Question about 70V output

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#1 Dmitry

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Posted 31 August 2005 - 09:26 AM

Under what conditions I could messure complete 70V with standard voltmeter on CH-1 amp 70V-output?

#2 DGlass



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Posted 31 August 2005 - 02:07 PM

Although it is called a Constant Voltage System it is more appropriately a 70.7-volt Distribution System. 70.7 volts can be read on the speaker line when the 70v amplifier is at full output. Voltage has to vary to get the speaker to move in and out as well as to get differents levels of output.

In a 70.7 volt system 70.7 volts RMS is the voltage that will drive the speakers to full output for whatever the speaker(s) line transformer(s) are tapped at. So if a speaker is tapped at 1 watt you will get 1 watt of output from that speaker. If another speaker is tapped at 10 watts you will get 10 watts of output from that one when 70.7 volts is reached from the amplifier output.

In a 70v/100v/140v etc system the line voltage is raised, like what is done by the power company for their High Voltage AC distribution lines. Voltage is raised; current is thusly lowered so the amount of energy lost due to heat from line resistance is reduced. A transformer is then used at the other end to tap off the amount of power each receiving device gets. This way you can mostly take out the line impedance and speaker impedances from the calculation and work primarily with power. i.e. Ten 70.7-volt speakers tapped at 5 watts each would present about a 50 watt load to a 70v amplifier. Such a system is a necessity when driving many speakers over long speaker lines.

With the basic description out of the way  blink.gif  I can now say that  the term “Constant Voltage” is purely an “engineering term” because the voltage (by definition) does not vary with the load. The voltage source (the amp) has enough current supply to prevent significant voltage changes at the outputs due to changes in the load. You can basically change the speaker load impedance and the output voltage will remain the same.  smile.gif

#3 Bradford Benn

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Posted 09 September 2005 - 04:39 PM

You may also want to review the document about Constant Voltage Systems at http://www.crownaudio.com/pdf/amps/138905-...age_article.pdf

Bradford Benn
Business Development Manager - Crown International