| Peter Daniel |
Since it seems like Zobel issue becomes more and more controversial, I'm looking for cases when implementing a zobel network in a chip amp helped to stop oscillations.
Please post here a link to any posts (on this forum, or the other, Chip Amps forum) that reported fixing the oscillation problem when Zobel was added.
I'm offering Brian's board to anybody that submits such link. |
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| grataku |
| Are you "collecting the facts" about zobel? Fred's gonna get you, too. ;) |
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| Peter Daniel |
| Well, I'm making sure if my warranty isn't too generous. And my research is not "for free" ;) |
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| moamps |
Hi,
on the picture below there is a characteristic example of LM3875 instability (oscillations within the range of a few MHz) when driven a bit harder. When the Zobel network is applied, the instability disappears. It would be a good idea for the people who have apparently never seen this to say what equipment they are using for their measurements. That is, it may well be the case that they have not been able to detect this instability due to the poor quality of the equipment.
Regards |
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| Peter Daniel |
| It would be also interesting to know what circuit, and how implemented, they use. I had also problems with instability, but it was fixed after changing grounds layout. |
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| grataku |
Sorry Mo, but no boards for you! ;)
That a textbook oscillation that I can even successfully produce on the AlephX under certain circumstances...and when I do it doesn't go away with a zobel. |
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| moamps |
| quote: | Originally posted by Peter Daniel
......what circuit, and how implemented, they use..... |
p2p, IGC, metalfilm resistors 22k/220k, Panasonic elcos 1000uF/100V +100nF on IC, standard bridge, 300VA/48Vsec CT transformer
If anything, I believe I know how to implement grounding correctly.
Regards |
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| BlackDog |
| quote: | Originally posted by moamps
Hi,
on the picture below there is a characteristic example of LM3875 instability (oscillations within the range of a few MHz) when driven a bit harder. When the Zobel network is applied, the instability disappears. It would quipment they are using for their measurements. That is, it may well be the case that they have not been able to detect this instability due to the poor quality of the equipment.
Regards |
Moamps,
Your scope trace didn't come out very clear.
I think increasing the intensity of your trace, or turning the background lighting down a bit would give a clearer picture..
So anyway, are you referring to the blurry region at the peak and trough of the sinewave as the MHz oscillations???
If yes, then what are your timebase and sensitivity set to on the 'scope, and what frequency is your input signal??
I'd like to try and reproduce this 'problem' on my GC, and would appreciate some information on your testing parameters.
SteveM |
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| moamps |
| quote: | Originally posted by grataku
Sorry Mo, but no boards for you! ;)
That a textbook oscillation that I can even successfully produce on the AlephX under certain circumstances...and when I do it doesn't go away with a zobel. |
Hi:
Board or no board, the Aleph doesn't need a zobel because of its topology. If it oscillates, this indicates the presence of a positive feedback (which is independent of the load) somewhere in the circuit. IMO
Regards |
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| Peter Daniel |
| quote: | Originally posted by moamps
If anything, I believe I know how to implement grounding correctly.
|
Seeing your previous work, I don't doubt that. I was rather referring to other people amps. |
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| moamps |
| quote: | Originally posted by BlackDog
So anyway, are you referring to the blurry region at the peak and trough of the sinewave as the MHz oscillations??? |
Blurry region is ca 2MHz oscillation at 10kHz sinewave.| quote: |
If yes, then what are your timebase and sensitivity set to on the 'scope, and what frequency is your input signal??
|
10kHz input, ca 40Vpp level on the IC output, a crappy Technics speaker
Regards |
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| Peter Daniel |
I wasn't looking for a definiton of Zobel
:confused: |
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| BlackDog |
| quote: | Originally posted by moamps
Blurry region is ca 2MHz oscillation at 10kHz sinewave.
10kHz input, ca 40Vpp level on the IC output, a crappy Technics speaker
Regards |
Thanks Moamps,
I'll try and replicate with similar parameters.
SteveM |
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| Fred Dieckmann |
"Zobel Network: A capacitor and resistor of specific values, placed in series across the loudspeaker terminals of an amplifier, to reduce oscillations which can cause instability and excessive heat-output from the chip."
From the http://ampchipdiy.com/phpBB2/viewtopic.php?t=224 link
"I wasn't looking for a definiton of Zobel"
Maybe you should ........... I think anyone with a basic understanding of
electronics should find enough information in the diyAudio Forums > Top > Amplifiers > Chip Amps > Do we need Zobel with chip amp thread to see how one works.
