BURK Technology LX-1 User manual

LX-1
Stereo Selector
INSTRUCTION MANUAL
7 Beaver Brook Road
Littleton, MA 01460
[phone]
FAX [phone]
Copyright 1992-1997 by Burk Technology, Inc.
REV A

2

3
Contents
Section One Features..............................................................
... 5
INTRODUCTION Matching Standard
Levels.................................... 6
Controls..............................................................
.. 7
Warranty.............................................................
.. 7
Section Two General...............................................................
... 8
INSTALLATION Memory..............................................................
.. 8
Connectors..........................................................
.. 8
Audio
Wiring........................................................ 9
Recommended
Practices....................................... 10
Connecting Unbalanced Sources.......................... 10
Setting Audio
Levels............................................ 11
Setting Alternate
Jumpers..................................... 12
Audio
Outputs...................................................... 13
Audio Output
Connectors..................................... 14
Deriving
L+R........................................................ 15
Control Connector
Wiring.................................... 16
Remote Control
Connections............................... 17
Logic Output Connection to External Devices..... 18
Section Three READY
Mode...................................................... 19
OPERATION Select Alternate
Mode.......................................... 19

4
MIX
Mode............................................................ 20
Bar Graph
Display................................................ 20
Section Four Audio
Board......................................................... 21
TECHNICAL DESCRIPTION Display
Board....................................................... 23
Logic
Board.......................................................... 24
Section Five Table of
Contents................................................. 27
DOCUMENTATION Schematics..........................................................
.. 28
Parts
Location....................................................... 36
Printed Circuit Board X-Ray Views..................... 38
Parts
List............................................................... 41

5

6
Section One
INTRODUCTION
Features
•Select or mix from six stereo input sources.
•Control and read the status of the unit from the front panel, through the individual source
connectors on the rear panel, or by remote control.
•Control cart, tape and satellite feeds with machine-follow audio.
•Match input levels of -10, 0, +4 or +8dBu. (Note: In this manual levels are expressed as dBu,
except where a 600Ωload is known to exist.)
•Use the LOOP function to switch a processor in/out of the program path. Monitor program
level on the dual 12 segment bar graph display.
•Distribute identical MAIN and SUB out-puts.
•Prevent accidental switching by locking out all control functions with the “safe” mode.
The Burk Technology LX-1 Stereo Selector simplifies and improves studio and transmitter
systems by providing elegant selection and mixing of program sources. Featuring quality;
flexibility and easy to use, the LX-1 can serve a number of station needs.
Designed to be the final “gateway” for broadcast systems, the LX-1 can serve as the hub of a
multi-studio complex, or as the switching center for satellite, network and studio feeds. As a
master control switcher, it can be controlled from a central point, by remote control, or from each
studio it serves. Where desired, each studio can have its own air control and ON-AIR indicator.
Low cost, ease of interface and machine-follow audio capability make the LX-1 a good choice as
a console input extender, or as a switcher for automation or production systems.
The usefulness of the LX-1 is enhanced by full remote control capability, external processor
switching, a SAFE mode and memory retention during power loss.
With the LX-1 you can:

7
Switching Quality
High Noise Rejection From all Sources
Matching Standard Levels
With the coming of the LX-1 it is time to do away with outmoded patch cords and relays. The
Burk LX-1 provides versatile and foolproof operation and a cleaner audio path.
The LX-1 sets new standards for switcher audio performance. It uses noiseless “soft” switching to
give clean program transitions. Instead of the “chopping” action of relays, switches, patch cords
and typical electronic switchers, the LX-1 makes a controlled transition from one source to the
next. The turn-on and turn-off transitions are never audible as such. The audio simply appears or
disappears. This effect is particularly impressive when working from live or digital sources. Clean
audio appears out of dead silence.
When a channel is turned on, its audio is passed through the LX-1 with very low distortion,
typically a few thousandths of a percent. When a channel is switched off, the LX-1 yields typically
100 dB of isolation. This assures there will be no audible noise or crosstalk from fast forwarding
of tape or hot inputs. Off is OFF.
Not only is the LX-1 a very low-noise device, its extraordinary 100dB common-mode rejection
will reduce hum and noise from ground loops and station cabling. An important design goal was
achieving high noise rejection from unbalanced sources such as consumer CD and DAT machines.
This performance, and the ability to accept typical “HI-FI” levels, makes the LX-1 the best way to
integrate consumer and semi-professional equipment into a studio environment.
It is recommended practice to calibrate all distribution signals to a standard level, typically +4
dBu. Unfortunately, manufactures do not always adhere to standards. For example, a cart
machine may be designed for “0” output level. Jumpers on the LX-l’s audio board for each
channel may be set to standard levels of-10, 0, +4 and +8 dBu.

