its software, including, without limitation, damages from loss of business profits, business interruption, loss of
business information or other pecuniary loss. Some states do not allow the exclusion or limitation of incidental or
consequential damages, so the above limitation or exclusion may not apply to you.
REPAIR POLICY
Please do not return the product without obtaining an RMA number first. Contact Digital Audio Labs at support@
digitalaudio.com to acquire an RMA number. Do not return the product to the place of purchase. Please write
the RMA number on the outside of the shipping carton. Any product sent to us without a valid RMA number will
be refused. Include the following with the product: a brief description of the problem, your name, return shipping
address, phone number and the RMA number. Do not include any accessories. DAL is not responsible for any
damage to or loss of the product during transit. We recommend that customers obtain a receipt and tracking
number for all packages shipped to us. Turnaround time on repairs is generally ten business days. If you live
outside of the United States, please contact your local distributor for warranty service.
Please return product to:
Digital Audio Labs
Attn: RMA Number
1266 Park Road
Chanhassen, MN 55317
USA
WARRANTY SERVICE
You will be required to pay the shipping charges when you ship your product to DAL. Digital Audio Labs will
pay for return shipping with a shipper of their choosing. We reserve the right to inspect any product that may
be the subject of any warranty claim before repair is carried out. For warranty service, we may require proof of
the original date of purchase if you have not registered your product with DAL. Final determination of warranty
coverage lies solely with Digital Audio Labs.
NON-WARRANTY SERVICE
If it is determined that the product does not meet the terms of our warranty, you will be billed for labor, materials,
return freight and insurance. There is a $80 USD minimum charge for materials and labor. Appropriate shipping
charges will be applied. We require payment in advance of repair by credit card; we accept Visa and Master
Card. In the event the charges are over the minimum charge, DAL will contact you and inform you of the cost of
the repair before any work is completed.

LACHAPELL AUDIO MODEL 983M
CONTENTS
SAFETY INSTRUCTIONS.................................................................................................................................................................II
IMPORTANT SAFETY INSTRUCTIONS.............................................................................................................................II
CARE...........................................................................................................................................................................................II
DIGITAL AUDIO LABS LIMITED WARRANTY........................................................................................................................1
REPAIR POLICY.......................................................................................................................................................................1
WARRANTY SERVICE ...........................................................................................................................................................1
NON-WARRANTY SERVICE...............................................................................................................................................1
INTRODUCTION...............................................................................................................................................................................3
BEFORE YOU GET STARTED........................................................................................................................................................3
SAFETY PRECAUTIONS ........................................................................................................................................................4
CONTROLS ........................................................................................................................................................................................5
CONTROL DETAILS ..............................................................................................................................................................5
GETTING STARTED ..........................................................................................................................................................................6
983 FREQUENCY RESPONSE.....................................................................................................................................................7
HPF - 50HZ.................................................................................................................................................................................7
HPF - 150HZ...............................................................................................................................................................................7
LPF - 5KHZ..................................................................................................................................................................................7
LPF - 10KHZ ...............................................................................................................................................................................7
LACHAPELL AUDIO 983M SPECIFICATIONS ......................................................................................................................8
LACHAPELL AUDIO SUPPORT...................................................................................................................................................8

