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 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
