Sonifex Redbox Series Instruction Manual

Manufacturers of audio & video
products for radio & TV broadcasters
Redbox
User Handbook No 5
HANDBOOK
RB-HD1 Stereo Headphone Amplifier With VCA Volume Control
RB-HD2 Dual Headphone Amplifier
RB-HD6 6 Way Stereo Headphone Distribution Amplifier
RB-DHD6 Digital 6 Way Headphone Distribution Amplifier
RB-MA1 Single Microphone Amplifier
RB-MA2 Dual Microphone Amplifiers
RB-MA2G Dual Microphone Amplifier with Gain
RB-DMA2 Dual Digital Microphone Amplifier
RB-ML2 Stereo Microphone & Line Level Limiter
RB-SL2 Twin Mono, Or Stereo, Limiter
RB-SM1 Single Stereo To Mono Converter
RB-SM2 Dual Stereo To Mono Converter
RB-LC3 3 Way Light/Power Controller

Redbox Handbook 5
Redbox User Handbook No 5
Stock Code: 30-343
Artwork: AW10835
Revision 3.01 September 2019
©Sonifex Ltd, 2019
All Rights Reserved
Sonifex Ltd, 61, Station Road, Irthlingborough,
Northants, NN9 5QE, England.
Tel: [phone]
Fax: [phone]
Email: [email protected]o.uk
Website: https://www.sonifex.co.uk
Information in this document is subject to change without notice and does not represent a
commitment on the part of the vendor. Sonifex Ltd shall not be liable for any loss or damage
whatsoever arising from the use of information or any error contained in this manual.
No part of this manual may be reproduced or transmitted in any form or by any means, electronic
or mechanical, including photocopying, recording, information storage and retrieval systems, for any
purpose other than the purchaser’s personal use, without the express written permission of Sonifex
Ltd. Unless otherwise noted, all names of companies, products and persons contained herein are
part of a completely fictitious adaptation and are designed solely to document the use of Sonifex
product.
Made in the UK by
Contents
Product Warranty - 2 Year Extended ii
Sonifex Warranty & Liability Terms & Conditions ii
1. Definitions ii
2. Warranty ii
Unpacking Your Product iii
Repairs & Returns iv
Conformity iv
Safety & Installation of Mains Operated Equipment iv
Voltage Setting Checks iv
Fuse Rating iv
Power Cable & Connection iv
WEEE Directive v
Atmosphere/Environment v
Fitting Redboxes v
1 RB-HD1 Stereo Headphone Amplifier With VCA
Volume Control 1
Introduction 1
System Block Diagrams 1
Front Panel Connections and Controls 2
Rear Panel Connections and Operation 2
Technical Specifications RB-HD1 4
2 RB-HD2 Dual Headphone Amplifier 5
Introduction 5
System Block Diagrams 5
Front Panel Connections and Controls 6
Rear Panel Connections and Operation 6
Technical Specifications RB-HD2 7
3 RB-HD6 6 Way Stereo Headphone Distribution Amplifier 8
Introduction 8
System Block Diagram 9
Rear Panel Connections and Operation 10
Front Panel Connections and Controls 11
Technical Specifications RB-HD6 12
4 RB-DHD6 Digital 6 Way Headphone Distribution Amplifier 13
Introduction 13
System Block Diagram 13
Rear Panel Connections and Operation 14
Front Panel Indicators & Controls 14
Technical Specifications RB-DHD6 16
For the latest Sonifex handbook information please visit the
Sonifex website at www.sonifex.co.uk

