I am not sure if this could come into your eye, but this is from the LM3875’s datasheet. Markings are mine:
Full document here:
http://cache.national.com/ds/LM/LM3875.pdf
Full document here:
http://cache.national.com/ds/LM/LM3875.pdf
Attachments
very informative
I'm just getting into this stuff and trying to learn the basics, as well as build a few things. This thread, thanks to the efforts of the contributors, while sometimes contentious, has been very informative - especially the last couple of pages (entertaining too!). So carry on, please.
I'd like to comment on the safety warning issues: This thread originated from an effort to propose a design for a basic chip amp. Most of the warnings given are completely appropriate for a product sold to the general public. But I don't view this as a commercial offering to the general public- more like a cooperative design and sourcing effort among enthusiasts. It should be obvious to anyone who has read the thread for this project and the prior one by Brian and Peter on the 3875 amp, that these are "minimalist designs" and have not gone through an extensive vetting process to eliminate potential problems. IOW, they are basically experimental designs that have worked well in a limited number of situations and will probably work well in typical applications - but it is up to the builder to make that determination. I have no problem with that.
The additional information developed in these threads could (should) certainly be cited as suggested reading for potential builders with limited experience (me, for instance). That, plus simple statement to the fact that these are experimental designs and should be undertaken with that understanding, is warranted. Beyond that, I'm completely willing to take the responsibility for whatever happens to my project.
Thanks again,
Sheldon
I'm just getting into this stuff and trying to learn the basics, as well as build a few things. This thread, thanks to the efforts of the contributors, while sometimes contentious, has been very informative - especially the last couple of pages (entertaining too!). So carry on, please.
I'd like to comment on the safety warning issues: This thread originated from an effort to propose a design for a basic chip amp. Most of the warnings given are completely appropriate for a product sold to the general public. But I don't view this as a commercial offering to the general public- more like a cooperative design and sourcing effort among enthusiasts. It should be obvious to anyone who has read the thread for this project and the prior one by Brian and Peter on the 3875 amp, that these are "minimalist designs" and have not gone through an extensive vetting process to eliminate potential problems. IOW, they are basically experimental designs that have worked well in a limited number of situations and will probably work well in typical applications - but it is up to the builder to make that determination. I have no problem with that.
The additional information developed in these threads could (should) certainly be cited as suggested reading for potential builders with limited experience (me, for instance). That, plus simple statement to the fact that these are experimental designs and should be undertaken with that understanding, is warranted. Beyond that, I'm completely willing to take the responsibility for whatever happens to my project.
Thanks again,
Sheldon
P-A amplifiers or If the kit fits you must aquit
"Why am I so eager? Not really but it would be interesting to see what you can come up with besides a Gainclone This is not meant as irony, I mean it." P-A
What is this fixation with me designing a gainclone! I built one pair point to point with copper clad unetched PCB board segments for low inductance ground. I have never laid out a PCB for one or sold one. My only real interest is that people build them so they are stable at high frequencies with a reasonable selection of speaker cables I have been an advocate for good stable amps for a long time on the forum and have been beaten up for it before. I have also read several post of people who have had oscillation problems due to poor bypassing, insuficient loop gain, poor grounding, and capacitive speaker cables. What is just beyond believe is that someone who has all three of these problems, during the learning curve of building good chipamps, is the biggest advocate of leaving off the Zobel network! What's wrong with this picture?
It was also without irony that I said that your PCB board looked looked the most fun to play with. A minimalist kit is great for the "I just want to build something that works that I don't have to mess with" builder. I am afraid I am in the "I want to mess with it" group that a kit with many options be more useful to.
"Why am I so eager? Not really but it would be interesting to see what you can come up with besides a Gainclone This is not meant as irony, I mean it." P-A
What is this fixation with me designing a gainclone! I built one pair point to point with copper clad unetched PCB board segments for low inductance ground. I have never laid out a PCB for one or sold one. My only real interest is that people build them so they are stable at high frequencies with a reasonable selection of speaker cables I have been an advocate for good stable amps for a long time on the forum and have been beaten up for it before. I have also read several post of people who have had oscillation problems due to poor bypassing, insuficient loop gain, poor grounding, and capacitive speaker cables. What is just beyond believe is that someone who has all three of these problems, during the learning curve of building good chipamps, is the biggest advocate of leaving off the Zobel network! What's wrong with this picture?
