Crown CTS1200 Reference Manual page 5

Choose a transformer with a power rating equal to or exceeding the wattage of the power amplifier. The
turns ratio should be adequate to provide 70.7V at the secondary when full sine-wave power is applied to
the primary. Use the following formula for a 70.7V line:
where
T = turns ratio
70.7 = voltage of constant-voltage line
P = amplifier power output in watts
Z = amplifier rated impedance
SQR means square root
Better yet, measure the amplifier's output voltage at full power into its rated load impedance, and use the
formula:
where
T = turns ratio
70.7 = voltage of constant-voltage line
E = measured output voltage at full power into the rated impedance.
Amplifier with built-in transformer
If the transformer is already built into the power amplifier, simply look for the output terminal labeled "70V,"
"25V," "100V," or "high impedance."
Amplifier with transformerless, high-voltage output
Figure 2 shows how a power amplifier with a high output voltage can power a distributed system without a
step-up transformer.
Figure 2. A constant-voltage system using a high-voltage power amplifier.
Many high-power amplifiers can drive 70V lines directly without an output transformer. Crown CH amplifiers
have an auto transformer (except CH 4). CTs amplifiers can provide direct constant-voltage
(70V/100V/140V/200V) or low-impedance (2/4/8 ohm) operation. In Dual Mode, the CTs 600/1200 can
power 25/50/70V lines; the CTs 2000/3000 can power 25/50/70/100V lines. In Bridge-Mono mode, the CTs
600/1200 can power 140V lines; the CTs 2000/3000 can power 140V and 200V lines.