[Boatanchors] Speech Amp

[rbethman]

Barrie,

I'll defer to John, BUT - I'll add that OLDer systems, such as Military 
systems. while using 70V systems, did indeed have a 600 ohm impedance.  
Matching transformers such as the ones that Rat Shack discontinued, you 
could input 4 ohm, 8 ohm, or 16 ohm AND get the 600 ohm 70V output.

Bob - N0DGN

Barrie Smith wrote:
> Thanks for the info regarding the speech amp.  However, I'm still 
> confussed.
>  
> Would I be better off using a regular 8 ohm output amp into a matching 
> transformer with a 600 ohm output?
>  
> 73, Barrie, W7ALW
>
>     ----- Original Message -----
>     *From:* J Forster <mailto:jfor at quik.com>
>     *To:* Barrie Smith <mailto:barrie at centric.net>
>     *Cc:* boatanchors at mailman.qth.net
>     <mailto:boatanchors at mailman.qth.net>
>     *Sent:* Monday, November 17, 2008 2:49 PM
>     *Subject:* Re: [Boatanchors] Speech Amp
>
>     Take a look here:
>
>     http://www.dvq.com/hifi/images/260a.pdf
>
>     AFAIK, 600 ohms is used for inputs, not outputs, and is typically
>     balanced.
>
>     A 70 V line means that the amp output is 70 V RMS at the amp's
>     rated output. The 70 V is usually stepped down at each speaker to
>     voice coil impedance. Typical transformers have taps for the
>     desired wattage to the speaker, so you can hook up a number of
>     transformer/speaker combos. So on a 10 W amp, you can hook up four
>     1 W and three 2 W speakers. The amp looks a lot like a voltage
>     source.
>
>     Since Power = V * V /R, if R=600 ohms and V=70 volts, there is
>     only one possible power output from the amp. (4900/600 = 8.1 W)
>
>     Nope, 600 ohm and 70 V are NOT the same.
>
>     -John
>
>     ==============
>
>     Barrie Smith wrote:
>
>>       It's my impression that the 70 volt output on a PA amp is 600
>>     ohms. 
>
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>     _______________________________________________
>
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>
> _______________________________________________
>   

-- 
Bob - NØDGN