8
Controls Displays and Connectors
•Audio board and power supply
•Logic board
•Display board
Warranty
The front panel switches (READY, LOOP, MIX and channels 1-6) have built-in status lights. The
dual 12-segment three color program level displays feature peak-hold on the upper five segments.
The LX-1 uses convenient Mini Combicon connectors that require only a screwdriver for
assembly. No crimping, soldering or special tooling is needed.
The rear panel has audio and control connectors for each of the six inputs as well as MAIN-SUB
and LOOP audio outputs. The LX-1 output stages more closely simulate high quality output
transformers than typical designs and will drive high levels into complex loads, such as long audio
lines and complex studio wiring.
Full remote control capability is provided through the ‘A” and “B” remote control connectors on
the rear. As an added convenience, power is provided for lighting LEDs for external status
indication.
The LX-1 circuitry is contained on three circuit boards:
Burk Technology warrants the LX-1 to be free of defects in materials and workmanship for a
period of 24 months from the date of purchase. Equipment will be repaired or replaced at the
option of Burk Technology and returned freight prepaid to the customer. Damage due to abuse or
improper operation or installation of the equipment or caused by fire or flood or harsh
environment is not to be covered by this warranty. Damage in shipping is not the responsibility of
Burk Technology A return authorization must be obtained before returning any equipment.
Materials returned under this warranty must be shipped freight prepaid and insured in the original
shipping carton or suitable substitute to Burk Technology
Repairs not covered under this warranty will be made at prevailing shop rates established by Burk
Technology.
THE WARRANTY SET FORTH ABOVE IS IN LIEU OF ALL OTHER WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. BURK
TECHNOLOGY SHALL NOT BE LIABLE TO ANY PARTY FOR ANY INCIDENTAL,
SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES ARISING FROM THE USE OF
THIS EQUIPMENT

9
Section Two
INSTALLATION
General
Memory
Connectors
CAUTION
Carefully unpack the LX-1 and save the packing material. The LX-1 should be installed in a well-
grounded equipment rack. High common-mode rejection, good case shielding and general
immunity to RF and magnetic fields make installation easy; however, good engineering practices
should be followed. The LX-1 and audio lines should be kept away from large power
transformers, RF generating devices and equipment that may produce inductive line transients.
The filtered power entry module and a well isolated toroidal power transformer contribute to
freedom from electrical noise.
Unless otherwise requested and marked, the LX-1 is wired for operation at 117 vac nominal,
50/60 Hz; 30 watts. The toroidal power transformer allows operation from UPS or inverter. See
the power supply schematic, page 37, for 230 volt strapping.
The LX-1 has memory retention that should be adequate for normal station shutdowns and power
outages; however, it is best not to power it from a switched power source. The best practice is to
leave the unit powered continuously If power is off too long, the LX-1 will reset all functions to
off and default to “safe.”
The LX-1 uses Mini Combicon connectors. These simplify installation and wiring changes. The
connectors are actually removable terminal strips. Wire strippers and a small blade screwdriver are
the only tools needed to attach the connectors.
The LX-1 uses six and twelve pin connectors for both audio and control functions. It is imperative
that plugs (removable terminal strips) are inserted into the correct rear panel connectors.
Interchanging audio and control connectors, especially the remote control connectors, can
damage the LX-1 and external devices.

10
Figure: 1 Input connectors
We recommend labeling each plug connected to the LX-1 . A “Sharpie” marking pen is ideal for
this purpose.
The top row of 6-pin rear panel connectors are for channel control. They provide Ready tally,
channel ON indication, start and stop pulses and permit channel selection. The two 12-pin
connectors on the top row permit full remote control.
The audio connectors are located along the lower portion of the rear panel. The six 6-pin
connectors are the channel audio inputs and the two 12-pin connectors are for program output
and Loop functions.
PIN #1Pin #1 of all connectors is located to the left. See figure 1.

