White Instruments 4926 User manual

5 January 2005 –This contact update page has been added to the
Acrobat document you have downloaded. Please disregard any contact
information printed within the document.
Our Mailing and Shipping Address:
White Instruments Div. C Van R, Inc.
1514 Ed Bluestein Blvd., Suite 201 (for U.S. Mail)
Austin, TX 78721 U.S.A.
Phone: [phone]
Fax: [phone]
Main Email Address: [email protected]
World Wide Web Site: http://www.whiteinstruments.com/
Note: Repairs and packages should be shipped to Suite 202

Model 4926
Distribution Amplifier
Users’ Manual

QUICK START
To connect your 4926 unit as quickly as possible, without having to read
the entire manual, just follow these steps.
1. Using the 4 mounting screws provided, mount the unit into your rack. Do not plug
the unit in.
2. Set the AC voltage back panel switch to the appropriate 115 or 230VAC setting.
3. Connect the input channel(s) for either balanced or unbalanced operation, paying
careful attention to the connections shown in Figure 1. Note: For unbalanced
operation, audio negative must be connected to signal common, otherwise a 6 dB
loss in signal level will result.
4. Connect the output cables for either balanced or unbalanced operation, paying
careful attention to the connections shown in Figure 2. Note: For unbalanced
operation, audio negative must be connected to signal common, otherwise a 6dB
loss in signal level will result.
5. Set the output assignments by setting the 2 left-most levers in each 7 position
output DIP switch to the desired signal routing configuration. A channel is ”on” if
its lever is up.
6. Check all signal connections. It is good practice to initially set the input signal
gain to unity (input DIP switch levers all up) on both inputs and the output
attenuation to 31 dB (output DIP switch levers all down) on all outputs. This will
help prevent overdriving any devices connected to the 4926 at initial power-up.
Plug the unit in.
7. Set the input gain and output attenuation to the desired setting. For example, 11
dB of gain would require the 8, 2 and 1 levers to be pushed down. For gain
adjustments, it is good practice to reset the DIP switch lever settings to the ”up”
position before entering the new gain setting. For attenuation adjustments, it is
good practice to reset the DIP switch levers to the ”down” position before
entering the new attenuation setting. These procedures prevent excessive output
signal amplitudes during level setting. Remember: It is desirable to use as little
output attenuation as possible when setting the 4926 gain structure. This
maximizes the 4926 dynamic range and reduces noise.
Figure 1 -Input Connections

UNPACKING
Carefully unpack and inspect your new 4926 for shipping damage. If the unit is damaged,
immediately notify the carrier and us. For U.S. orders, your unit was shipped with full
insurance unless you requested otherwise. The package should contain the following
items
1. The 4926 unit.
2. This manual.
3. Four rack mounting screws.
4. One user service card.
FRONT PANEL FEATURES
The 4926 intentionally does not have any front panel controls. Each input has a green (0
dB) and red (clip) LED which indicates the input level measured after the gain stage.
Each output has 2 green LEDs which indicate 0 dB and -10 dB levels at each individual
output. Power is indicated by a green LED. Figure 3 identifies all of the 4926 front panel
features.
Figure 2 – Output Connections
Figure 3 – Front Panel Features

REAR PANEL FEATURES
Each input and output in the 4926 is electronically balanced and interfaced with
removable screw terminal connectors. Input gain is set using a 4 lever DIP switch and
output attenuation is set using 5 of the 7 levers in each output DIP switch. Above each
input gain switch is a 0 dB calibration LED. Output assignments are made using the 2
remaining levers in each 7 position output DIP switch, which allow selection of
individual input channels or a sum of both inputs. The back panel also houses the AC
voltage select switch and the fuse holder. Figure 4 identifies all of the 4926 rear panel
features.
For convenience, a functional block diagram of the 4926 is provided on the unit top
panel.
SOUND SYSTEM CONNECTIONS
This manual is not intended to provide an exhaustive explanation of sound system
connections, however, in the interest of getting the absolute best performance from your
4926, a brief summary is given below.
NEVER remove the grounding lug from the AC power cable. To do so is dangerous and
unlawful in most areas! Further, it is unnecessary since the audio circuitry can be isolated
from earth ground by removing an internal jumper inside of the unit.
The shield should not be thought of as part of the audio circuit. Rather, it simply helps
protect the audio circuit from electromagnetic and RFI noise. It is a generally accepted
practice to connect the shield to earth ground at only ONE end of the audio cable. The
other end should be left open or connected to earth ground through a 0.01 microfarad
capacitor.
The 4926 circuit common is tied to chassis ground through an internal jumper. The user
may isolate circuit common from chassis ground by removing the top panel and
unplugging the jumper, labeled ’E1’, which is located on the pc board near the
transformer.
Figure 4 – Rear Panel Features

