[Elecraft] K3 Turn on Pop(WAS K3 Audio)

[Brett Howard]

Yea I remember having to add relays to our amps when I was working at
Phoenix Gold to kill the TINIEST of pops!  The sales guys would put the
speaker up to their ear and if they heard ANYTHING it was too loud...  I
found another really good way to pass is to accidentally have music
playing on the first test...  So then BOOM music comes out really loud
right into their ear... Then just say oh oops forgot that was on...
Then test it again once their ear drum is slightly compressed and they
tend to not be able to hear the faint ones! :)

Yea I was just thinking that that cap would effectively do the same
thing in holding the amp off until the pop was done past....  Not sure
why the head phone amp would affect that...  Usually the turning on/off
of the speaker output is so slow in relation to the headphones that
seems surprising that cap would affect that...

Hrm.  Oh well.  I do think that the audio section would benefit from a
rejiggering of quite a few of those caps for more LF.  I think even
beyond the page you wrote up that there may even be a few more that
would be helpful...  Also kinda wish I had another radio so I could
listen to the mic audio and see if I felt like the additional LF was
needed there.

Anyway thanks for your input!

~Brett

On Tue, 2009-07-07 at 08:58 -0400, Paul Christensen wrote:
> > Looks like making C8 a little bigger (like 10uF) would help to reduce
> > some of the turn on pop that you see on the speakers when powering the
> > unit on.  There is mention of this on page 17 under "Selecting External
> > Components" > "Bypass Capacitor Value".
> 
> A couple thoughts...
> 
> First, that may, or may not be the only area contributing to the pop. 
> Secondly, the LM4950's click/pop artifact is also a function of the Cin 
> value in addition to the Cb value.  National recommends a Cin value no 
> larger than 0.39 uF whereas the K3's Cin is 0.47 uF through 20K of series R. 
> With the exception of this slight Cin value difference, the K3 uses nearly 
> the identical input structure as shown in Figure 2 of the datasheet.  I 
> doubt it makes much a difference but experimenting is the only real way to 
> know.
> 
> From the datasheet, the only internal workings of the chip are shown with a 
> block diagram where Cb controls a bias block.  I would presume that making 
> Cb in larger would have the effect of keeping the amp off longer until 
> stabilized.  Just a guess though...
> 
> In a recent firmware release, I believe the K3's power-on pop was minimized 
> although I still hear it on my K3.  Another possibility is to use an 
> outboard R/C time-delay relay (set for 1-2 sec), and powered by the rig's 
> rear panel aux power connector. That would mimic the manner in which the 
> classic '60s and '70s audiophile amplifiers and receivers accomplished the 
> pop muting at power-up.  Speaker audio from the K3 would then route to the 
> relay contacts before heading off toward the speaker.  Mission accomplished 
> and no internal mods to the rig.
> 
> Paul, W9AC 
>