[Elecraft] Re: sidetone mod now works (RP5, etc., explained)

[wd4lst at windstream.net]

Bob Pease would be proud!!!
That is  a really cool application - not to 
mention you taking time to explain it.
73s,
Pete
> 
> From: wayne burdick <n6kr at elecraft.com>
> Date: 2007/03/10 Sat AM 12:03:56 CST
> To: va7to at yahoo.ca
> CC: elecraft at mailman.qth.net
> Subject: [Elecraft] Re: sidetone mod now works (RP5, etc., explained)

> There's some subtlety to this circuit. Among the various goals was to 
> minimize component count.
> 
> C32, on pin 8 of U9, is the AF amp's supply decoupling capacitor. It 
> would normally be returned to ground, as shown in any LM380 datasheet. 
> However, we played a trick here, using pin 8 as the sidetone injection 
> point. In other words, we're treating pin 8 as a low-gain, single-ended 
> third input to the amplifier.

> 73,
> Wayne
> N6KR
> 
> 
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> 
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Pete Axson
WD4LST
17901 NE 18th Ave
Citra, FL 32113