Contents
5 RB-MA1 Single Microphone Amplifier 17
Introduction 17
System Block Diagram 17
Rear Panel Connections and Operation 18
Technical Specifications RB-MA1 19
6 RB-MA2 Dual Microphone Amplifiers 20
Introduction 20
System Block Diagram 20
Rear Panel Connections and Operation 21
Technical Specifications RB-MA2 22
7 RB-MA2G Dual Microphone Amplifier with Gain 23
Introduction 23
System Block Diagram 24
Rear Panel Connections and Operation 24
Front Panel Controls 25
Technical Specifications RB-MA2G 26
8 RB-DMA2 Dual Digital Microphone Amplifier 27
Introduction 27
System Block Diagram 28
Front Panel Indicators & Controls 28
Rear Panel Connections and Operation 29
Rear Panel Controls 30
Technical Specifications RB-DMA2 32
9 RB-ML2 Stereo Microphone & Line Level Limiter 34
Introduction 34
System Block Diagram 35
Rear Panel Connections and Operation 35
Technical Specifications RB-ML2 37
10 RB-SL2 Twin Mono, Or Stereo, Limiter 38
Introduction 38
System Block Diagram 39
Rear Panel Connections and Operation 39
Technical Specifications RB-SL2 41
11 RB-SM1 Single Stereo To Mono Converter 42
Introduction 42
System Block Diagram 42
Rear Panel Connections and Operation 43
Technical Specifications RB-SM1 44
12 RB-SM2 Dual Stereo To Mono Converter 45
Introduction 45
System Block Diagram 45
Rear Panel Connections and Operation 46
Technical Specifications RB-SM1, RB-SM2 47
13 RB-LC3 3 Way Light/Power Controller 48
Introduction 48
System Block Diagram 49
Rear Panel Connections and Operation 49
Technical Specifications RB-LC3 54

Figures
Figures
Fig A: RB-RK1 Small Redbox Front Rack-mount Kit . v
Fig B: RB-RK2 Small Redbox Rear Rack-mount Kit. vi
Fig C: RB-RK3 Large Redbox Rear Rack-mount Kit. vi
Fig 1-1: RB-HD1 Front Panel 1
Fig 1-2: RB-HD1 System Block Diagram 1
Fig 1-3: RB-HD1 Front Panel Controls 2
Fig 1-4: RB-HD1 Rear Panel 2
Fig 1-5: RB-HD1 Remote Connector 3
Fig 2-1: RB-HD2 Front Panel 5
Fig 2-2: RB-HD2 System Block Diagram 5
Fig 2-3: RB-HD2 Front Panel Controls 6
Fig 2-4: RB-HD2 Rear Panel 6
Fig 3-1: RB-HD6 Front Panel 8
Fig 3-2: RB-HD6 System Block Diagram 9
Fig 3-3: RB-HD6 Rear Panel 10
Fig 3-4: RB-HD6 Jumper Assignments 11
Fig 3-5: RB-HD6 Jumper Positions 11
Fig 3-6: RB-HD6 Front Panel Controls 11
Fig 3-7: RB-HD6 Master Level Control 11
Fig 4-1: RB-DHD6 Front Panel 13
Fig 4-2: RB-DHD6 System Block Diagram 13
Fig 4-3: RB-DHD6 Front Panel Controls 14
Fig 4-4: RB-DHD6 Rear Panel 14
Fig 4-5: RB-DHD6 Status Select Switches 15
Fig 5-1: RB-MA1 Front Panel 17
Fig 5-2: RB-MA1 System Block Diagram 17
Fig 5-3: RB-MA1 Rear Panel 18
Fig 5-4: Switch to Control LF Filter and Phantom Power 18
Fig 6-1: RB-MA2 Front Panel 20
Fig 6-2: RB-MA2 System Block Diagram Single Channel 20
Fig 6-3: RB-MA2 Rear Panel. 21
Fig 6-4: Switch to Control LF Filter and Phantom Power 21
Fig 7-1: RB-MA2G Front Panel 23
Fig 7-2: RB-MA2G System Block Diagram 24
Fig 7-3: RB-MA2G Rear Panel 24
Fig 7-4: Switch to Control LF Filter and Phantom Power 25
Fig 8-1: RB-DMA2 Front Panel 27
Fig 8-2: RB-DMA2 System Block Diagram 28
Fig 8-3: RB-DMA2 Front Panel 28
Fig 8-4: Jumpers to Disable Fine Gain Control 29
Fig 8-5: RB-DMA2 Rear Panel 29
Fig 8-6: RB-DMA2 Status Select Switches 30
Fig 8-7: RB-DMA2 Frequency and Sync Rotary Switch Selections 32
Fig 9-1: RB-ML2 Front Panel 34
Fig 9-2: RB-ML2 System Block Diagram 35
Fig 9-3: RB-ML2 Rear Panel 35
Fig 9-4: Switch to Control LF Filter and Phantom Power 36
Fig 10-1: RB-SL2 Front Panel 38
Fig 10-2: RB-SL2 System Block Diagram 39
Fig 10-3: RB-SL2 Rear Panel 39
Fig 11-1: RB-SM1 Front Panel 42
Fig 11-2: RB-SM1 System Block Diagram 42
Fig 11-3: RB-SM1 Rear Panel 43
Fig 12-1: RB-SM2 Front Panel 45
Fig 12-2: RB-SM2 System Block Diagram Single Channel 45
Fig 12-3: RB-SM2 Rear Panel 46
Fig 13-1: RB-LC3 Front Panel 48
Fig 13-2: RB-LC3 System Block Diagram 49
Fig 13-3: RB-LC3 Rear Panel 49
Fig 13-4: Output 1 Configuration Setting 51
Fig 13-5: Output 2 Configuration Settings 52
Fig 13-6: Output 3 Configuration Settings 53

