> 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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