25v / 70v / 100v in-line constant
voltage
distributed audio transformers
(70v installation guidelines i)
Connecting speaker systems in a 25v /
70v / 100v
constant voltage distribution systems
(These systems are typically
used for paging and background music and other multiple inputs, where high sound
volume or even, sometimes, quality of sound is not the main consideration.)
TIC Corporation ed. note: the following is
meant as a general guide to assist our customers world-wide in their
basic understanding of the wiring and installation of TIC Corporations
range of audio products and exterior speakers in general. Due to the
many diverse conditions and requirements for individual installations
and site conditions no guarantees are expressed or implied within this
document by TIC Corporation.
TIC Corporation ed. note; this printed guide
comprises a simplified explanation of general 25v/ 70v/ 100v transformer
use and is not meant to be or imply a theoretical or experts
dissertation of 70-volt in-line distribution systems transformers.
How to install 70v distributed audio systems
The section previously, TIC Audio Installation Basics
II, explained how to connect speaker systems in a typical sound
reinforcement system. Public address (PA) systems typically use a
different mechanism for connecting speaker systems. Each speaker system
is connected to a special transformer, called a line transformer, which
is connected to the 70-volt distribution line from the power amplifier.
Many 70v power amplifiers designed for PA systems provide both standard
4/8/16-Ohm speaker connections and the 70v in-line distribution
connection.
Fig. 3
Fig. 3 shows a typical PA system using a 70v constant voltage
distribution system. Note that a separate line transformer is used for
each speaker system. Each line transformer has multiple taps so that you
can control the amount of power reaching the speaker system. Typical
taps are 2.5, 5.0, 10, 15 and 20 watts. To install a constant voltage PA
system, you must solder the wires from the primary of the line
transformer to the distribution line and the secondary of the line
transformer to the speaker system. Plug and Jack connectors usually are
not used because PA systems are typically semi-permanent.
Constant voltage distribution, as used in public address systems,
uses tapped transformers, such as the TIC Corporation model number SP
70T unit, to provide the signal to each speaker system on the line. The
transformer taps allow you to select a different wattage for each
speaker to control the volume level for different areas of the building.
One benefit of the constant voltage distribution system is that you
don’t need to worry about the aggregate impedance of speaker systems you
attach to the 70v power amplifier. You can add or remove speaker systems
anytime and it will not make any difference in the performance of the
amplifier or the speaker systems, as long as the maximum number allowed
is not exceeded. This total depends on the wattage taps used and the
design of the power amplifier. Note; Consult the operator’s
manual that came with the 70v power amplifier you are using to determine
the practical maximum number of speaker systems you can attach to the
constant voltage line.
Another benefit is that wire length is not a major consideration as
it is with standard sound system speaker system connections. The 70v
distribution line can be hundreds of feet long (because it feeds
high-impedance line transformer primaries) and it will have little
effect on the power delivered to each speaker system. Each line
transformer is usually mounted very near its speaker system so the wires
connecting the low-impedance, high-current secondary to the speaker
system are short.
General;
Many TIC products are supplied with 30 or 50 Ft. of double insulated
burial cable, model dependent, therefore the unit must be opened to make
use of the factory-installed (SP 70T) 25/70v line transformer supplied
with these models. As each installation is potentially different, the
70v line transformer is not pre-tapped. Selection must be installation
specific.
Note: many of the professional - commercial grade TIC outdoor
speaker units have factory installed 25v / 70v transformers, which are
easily switch-able at load.
Example; a typical installation requiring a 5 watt supply at 8-Ohms
would require accessing the Driver of the speaker system. Disconnecting
the standard, direct wired, 8-Ohm connections. Isolating, then soldering
the 8-Ohm and common taps from one side of the line transformer to the
positive and negative spades of the driver. Isolating, then soldering
the 5 watt and 70v common taps to the incoming power amplifier line.
Most of TIC Corporations “Pro” series i.e. GS3, GS7L, TFS6 thru TFS25
come fitted with a factory installed “on the fly” switch-able 8 ohm
standard to 70v distribution system.
The standard 25v / 70v in-line distribution transformer supplied with
TIC Corporations professional/ commercial models is perfectly capable of
providing adequate usage throughout North America, and usually in South
American 50v, US 70v and EEC 100v applications. A rough example of how
this breaks down is, when using the TIC Corporation standard 70v
transformer line: 50v x 5W, 70v x 10W & 100v x 15W are equivalent output
taps.
A note on testing 70v
line transformers
25v / 70v / 100v line transformers are notoriously “power hungry”. It
is entirely common for the line transformer to absorb 30% – 40% of the
incoming line current. Example: Using the same 5W installation mentioned
above, if you were to test the system using a Taos® testing device, set
at 1000hz input, you may only read approx. 3W output from the line
transformer. In a real world example the reading will rarely be precise
being dependent upon too many other factors. It should be mentioned
however, that a defective transformer would rarely read low, but most
commonly provide no reading at all.
vu meter for 25v / 70V / 100V systems
Note: Just Garden
Speakers Corporation
always recommends the services of a trained professional when completing an
exterior audio installation. This is particularly true when dealing with some of
the complexities that may arise during a 70v installation.
Just
Garden Speakers cannot
be held responsible for typographical errors contained within company literature
or this website. Pricing and availability subject to change without notice, when
placing an order the customer accepts and agrees to all Just Garden Speakers general terms and
conditions. Note on pictures shown; all pictures shown for web purposes are low
resolution. All Just Garden Speakers products shown are expected to improve or exceed their
visual characteristics as shown.
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