It was also without irony that I said that your PCB board looked looked the most fun to play with. A minimalist kit is great for the "I just want to build something that works that I don't have to mess with" builder. I am afraid I am in the "I want to mess with it" group that a kit with many options be more useful to.
Oh we've come out of hiding eh?
"What is just beyond believe is that someone who has built only one of those amps has so much to say about them. And he didn't even read the datasheet." P-D
The Zobel network is common on many amplifiers. I have built one set of chip amps............ not just one set of amplifiers. Perhaps the LM3875 is a magic amp and doesn't follow the laws of physics and electronics? Tell me who hasn't read the data sheet, someone who is trying to explain what the network does and quantify some of the unknowns like how much capacitance is typical for a speaker cable; and maybe even getting some people to measure them. Who is benefiting and who is hurt by shining some light on building chip amps with good high frequency stability? Some members want some fairly basic amplifier issues to be understood without being called a liar, an idiot, or someone with some hidden agenda. They prefer to talk about design details to take this debate out the area of slander and into some engineering to see what other designers think hear, and measure. What anyone thinks of me is not going influence how their amplifier sounds or performs. Trying some well established design details very likely will. BTW.... relax, I am not going into the chip amp business. A designer I have known some time and who's DACs I consider some of the best I have ever heard, is building too good a series of chip amps for me to want to compete with. I won't use the forum to give hive free advertising either ......... but then again he has a market based on two decades of great sounding products (and trust from me for the excellent design advice he has given me over the same period). He doesn't need to use the forum in search of customers or to build a cult following.
"What is just beyond believe is that someone who has built only one of those amps has so much to say about them. And he didn't even read the datasheet." P-D
The Zobel network is common on many amplifiers. I have built one set of chip amps............ not just one set of amplifiers. Perhaps the LM3875 is a magic amp and doesn't follow the laws of physics and electronics? Tell me who hasn't read the data sheet, someone who is trying to explain what the network does and quantify some of the unknowns like how much capacitance is typical for a speaker cable; and maybe even getting some people to measure them. Who is benefiting and who is hurt by shining some light on building chip amps with good high frequency stability? Some members want some fairly basic amplifier issues to be understood without being called a liar, an idiot, or someone with some hidden agenda. They prefer to talk about design details to take this debate out the area of slander and into some engineering to see what other designers think hear, and measure. What anyone thinks of me is not going influence how their amplifier sounds or performs. Trying some well established design details very likely will. BTW.... relax, I am not going into the chip amp business. A designer I have known some time and who's DACs I consider some of the best I have ever heard, is building too good a series of chip amps for me to want to compete with. I won't use the forum to give hive free advertising either ......... but then again he has a market based on two decades of great sounding products (and trust from me for the excellent design advice he has given me over the same period). He doesn't need to use the forum in search of customers or to build a cult following.
Re: Oh we've come out of hiding eh?
Slowly, I'm beginning to grasp the real reason for your Zobel crusade. A bit too late though.
Fred Dieckmann said:A designer I have known some time and who's DACs I consider some of the best I have ever heard, is building too good a series of chip amps for me to want to compete with. I won't use the forum to give hive free advertising either ......... but then again he has a market based on two decades of great sounding products (and trust from me for the excellent design advice he has given me over the same period). He doesn't need to use the forum in search of customers or to build a cult following.
Slowly, I'm beginning to grasp the real reason for your Zobel crusade. A bit too late though.
I have checked a few National datasheets to figure the logic behind the appearance of the Zobel and have found what: that they show the Zobel in the single supply applications to terminate the output for HF because of the (inductance of the necessary) huge signal coupling capacitor there.
Fanny.
Fanny.
If you mean to accuse PD for that I think you are hitting below the belt pal. I thought you were a man of ethics Fred but I guess I was wrong.
No free advertising for the designer you mention but negative publicity for his competitors instead by mentioning unlikely problems that don't even occur with PDs amps. All that comment after having only one ( 1 ) amp built. And you accuse others of being armchair designers while having a +/- 30 part amp built by someone else...
