YORKVILLE CR 670 Manuel De L'utilisateur page 5

Design And Installation of 70 Volt Audio
Systems
1. When do you need a 70V system?
70 volt systems are needed when there are either a large number of loudspeaker locations or the dis-
tance between the source amplifier and the loudspeakers is greater than 100 feet (30 meters).
2. What do I need?
First, you need an amplifier that is capable of supplying 70 volts. The CR670 will do just fine. Then,
for the loudspeakers, you'll need loudspeakers with built in 70 volt step-down matching transformers,
or add 70 volt step-down transformers to low impedance (4 or 8 ohm) loudspeakers. (Loudspeakers
like the Yorkville C110 and C120/70 have built-in matching transformers.)
3. Putting it all together
a) Amplifier Power. 70V systems require a certain amount of power to distribute the signal properly.
The total number of loudspeakers you can connect correlates directly to the power output (watts) of
your amplifier (and the loudspeaker's 'power tap' that you have chosen on your loudspeaker's match-
ing transformer). For example, if you're using a CR670, which is a 600 watt power amplifier, you can
connect up to a maximum** of 98 loudspeakers (with transformers) by using the 5 watt power taps on
their matching transformers. (600W divided by 5W = 120, less 20% as a safety margin = 98.) Now
that's a lot of loudspeakers!
**NOTE: it's recommended to allow approximately 15-20% as a safety margin for headroom
accounting for the losses in the transformers when calculating how many loudspeakers
b) Calculating Amplifier Power. The power demand of the system will depend on the total of your
loudspeaker's transformer power tap selections. once you've set the power taps for each loudspeaker/
transformer, just add it up. If you have to guess, guess on the high side then add about 20%. For gen-
eral (quiet room) applications, about 10 watts per loudspeaker is more than adequate.
c) Power Taps. 70 volt loudspeaker transformers usually have several 'power taps' (wires or solder
tabs) so you can set the comparative loudness of each loudspeaker during installation. As an example,
the Yorkville C110 and C120/70 loudspeakers have a rotary switch with 3 power settings as well as a
straight-through setting (which bypasses the built-in transformer for conventional usage and presents an
8 ohm load to the amplifier) Do not operate your CR670 with several loudspeaker in parallel when the
loudspeaker's switch is set to the "straight through" setting.
d) Connecting the loudspeaker transformers to the loudspeakers. If your chosen loudspeaker does not
contain a 70 volt step-down transformer, then you will have to connect a transformer in series to the
input terminals of the loudspeaker. The loudspeaker matching transformer should have various power
tap leads (or terminals) plus one marked COM on the 'system' side (the side that connects to the
amplifier). The other side of the transformer (for connection to the loudspeaker) will usually have two
or three leads (or terminals), one probably marked 4 ohms, one 8 ohms and the other marked COM
(or C). That is the side that you attach to the loudspeaker. Using a short length of loudspeaker cable,
attach the transformer's COM lead or terminal to the negative loudspeaker terminal. Then attach the
other lead (marked 8 ohms) to the positive loudspeaker terminal.
e) Connecting the loudspeaker transformers to the system leads. The loudspeaker's matching transform-
er's COM (or C) lead should connect directly to the 'systems' COM wire. Connect the chosen trans-
former power tap lead to the 70 volt system live wire. Each loudspeaker connects to the 70 volt system
wire in parallel. See the Diagram on last page.
f) What if the loudspeakers have built-in transformers? Just connect the 70 volt system COM wire to the
negative loudspeaker terminal and the 70 volt system live wire to the positive loudspeaker terminal.
5