[Boatanchors] Speech Amp

[rbethman]

Al,

The BC-610, or the HT-4 that Barrie has will be very happy with around 2 
to 4 watts and NOT over-modulate.

Bob - N0DGN

Al Klase wrote:
> Barrie,
>
> What this means is that your 20-watt amp will be perfectly happy 
> delivering 8.1 watts to a 600-ohm load.  It's output is actually less 
> than 600 ohms, but that doesn't matter.  Impedance matching is like 
> horseshoes and nuclear weapons:  close counts.  Give it a shot.  
> You're not really concerned with optimal power transfer, just that you 
> can deliver sufficient power to the load.  I'd expect 8 watts is way 
> more than enough.
>
> Al
>
> 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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>

-- 
Bob - NØDGN