Re: Oh we've come out of hiding eh?
Since I don't know everything Fred, who is the Gainclone builder you are talking about? Is it Jeff Rowlands?
Fred, I didn't like PD's gainclone either (just the feeling of it, nothing personal Peter. I'm the overkill guy) so I did my own and I am quite happy with it and it works good and of course has all the options I and everyone else need (including zobel networks).... almost. But Fred why do you have to be so hostile? Peter is doing his thing and was there a serious bug in his design sooner or later people would noticed it. Can't you be a bit humble?Fred Dieckmann said:
Since I don't know everything Fred, who is the Gainclone builder you are talking about? Is it Jeff Rowlands?
What's that supposed to mean ? Why do we all need that options, I certainly don't need all the options you provide on your welldesigned PCB ? Did you compare your gainclone to Peters, Per-Anders ? I have a cartload of gear that works good but stays in the barn
It is sad to see the accusations and the negative comments ( not necessarily in just this thread ) at the adress of Peter Daniel. I am never going to howl with the wolves because it's fashion to do so. Peter has an excellent ability to make nice looking and from what I read excellent sounding gear and he may not be the best electronic designer but he really listens to what he builds. Something some designers forget. Did I mention he really builds gear ?
He and BrianGT made a very nice troublefree kit around LM3875 that was an excellent opportunity for starters that lurked here to go out and buy a soldering gun and build an amp. It was absolutely a low or non profit attempt to do something for the community here. That's a lot more than the foul words some like to speak about him, mostly from people that contribute not much more than useless quarrels about non existing problems or rarely occuring issues. The kit is of a high level, much higher level and less problems than most DIYers could have achieved on their own ( with or without Zobel ).
BTW the answer to the endless debate about to Zobel or not to Zobel could just be one sentence: "As an option it is possible to solder a RC series network parallel to the output jacks with values X and Y to prevent possible oscillation or ( fill in whatever other reason there may be )".
Fred is almost certainly speaking about Scott Nixon. Please let us keep this excellent designer out of this. Scott deserves better as does Peter.
Re: P-A amplifiers or If the kit fits you must aquit
Anyway I get a kick of making a nice pcb which also happen to work good. Personally I think P2P is real boring. I use it only when I want to test something.
Have you never made a pcb? If not,try it because it's a challange to get it right. It's not the same thing as telling others how they should do.Fred Dieckmann said:
Anyway I get a kick of making a nice pcb which also happen to work good. Personally I think P2P is real boring. I use it only when I want to test something.
More slowly that you think.........
"Slowly, I'm beginning to grasp the real reason for your Zobel crusade. A bit too late though." -PD*
Peter you really haven't a clue do you? Do you really think what my veiws on anything are going to effect anybody sales? Do I write reviews of audio equipment? People can buy what ever they like. They can always tack a Zobel on top of Kit PCB without holes for it very easily if that's want they want. I get no royalties from Zobel networks or money or perks to promote anybody's product. What is the reason for your anti-Zobel crusade is what everyone is starting to wonder I think. If I really wanted to promote one manufactures products I think it would be wisest to leave any potential competitors to muddle along without a clue. And mention the name of the company, which I have not. You can drag me through the mud all you want. I am not selling any products here and have nothing to lose. You might want want to ask yourself how you plan to continue to slander me,..... and post idle speculation on the reasons for my actions, without getting dirty yourself.
* to help P-A of course, he is the only one I have given a real plug to on the forum.
"Slowly, I'm beginning to grasp the real reason for your Zobel crusade. A bit too late though." -PD*
Peter you really haven't a clue do you? Do you really think what my veiws on anything are going to effect anybody sales? Do I write reviews of audio equipment? People can buy what ever they like. They can always tack a Zobel on top of Kit PCB without holes for it very easily if that's want they want. I get no royalties from Zobel networks or money or perks to promote anybody's product. What is the reason for your anti-Zobel crusade is what everyone is starting to wonder I think. If I really wanted to promote one manufactures products I think it would be wisest to leave any potential competitors to muddle along without a clue. And mention the name of the company, which I have not. You can drag me through the mud all you want. I am not selling any products here and have nothing to lose. You might want want to ask yourself how you plan to continue to slander me,..... and post idle speculation on the reasons for my actions, without getting dirty yourself.