The only controversy on zoble networks seems to be your refusal to show the slightest interest in how they work in order to derive some criteria of when they are required and when they are not. Well maybe spliting the thread, for reasons that escape me, is controversial. I think everyone would be quite happy to discuss this in a new thread if desired. I would be happy to rehash to relevent points in this thread as well. |
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| Peter Daniel |
Fred,
If I still was a moderator, I would ask you to stay on topic. Go back to your other favourite thread, if you have nothing (else related to the main subject) to say.
I didn't expect you'd be a game for GC boards;)
To make it clear for you, I'm looking for actual cases where Zobel was find useful, not theoretical. I don't know why this bothers you. |
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| Fred Dieckmann |
| quote: | Originally posted by Peter Daniel
It would be also interesting to know what circuit, and how implemented, they use. I had also problems with instability, but it was fixed after changing grounds layout. |
Why is it such a stretch that problems of instability should respond to the correct application of a Zobel network then? I am really confused with where you are going with this........ Are you trying to concede gradually or is this latest information supposed to support your position? Hasn't this been beat into the ground enough at this point? :smash: We really don't want to cut into your amp building time over an 'agree to disagree' type issue. |
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| Peter Daniel |
Fred,
If you want to play the game, I'm looking for posts like #23 in this thread: http://www.diyaudio.com/forums/show...obel#post387284
But again, the guy had 10,000U caps way off the chip, and no caps at the chip, so his setup might have beeen compromised. |
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| Peter Daniel |
#2279 in this http://www.diyaudio.com/forums/show...ght=#post379186
But again, home made triple Cat cables. BTW, this amp performed splendidly in my setup, was built the same as all the other. First complain from field customer, probably the first customer with home made Cat 5 speaker cables;) |
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| Fred Dieckmann |
| quote: | Originally posted by Peter Daniel
Fred,
If I still was a moderator, I would ask you to stay on topic. Go back to your other favourite thread, if you have nothing (else related to the main subject) to say.
I didn't expect you'd be a game for GC boards;)
To make it clear for you, I'm looking for actual cases where Zobel was find useful, not theoretical. I don't know why this bothers you.
|
It doesn't. On the subject of moderation, your not a moderator, you resigned remember?
I believe I am still on topic. Your efforts to say otherwise smell of censorship. Maybe an official moderator can step in to make the judgment call. The measurements have been shown and you wanted to know more about moamps setup. I think you need enough theory to ask him what the capacitance of the speaker wire is. One can only wonder why you are trying so hard not to understand how the network works and how much capacitance is enough to be problematic without a zobel. What exactly is your agenda? You seem to think mine is selling everyone zobel networks I guess. I would just like people to understand how the circuit works and seem to be joined by others in this desire. Efforts to the contrary and self-serving motivations hardly contribute to learning and the free exchange of factual and verifiable information on the forum. This is not a matter of opinion type discussion or indecipherable theory. This is very straight forward electronics and an excellent subject for measurement and simple circuit explanations. Tell me in whose interest you are speaking and what is hurt (other than maybe your pride) by an understanding of how a zobel works. I really don't understand what you are afraid of ..... :confused: |
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| till |
| peter, your examples above: should we really look on cases were people are not even able to put decoupling caps on the chips? |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
It doesn't. On the subject of moderation, your not a moderator, you resigned remember?
I believe I am still on topic. Your efforts to say otherwise smell of censorship. Maybe an official moderator can step in to make the judgment call. The measurements have been shown and you wanted to know more about moamps setup. I think you need enough theory to ask him what the capacitance of the speaker wire is. One can only wonder why you are trying so hard not to understand how the network works and how much capacitance is enough to be problematic without a zobel. What exactly is your agenda? You seem to think mine is selling everyone zobel networks I guess. I would just like people to understand how the circuit works and seem to be joined by others in this desire. Efforts to the contrary and self-serving motivations hardly contribute to learning and the free exchange of factual and verifiable information on the forum. This is not a matter of opinion type discussion or indecipherable theory. This is very straight forward electronics and an excellent subject for measurement and simple circuit explanations. Tell me in whose interest you are speaking and what is hurt (other than maybe your pride) by an understanding of how a zobel works. I really don't understand what you are afraid of ..... :confused: |
Read again, I'm not concerned with Moamp setup, I know it's good.
I merely suggested that other people setups may not be up to the task. |
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| Peter Daniel |
#2060http://www.diyaudio.com/forums/showthread.php?s=&postid=201392&highlight=#post201392
Frank admits that zobel is better than nothing;) |
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| netgeek |
| quote: | Originally posted by moamps
Hi,
on the picture below there is a characteristic example of LM3875 instability (oscillations within the range of a few MHz) when driven a bit harder. When the Zobel network is applied, the instability disappears. It would be a good idea for the people who have apparently never seen this to say what equipment they are using for their measurements. That is, it may well be the case that they have not been able to detect this instability due to the poor quality of the equipment.
