[Boatanchors] Speech Amp

[Barrie Smith]

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 
  To: Barrie Smith 
  Cc: 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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