The AM Forum

I picked up a nice, used Bogen speaker and I think it would mate up nicely with my Racal RA-17 receiver. The speaker has a selector on the back for 8 ohms or line input, and outputs from 1 watt to 15 watts @ 70 volts.

The cabinet is sealed so I can't look at the line amp. I presume the 70 volts is phantom power and duplexed on the line input so I will need to build a supply but I need to ask you guys what you think or know about this.

Would this be 70 volts ac or dc? How much current would you provide for 15 watts of audio and to power the amp inside? How would I strip off the voltage at the line level input?

Here is a link to a spec sheet. Thanks in advance.

Mike

http://www.bogen.com/products/pdfs/foregroundspeakerpdfs/FG15s.pdf (http://www.bogen.com/products/pdfs/foregroundspeakerpdfs/FG15s.pdf)

Not so sure this is a powered speaker. It will work though. http://www.yorkville.com/default.asp?p1=6&p2=17&p_id=73
Anything is better than the Racal speaker.

70 volt speakers were designed to be used with a PA system feeding many speakers. The higher voltage reduced the conductor loss over long distances. Each speaker then had a transformer than would convert back to 4 or 8 Ohms and allow for a selection of power levels (which translates into sound level coming out of the speaker). This allowed for adjustment of levels without messing with potentiometers.

If you want to use the speaker, just bypass the 70 volt transformer. Connect the 8 Ohm out directly to the terminals on the speaker.

I think I see now Steve. The 70 volts is for transmission so each satellite speaker has the same input regardless of the wire length and loss. Fortunately the speaker dose have an 8 ohm input. It sounds great and best of all it was free. Too bad it isn't powered. I thought I found the RA-17 cure. Thanks also to Dave, VW, neat call

Mike

FYI 70 volt audio distribution technique info here http://www3.telus.net/Whalco/Audio70v.htm (http://www3.telus.net/Whalco/Audio70v.htm)

The 70 volt line is certainly amazing. I was amazed as a teen in high school how they fed the entire building using several hundred 8 inch speakers in the usual wall mounted baffle with just a simple 100 watt amplifier. And to my young ears it could be very loud. Sounded good too.
By the way, for what it's worth, I copied the amplifier Dukane used in the PA console.
It had dual 5U4's in the P.S. and 4-6CD6's push-pull parralel and a VR150 for the screens.
G'day
Fred

Fred,
School intercom systems use 25 volt systems, not 70 volt. Same principle though.
I install these things so I know!!!!!!  ;)