Warranty Registration
Sonifex Limited y 61 Station Road y Irthlingborough y Northamptonshire y NN9 5QE y United Kingdom
Tel: [phone] y Fax: [phone] y Email: [e-mail] y Internet: www.sonifex.co.uk
Register Online for an
Extended 2 Year Warranty
As standard, Sonifex products are
supplied with a 1 year back to base
warranty.
If you register the product online, you
can increase your product warranty
to 2 years and we can also keep
you informed of any product design
improvements or modifications.
To register your product, please go online to www.sonifex.co.uk/register
Product:
Serial No:

ii
Warranty
Product Warranty - 2 Year Extended
As standard, Sonifex products are supplied with a 1 year back to base
warranty. In order to register the date of purchase and so that we can keep
you informed of any product design improvements or modifications, it is
important to complete the warranty registration online. Additionally, if you
register the product on the Sonifex website, you can increase your product
warranty to 2 years. Go to the Sonifex website at: https://www.sonifex.
co.uk/technical/register/index.asp to apply for your 2 year warranty.
Sonifex Warranty & Liability Terms & Conditions
1. Definitions
‘the Company’ means Sonifex Ltd and where relevant includes companies
within the same group of companies as Sonifex Limited.
‘the Goods’ means the goods or any part thereof supplied by the Company
and where relevant includes: work carried out by the Company on items
supplied by the Purchaser; services supplied by the Company; and software
supplied by the Company.
‘the Purchaser’ means the person or organisation who buys or has agreed
to buy the Goods.
‘the Price’ means the Price of the Goods and any other charges incurred by
the Company in the supply of the Goods.
‘the Warranty Term’ is the length of the product warranty which is usually
12 months from the date of despatch; except when the product has been
registered at the Sonifex website when the Warranty Term is 24 months
from the date of despatch.
‘the Contract’ means the quotation, these Conditions of Sale and any
other document incorporated in a contract between the Company and the
Purchaser.
This is the entire Contract between the parties relating to the subject
matter hereof and may not be changed or terminated except in writing in
accordance with the provisions of this Contract. A reference to the consent,
acknowledgement, authority or agreement of the Company means in
writing and only by a director of the Company.
2. Warranty
a. The Company agrees to repair or (at its discretion) replace Goods
which are found to be defective (fair wear and tear excepted) and
which are returned to the Company within the Warranty Term
provided that each of the following are satisfied:
i. notification of any defect is given to the Company immediately
upon its becoming apparent to the Purchaser;
ii. the Goods have only been operated under normal operating
conditions and have only been subject to normal use (and
in particular the Goods must have been correctly connected
and must not have been subject to high voltage or to ionising
radiation and must not have been used contrary to the
Company’s technical recommendations);
iii. the Goods are returned to the Company’s premises at the
Purchaser’s expense;
iv. any Goods or parts of Goods replaced shall become the
property of the Company;
v. no work whatsoever (other than normal and proper
maintenance) has been carried out to the Goods or any part of
the Goods without the Company’s prior written consent;

