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

[Joe Subich, W4TV]

> 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 can think of a fair number of power amplifiers and mixing board
monitor amplifiers that include *delay relays* in the speaker lines
that leave the speakers disconnected for two to three seconds after
power is turned on specifically to prevent the thump (and potential
damage to speakers and/or hearing).

73,

    ... Joe, W4TV



On 9/4/2011 8:16 PM, David Herring wrote:
> 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
>>
>>
>
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