11
Audio Wiring
Figure 2: Audio Input Connector Wiring
1 2 3 4 5 6
L+ L- GND R+ RGND
Recommended Practices
Connecting Unbalanced Sources
The audio input and output connectors have ground terminals for each balanced line. This permits
use of separate cables (Belden 8451) or more convenient two pair cables that have a single shield
drain (8723).
Refer to input connector wiring, figure 2, page 7.
The “hot” front-end the LX-1 uses a multi-stage “instrumentation amplifier” with a 50KΩload
impedance. The LX-1 should bridge input devices. Most non-reactive devices (solid-state
amplifiers and consumer devices) do not require termination. In some cases termination is
required to maintain correct output level. Source devices that require termination should be
terminated with the proper resistor.
In general, studio systems with self-terminating outputs and bridging inputs are easier to work
with and deliver higher performance. Avoid the use of pads at the input and output of the LX-1.
Pads may reduce total system dynamic range and common-mode rejection.
Balanced sources should be handled as if the LX-1 input is a transformer. Generally, the shield
should be connected to the LX-1 audio input ground terminal and left open at the source end.
Both the LX-1 and the sources should be connected to a secure ground. A
“star” or “transmission” ground system is recommended. That is, there should be only one path
from each device to station ground.
It will be observed in practice that the 100dB plus CMR of the LX-1 will tend to make grounding
and shielding less critical. This, however, is no license to violate good engineering practices. It is
possible, for example, that input lines will have unequal noise voltages induced on the signal legs.
Unbalanced sources present a special case. Since the LX-1 inputs are high impedance, and high
common-mode rejection is maintained even with unequal source impedances, unbalanced sources
should be treated the same as balanced sources.
The best way to connect unbalanced sources, like consumer CD players, is shown in figure 3
below. The + input line is connected to the “hot” side of the source while the - line is connected
the ground of the unbalanced source. The cable shield is tied to the ground terminal of the LX-1
Both the LX-1 and the source should be tied to the same system ground. Only one ground should
be used for each device.

12
Figure 3: Unbalanced Sources
Setting Audio Levels
Figure 4: Input Jumpers
Wired this way noise voltages along the shielded audio line will still be canceled. In addition, the
typically low impedance of the source, when connected to the high impedance of the LX-1, will
cause ground effect noise to be attenuated by the LX-1,5 high common-mode rejection.
There is a natural tendency to want level tweaks at various points within the audio system. This
temptation should be resisted. A house level should be established and strictly adhered to. Ideally,
each source should be calibrated to a house level, such as +4dBu.
Installation of the LX-1 is a good time to think through your house audio level practices. We
strongly recommend that a house level standard be established FIRST. Field tests have
demonstrated that the duplication of level tweaks throughout an installation can deteriorate total
system performance. Your station can measure better and sound better if the least amount of
amplification and the least amount of attenuation is used in the program path.
For example, a line-level network, news or satellite feed should not be padded down to mic level
so that it can be fed into a console mic channel. The LX-1 offers a better solution. Using it to
select from among several high level sources will give cleaner sound, simplify program switching
and it may even free up a console.
The gain structure of the LX-1 is very accurate and stable. If input sources have been properly
calibrated earlier in the system, only level range adjustment should be required in the stereo
selector. The input sensitivity of the LX-1 can be set for standard levels of-10, 0, +4 or +8 dBu.

13
Select Alternate Jumpers
Figure 5: Output Jumpers
Level programming should be done at the time of installation. Remove the unit’s top cover and
locate the six pairs of 2 x 4 headers along the front of the main (lower) printed circuit board. Each
input has headers for left and right channels. The header pairs are numbered 1 to 6.
Jumpers on the headers are used to set channel input sensitivity. A position guide is printed on the
circuit board near input two. Move the push-on jumpers for left and right channels to the desired
position. For example, for a +4 dBu input set the jumpers to the second position from the left. See
figure 4.
When input jumpers are set correctly, all inputs will produce the same internal level on the LX-1’s
mixing busses. This internal level will produce +4 dBu or +8dBu at the output, depending on the
setting of the output level jumpers.
The LX-1 12-segment program level bar displays may be used as a convenient aid for trimming
the source levels. This is especially handy when a level meter is not available, or would be
inconvenient to use.
Normal program output level, or “0,” is indicated by the left and right channel yellow LEDs. “0”
on the display indicates either +4 or +8 dBu output. The point where the LED comes on is a very
accurate indication of “0” level. There is a very narrow “flutter” range as the LED comes on.
This, plus the visibility of the distinctive yellow LED, permits accurate level setting even from
across the room.
The next step is selecting the nominal program output level of the LX-1 This can be either +4 or
+8 dBu. The output level jumpers are located to the left of the main buss jumpers near cable
connector J 1. For +4 dBu output the jumpers should be on the two outer pins. For +8 dBu the
jumpers should be on the two inner pins. See figure 5.
While the cover is removed from the LX-1, you should decide how the SELECT mode will
function. In the normal SELECT mode (while MIX is not on) selecting a new source will switch
to that source and cancel the previously selected choice. Selecting the same source again will not
do anything. When the 51 juniper on the logic board is moved from SEL to ALT, the LX-1 will
respond to channel selection by alternately turning the selected channel on and off See figure 6.