iii
Warranty
vi. the defect has not arisen from a design made, furnished or
specified by the Purchaser;
vii. the Goods have been assembled or incorporated into other
goods only in accordance with any instructions issued by the
Company;
viii. the defect has not arisen from a design modified by the
Purchaser;
ix. the defect has not arisen from an item manufactured by
a person other than the Company. In respect of any item
manufactured by a person other than the Company, the
Purchaser shall only be entitled to the benefit of any warranty
or guarantee provided by such manufacturer to the Company.
b. In respect of computer software supplied by the Company the
Company does not warrant that the use of the software will be
uninterrupted or error free.
c. The Company accepts liability:
(i) for death or personal injury to the extent that it results from the
negligence of the Company, its employees (whilst in the course
of their employment) or its agents (in the course of the agency);
(ii) for any breach by the Company of any statutory undertaking as
to title, quiet possession and freedom from encumbrance.
d. Subject to conditions (a) and (c) from the time of despatch of
the Goods from the Company’s premises the Purchaser shall be
responsible for any defect in the Goods or loss, damage, nuisance
or interference whatsoever consequential economic or otherwise or
wastage of material resulting from or caused by or to the Goods. In
particular the Company shall not be liable for any loss of profits or
other economic losses. The Company accordingly excludes all liability
for the same.
e. At the request and expense of the Purchaser the Company will test
the Goods to ascertain performance levels and provide a report of
the results of that test. The report will be accurate at the time of the
test, to the best of the belief and knowledge of the Company, and the
Company accepts no liability in respect of its accuracy beyond that
set out in Condition (a).
f. Subject to Condition (e) no representation, condition, warranty or
other term, express or implied (by statute or otherwise) is given by
the Company that the Goods are of any particular quality or standard
or will enable the Purchaser to attain any particular performance
or result, or will be suitable for any particular purpose or use
under specific conditions or will provide any particular capacity,
notwithstanding that the requirement for such performance, result or
capacity or that such particular purpose or conditions may have been
known (or ought to have been known) to the Company, its employees
or agents.
g. (i) To the extent that the Company is held legally liable to the
Purchaser for any single breach of contract, tort, representation
or other act or default, the Company’s liability for the same
shall not exceed the price of the Goods.
(ii) The restriction of liability in Condition (g)(i) shall not apply to
any liability accepted by the Seller in Condition (c).
h. Where the Goods are sold under a consumer transaction (as defined
by the Consumer Transactions (Restrictions on Statements) Order
1976) the statutory rights of the Purchaser are not affected by these
Conditions of Sale.
Unpacking Your Product
Each product is shipped in protective packaging and should be inspected
for damage before use. If there is any transit damage take pictures of the
product packaging and notify the carrier immediately with all the relevant

iv
CE Conformity
details of the shipment. Packing materials should be kept for inspection and
also for if the product needs to be returned.
The product is shipped with the following equipment so please check to
ensure that you have all of the items below. If anything is missing, please
contact the supplier of your equipment immediately.
Item Quantity
Product unit 1
IEC mains lead fitted with moulded mains plug 1
Handbook and warranty card 1
If you require a different power lead, please let us know when ordering the
product.
Repairs & Returns
Please contact Sonifex or your supplier if you have any problems with your
Sonifex product. Email [e-mail] for the repair/
upgrade/returns procedure, or for support & questions regarding the
product operation.
Conformity
The products in this manual comply with the essential requirements of the
relevant European health, safety and environmental protection legislation.
The technical justification file for this product is available at Sonifex Ltd.
The declaration of conformity can be found at:
https://www.sonifex.co.uk/declarations
Safety & Installation of Mains
Operated Equipment
There are no user serviceable parts inside the equipment. If you should
ever need to look inside the unit, always disconnect the mains supply
before removing the equipment covers. The cover is connected to earth
by means of the fixing screws. It is essential to maintain this earth/
ground connection to ensure a safe operating environment and provide
electromagnetic shielding.
Voltage Setting Checks
Ensure that the machine operating voltage is correct for your mains power
supply by checking the box in which your product was supplied. The voltage
is shown on the box label. The available voltage settings are 115V, or 230V.
Please note that all products are either switchable between 115V and 230V,
or have a universal power supply.
Fuse Rating
The product is supplied with a single fuse in the live conducting path of the
mains power input. For reasons of safety it is important that the correct
rating and type of fuse is used. Incorrectly rated fuses could present a
possible fire hazard, under equipment fault conditions. The active fuse is
fitted on the outside rear panel of the unit.
Power Cable & Connection
An IEC power connector is supplied with the product which has a moulded
plug attached.
The mains plug or IEC power connector is used as the disconnect device.
The mains plug and IEC power connector shall remain readily operable to
disconnect the apparatus in case of a fault or emergency.
The mains lead is automatically configured for the country that the product
is being sent to, from one of:

