HX-3 User Guide


Headphone Distribution Amplifi er

User Guide and Technical Information

Sound Devices, LLC

300 Wengel Drive • Reedsburg, WI • USA

+1 (608) 524-0625 • fax: +1 (608) 524-0655

Toll-Free: (800) 505-0625 www.sounddevices.com

[email protected]

HX-3 User Guide and Technical Information

General Description

The HX-3 from Sound Devices is a portable, stereo headphone amplifi er designed for critical audio monitoring. The audiophile-quality headphone amp is ideal for adding headphone feeds for portable and studio applications.

The HX-3 provides three independent headphone feeds from balanced or unbalanced, line sources. Each headphone output has its own level control, peak LED, and ¼-inch output connector. With its extended bandwidth and high drive capability the HX-3 can drive headphones of various impedances to high levels with very low distortion, important for monitoring in high SPL environments. It is powered from two-AA batteries or external DC.

The HX-3 will provide years of superb audio performance under the most punishing fi eld conditions.


High Performance Headphone Amplifi er

• Three independent headphone outputs with individual volume controls.

• Dynamic range exceeding 120dB.

• 10 Hz to 50 kHz audio bandwidth.

• Capable of driving headphones to high levels with very low distortion.

• Peak indicators show overload of each headphone feed.

• Stereo / Mono switch.

Flexible Inputs / Outputs

• Two balanced XLR line level inputs or unbalanced ¼-inch and 1/8-inch stereo inputs.

• Loop output to connect additional HX-3’s in series for extra headphone outputs.

Flexible Powering

• Internal battery power (two AA) for convenient, low cost power.

• Excellent battery life - greater than 10 hours (nominal drive level with alkaline batteries).

• External 5-17 VDC powering.

Durable Mechanical Construction

• High strength aluminum chassis withstands punishing fi eld conditions.

• Strap loops on each side for easy mounting or wearing.

• Panel-mounted connectors for strength and reliability.

• Easy access battery compartment for quick battery changes.


Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.

HX-3 User Guide and Technical Information

Specifi cations

Frequency Response:

10 Hz – 50 kHz, +/-1.0 dB, any input to any output, gain control set to 50%

Voltage Gain:


Bal. Line

HP Input

Loop Out

–3 dB

–1 dB

Output Clipping Level:

+18 dBu minimum with 600 ohm load

+16 dBu minimum with 300 ohm load

Headphone Output Impedance:

200 ohms

Headphone Output (1,2,3)

34 dB

35 dB

Input Clipping Level:

XLR: +24 dBu minimum

Dynamic Range:

(Balanced line inputs)

THD + Noise:

120 dB minimum


Loop Output:

0.03% maximum (from 10 Hz – 22 kHz @ +10 dBu input and output level, 300 ohm load, 10 Hz – 22 kHz filter bandwidth)

XLR: electronically balanced, 22k ohm input impedance

1/4-inch unbalanced: 9.1k ohm impedance

1/8-inch unbalanced: 9.1k ohm impedance

Note: only one set of inputs (balanced or unbalanced) should be connected at a time.

Unbalanced, 200 ohm output impedance

Internal Voltage Rails:

±15 V and –15V, regulated


Power LED:

Internal: 2 AA alkaline batteries, 12 hours life typical driving one 75 ohm headset.

External: 5–17 VDC via threaded coaxial connector, (5.5 mm outer diameter, 2.1 mm inner diameter), pin positive, sleeve negative. Voltages above 17 VDC cause no damage to unit, but will open an internal poly fuse. Poly fuse will reset when voltage is removed.

Green indicates power and good battery. Red indicates power with low batteries. LED turns red when approximately 4 hours of battery life remain.

Operating Temperature Range:

0 to 70° C

32 to 160° F


Weight: (unit only)

43 mm x 94 mm x 140 mm (h x w x d)

(1.7” x 3.7” x 5.55”)

0.56 kg, 1.24 lbs.

Included Accessories:

1/4-inch to 1/8-inch

Tip-Ring-Sleeve interconnect cable rubber feet (4)


HX-3 User Guide and Technical Information

Front Panel Controls

1 2 3

Sums stereo and two-channel audio program to mono for mono headphone monitoring.


Headphone Gain

Controls Volume of each headphone output.

3. Headphone Peak LED

Illuminates 3 dB before clipping to indicate onset of headphone distortion.

4 5

Bi-color LED illuminates green when the unit is powered and changes to red when approximately four hours of battery life remain.

5. POWER Switch

Powers the unit from either Internal batteries, or External DC. Seamless switchover from each power source.


Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.

Input Panel Connectors

HX-3 User Guide and Technical Information

1 2

1. XLR Line Inputs

Line level, balanced inputs.

