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New to 70 Volt Systems


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#1 one-highlander

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Posted 22 June 2011 - 06:49 PM

Hello everyone,

I've been building live sound systems for nearly 20 years (8/4/2 ohm systems), and only in the last month have learned about 70 volt systems, due to the fact that I have a client who wants build an outdoor system for them.

They are, obviously, very different. But I think I understand 70 volt systems now, and they're actually pretty simple -- assuming my research was done correctly. But I wanted to confirm with the experts I'm sure are browsing this board.

The speakers for my system will be JBL Control 29AV. I want to use Crown Amps

These 70 volt JBLs have Transformer taps @ 110W, 55W, 28W & 14W

For my question, I've assumed that I'll use them at the 110w settings

Config. #1: So, if I buy the CTs 600 amplifiers, and use them in 70v dual/two-channel mode, I can get 2 speakers per channel and be 80 watts under the power rating. Is this correct?

Config. #2: Or, conversely, if my final design needs more speakers, I can buy the CTs 1200, and put 4 speakers on each channel?

In the long run, this outdoor system will have between three and five geographical zones. Since I'll control audio through a Matrix audio switcher, I'm thinking that I'll need something like 16 speakers, and up to 4 amps.

Have I gotten the calculations right, or horribly wrong?

Thanks in advance!

#2 Kevin Heber

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Posted 28 June 2011 - 08:34 AM

Yes, yes, and right.  Generally you assign one channel to each zone in a 70V system, but your thinking looks all correct.

#3 one-highlander

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Posted 03 August 2011 - 12:47 AM

QUOTE(Kevin Heber @ Jun 28 2011, 08:34 AM) View Post
Yes, yes, and right.  Generally you assign one channel to each zone in a 70V system, but your thinking looks all correct.



Hi Kevin,

Thank you so much. I just ordered a CTS1200. I have a question, though. I couldn't seem to find an answer in the manual, and I didn't see it in any of the diagrams.

How do you select 70V mode? On the old Com-Tech series, there was a sliding switch on the rear of the amplifier that said something like "8/4/2" on one side and "70 Volt" on the other. I haven't seen any sort of selector switch on the CTS series amps. Where is it located?

Thanks!



#4 Tom Lureman

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Posted 03 August 2011 - 09:19 AM

Check out page 19 of the manual
http://crownaudio.com/pdf/amps/137000.pdf

It's actually on the inside of the input card cavity.  You want to push the switch for each channel all the way towards the front panel of the amp.