Maintaining a Vbe Multiplier's bias value
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From: JosephKK on 13 Feb 2010 20:34 On Thu, 11 Feb 2010 19:37:27 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Thu, 11 Feb 2010 19:23:04 -0800 (PST), George Herold ><ggherold(a)gmail.com> wrote: > >>On Feb 11, 3:24 am, Jon Kirwan <j...(a)infinitefactors.org> wrote: >>> On Wed, 10 Feb 2010 19:55:44 -0800 (PST), George Herold >>> >>> <ggher...(a)gmail.com> wrote: >>> >I'm perhaps more of a novice than you... >>> >>> Somehow, I doubt that. I barely rate "hobbyist." >>> >>> >but I find opamp circuits complicated enough.... >>> >>> Don't sweat it. While some opamps leave _some_ issues nearly >>> ignorable, there is always some tough problem at that scale >>> that makes it non-trivial and interesting to work on, I >>> imagine. Each macroscale view has it's own complexity. >>> Telescoping levels, where the complexity at one stage doesn't >>> take away from interesting complexity at another level. >>> >>> (I would say more but I'm keeping in mind your warning about >>> long-windedness and will now muzzle myself.) >>> >>> >And tend to stick transistors >>> >only on the edges of things. (Mostly on the output side... on the >>> >input you have to 'know more' than the guys who designed the opamp.. >>> >hard to do for a novice.) >>> >>> I do the same things except that I enjoy math and BJTs give >>> me an excuse, perhaps. Maybe that's the only difference. >>> >>> >I guess if I was designing an audio amp I'd figure on an opamp driving >>> >some sort of FET output stage. The question of how to bias the output >>> >stage is interesting. And also of how all the NFB works. >>> >>> Might as well just get a power opamp like the OPA502 and be >>> done with it. Give it two rails, feed the input, and just >>> drive the hell out of a speaker. Or get two of them and do a >>> bridge amplifier. But where is the enjoyment in that? Or >>> the learning? Someone else already did most of the fun stuff >>> and there's nothing really left to do except some hook up and >>> heat sinking. It's not at all satisfying to me, anyway. >>> >>> An audio amplifier is basically a power opamp. Using an >>> opamp to make one feels to me like building a car by first >>> buying a car without the tires, selecting and installing some >>> tires, and then saying you designed and built yourself a car. >>> >>> Jon >> >>Big Grins! >> >>Yeah I applaud your effort, I wait for further posts. >> >>For me, Im building electronics to either detect something or drive >>something thats detecting something. So the fun is in making good >>detectors or drivers. >> >>George H. > >Well, I am wanting, eventually, to build something I need. >Something I cannot buy in the market because the need is >unique. > >This divides into two parts. Design and build. Since the >item is unique, I can't just go out and buy it. And getting >the features I need cannot just be "hacked" into existing >designs without at least knowing _some_ stuff, first. I >might as well turn the "design" part into a fair learning >experience, as a separate project of its own. Get past that >and when it comes time to build what I want I'll be able to >build on what I learned and add what I need and then do a >modest hobbyist level whack at actually making what I want to >make. > >If someone else were to do this for me (hire a designer), >they'd get all the fun of learning on the job and taking my >money with it. They get the money, they get to further their >own education, and I get a tool. One tool. Once. Next >time, I get to pay someone else to learn for me. > >It almost feels like paying someone to go do your exercising >for you. No satisfaction and no weight loss. They get all >the _real_ benefits. > >Part of the fun isn't the destination itself but it is what >you see and enjoy while getting there, too. You take a plane >when all you need is to "get there" quick, but you drive when >you want to enjoy stops along the way. I used to fly to >Burbank every week for a year and a half. Slept in a hotel >for 3 nights a week, worked day and night in between, flew >home. Barely saw anything but hotel room walls, cubical >walls, a few cement roads, pollution so thick you couldn't >see the Burbank hills from the Lockheed center, and not much >else. The destination was important, of course. Paid the >bills and I enjoyed the work, too. But there is a lot more >to see in the 1000 miles from here to there. > >Anyway, I'm driving this time, not flying. > >Besides, I'd rather _keep_ the money and _keep_ the education >for myself. That way it pays off, again and again. > >Jon Spot on. That is why i am rebuilding my tinkering kit.
From: JosephKK on 13 Feb 2010 20:51 On Fri, 12 Feb 2010 08:24:24 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 12 Feb 2010 10:03:11 -0500, Phil Hobbs ><pcdhSpamMeSenseless(a)electrooptical.net> wrote: > > >> >>Build a man a fire, you keep him warm for a night. Set a man afire, you >>keep him warm for the rest of his life. ;) >> >>Cheers >> >>Phil Hobbs > > >Got snow? > >John My brother in Dallas TX does.
From: Richard Torrens (News) on 14 Feb 2010 04:59 In article <jg91n5d684ru5imsq1cfcjpjd1vddg2b2l(a)4ax.com>, Jon Kirwan <jonk(a)infinitefactors.org> wrote: > I'd like to consider the Vbe multiplier often used in audio > amplifiers to maintain a bias voltage for the output stage. > The purpose is to better mitigate against ripple in the > unregulated power supply rails and against the the VAS > voltage output resulting from amplified signal voltages. Two things sprng to mind: 1: run the circuit at a constant current. See http://www.4qdtec.com/pwramp.html which uses two diodes, but at a constant current. 2: bootdstrap it. See http://www.4qdtec.com/Audio/Neoteric/cct.png which is the ciurcuit of sir Clive Sinclair's Neoteric - a very high quality amp of its day. Why do so many people here insist on quoting the whole of the original article... -- ------------------------------------------------------------------ Richard Torrens. News email address is valid - for a limited time only. http://www.Torrens.org.uk for genealogy, natural history, wild food, walks, cats and more!
From: John Larkin on 14 Feb 2010 10:16 On Sun, 14 Feb 2010 09:59:56 +0000 (GMT), "Richard Torrens (News)" <News+14654(a)Torrens.org.uk> wrote: >In article <jg91n5d684ru5imsq1cfcjpjd1vddg2b2l(a)4ax.com>, > Jon Kirwan <jonk(a)infinitefactors.org> wrote: >> I'd like to consider the Vbe multiplier often used in audio >> amplifiers to maintain a bias voltage for the output stage. >> The purpose is to better mitigate against ripple in the >> unregulated power supply rails and against the the VAS >> voltage output resulting from amplified signal voltages. > >Two things sprng to mind: > >1: run the circuit at a constant current. >See >http://www.4qdtec.com/pwramp.html >which uses two diodes, but at a constant current. > >2: bootdstrap it. >See >http://www.4qdtec.com/Audio/Neoteric/cct.png >which is the ciurcuit of sir Clive Sinclair's Neoteric - a very high >quality amp of its day. > > > 3. Hang a big cap across it. John
From: Jon Kirwan on 14 Feb 2010 14:14
On Sun, 14 Feb 2010 07:16:38 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >3. Hang a big cap across it. Assume, just for a moment, that one wants to actually learn a little about _designing_ the part that goes across those cap terminals. Jon |