* to help P-A of course, he is the only one I have given a real plug to on the forum.
Surely your joking......... please tell me your joking
"Have you never made a pcb? If not,try it because it's a challange to get it right. It's not the same thing as telling others how they should do." P-A
Let see if I understand your question......... after over a decade and a half as a telecom design engineer and designed audio for 25 years you want to know if I have I have ever laid out a PCB?
After my head spun completely 360 degrees around on my shoulder like that poor little girl in The Exorcist, I thought myself "You melon head .....are you out of your mind PA?" Then it dawned on me that had to be humor! No other explanation would be possible.
I have lost count of the number of boards I have laid out with both CAD designers for and by myself for audio products. I worked with CAD designers with everything from Recal-Redac system in the mid 1980s to Mentor Graphics in a Unix environment a few years ago. Boards with EMI considerations as well as power cross and lightning strike survivability. I gave a lecture on design of two layer PCBs for EMI reduction to a group of over 100 board designers and design engineers at Alcatel.
I have laid out several dozen of my own boards with a Beta version of CADPoint which only ran under Windows 2 and with Tango PCB in a Windows environment. I have designed boards for low noise analog, CMOS digital, mixed signa, l and RF applications. I picked a few from a stack in a box. There are many audio products that combine point to point with PCBs. There are applications where that sounds better. FR4 is a pretty nasty dielectric. I would be insulted if I thought there was the slightest possibility that you were serious, but surely you weren't........... right? And people say my sense of humor is warped!
"Have you never made a pcb? If not,try it because it's a challange to get it right. It's not the same thing as telling others how they should do." P-A
Let see if I understand your question......... after over a decade and a half as a telecom design engineer and designed audio for 25 years you want to know if I have I have ever laid out a PCB?
After my head spun completely 360 degrees around on my shoulder like that poor little girl in The Exorcist, I thought myself "You melon head .....are you out of your mind PA?" Then it dawned on me that had to be humor! No other explanation would be possible.
I have lost count of the number of boards I have laid out with both CAD designers for and by myself for audio products. I worked with CAD designers with everything from Recal-Redac system in the mid 1980s to Mentor Graphics in a Unix environment a few years ago. Boards with EMI considerations as well as power cross and lightning strike survivability. I gave a lecture on design of two layer PCBs for EMI reduction to a group of over 100 board designers and design engineers at Alcatel.
I have laid out several dozen of my own boards with a Beta version of CADPoint which only ran under Windows 2 and with Tango PCB in a Windows environment. I have designed boards for low noise analog, CMOS digital, mixed signa, l and RF applications. I picked a few from a stack in a box. There are many audio products that combine point to point with PCBs. There are applications where that sounds better. FR4 is a pretty nasty dielectric. I would be insulted if I thought there was the slightest possibility that you were serious, but surely you weren't........... right? And people say my sense of humor is warped!
Re: Oh we've come out of hiding eh?
Perheaps Pedja's post in the other thread was to subtle for you to comprehend?
So here I'm putting it out for you in layman terms. If you still argue that National recommends Zobel for LM3875, I might suspect that you are doing it for reasons other than your usual care for members trying to "understand some basic amplifier issues".
I assume you know what word "Typical" means.
Fred Dieckmann said:
Perheaps Pedja's post in the other thread was to subtle for you to comprehend?
So here I'm putting it out for you in layman terms. If you still argue that National recommends Zobel for LM3875, I might suspect that you are doing it for reasons other than your usual care for members trying to "understand some basic amplifier issues".
I assume you know what word "Typical" means.
Attachments
It is beyond me why Peter or anybody would view Freds postings
on Zobel filters as any kind of personal attacks or crusades. He
is explaining what the filter is for and why it is sensible to use
it. It is all just normal worst-case analysis. Often theoriticians
have a hard time explaining to practitioners why it is sensible
to do worst-case analyses, not the least in computer science.