LACHAPELL AUDIO MODEL 983M 3
INTRODUCTION
The LaChapell Audio 983M is a single channel microphone and instrument preamplifier in a half
rack space format. It features a Cinemag input transformer with a turns ratio of 1:10, a Jensen output
transformer and one ECC83/12AX7 vacuum tube. The instrument input stage bypasses the transformer
and goes straight to the tube. The output stage utilizes premium Burr-Brown and THAT Corporation line
drivers along with an 80% nickel alloy core transformer to generate a balanced line-level output signal
with very low 8 ohm output impedance. With this precision, double-balanced output stage, the 983M is
capable of driving many hundred of feet of cable without significant less of signal quality
BEFORE YOU GET STARTED
Please take time to read the information below before you install and use your LaChapell Audio 983M.
• UNPACKING: Inspect thoroughly. Although we take extreme care at final assembly and packing,
things can happen during transit. It is very important that you contact Digital Audio Labs if there is
anything broken or damaged upon receipt of package. Included in every package should be:
(1) preliminary operating manual, (1) packet of mounting screws, (1) registration card. It is a good
idea for you to retain the packaging (box & foam case) in case there is a need to return the unit
for service or repair at a later date.
• SERVICE/REPAIR - WARNING: The user should NOT attempt to service this unit in any way, due to
the risk of electrical shock and the presence of lethal voltages inside the 983M. It is recommended
that tube replacement be performed only when necessary by technically competent individuals.
Tube replacement: Turn power supply off and remove 983M from the chassis, wait five
minutes to allow the vacuum tube to cool before attempting to remove it. Using your fingers,
apply a slight circular/rotating motion as you pull it away from the socket. It is important to
replace the tube with the same type. When a replacement tube is installed, ensure that the
correct tube type has been inserted into the 983M’s tube socket BEFORE powering up.
• MOUNTING: Always allow for plenty of ventilation around the sides and top of preamp. When
using the optional Rack Mounting Kit, mounting in travel racks is not recommended. Keep in mind
that the vacuum tubes are mounted in sockets and on rare occasions can shake lose if subjected
to prolonged rough handling. The 983M should never be mounted or placed in areas that would
expose it to any form of moisture.
• SERVICE/REPAIR - WARNING: With the exception of tube replacement (see below) the user should
NOT attempt to service this unit in any way, due to the risk of electrical shock and the presents of
lethal voltages inside the 983M. The user should also take note that excessive ‘swapping’ of tubes
will Introduce undue wear on the tube socket. It is therefore recommended that tube replacement
be performed only when necessary and by technically competent individuals
Tube replacement: Turn power off, disconnect the power cable and wait 20 minutes
to allow the vacuum tube to cool before attempting to remove it. Waiting 20 minutes
also allows the power supply caps to discharge adequately. Using your fingers, apply a slight
circular/rotating motion as you pull the tube away from the socket. It is important to replace
the tube with the same type of tube.
WARNING: Warranty may be voided if tubes other than the 12AX7/ECC83 are used.

LACHAPELL AUDIO MODEL 983M 4
SAFETY PRECAUTIONS
• Always provide adequate ventilation. Due to the vacuum tube and high voltage internal power
supply, the 983M will get warm. Blocking or defeating any existing vent(s) is not recommended.
• Never position the 983M directly above other heat generating sources such as a power amplifier.
• Do not place the 983M in an area where there is a potential for fluids to fall, spill onto or come in
contact with the 983M. If you notice fluids or moisture present inside the unit DO NOT turn power on!
Contact Digital Audio Labs for direction.

LACHAPELL AUDIO MODEL 983M 5
CONTROLS
CONTROL DETAILS
• TUBE DRIVE: TUBE DRIVE controls how much of the source signal is fed to the vacuum tube. Higher
levels will drive the tube harder and result in more harmonics. Think of this control as your amount
of tube coloration/harmonics (distortion).
• LEVEL: Provides variable control over line level signal strength. Think of this control as your source for
clean gain. Typically, this control is used to establish the desired line level after the input gain has
been set but it can work interactively with the TUBE DRIVE for a wide array of tonal possibilities.
• 48V: The 983M features TRUE48™, a dynamic phantom
power supply that provides a 48 volt supply of DC current
for condenser microphones. Unlike other phantom power
supplies, TRUE48 provides a full 44-48V of phantom power
regardless of the source resulting in more headroom, lower
distortion and quicker transient recovery.
• HI-Z INPUT: The Hi-Z input stage is transformerless and operates
with an input impedance of 100Kohm. The input pad has no
effect on the Hi-Z input.
• 20dB INPUT PAD (-20): When engaged, the microphone input
source signal is reduced by 20dB.
• POLARITY REVERSE: Reverses the polarity of the output signal.
• MUTE: Output level mute. The MUTE LED will illuminate red when the channel is muted.
• VU METER: This detects the microphone input signal (not output level). The LED is calibrated to
detect input signals as low as -50dBu. When +4 is illuminated, it indicates that line level has been
achieved. The Clip LED is intended to be a warning that clipping may occur if output signal
strength is pushed further. It is calibrated to illuminate when the output is driving +23dBu into a
40kohm source. It does not necessarily indicate that the output stage has reached its limit.
• HIGH-PASS FILTER (HP): Select no filter (center position), cut at 50hz (down position) or cut at 150hz
(up position).
• LOW-PASS FILTER (LP): Select no filter (center position), cut at 5Khz (down position) or cut at 10Khz
(up position).
• POWER SWITCH: Master power rocker switch. LED will illuminate red when power is on.
CREATIVE TIP:
For near transformer-less sound,
consider engaging this pad
function and compensate for
the loss of gain by increasing
the input gain control. This
approach effectively minimizes
the input transformer gain
while drastically increasing the
character of the vacuum tube
(this is only possible with the
microphone path).
TUBE DRIVE
CONTROL
VU
METER
HI-Z
INPUT
TRUE48
PHANTOM
POWER
POLARITY
REVERSE
LEVEL
CONTROL
HIGH-PASS
FILTER
LOW-PASS
FILTER
-20 dB
PAD
CHANNEL
MUTE
AC
POWER