2. ¼-Inch and 1/8-inch Tape Level Inputs

Unbalanced, stereo, Tip-Ring-Sleeve inputs.

Output Panel Connectors



Loop Output

Output connection enabling interconnection of multiple HX-3’s. Loop Out is

T-R-S, unbalanced stereo connection.


Panel mounted headphone jack for each output. Output 1 has 1/8-inch jack in parallel with ¼-inch jack.

Requires two AA batteries for operation.

Insert positive (+) end of battery fi rst.

1 2 3


DC Input

Locking coaxial DC input accepts voltages from 5 to 14 VDC.


HX-3 User Guide and Technical Information

Operational Notes

Headphone Outputs

The HX-3 uses independent drive circuits for each of its three isolated headphone circuits. Because of the bi-polar power supply, the HX-3 can provide high levels of power to each headphone feed.

The HX-3 is capable of driving headphones to dangerous levels. Take precautions to prevent hearing damage.

Powering the HX-3

The HX-3 is designed to operate on two AA alkaline cells for approximately 15 hours into 75 ohm headphones (at nominal levels). The audio performance of the HX-3 does not vary throughout the life of the batteries.

Several factors affect battery life including: battery chemistry, ambient temperature of operation, headphone impedances, headphone drive levels, and the number of headphones in use. The chart below can be used as a starting point to estimate battery life. Experimentation is recommended to determine battery life for each individual setup. Note: Nickel-Cadmium batteries are not recommended in the HX-3 since these batteries have lower energy per cell than other types and will result in very short service.

Battery Type

Duracell AA MN 1500

Duracell AA MN 1500

Duracell AA MN 1500

(Test conditions: 70º F)

Operational Characteristics

powered, idle driving single, 75 ohm headphones at nominal level driving three, 75 ohm headphones at high levels

Battery Life

15 hrs.

9 hrs.

8 hrs.


Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.

HX-3 User Guide and Technical Information

Connection Diagrams

The HX-3 can be used in a variety of headphone applications. Below are a few examples of interconnection setups using the HX-3.



Monitor L

Monitor R

One or more units can be added and “daisy-chained” for additional headphone feeds from a mixing console. Loop additional HX-3 amplifi ers with the included Link cable.

The headphone outputs of portable audio electronics can be connnected to the HX-3 for additional headphone feeds. The included 1/4-inch to 1/8-inch can be used to connect the line-out or headphone output to the HX-3.


HX-3 User Guide and Technical Information

CE Declaration of Conformity

According to ISO/IEC Guide 22

Sound Devices, LLC

300 Wengel Drive

Reedsburg, WI 53959 USA declares that the product, HX-3 is in conformity with and passes:

EN55103-1, (1997)

EN55103-2, (1997)

Emissions standard for product family audio devices for professional use

Immunity standard for product family audio devices for professional use

EN55022 (1995)/

CISPR22 (1997)

Radiated and Conducted emissions, Class B

EN61000-4-2 (1997)/

IEC1000-4-2 1995

EN61000-4-3 (2001)/

IEC1000-4-3 (2001)

ESD - 6kV contact, 8kV air-discharge

Radiated RF immunity, 10 V/m, 80% 1 kHz amplitude modulation

EFT Burst, I/O lines, ±0.25 kV to ±1.0 kV, EN61000-4-4 (1995)/

IEC1000-4-4 (1995)

EN61000-4-6 (1996)/

IEC61000-4-6 (1996)

Conducted RF immunity, 10 V, 80% @1 kHz amplitude modulation

Tested by L. S. Compliance, Inc. Cedarburg, Wisconsin

February 15, 2003

Matthew Anderson

Director of Engineering

Sound Devices, LLC


Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.

HX-3 User Guide and Technical Information

FCC Statement

This device has been tested and found to comply with the limits for a class B digital device, pursuant to part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation.


Sound Devices, LLC warrants the MM-1 Microphone Preamp with Headphone Monitoring against defects in materials and workmanship for a period of ONE (1) year from date of original retail purchase.

This is a non-transferable warranty that extends only to the original purchaser. Sound Devices, LLC will repair or replace the product at its discretion at no charge. Warranty claims due to severe service conditions will be addressed on an individual basis. THE WARRANTY AND REMEDIES SET FORTH





DER ANY OTHER LEGAL THEORY. Because some jurisdictions do not permit the exclusion or limitations set forth above, they may not apply in all cases.

For all service, including warranty repair, please contact Sound Devices for a return authorization number (RMA) before sending the unit for service. Service returns should be sent to:

Sound Devices, LLC

Service Repair (RMA # XXXX)

300 Wengel Drive

Reedsburg, WI 53959 USA telephone: (608) 524-0625


HX-3 User Guide and Technical Information- Printed in U.S.A.

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