K3 Speaker Amp Protection

[Paul Kirley]

Last August, Wayne N6KR posted:

>The mod I was talking about is newer (2010, I believe). It involves a
 
>pair of very small-valued resistors in series with the AF output  
>coupling capacitors. This, too, is in production.
>
>However, I just looked on the K3 mods page, and it appears that we  
>never did turn this into a mod kit. We'll get this corrected right
away.

http://elecraft.365791.n2.nabble.com/K3-speaker-audio-gone-td7561739.htm
l#a7561747

Because I prefer to open my K3 only in low-static months, it's time to
ask about the status of this mod, which hasn't yet appeared on the K3
mod webpage.  Will it be available within the next few months?

73, Paul W8TM

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[David Pratt]

I wouldn't have thought this needed a mod kit, Paul. It only requires
two 470 ohm resistors which the application note states will be supplied
by sending an e-mail if required.

http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf

73 de David G4DMP

In a recent message, Paul Kirley <[hidden email]> writes

>http://elecraft.365791.n2.nabble.com/K3-speaker-audio-gone-td7561739.htm
>l#a7561747
>
>Because I prefer to open my K3 only in low-static months, it's time to
>ask about the status of this mod, which hasn't yet appeared on the K3
>mod webpage.  Will it be available within the next few months?
>
>73, Paul W8TM

--
 + - - - - - - - - - - - - - - - - +
 | David M Pratt, Kippax, Leeds.   |
 | Website: http://www.g4dmp.co.uk |
 + - - - - - - - - - - - - - - - - +

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[Joe Subich, W4TV-4]

 > http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf

This is an entirely different (and older) modification.  Output Mod
Rev C is designed to prevent damage to the right channel of the AF
amp when it is "open circuit" as it is when SPEAKERS=2 with a single
speaker attached.

The modification that Paul is inquiring about is designed to protect
the AF amplifier when the output is short circuited - e.g. connecting
a *mono* plug with SPEAKERS=2 - or in case of overload (a sudden static
"crash" or high level carrier with AGC=OFF) when using low (4 Ohm)
impedance speakers.

The latter modification has never been documented but I assume it
involves adding 2R2 or 2R7 resistors in series with the blocking
capacitor - perhaps replacing L13 and L16 on the KIO3 Audio Board.

73,

    ... Joe, W4TV


On 3/11/2013 10:41 AM, David G4DMP wrote:

> I wouldn't have thought this needed a mod kit, Paul. It only requires
> two 470 ohm resistors which the application note states will be supplied
> by sending an e-mail if required.
>
> http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf
>
> 73 de David G4DMP
>
> In a recent message, Paul Kirley <[hidden email]> writes
>
>> http://elecraft.365791.n2.nabble.com/K3-speaker-audio-gone-td7561739.htm
>> l#a7561747
>>
>> Because I prefer to open my K3 only in low-static months, it's time to
>> ask about the status of this mod, which hasn't yet appeared on the K3
>> mod webpage.  Will it be available within the next few months?
>>
>> 73, Paul W8TM
>

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[Bruce Beford-2]

I also inquired about this mod on the list a couple months ago. No replies
or posting of the relevant info yet.
73,
Bruce N1RX

Last August, Wayne N6KR posted:

>The mod I was talking about is newer (2010, I believe). It involves a
 
>pair of very small-valued resistors in series with the AF output  
>coupling capacitors. This, too, is in production.
>
>However, I just looked on the K3 mods page, and it appears that we  
>never did turn this into a mod kit. We'll get this corrected right
away.

http://elecraft.365791.n2.nabble.com/K3-speaker-audio-gone-td7561739.htm
l#a7561747

Because I prefer to open my K3 only in low-static months, it's time to
ask about the status of this mod, which hasn't yet appeared on the K3
mod webpage.  Will it be available within the next few months?

73, Paul W8TM




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[F. Barry McWilliams]

Joe, you may be right, but the description of the Revision C mod says, "This modification protects the K3's audio amplifier if either speaker output is connected to a short circuit or very low impedance load."

Since I've made this mod, I'd like (hope) to know that this protects the audio amp.
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[Don Wilhelm-4]

But why push the limits?  Using a stereo plug will eliminate the
possibility of a future failure initiated by the shorted output.  A
short on the output *does* stress the components even if they can handle it.
Changing to a stereo plug should not be difficult for any ham who can
solder - or build an adapter if you don't like cutting the headphone cord.

73,
Don W3FPR

On 3/12/2013 8:21 PM, F. Barry McWilliams wrote:
> Joe, you may be right, but the description of the Revision C mod says, "This modification protects the K3's audio amplifier if either speaker output is connected to a short circuit or very low impedance load."
>
> Since I've made this mod, I'd like (hope) to know that this protects the audio amp.
>

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[F. Barry McWilliams]

Don, Joe --

Don,
You missed my point. of confusion,  Joe said "open circuit".

Yep, I do use a stereo plug, thus I have an right channel "open circuit" when I connect an external
speaker.  

But there seems to be something else that Joe is warning against  other than
"open circuit".  Referring to Rev C, he says,
"This is an entirely different (and older) modification.  Output Mod
Rev C is designed to prevent damage to the right channel of the AF
amp when it is "open circuit" as it is when SPEAKERS=2 with a single
speaker attached."
So what is the problem with an "open circuit" right channel speaker?
TNX again


 
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[Joe Subich, W4TV-4]

Barry,

I can see "Mod Rev C" protecting against speaker ringing or the sudden
removal of a low impedance load by damping the inductive kick but it
certainly does not protect against sustained high levels into a very
low impedance (or short circuit) load.  470 Ohm resistors in parallel
with a short circuit or paralleled 4 Ohm speakers are not going to do
anything to change the behavior of the circuit.

73,

    ... Joe, W4TV


On 3/12/2013 8:21 PM, F. Barry McWilliams wrote:

> Joe, you may be right, but the description of the Revision C mod says, "This modification protects the K3's audio amplifier if either speaker output is connected to a short circuit or very low impedance load."
>
> Since I've made this mod, I'd like (hope) to know that this protects the audio amp.
> ______________________________________________________________
> Elecraft mailing list
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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