Regards |
Doesn't this pretty much say it all? Moamps has demonstrated an example which, it seems to me, is a classic. If you're going to ask people to describe a problem wherein a zoebel either did or did not fix it - then they should be required to present evidence equivalent to what Moamps has provided here. Otherwise, we can argue forever about what the "problem" was (e.g. it didn't have as much "air" or "forwardness" as when I used zipcord for speaker interconnect) - and what the ultimate "solution" was (e.g. "I packed the cables in ice for two hours and it really opened the sound")...
All this argument isn't advancing DIY without some evidence and real discussion instead of personal bickering is it? Let's see some real proof instead of conjecture and intuition only...
:apathic: :apathic:
I'd be happy to make some test equipment available if need be.
Bill
"Absence of evidence is not the same as evidence of absence" - Carl Sagan |
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| jam |
| Maybe this will help..............to bring it into more simple terms. ;) |
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| Peter Daniel |
You are missing a bigger picture here, jam. After the search is over, we might ask a modearator to change the title to "GainClone Troubleshooting Thread".
It may become helpful to anybody having problem with their amps, providing of course Fred's post will be removed, as they might be causing too much confusion.;) |
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| andy_c |
Hi Peter,
Douglas Self has a section in his book about his experiments with Zobel networks. Here's a quote from part of it.
"...I removed the standard 10 Ohm / 0.1 uF Zobel from a Blameless Class-B amplifier with CFP output and the usual NFB factor of 32dB at 20 kHz. With an 8 Ohm resistive load the THD performance and stability were unchanged. However, when a 0.47 mH inductor was added in series to roughly simulate a single-unit loudspeaker, there was evidence of local VHF instability in the output stage; there was certainly no Nyquist instability of the global NFB loop."
Though you may strongly disagree with his anti-subjectivist rants, there's tons of tidbits of info like this in the book, making it well worth reading. |
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| Peter Daniel |
| quote: | Originally posted by andy_c
Though you may strongly disagree with his anti-subjectivist rants, there's tons of tidbits of info like this in the book, making it well worth reading. |
I'm not much of subjectivist or objectivist. I'm always after the the best soulutions, whatever they are. That's why I'm doing this research.
Thanks for input. |
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| Peter Daniel |
That's about all I could find on Zobel in Chip Amp section.
I believe, there is more inf0, but I'm not that dedicated to look for it. From whatever I posted here, it is not really clear if Zobel was definitely neccessary to remove oscillations. In some cases it seems like other fixes were actually better.
That is exactly how I remember all those troubleshoothing posts. It was always a first suggestion to try Zobel, but it later appeared that something else was to blame. |
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| sam9 |
| The only IC based amp (hate the word "gainclone") was Marchand's PM21 based on the LM3886. It used a zobel consisting of a .01uF cap and a 5.6R resistor. Not the "conventional" values. I didn't try it without the zobel but certainly it continues to function quite well a few years later with one. |
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| Peter Daniel |
| quote: | Originally posted by sam9
The only IC based amp (hate the word "gainclone") was Marchand's PM21 based on the LM3886. It used a zobel consisting of a .01uF cap and a 5.6R resistor. Not the "conventional" values. I didn't try it without the zobel but certainly it continues to function quite well a few years later with one. |
All right then, if you provide me your address, I'll send you Brian's board;) |
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| grataku |
| quote: | Originally posted by andy_c
Hi Peter,
Douglas Self has a section in his book about his experiments with Zobel networks. Here's a quote from part of it.
"...I removed the standard 10 Ohm / 0.1 uF Zobel from a Blameless Class-B amplifier with CFP output and the usual NFB factor of 32dB at 20 kHz. With an 8 Ohm resistive load the THD performance and stability were unchanged. However, when a 0.47 mH inductor was added in series to roughly simulate a single-unit loudspeaker, there was evidence of local VHF instability in the output stage; there was certainly no Nyquist instability of the global NFB loop."
