Maintaining a Vbe Multiplier's bias value
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From: Jim Thompson on 10 Feb 2010 09:46 On Tue, 09 Feb 2010 22:21:12 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Tue, 9 Feb 2010 20:55:07 -0800 (PST), "miso(a)sushi.com" ><miso(a)sushi.com> wrote: > >>I just lose interest if I have to look at ascii circuits. You really can't convey much more than a "basics" circuit with ASCII. Post links or use LTspice listings... everyone seems to have that ;-) > >I have a domain I can use. It is just that it hardly seemed >necessary, given the simplicity involved and the fact that >this group is quite used to ASCII schematics, given the years >I've been watching here. It has advantages in that it is >archived for very long times, this way, as well. > >However, I will try and take your concerns into account and >see about organizing a directory and smoothing through issues >of dropping files there which have been massaged and arranged >for easier viewing. > >>You realize you can just string diodes. Nobody says you have to VBE >>multiply. It's just one of many biasing techinques. > >Yes, I think that's been well-posted in the thread and I was >aware of it, before. It's one of the first things I saw when >starting on this trek 2 weeks back. Hard to miss. The issue >is more about learning, though. Not picking a specific >solution and ignoring the others. I'd like to have some >spectrum of options I've looked at well and discarded (as >well as retained.) > >Jon ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Jim Thompson on 10 Feb 2010 09:55 On Wed, 10 Feb 2010 03:41:23 -0500, Bitrex <bitrex(a)de.lete.earthlink.net> wrote: >Jim Thompson wrote: >> On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan >> <jonk(a)infinitefactors.org> wrote: >> >>> On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson >>> <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >>> >>>> What in the world ?:-) >>> View in fixed-spaced font. And it's a rendition of the >>> schematic that Bob Monson had posted, earlier, from EDN. He >>> wrote, "On a related note, there was an article in a recent >>> EDN about a self biasing preamp which was kinda cool. Instead >>> of trying to track the difference using diodes or a >>> multiplier, it used a couple of transistors and an opamp to >>> set the correct values at the bases of the pass transistors. >>> It was so novel (at least to me) that I typed it into >>> LTSpice." >>> >>> I merely re-arranged it in LTspice to be a little more to my >>> taste and then passed it through a program that generates >>> ASCII from that. >>> >>> Jon >> >> Burr-Brown was famous for using bias compensation like that in the >> front ends of some of their operational amplifiers, but I doubt its >> efficacy in power output stages. >> >> The Burr-Brown scheme is similar to a discussion here a few (seven :-) >> years ago... >> >> http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf >> >> ...Jim Thompson > > >Could you give a quick explanation of how the circuit in the link works? >I'm having a bit of trouble following what's going on... Start with IB coming out (*) of IN+ and IN- of EACH section of the LM324. (*) LM324 has as inputs PNP diff pairs. Then simply compose loop and node equations. If any of you are struggling with this kind of analysis, I'll mark it up and show how to solve it. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Jim Thompson on 10 Feb 2010 11:23 On Wed, 10 Feb 2010 07:55:09 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Wed, 10 Feb 2010 03:41:23 -0500, Bitrex ><bitrex(a)de.lete.earthlink.net> wrote: > >>Jim Thompson wrote: >>> On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan >>> <jonk(a)infinitefactors.org> wrote: >>> >>>> On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson >>>> <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >>>> >>>>> What in the world ?:-) >>>> View in fixed-spaced font. And it's a rendition of the >>>> schematic that Bob Monson had posted, earlier, from EDN. He >>>> wrote, "On a related note, there was an article in a recent >>>> EDN about a self biasing preamp which was kinda cool. Instead >>>> of trying to track the difference using diodes or a >>>> multiplier, it used a couple of transistors and an opamp to >>>> set