I don't think Fred would label himself a theoritician, but I think
it is fair to say he is an experienced practicioner with a good
theoretical knowledge, and now he has a hard time explaining
to non-eningeers why worst-case scenarios should be
considered. I recognize the situation completely from similar
situations in computer science.
Some people seem to be afraid of Zobel filters. Maybe a
half-year treatment with Zo(be)loft would help?
BTW, who was or is Mr. Zobel? Anybody who knows?
on Zobel filters as any kind of personal attacks or crusades. He
is explaining what the filter is for and why it is sensible to use
it. It is all just normal worst-case analysis. Often theoriticians
have a hard time explaining to practitioners why it is sensible
to do worst-case analyses, not the least in computer science.
I don't think Fred would label himself a theoritician, but I think
it is fair to say he is an experienced practicioner with a good
theoretical knowledge, and now he has a hard time explaining
to non-eningeers why worst-case scenarios should be
considered. I recognize the situation completely from similar
situations in computer science.
Some people seem to be afraid of Zobel filters. Maybe a
half-year treatment with Zo(be)loft would help?
BTW, who was or is Mr. Zobel? Anybody who knows?
Character margin and amplifier stability...Related?
Jean-Paul, you are reading stuff into my post as well. The only dispute I have with anybody, is over whether it would be prudent to include a Zobel network in the chip amp design. I and others have provided evidence that it is. Moamps even showed parasitic oscillations on a scope which seemed to me conclusive evidence, unless someone is going to accuse him of ulterior motives as well. The guy most resistant to including the network has even stated that amp's stability is sensitive to grounding in the layout and very capacitive speaker cables, two things I could not agree with more! As I recall the real controversy seemed to start after I recommended including the networks on the PCB the Brain GT is working on. I even believe that Brian was soliciting ideas to improve the PCB layout. Like they say......no good deed goes unpunished. You know I could sit back a not say another word and this debate will still continue. Hopefully without attacks on my character........ my character having absolutely no influence on the stability of anyone's amp.
Jean-Paul, you are reading stuff into my post as well. The only dispute I have with anybody, is over whether it would be prudent to include a Zobel network in the chip amp design. I and others have provided evidence that it is. Moamps even showed parasitic oscillations on a scope which seemed to me conclusive evidence, unless someone is going to accuse him of ulterior motives as well. The guy most resistant to including the network has even stated that amp's stability is sensitive to grounding in the layout and very capacitive speaker cables, two things I could not agree with more! As I recall the real controversy seemed to start after I recommended including the networks on the PCB the Brain GT is working on. I even believe that Brian was soliciting ideas to improve the PCB layout. Like they say......no good deed goes unpunished. You know I could sit back a not say another word and this debate will still continue. Hopefully without attacks on my character........ my character having absolutely no influence on the stability of anyone's amp.
Peter Daniel said:
Well, I admit I am taking Freds advice as general recommendation
for amplifier design. Maybe these chips are designed so that
no Zobel is required under any circumstances, but if you are
serious about it and selling amps, you should do a proper
analysis of the circuit and see how it might behave under
various worst-case conditions. Datasheets do not always
tell the whole truth, and for these chips I am tempted to
think that they are providing cook-book rules of thumb.
Besides, datasheets may contain errors. I am not saying you
should absolutely keep the Zobel in, but I think you should
do proper analyses and simulations of what happens with
and without Zobel filters for various worst-case scenarios.
If you go commercial, it is your responsibility to make sure
your product is safe. Maybe you can sue National if something
happens, but don't count on it.
But what do I care. It is not me your customers will phone
if their speakers blow or their amps stop working, or
god forbid, their houses catch fire.
Edit: I also believe these chips are mainly intended to be
built into integrated amp-speaker systems where the designer
has full control over the load condition. They probably never
were intended for general amplifier usage with arbitrary
unknown loads.
Fred Dieckmann said:
But I also posted in this thread numerous (real life) examples where Zobel was of no use in eliminating those bad design practices. When the amps is done properly, Zobel represents no real advantage. It is not recommended in National's data sheet and it's even stated that it may have "certain undesirable effects when it interacts" with other components. Indeed, one of my first examples (in this thread) shows that Zobel actually makes the amp to "disbehave" (I know you like this expression).
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