[R-390] R392 Audio

[Bernie Doran]

I have to agree completly with Perry. The Lm and other series of audio amps 
offer performance that can not even be dreamed about with Vacuum tubes. 
Distortion is so low that I sometimes wonder how they can measure it. 
Frequency response is also outstanding.  Lower and higher that any speaker 
system I could afford.   I can only assume that someone has not taken the 
time to look at the specs for these devices.  To me it is very easy to 
install one of these, they are small and for power simply bring it in from 
an external source, also not all require a split power source some will do 
fine with one source.  Unless you need? 30 or 40m watts.    Bernie W8RPW


----- Original Message ----- 
From: "Charles Steinmetz" <csteinmetz at yandex.com>
To: "390 list" <r-390 at mailman.qth.net>
Sent: Friday, January 24, 2014 5:07 AM
Subject: Re: [R-390] R392 Audio


> 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
>
>
>
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