14
Figure 6: Select Jumper
Audio Outputs
Once the levels have been programmed, and jumper S1 set, you can replace the cover and
proceed to completing installation.
Note: When replacing the top cover, be sure to place the short screw in the front center hole.
The LX-1 has outputs for left and right MAIN, SUB and LOOP functions. The MAIN and SUB
outputs are identical feeds driven by separate amplifiers that deliver either +4 or +8 dBu at meter
“0.” The LOOP output is +4 dBu and duplicates the signal on the mixing bus .
When LOOP is not active, the mixing bus is passed to MAIN and SUB outputs. When LOOP is
on, the signal on the LOOP input connector is passed to the MAIN and SUB outputs.
The LOOP function is intended to switch an external audio processor in or out of the program
path; however, it can be used for many other purposes such as switching an EBS generator. Its
ability to be controlled remotely, and the fact that the LX-1 will return to normally selected audio
when LOOP is turned off add to the usefulness of the LX-1.
The “600Ω” Main and Sub outputs can drive 300Ωloads with only slight effect on maximum
output level, and no loss of level below maximum output. The Loop output load should not be
less than 600Ω. The LOOP input is 25KΩbridging, at +4dBu.
The output stages of the LX-1 are more complex than the conventional push-pull arrangement.
Grounding an output leg of the LX-1 will have little effect on output level, except that maximum
power output will be reduced to half
Lowest distortion and noise will be achieved when the LX-1 outputs drive balanced loads but the
LX-1 can directly feed unbalanced inputs. Simply connect the unbalanced input between ground
and the + signal line.

15
Figure 7 Output and Remote connectors
Audio Output Connectors
1 2 3 4 5 6 7 8 9 10 11 12
L- L+ GR- R+ G L- L+ GR- R+ G
←--------------Main----------------→←---------------Sub------------------→
1 2 3 4 5 6 7 8 9 10 11 12
L- L+ GR- R+ G L- L+ GR- R+ G
←-----------Loop Out-------------→←--------------Loop In---------------→
Figure 8: MAIN-SUB OUTPUTS
Figure 9: LOOP OUTPUT-INPUT
The flexible output configuration of the LX-1 can be a real problem solver. A typical example
would be feeding MAIN audio to a transmitter and using SUB audio for studio distribution. The
separate outputs could also feed a second transmitter.
In AM/FM stations the LX-1 could continuously feed an FM transmitter via the LOOP output
while an AM feed could be sent from the MAIN outputs. The LOOP function, under remote
control, could then switch between simulcasting FM on AM, or select from a separate AM source
via the LOOP input.
Another use for the LOOP function is for selecting an alternate program source when it is desired
to return to the previously selected source. This is an ideal way to generate an EBS test. Another
possibility is relaying EBS tests under control of the originating station.
The LX-1 is ideal for use at unattended transmitter sites. By remote control the LX-1 could select
a satellite down link or automation feed and switch back to the studio feed.
There are times when a monophonic feed is needed for an AM transmitter. There is a simple way
to achieve this with the LX-1 An L+R feed can be derived by making a simple resistive combiner
using four 300O resistors. See figure 10.

16
Deriving L+R
Control Connector Wiring
Figure 10
The balanced left and right LX-1 outputs are combined to form an L+R feed. The combining pad
loss is less than 4 dB when driving a 6000 loads. This circuit can be attached to either program
output (MAIN or SUB) or the LOOP output.
It is possible to drive this combiner in parallel with the normal 6000 load. Since the pad will
reduce channel separation to approximately 30dB, it is suggested that it be attached to an output
that is not feeding an FM transmitter.
Each of the six channel control connectors provides tally of READY and channel selection. See
figure 11, Channel Control Wiring Momentarily switching pin 3 to ground will select the channel.
Pin 6 is control common.
READY toggle is available on Remote Control connector ‘A,” pin 10. Pins 1 and 11 of remote
control connector ‘A,” the left most of the two 12-pin remote connectors, have 6 VDC available
for driving external LEDs. Current limiting resistors of 3300 to 4700 must be used in series with
each external LED. See figures 11-15.