v
Safety & Installation
Fig A: RB-RK1 Small Redbox Front Rack-mount Kit .
Territory Voltage IEC Lead Type Image
UK & Middle East 230V UK 3 pin to IEC lead
Europe 230V European Schuko round 2 pin to
IEC lead
USA, Canada and
South America 115V 3 flat pin to IEC lead
Australia & New
Zealand 230V Australasian 3 flat pin to IEC lead
Connect the equipment in accordance with the connection details and
before applying power to the unit, check that the machine has the correct
operating voltage for your mains power supply.
This apparatus is of a class I construction. It must be connected to a mains
socket outlet with a protective earthing connection.
Important note: If there is an earth/ground terminal on the rear panel of
the product then it must be connected to Earth.
WEEE Directive
The Waste Electrical and Electronic Equipment (WEEE)
Directive was agreed on 13 February 2003, along with the
related Directive 2002/95/EC on Restrictions of the use of
certain Hazardous Substances in electrical and electronic
equipment (RoHS). The Waste Electrical and Electronic Equipment Directive
(WEEE) aims to minimise the impacts of electrical and electronic equipment
on the environment during their life times and when they become waste.
All products manufactured by Sonifex Ltd have the WEEE directive label
placed on the case. Sonifex Ltd will be happy to give you information about
local organisations that can reprocess the product when it reaches its “end
of use”, or alternatively all products that have reached “end of use” can be
returned to Sonifex and will be reprocessed correctly free of charge.
Atmosphere/Environment
This apparatus should be installed in an area that is not subject to excessive
temperature variation (<0°C, >50°C), moisture, dust or vibration.
This apparatus shall not be exposed to dripping or splashing, and no objects
filled with water, such as vases shall be placed on the apparatus.
Fitting Redboxes
Redboxes can be fixed to the underside of a desk, or other surfaces
using 4.2mm holes in the sides and fixed with 2 x M4 screws or 2 x No. 6
countersink wood screws.

vi
Safety & Installation
They can also be rack-mounted, with either the front, or rear of the Redbox positioned at the front of the rack (Note: this product is front rack-mounted as
standard):
Front Mounting Redboxes: For rack mounting smaller (28cm) units the optional RB-RK1 (Red) or RB-RK1B (Black) kit can be used (which include
4 off M6 panel fixing screws).
Rear Mounting a Redbox: For rear panel mounting you can use either the RB-RK2 (in this case), or RB-RK3, depending on the size of your Redbox.
Fig B: RB-RK2 Small Redbox Rear Rack-mount Kit.
Fig C: RB-RK3 Large Redbox Rear Rack-mount Kit.

1
Headphone Distribution Amplifiers - RB-HD1 1
1 RB-HD1 Stereo Headphone Amplifier With VCA Volume Control
Introduction
Fig 1-1: RB-HD1 Front Panel
The RB-HD1 is a 1U rack-mount stereo headphone amplifier for driving
up to two pairs of professional stereo headphones from a single stereo or
mono input. One headphone socket is on the front panel with one on the
rear.
The main stereo input uses electronically balanced XLR-3 connectors on
the rear panel, which can be wired un-balanced. The output volume for the
headphones can be controlled either by a pot situated on the front panel or
a VCA signal supplied externally via the remote connector.
A mono input can be mixed into the main headphone feed, for example,
for mixing in talkback to the headphones. This has an input level control
via a recessed adjustable potentiometer. The mono mix input can also be
controlled remotely.
A stereo/mono switch is recessed on the rear panel to prevent accidental
knocking. With mono selected, audio is sent to both left and right ear
pieces. A LED power indicator on the front panel displays the power supply
connection.
Left Input
Audio XLR
Audio Input
Amplifier
Stereo Jack
Output
Stereo Jack
Output
Audio Output
Amplifier
VCA
Right Input
Audio XLR Push
Switch
Input
Mono
Mix
Stereo/Mono
Control Switch
Gain
Remote Connector Volume
Local/Remote
Control Switch
System Block Diagrams
Fig 1-2: RB-HD1 System Block Diagram

