[Elecraft] K3: switching on click -- One wonders...

[David Herring]

Hi All!

I know we've milked this one quite a bit, but I do have a point to make that I think will frame this "power-on thump" issue in a little better light...

First off, I have K3 #3019 and there is a very detectable power-on AND power-off thump in the built-in speaker and in the cans.  I don't have external speakers so I can't say about that.

BUT, what I wanted to point out is that this behavior, this power-on and power-off click or thump is widespread and not strictly a K3 problem.  While there are others on this list with way more experience in the field of audio, I can say that in my younger days I was very much an audiophile.  I can tell you with certainty that all the high end audio equipment I owned (and wished I owned!) thumped when powering on and powering off.

Outside of my own equipment, I have worked mixing boards and commercial sound systems which all thumped on power-on/off.  Some loud enough to nearly blow your hair off.

I have even witnessed this in concert halls -- I'm thinking, as one example, of the Pacific Amphitheater one night in LA which very clearly had the power-on/off thump.  I can think of others probably if I worked my brain cell really hard.

The point is that this phenomenon seems to be part and parcel of the powering-on and powering-off of solid state audio amplification.  As this exists in the high quality and commercial equipment I've had the pleasure of working with, I don't feel it detracts from the K3.  I think the K3 is actually in pretty good company.

I know that being common doesn't make it right...but it probably does indicate that most in the business don't regard it as particularly important.

IMHO if it costs more than a nickel to fix, I wouldn't bother.  However I understand that others, perhaps with amplified speakers, are well within their rights to feel differently.  :-)

Alrighty then...back to the honey-do list...

73 & Aloha,
Dave  AH6TD

On Sep 4, 2011, at 12:25 PM, Joe Subich, W4TV wrote:

> 
> I suppose the "click" - or in my case a "thump" - depends on the timing
> of the "mute" signal from the controller and the value of the bypass
> capacitor on pin 8 of the speaker amplifier.  The chip manufacturer
> recommends 10 uF for the bypass capacitor but I notice that Elecraft
> use 3.3 uF in the K3.  The manufacturer's data sheet shows:
> 
>      Cb (uF)              Ton (Ms)
>       1.0                   120
>       2.2                   120
>       4.7                   200
>      10.0                   440
> 
> The manufacturer's data sheet also calls for the time constant of the
> input coupling capacitor and Ri+Rf (input and feedback resistors of
> the amplifier) to be less than the turn on time set by Cb.  In the
> K3,  I don't know how critical the ratio of input time constant to
> turn on time is but the reference design has an input time constant
> less that 5% of the turn on time while in the K3 the input time
> constant is about 30% of the turn on time.
> 
> In addition, I suspect there may be some variation in early vs. late
> production due to the change in the DC resistance of the RF choke in
> the DC line feeding the speaker amplifier.
> 
> 73,
> 
>    ... Joe, W4TV
> 
>