17
Figure 11: channel control Wiring
PIN USE
1READY LIGHT
2CHANNEL ON LIGHT
3TAKE SWITCH
4STOP PULSE
5RUN PULSE
6GROUND
Each of the six control connectors provide start and stop pulses for controlling external devices.
When a channel is switched on, an open collector output on pin 5 will pulse low. When a channel
is switched off, pin 4 will pulse low.
The start and stop pulses are approximately one second long. Lamp control and start and stop
pulses are open collector outputs that can sink 250 mA., 28 volts. See figure 15 for methods of
interfacing these control functions to other equipment.
Figure 12: Control Connector Wiring

18
Remote Control Connections
REMOTE CONTROL CONNECTORS
Figure 13: Figure 14:
Figure REMOTE “A’ Figure REMOTE “B”
PIN USE PIN USE
16 VDC @ 25O mA* 1CH 1 LIGHT
2GROUND* 2CH 1 SWITCH
3LOOP LIGHT* 3CH 2 LIGHT
4MIX LIGHT* 4CH 2 SWITCH
5LOOP LIGHT 5CH 3 LIGHT
6LOOP SWITCH 6CH 3 SWITCH
7MIX LIGHT 7CH 4 LIGHT
8MIX SWITCH 8CH 4 SWITCH
9READY LIGHT 9CH 5 LIGHT
10 READY SWITCH 10 CH 5 SWITCH
11 6 VDC @ 250 mA 11 CH 6 LIGHT
12 GROUND 12 CH 6 SWITCH
•Pins 1-4 can be used to extend the flexibility of the control connectors for channels 1-6 by
providing LOOP and MIX light outputs. Except for common ground, these pins are
electrically isolated from LOOP and MIX light outputs (pins 5, 7) for remote control system
use.
A full remote control interface adds to the flexibility of the LX-1 . Control is possible from either
the channel control connectors or from the remote control connectors. This flexibility allows the
LX-1 to be controlled from external control panels or the station’s remote control system, or
both.
Open-collector status outputs on the remote control connectors are separate from those for the
front panel and those provided on the channel control connectors. All control circuits have a
common ground. This is ideal for use with the Burk TC-8 or ARC-16 remote control systems.
Remote Control Connector “A” provides mode control and system status. Note that switch
connections for a given function are wired in parallel. LOOP and MIX lights appear twice on this
connector. Pins 3 and 4 can be used to extend the capability of control connectors
1-6. Pins 5 and 7 are for remote control system use. Remote control connector “B” provides
status outputs and controls for the six audio channels.

19
Logic Output Connections to External Devices
Figure 15: Logic Output Connections to External Devices
Methods of interfacing the open-collector outputs of the LX-1 to external lamps, status indicators
and machine start and stop circuits.

20
Section Three
OPERATION
READY Mode
Select Alternate Modes
When the LX-1 Stereo Selector is first powered up, and has lost memory, it defaults to the SAFE
mode. All lights, all channels, LOOP and
MIX will be off In this mode the LX-1 will only respond to a command to enter the READY
mode.
To enter the READY mode, press the READY button on the front panel, or execute a READY
command from the remote control connector. The READY light will light and the LX-1 will now
accept all commands.
The READY mode provides security for those times when all switching is to be disabled. When
used as a master control switcher it may be desirable to set READY off until just before switching
is desired. This feature is useful when each studio has its own selection button. Accidentally
pressing a button will not then switch studios.
In the READY mode channel selection, LOOP and MIX control is possible from the front panel
or from remote locations. Momentary closure on any channel select pin will select that channel
and illuminate the selection status indicators (front panel lights and remote control status).
When the MIX light is off the LX-1 functions as a one-at-a-time input selector. Once a source is
on, further attempts to select that source will have no effect. This is the normal, or SELECT
mode, of operation.
The LX-1 can be programmed for alternate action (press on, press off) in the select mode. This is
accomplished by moving the jumper on 51 on the logic board from SEL to ALT. See figure 6,
page 8, “SELECT ALTERNATE JUMPERS.” This feature is handy when a source needs to be
repeatedly turned on or off while in the SELECT mode.