[R-390] R392 Audio

[Charles Steinmetz]

Perry wrote:

>Perhaps a simpler alternate to Charles tube re-design of the audio 
>output circuit would be to use one the LM series of audio output 
>IC's.  They range from 2 to 70 watts or so output and many have been 
>designed for high-end audiophile equipment so they have low 
>THD.  Besides needing minimum additional components to use, most are under $10.

Perry, you have no idea how involved (or not) the R392 audio mod 
is.  In fact, installing a power amp IC would be much more work.  And 
while power ICs are fine in a lo-fi application like a communications 
radio, the idea that power output ICs are useful "for high-end 
audiophile equipment" is simply laughable.  Even halfway-decent 
mid-fi consumer products don't use them.

In the context of an R392, which has a unipolar power supply, using a 
power IC would require either (i) a whopping big output capacitor or 
(ii) a bridge-type output with a DC offset of 1/2 the power supply 
voltage.  Both are problematic (the latter is a great way to blow up 
the IC and/or a speaker when you forget about the offset).

Best regards,

Charles