Unbalanced Operation
The 4926 can have each of its signal inputs or outputs independently connected for either
balanced or unbalanced operation. This feature, for example, allows the user to take an
unbalanced input signal going into the 4926 and generate balanced output signals. For
minimum external noise pick-up, balanced connections are usually chosen. Unbalanced
connections are sometimes chosen when cable cost is a factor and when external
electromagnetic interference is minimal.
Balanced Operation
A balanced audio transmission line is a system which, like the shield, provides protection
from electromagnetic disturbances or RFI noise.
In order forbalancing to effectively reduce external noise, two conditions must be
met:
1. The+ and –input or output conductors must be in close proximity to each other so
that any external electromagnetic disturbance is equally imposed on both
conductors.
2. Both+ and -leads must be referenced to a common point in the circuit.
When operating in balanced mode, the 4926 only amplifies the difference signal between
the +and -leads, rejecting any signal common to both leads. Thus, any external
interference present on both + and -input leads is rejected in the input stage of the 4926.
The effectiveness of this rejection is measured by the common mode rejection ratio
(CMRR)
Important: A device’s internal circuit design, not the audio interface (cables or
connectors), defines whether the unit is balanced or not. A balanced device may be
externally configured to operate unbalanced. However, an unbalanced device cannot be
balanced. A balanced transmission line requires balanced driving and terminating devices
as well as a balanced cable configuration. If any of these conditions is not met, the
transmission line will not be balanced.
SYSTEM SET-UP
In order to obtain the maximum performance from your 4926, use the following set-up procedure
and refer to the block diagram in figure 5.
1. Connect the 4926 to the rest of the sound system as explained in the ’Quick Start’ section
at the beginning of this manual.
2. Set the gain levels of the distribution amplifier while maximizing the dynamic range
used.
A. Turn off all devices driven by the 4926.
B. Set the 4926 output assignments using the 2 dedicated levers in each
output DIP switch. Refer to figure 5, if necessary.

C. Send program material at the maximum anticipated signal level into both
input channels of the 4926. Set the input gain such that the red input clip
indicators occasionally flash. If the input signal level is unknown, its level
may be determined to within 1 dB by adjusting the input gain in 1 dB
steps until the green ’0 dB’ back panel LED turns on. The amount of gain
added is the amount the input signal level is below 0 dB.
D. Adjust the attenuation on all outputs to maximum by setting all the DIP
switch levers to their down or ’on’ position. Turn on all of the devices
driven by the 4926. Reduce the attenuation of the appropriate output to the
desired level in 1 dB increments following the recommended procedure of
step 7 in the ’Quick Start section.
PleaseNote:If a particular output has been assigned to the a sum
of (the inputs. The input signals are simply added and therefore,
may be higher than the individual input levels. Also, remember if
the device driven by the 4926 has a gain setting, it is desirable to
use as little attenuation as possible in the 4926 output stages so that
minimum gain is required in the following device.
This set-up results in maximum utilization of the 4926 dynamic range and ensures good
gain structure to minimize audible noise.
Figure 5 – Block Diagram

Specifications
Number of Channels:
Input two
Output six
Frequency Range:
20 Hz –20 kHz, ±0.5 dB
Maximum Operating Level:
+21 dBu
Input Gain:
15 dB in 1 dB increments using 4 position DIP switch.
Input Level indicators:
Front Panel:
Red (clip) and green (0 dB) LEDs.
Rear Panel:
Green (0 dB) LED.
Output Attenuation:
31 dB in 1 dB increments using 5 position DIP switch
Output Level indicators:
Front Panel:
Green (0 dB) and green (-l0 dB) LEDs.
Output Assignment:
Assigned from either input or sum of both using 2 levers on each output DIP switch.
Dynamic Range:
>114 dB.
Distortion:
Less than 0.01% into 600 ohms, 20Hz -20kHz.
Crosstalk:
Less than -90 dB at 1 kHz.
Input Impedance:
30 kΩbalanced, l0 kΩunbalanced.
Input Circuit:
Active servo-balanced. Can operate unbalanced with no gain change.
Output Impedance:
102 ohms balanced, 51 ohms unbalanced.

Output Circuit:
Active servo-balanced. Can operate unbalanced with no gain change.
Connector Types:
Input/output -removable screw terminals.
Power Requirements:
100-130 or 200-260 VAC, 50/60 Hz, 30 Watts.
WARRANTY POLICY
Your White Instruments 4926 is warranted against defects in manufacturing, workmanship and
original components for a period of THREE YEARSfrom the date of purchase During this
period, White Instruments will repair or replace the unit, at our option, so long as it has not been
subjected to abuse. Abuse may be physical and/or electrical in nature White Instruments will be
the sole judge of these criteria
White Instruments is the only warranty repair facility in the United States. Outside the United
States, White Instruments distributors are authorized to make warranty repairs
Warranty Repairs
Your 4926 should be securely packed and shipped, prepaid, to White Instruments or one of its
authorized offshore distributors. Our U.S.A. shipping address is given in the
COMMUNICATIONS section below. Contact the factory for the name and address of the
distributor nearest you
A copy of your sales receipt should be included to establish the warranty date in addition to a
letter detailing the unit’s malfunction.
Every effort will be made to complete warranty repairs within 5 working days of receipt of the
unit. Your 4926 will be returned to you prepaid via surface freight. If you instruct us to return
your 4926 via air freight, it will be shipped with freight charges collect.
Out-of-Warranty Repairs
Should the required repairs not be covered by our warranty you will be charged for the parts and
labor required to repair the unit. Should you require an estimate of charges prior to repairing the
unit you should notify White Instruments of this when returning the unit. Every effort will be
made to complete the repair within 5 working days. The unit will be returned C.O.D. unless other
arrangements have been made.
As a service to our customers, our repair center is non-profit.
Communications
White Instruments
Telephone: [phone]
Fax: [phone]
1514 Ed Bluestein Blvd., Ste. 108
Austin, Texas 78721