[Jukebox-list] Speaker ground

[Jay Hennigan]

Bill Taylor wrote:
> Hi Jay,
> 
> Thanks for the tip about the dummy load for my speaker
> output.  It's cheap, and I'll get one at express
> (that's also a tip, I never went to that website
> before).
> 
> Now question though, to use the dummy load with a
> small speaker... I assume using a 100 resistor in
> series with the speaker is to keep the sound low, or
> something else?  Is this how I should set it up?

More like...

+OUTPUT------------+----------/\/\/\/\/-------
                    |       50 to 100 ohm      | /
                    |                          -/ test
                    /                         |   speaker
                    \                          -\ or headphones
                    / 8-ohm                    | \
                    \ power res.               |
                    /                          |
                    \                          |
-OUTPUT------------+--------------------------

The 8-ohm power resistor takes the place of the jukebox speaker.  The 50 
to 100 ohm resistor reduces the voltage applied to the test speaker so 
that it plays at reduced volume without loading the amplifier excessively.



> I don't really understand why the voltages would hurt
> the transformer without the load. In theory the
> circuit shouldn't pull anymore current then it needs,
> from my thinking, but I won't try it again and will
> except what the engineers tell us.

The transformer has inductance and when the current is suddenly removed 
each half-cycle of the audio, the collapsing magnetic field can induce 
high voltages.  A speaker load causes the transformer to work as an AC 
voltage converter more than an open-circuited inductor.

-- 
Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
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