LACHAPELL AUDIO MODEL 983M 6
BACK PANEL CONNECTORS
BACK PANEL CONNECTOR
• AC POWER IN: Connect the included AC power supply to the AC POWER IN. Press it until it locks
into place. To disconnect the power supply, press the locking mechanism on the AC POWER
connector.
• MIC INPUT: This XLR connects to the microphone.
• LINE OUTPUT: Connect this XLR to your line level input.
INSTALLING RACK MOUNT KIT
To mount the 983M in a standard 19” rack, use the optional Rack Mount Kit (RK1U-DP). The Rack Mount
Kit is a dual position kit and comes with everything needed to mount either one or two 983M units in a
standard rack.
RACK KIT CONTENTS
2x L Shaped Rack Brackets
1x U Shaped Center Bracket
1x Hex Tool
12x Mounting Screws
MOUNTING A SINGLE 983M UNIT
To mount a single 983M unit in a 19” rack with the Rack Mount Kit, position the L Brackets as shown in
the image above. The brackets will attach to the 983M with 2 mounting screws per side. Using the Hex
Tool, screw two Mounting Screws into the provided holes on either side of the 983M.
MOUNTING TWO 983M UNITS
To mount two 983M units, position the L Brackets as shown in the image above and use the U Shaped
bracket between the two units. The L and U brackets will attach to each of the two 983M units with 3
mounting screws per side. Using the Hex Tool, screw three Mounting Screws into the provided holes on
either side of each 983M.
MIC
INPUT
AC POWER IN LINE
OUTPUT

LACHAPELL AUDIO MODEL 983M 7
GETTING STARTED
-20 dB PAD
ON
OFF
-20 dB PAD
ON
OFF
-20 dB PAD
ON
OFF
CLEAN GAIN, HIGH HEADROOM
With the TUBE-DRIVE knob set at around 25% and
LEVEL (output) around 75%, with the PAD off, you will
get a very clean and pristine sound. The distortion
is very low with no added harmonics and there is a
ton of headroom. This is a great starting position for
those wanting a clean tube sound regardless of the
microphone type.
TUBE HARMONICS AND COMPRESSION
With the TUBE-DRIVE set at around 75%, LEVEL around
25%, and the PAD off, you will get incredible tube
harmonics and natural tube compression. This would
be a great starting position for those wanting to hear
what the 983M’s harmonics are all about. It’s also a
great place to start when using ribbon or dynamic
mics.
HEADROOM AND WARMTH
The 983M provides great sonic versatility. With the -20 dB
PAD engaged and the TUBE-DRIVE set to around 50%
you will hear a rich roundness and warmth. With these
settings, the mid-range will move forward and the input
headroom is increased as well.

LACHAPELL AUDIO MODEL 983M 8
983M FREQUENCY RESPONSE
HPF - 150HZ
LPF - 10KHZ
HPF - 50HZ
LPF - 5KHZ

LACHAPELL AUDIO MODEL 983M 9
LACHAPELL AUDIO SUPPORT
Phone Support: 952-401-7700
Toll Free: 844-DAL-INFO
Email Support: suppor[email protected]
Website: www.digitalaudio.com/support
DIGITAL AUDIO LABS
1266 Park Rd
Chanhassen, MN 55317
LACHAPELL AUDIO 983M SPECIFICATIONS
Internal Gain (microphone) 72.5dB
Internal Gain (Hi-Z) 53.8dB
Max output gain +27.8dBu (1% THD+N, 22Hz - 20kHz)
Frequency Response 9Hz - 40kHz
THD+N Variable: 0.01% - 18% (per tube drive (input) gain control
with -40dBu input at 1Khz)
Noise (EIN) -124dB
S/N Ratio 92dB (30dB of gain, 22Hz - 20kHz)
Input Impedance (microphone) 1.5 KOhm
Input Impedance (Hi-Z) 100K Ohm
Output Impedance 8 Ohm
Tube Complement/Type 1 x 12AX7/ECC83 (one per channel)
NOTE: Stated specifications are typical measurements but subject to change without notice due to individual traits unique to
each tube. All measurements taken while driving a 100Kohm load and using a 1Khz tone.

® 2014, 2015 Digital Audio Labs. ™ & © 2017, 2018 Digital Audio Labs.
Patents pending.