2
1 Headphone Distribution Amplifiers - RB-HD1
Stereo
Output
Volume
Level
Control
Mono Mix
Input
Mono Mix Input
Gain Adjustment
Stereo/ Mono
Switch
Local/ Remote
Control Switch
Remote
Connector
Main
Stereo Inputs Headphone
Front Panel Connections and Controls
Fig 1-3: RB-HD1 Front Panel Controls
Stereo Outputs 1-2 (Mono Outputs1-2)
The outputs available on the front and rear panel through ¼” stereo
ũĂĐŬƐŽĐŬĞƚƐĂƌĞƉƵƐŚͲƉƵůůĚĞƐŝŐŶĞĚƚŽĚƌŝǀĞϭϱϬŵtŝŶƚŽϯϮɏƚŽϲϬϬɏ
professional headphones. Each output is individually buffered.
Volume Level Control
The volume level control sets the output level of the two stereo headphone
sockets. The two headphone outputs have a maximum output of +11dBu.
Rear Panel Connections and Operation
Fig 1-4: RB-HD1 Rear Panel

3
Headphone Distribution Amplifiers - RB-HD1 1
Main Stereo Inputs (Left and Right)
The XLR-3 input connectors can take balanced professional levels, or
unbalanced by using the volume control to increase the input level, and by
connecting the non-phase to the signal ground. The input can be configured
as either a stereo input with two stereo outputs or a mono input with two
mono paired outputs. The XLR 3 pin input has the following connections:
Pin 1: Screen
Pin 2: Phase
Pin 3: Non-phase
Stereo Input Gain Adjustment
There are two preset controls on the rear panel that adjust the level of the
master input signal to the outputs from -12dB to +20dB gain.
Stereo/Mono Operation
The mode of operation may be switched between a stereo distributed
channel to 2 stereo channels, or a mono channel to two mono paired
outputs (i.e. the same signal to both ear pieces) by using the push button,
mounted on the rear panel to prevent accidental switching.
Mono Mix Input
The XLR-3 input connector can take balanced professional levels, or
unbalanced by connecting the non-phase to the signal ground. This input is
used for mixing with the main stereo input, which is controlled by the MIX_
EN pin (pin 8 on the remote connector) on the remote connector. While
this signal is shorted to the ground pin (pin 9 on the remote connector)
mixing is enabled and is only disabled once the signal from MIX_EN to pin
9 is open on the remote connector. The XLR 3 pin input has the following
connections:
Pin 1: Screen
Pin 2: Phase
Pin 3: Non-phase
Mono Mix Input Gain Adjustment
A rotary pre-set potentiometer can be used to adjust the gain of the mono
mix input by 22dBu.
Local/Remote Control Operation
The level to the two outputs can be controlled in one of two ways, either
locally, by the pot situated on the front panel or remotely, by a VCA signal
supplied externally to the remote connector.
Remote Connector
The remote connector is a 9-pin D-type socket, which is situated on the rear
panel. It has connections as shown below.
Pin No. Signal I/O Description
Pin 1 Pot wiper I Volume control signal
Pin 2 Pot top O +5V
Pin 3 N/C - No connection
Pin 4 N/C - No connection
Pin 5 N/C - No connection
Pin 6 Pot bottom - Ground
Pin 7 N/C - No connection
Pin 8 MIX_EN I Make to pin 9
Pin 9 0V - Ground
Fig 1-5: RB-HD1 Remote Connector

4
1 Headphone Distribution Amplifiers - RB-HD1
Technical Specifications RB-HD1
Audio Specifications RB-HD1 & RB-HD2:
Maximum Input Level: +28dBu
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Input Gain Range: -12dB to +20dB (pre-set pots) (RB-HD2)
KƵƚƉƵƚ>ĞǀĞů ƌŝǀĞƐϭϱϬŵtŝŶƚŽϯϮɏƚŽϲϬϬɏŚĞĂĚƉŚŽŶĞƐ
Volume Control: -80dB to +11dB gain
Mono Mix Input Gain Range: 22dBu (RB-HD1)
Connections
Main Stereo Input: 2 x XLR 3 pin female (Balanced, can be wired
unbalanced)
Mono Mix Input: 1 x XLR 3 pin female (Balanced, can be wired
unbalanced)
Outputs: 2 x ¼” (6.35mm) A/B gauge 3-pole stereo
jack sockets
Remote Control: 9-pin D-type socket
Mains Input: Filtered IEC, 110V-120V, or 220-240V
switchable, fused, 9W maximum
Fuse Rating: Anti-surge fuse 100mA 20 x 5mm (230VAC)
Anti-surge fuse 250mA 20 x 5mm (115VAC)
Equipment Type
RB-HD1: Stereo headphone amplifier
Physical Specifications
Dimensions (Raw): 48cm (W) x 10.8cm (D) x 4.2cm (H) (1U)
19” (W) x 4.3” (D) x 1.7” (H) (1U)
Dimensions (Boxed): 53cm (W) x 20.5cm (D) x 6cm
21” (W) x 8” (D) x 2.4”
Weight: Nett: 1.35kg Gross: 2.0kg
Nett: 3lbs Gross: 4.4lbs