the correct values at the bases of the pass transistors. >>>> It was so novel (at least to me) that I typed it into >>>> LTSpice." >>>> >>>> I merely re-arranged it in LTspice to be a little more to my >>>> taste and then passed it through a program that generates >>>> ASCII from that. >>>> >>>> Jon >>> >>> Burr-Brown was famous for using bias compensation like that in the >>> front ends of some of their operational amplifiers, but I doubt its >>> efficacy in power output stages. >>> >>> The Burr-Brown scheme is similar to a discussion here a few (seven :-) >>> years ago... >>> >>> http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf >>> >>> ...Jim Thompson >> >> >>Could you give a quick explanation of how the circuit in the link works? >>I'm having a bit of trouble following what's going on... > >Start with IB coming out (*) of IN+ and IN- of EACH section of the >LM324. > >(*) LM324 has as inputs PNP diff pairs. > >Then simply compose loop and node equations. > >If any of you are struggling with this kind of analysis, I'll mark it >up and show how to solve it. > Examine this mark-up... http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps_MarkedUp.pdf ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: George Herold on 10 Feb 2010 11:35 On Feb 9, 4:05 pm, Jon Kirwan <j...(a)infinitefactors.org> wrote: > On Tue, 9 Feb 2010 11:35:36 -0800 (PST), George Herold > > > > > > <ggher...(a)gmail.com> wrote: > >On Feb 9, 5:39 am, Jon Kirwan <j...(a)infinitefactors.org> wrote: > >> On Mon, 8 Feb 2010 19:16:24 -0800 (PST), George Herold > > >> <ggher...(a)gmail.com> wrote: > >> >><snip> > >> >"I'm wondering about additional topology changes to improve > >> >the performance still more." > > >> >Hi Jon, I've been 'sorta' following your thread on s.e.basics. I > >> >wonder if you abandoned class A operation too early? Why not keep > >> >things linear evreywhere and avoid the dead band? So what if you > >> >need a bigger heat sink. Its certainly a lot simpler. > > >> >George H. > > >> Well, George... No, I've not abandoned it. Actually, it's my > >> hope to wind up building the amplifier and then operating it > >> (by hopefully choosing a design where that is possible) in > >> different modes for the learning experience of it. I hope > >> that is in the cards. I really do. > > >> But to make a sharp point on it, although it's probably just > >> an extreme case, I remember reading about a 10W amplifier, > >> single channel, dissipating 120W! Creeps me out. So I > >> definitely _want_ to consider other classes of operation. And > >> cripes, I want to learn, anyway. So why not keep my options > >> open? > > >> Jon > > >" I remember reading about a 10W amplifier, > >> single channel, dissipating 120W! " > > >It might have been here, > >http://www.passdiy.com/default.html > >I got to reading about amplifiers on the above site... Do in part to > >your interest. > > >George H. > > Egads. Loads of PDF files. Now I have to create a > directory, download them one by one, and then call them up > with my slow machine to look. Any particular page or file > where you saw it? (No, that isn't where I saw the comment.) > > But thanks for the link. I'll add it to those I read, also. > > Jon- Hide quoted text - > > - Show quoted text - Ohh sorry about that... Don't bother reading them... He (Nelson Pass) has designs for Class A amps using a FET. (named Zen) One of his variations (son of Zen?) was made with no NFB and I think wasted your stated 120 Watts of power for 10W into the speaker. But this seemed pretty pointless to me... some audio guys wanted an amp with out NFB.... Don't aks me why! Say can you make a push-pull stage run class A? (Or is that just a silly idea?) George H.
From: Tim Williams on 10 Feb 2010 11:43
"George Herold" <ggherold(a)gmail.com> wrote in message news:b603649e-8d7c-4349-9edd-0f7ae3e6cffb(a)a5g2000yqi.googlegroups.com... > Say can you make a push-pull stage run class A? (Or is that just a > silly idea?) You can, but it stops being class A for large signal swings or low load impedances. There's a monolithic structure which bends the output transistors' characteristics so they never cut off. I forget who owns it. I suppose that would count as class A at any signal/load condition. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |