Discussing audio amplifier design -- BJT, discrete
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From: David Eather on 24 Feb 2010 22:42 On 25/02/2010 1:38 PM, Jon Kirwan wrote: > On Thu, 25 Feb 2010 13:13:12 +1000, David Eather > <eather(a)tpg.com.au> wrote: > >> <snip> >> I don't get wound up very easily by this sort of thing - I know you >> aren't trolling. I do hop I do not sound too harsh when I disagree - it >> is not my intention to bully. When I see the other person is sincere I >> try to put my cynical factor on hold. >> <snip> > > Sometimes, the fastest way from A to B is through some > 'oscillation' in discussion. I think of this as critically > damped in the best of cases and maybe a little underdamped > more than would be liked, most of the time. I don't mind > that if you don't. It would be a slower discussion if we > spoke way overdamped and never oscillated. > > Yes, I am seriously studying and seriously trying to engage > myself to every sentence I'm gifted with by you or Paul or > pimpom (and others, too.) I'm pouring through Self's latest > book every night, working some equations on my own. So this > is a serious attempt on my part. Whether or not it is > serious to anyone else, of course, is a different matter. I'm > pretty hard to teach, at times, and won't pretend otherwise. > > I do appreciate everything you add. I just hope that my > responses aren't off-putting. No. Just keep going > > Jon
From: Jon Kirwan on 24 Feb 2010 23:33 On Thu, 25 Feb 2010 13:42:10 +1000, David Eather <eather(a)tpg.com.au> wrote: >On 25/02/2010 1:38 PM, Jon Kirwan wrote: >> On Thu, 25 Feb 2010 13:13:12 +1000, David Eather >> <eather(a)tpg.com.au> wrote: >> >>> <snip> >>> I don't get wound up very easily by this sort of thing - I know you >>> aren't trolling. I do hop I do not sound too harsh when I disagree - it >>> is not my intention to bully. When I see the other person is sincere I >>> try to put my cynical factor on hold. >>> <snip> >> >> Sometimes, the fastest way from A to B is through some >> 'oscillation' in discussion. I think of this as critically >> damped in the best of cases and maybe a little underdamped >> more than would be liked, most of the time. I don't mind >> that if you don't. It would be a slower discussion if we >> spoke way overdamped and never oscillated. >> >> Yes, I am seriously studying and seriously trying to engage >> myself to every sentence I'm gifted with by you or Paul or >> pimpom (and others, too.) I'm pouring through Self's latest >> book every night, working some equations on my own. So this >> is a serious attempt on my part. Whether or not it is >> serious to anyone else, of course, is a different matter. I'm >> pretty hard to teach, at times, and won't pretend otherwise. >> >> I do appreciate everything you add. I just hope that my >> responses aren't off-putting. > >No. Just keep going > >> >> Jon One thing that's become pretty obvious is that audio amplifiers are roughly the same thing as big, monster opamps. The main difference is that they hard-wire the power supply design instead of offering connections, tend to require a ground reference (though that isn't necessary, I'm seeing that it can help a little bit), limit one to single-ended drive and hard-wire their feedback. Some of the thoughts about how to design in better CMRR in an audio amplifier may very well be almost the same thoughts used with designing some opamps, for example. So in ways what I'm trying to learn is also applicable to opamps in near equal measure. Does anyone build and sell a giant 500W opamp? ;) This is actually very useful for me and not the least bit of waste, I think. Glad to have started about a month back. Glad for occasional company, too. Jon
From: Paul E. Schoen on 25 Feb 2010 13:58 "Jon Kirwan" <jonk(a)infinitefactors.org> wrote in message news:qpubo5l2o2f14ev2jhi1bg2hhk60mmu9dp(a)4ax.com... > > One thing that's become pretty obvious is that audio > amplifiers are roughly the same thing as big, monster opamps. > The main difference is that they hard-wire the power supply > design instead of offering connections, tend to require a > ground reference (though that isn't necessary, I'm seeing > that it can help a little bit), limit one to single-ended > drive and hard-wire their feedback. > > Some of the thoughts about how to design in better CMRR in an > audio amplifier may very well be almost the same thoughts > used with designing some opamps, for example. So in ways > what I'm trying to learn is also applicable to opamps in near > equal measure. > > Does anyone build and sell a giant 500W opamp? ;) > > This is actually very useful for me and not the least bit of > waste, I think. Glad to have started about a month back. > Glad for occasional company, too. This company sells op amps to 450W: http://www.powerampdesign.net/downloadfullcatalog.html Apex has been around a long time. Here is a 400W amp (40A, 200V): http://www.cirrus.com/en/products/pro/detail/P1150.html A list of all their amps, including a 250W PWM device: http://www.cirrus.com/en/products/pro/areas/PA139.html#PA142_open National has had the LM12 for quite a while. It'll do 90W in a TO-3 package: http://cache.national.com/an/AN/AN-446B.pdf Around 1982 I used an RCA monolithic 100W power Op-Amp for the amplifier in a frequency test set that had to produce 0-140 VAC at 45-450 Hz. It was in a large square package with flying leads of perhaps #16 AWG. I still have one that I cut open after it fried. Paul
From: David Eather on 2 Mar 2010 01:13 For anyone interested I have placed some interesting app notes here http://www.filedropper.com/amps It is a free file host, so the files won't be around that long. I am sorry the total package comes to just shy of 18 MBytes. One is an Hitachi Mosfet app note that pretty much redefined most amp's topology. The other is an RCA app note, sorry each page is a separate file, which has a practical approach to the output stages and other useful. The last "thing" is a JPG of an amp design posted on the internet. According to the blogger, it has been extensively simulated - how many mistakes can you find?
From: Jon Kirwan on 2 Mar 2010 16:10
On Tue, 02 Mar 2010 16:13:34 +1000, David Eather <eather(a)tpg.com.au> wrote: >For anyone interested > >I have placed some interesting app notes here > >http://www.filedropper.com/amps Thanks. >It is a free file host, so the files won't be around that long. I am >sorry the total package comes to just shy of 18 MBytes. I got it in time, I guess. >One is an Hitachi Mosfet app note that pretty much redefined most amp's >topology. Thanks. I scanned over it and will read it in more detail, later on. Just by way of demonstrating that I've at least seen it, I immediately saw Figure 3-5 (b) as typical for push-pull class-B output stages. >The other is an RCA app note, sorry each page is a separate file, which >has a practical approach to the output stages and other useful. I've converted it to a single, 16-page PDF file. If you want, I can post it up on the web and make it available at my site. >The last "thing" is a JPG of an amp design posted on the internet. >According to the blogger, it has been extensively simulated - how many >mistakes can you find? Thanks for that. I'll look, a little later on. That will be good for me to do. It uses "current mirror" structures as a method where constant current is desired and with varying Vee these will _not_ be constant current, at all, as layed out there. R4 and R9 will experience varying voltages and since they set the currents for the mirror, that might be a problem for the circuit unless a well-regulated power rail is applied and is maintained at the exact value those mirrors were designed for. So fixed, regulated rails. Which then also suggests that its PSRR, at least for the negative rail, will be a mess -- even low impedance at the negative rail will still allow output signal (which hauls large currents around) to feed back into the current sinks and that will feed back into the amplifier, I think. But that's two minute's thought. I need to go look more seriously. Jon |