5
Headphone Distribution Amplifiers - RB-HD2 2
2 RB-HD2 Dual Headphone Amplifier
Introduction
The RB-HD2 is a high performance 2-way stereo headphone distribution
amplifier for driving up to 2 pairs of professional stereo headphones from
a single stereo or mono input. A switch on the rear panel enables the
distribution of a mono signal to all four outputs (i.e. both earpieces of a pair
of stereo headphones) via the left channel input. The stereo/mono switch is
located on the rear panel to prevent accidental knocking.
The XLR-3 inputs are electronically balanced and can be wired unbalanced.
There are two pre-set controls on the rear panel that adjust the level of the
master input signal to the outputs.
Each output is on a ¼” stereo jack socket and is designed to drive 150mW
into 32 ohm to 600 ohm stereo headphones. The outputs are individually
buffered with their own front panel volume control. A LED power indicator
on the front panel displays the power supply connection.
Fig 2-1: RB-HD2 Front Panel
System Block Diagrams
Audio Input
Amplifier Stereo
Jack
Output
Stereo
Jack
Output
Audio
Output
Amp
Audio
Output
Amp
Master
Input
Stereo/Mono
Control Switch
Push
Switch
Stereo
Volume
Volume
XLR
Fig 2-2: RB-HD2 System Block Diagram

6
2 Headphone Distribution Amplifiers - RB-HD2
Front Panel Connections and Controls
Fig 2-3: RB-HD2 Front Panel Controls
Stereo Outputs 1-2 (Mono Outputs 1-2)
The outputs available on the front panel through ¼” stereo jack sockets
ĂƌĞƉƵƐŚͲƉƵůůĚĞƐŝŐŶĞĚƚŽĚƌŝǀĞϭϱϬŵtŝŶƚŽϯϮɏƚŽϲϬϬɏƉƌŽĨĞƐƐŝŽŶĂů
headphones. Each output is individually buffered.
Channel Volume Controls
Each channel has its own volume control so that you have control of the
signal volume to an individual output from the master input.
Rear Panel Connections and Operation
Fig 2-4: RB-HD2 Rear Panel
Volume
Level Control
Volume
Level Control
Stereo
Output
Stereo
Output
Stereo/
Mono Switch
Main Stereo
Inputs
Stereo Input Gain Adjustment

7
Headphone Distribution Amplifiers - RB-HD2 2
Main Stereo Inputs (Left and Right)
The XLR-3 input connectors can take balanced professional levels, or
unbalanced by using the volume control to increase the input level, and by
connecting the non-phase to the signal ground. The input can be configured
as either a stereo input with two stereo outputs or a mono input with two
mono paired outputs. The XLR 3 pin input has the following connections:
Pin 1: Screen
Pin 2: Phase
Pin 3: Non-phase
Stereo/Mono Operation
The mode of operation may be switched between a stereo distributed
channel to 2 stereo channels, or a mono channel to two mono paired
outputs (i.e. the same signal to both ear pieces) by using the push button,
mounted on the rear panel to prevent accidental switching.
Technical Specifications RB-HD2
Audio Specifications RB-HD2:
Maximum Input Level: +28dBu
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Input Gain Range: -12dB to +20dB (pre-set pots) (RB-HD2)
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Volume Control: -80dB to +11dB gain
Mono Mix Input Gain Range: 22dBu (RB-HD1)
Connections
Main Stereo Input 2 x XLR 3 pin female (Balanced, can be wired
unbalanced)
Outputs: 2 x ¼” (6.35mm) A/B gauge 3-pole stereo
jack sockets
Mains Input: Filtered IEC, 110V-120V, or 220-240V, fused,
switchable, 9W maximum
Fuse Rating: Anti-surge fuse 100mA 20 x 5mm (230VAC)
Anti-surge fuse 250mA 20 x 5mm (115VAC)
Equipment Type
RB-HD2: Dual stereo headphone amplifier
Physical Specifications
Dimensions (Raw): 48cm (W) x 10.8cm (D) x 4.2cm (H) (1U)
19” (W) x 4.3” (D) x 1.7” (H) (1U)
Dimensions (Boxed): 53cm (W) x 20.5cm (D) x 6cm
21” (W) x 8” (D) x 2.4”
Weight: Nett: 1.35kg Gross: 2.0kg
Nett: 3lbs Gross: 4.4lbs

8
3 Headphone Distribution Amplifiers - RB-HD6
3 RB-HD6 6 Way Stereo Headphone Distribution Amplifier
Introduction
Fig 3-1: RB-HD6 Front Panel
The RB-HD6 is a high performance 6-way stereo headphone distribution
amplifier for driving up to 6 pairs of professional stereo headphones from
a single stereo or mono input. A switch on the rear panel enables the
distribution of a mono signal to all twelve outputs (i.e. both earpieces of a
pair of stereo headphones) via the left channel input.
Alternatively, the RB-HD6 can be used as six separate stereo headphone
amplifiers by using the override (insert-point, or break-jack) input
associated with each outlet. A typical application might be to provide
common headphone feeds for guests around a table in a radio studio, with
a separately derived feed, perhaps including talkback, for the presenter.
The over-ride inputs can also be configured as parallel outputs (to the front
outputs) by altering jumper settings inside the unit.
The XLR-3 inputs are electronically balanced and can be wired unbalanced.
There is a master control that adjusts the level of the master signal to all
the outputs. This master control can be disabled by the use of internal
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headphones and is individually buffered with its own volume control.
The input level and output volume controls are all potentiometers on
the front panel. The stereo/mono switch is recessed on the rear panel to
prevent accidental knocking. A LED power indicator on the front panel
displays the power supply connection.

9
Headphone Distribution Amplifiers - RB-HD6 3
System Block Diagram
Fig 3-2: RB-HD6 System Block Diagram

10
3 Headphone Distribution Amplifiers - RB-HD6
Rear Panel Connections and Operation
Fig 3-3: RB-HD6 Rear Panel
Stereo Input (Left and Right)
The XLR-3 input connectors can take balanced professional levels, or
unbalanced by using the front panel master control to increase the input
level, and by connecting the non-phase to the signal ground. The input can
be configured as either a stereo input with six stereo outputs or a mono
input with six mono paired outputs. The XLR 3 pin input has the following
connections:
Pin 1: Screen
Pin 2: Phase
Pin 3: Non-phase
Stereo/Mono Operation
The mode of operation may be switched between a stereo distributed
channel to 6 stereo channels, or a mono channel to six mono paired
outputs (i.e. the same signal to both ear pieces), by the push button on the
rear panel which is recessed to prevent accidental switching.
Channel Insertion Inputs/Parallel Outputs
Each channel has an unbalanced override/insertion input via a ¼” stereo
audio jack socket on the rear panel, which overrides the master input.
Stereo/Mono Operation
Channel Insertion Inputs
Stereo
Inputs
Each connector can also be individually configured as a parallel output
providing the same signal as the output on the front of the unit. To
configure the jack connector as an output, you’ll need to alter some jumper
settings inside the unit.
Removing the Equipment Covers
To get inside the RB-HD6, first ensure that it has been disconnected from
the mains power and that the mains IEC lead to the unit has been removed.
Observing anti-static precautions, undo the four cross-head screws on the
back panel at the far left and far right of the panel (2 at each end). Also
undo the small brass screws which hold the top and bottom panels to the
rear panel. The rear panel should slide backwards out of the unit together
with the main circuit board.
Configuring Insert Inputs/Parallel Outputs
On the main circuit board, you’ll see some jumpers (small black rectangles),
the position of which will define whether a particular jack socket operates
as an input or output. The drawings below show the different jumper
settings available. Each input/output can be configured individually, so you
could have three jacks set as inputs and three as outputs if needed.