Though you may strongly disagree with his anti-subjectivist rants, there's tons of tidbits of info like this in the book, making it well worth reading. |
VHF? As in very high frequency? With a .47 mH inductor? Must have been a fantastic inductor |
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| andy_c |
| quote: | Originally posted by grataku
VHF? As in very high frequency? With a .47 mH inductor? Must have been a fantastic inductor |
Well, I don't see him claiming that the inductor is actually inductive at these frequencies. Just that he added it and the output stage oscillations occurred. Maybe you should send him an email complaint? |
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| Fred Dieckmann |
| "Is there a Zobel in that picture? I couldn't figure it out." |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
X Ray vision |
Nice try Fred, but looking at the drilled holes on the board and missing components (front and right), I would rather suspect that both the resistor and capacitor forming Zobel are missing. Underneath traces also indicate that this was a place for Zobel. Why isn't not installed? Maybe for testing purposes? |
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| Fred Dieckmann |
"Is there a Zobel in that picture? I couldn't figure it out." - all quotes are from PD
Maybe because you can't see through the PCB? You know who to ask if you are actually want to know, the guy that designed it. Tell him I sent you........
"I'm not much of subjectivist or objectivist. I'm always after the best solutions, whatever they are. That's why I'm doing this research."
This could be part of your research. I fully agree with you on the objectivist part.
"I believe, there is more inf0, but I'm not that dedicated to look for it. From whatever I posted here, it is not really clear if Zobel was definitely necessary to remove oscillations. In some cases it seems like other fixes were actually better.
That is exactly how I remember all those troubleshooting posts. It was always a first suggestion to try Nobel, but it later appeared that something else was to blame.'
I don't think a Zobel is a cure for poor layout, grounding, and decoupling. I notice everyone wants leave off the 0.1 uF high frequency decoupling caps as well. I have expressed concerns about this as well in the past. If you are going to use just electrolytic caps the layout and grounding are even more of an issue to get right and the caps had better have a very low ESR and ESL. Another example of second guessing the guys at National Semiconductor that can get you in trouble. A Zobel is not going to cure a poor layout for the power supply cap connections to the IC. Read the data sheets for the amplifier chips and see how much importance is placed on these issues.
"I'm not that dedicated to look for it." Here is something I could not agree with more. I'm am releived that there issomething in this debate that we see eye to eye on. |
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| Peter Daniel |
You are not suggesting there is zobel in this picture?
PS: I believe you misquoted me at least in one case. Nice to see your little amp, but there is still much room for improvement in that board. |
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| Jocko Homo |
"That would be telling"
1.) Who can't read the 'scope trace that moamp posted? Looks fine to me. Those of us who have built our share of amps have seen that more times than we care to admit.
2.) Using the example of a CFP output that D.Self refers to is really disingenuous here. Those stinking things oscillate if you look at them wrong. I should know. See #1 above.
3.) It is hard to make a product idiot proof, because idiots are so damn clever. If there is a way to make CAT 5 cable even more capacitive than it already is.......and therefore blow up an amp......rest assured that there is at least one out there with your product in their crosshairs.
Consider yourself lucky if it is only one.
Jocko |
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| fdegrove |
Hi,
| quote: | | PS: I believe you misquoted me at least in one case. |
Probably....and it appears he still has hopes for winning the Nobel prize too.
Still, IMHO he's absolutely right in what he says here.
Oscillations are more often than not caused by instability in the circuit proper and if that's the case Zobel networks can attempt at masking them but sooner or later something going to smoke...
What I usually do before even thinking about hooking up a speaker is doing all kinds of torture tests on the amp with dummy loads iso speakers.
If everything passes that succesfully then only the most unfortunate of unfortunate situations are going to upset the amp to the point where it can oscillate into self-destruction.
Note, I am only talking about topologies that do not require a Zobel network per definition.
So what should you do?
If it were me I'd take a gamble and play the same game the software publishers play; use Joe Consumer as a test bed, but only after I'd gain enough confidence in my product though.
Come to think of it, all these problems could be swept under the table with a simple output trannie...Mucho better than all Nobels and Zobels combined.
Handy stuff and those fancy cables with their crazy capacitance are only trying to limit/filter the HF bandwidth in the first place...
But that's another chapter entirely...
Errr...Frankenstein out of the basement yet?:vampire3: :yikes:
Cheers,;) |
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| Fred Dieckmann |
"Nice try Fred, but looking at the drilled holes on the board and missing components (front and right), I would rather suspect that both the resistor and capacitor forming Zobel are missing. Underneath traces also indicate that this was a place for Zobel. Why isn't not installed? Maybe for testing purposes?" - who else but PD.......
What is this the P-A design espionage school or an example of the GR "I saw a picture so I know what he is doing in the design school"? You would think somebody so passionate about Chip amps would keep an eye on the competition. Or just maybe........... he was trying to cash in on the lucrative Zoble free market! Is this humor, thick headiness, or an attempt at slander? It sure doesn't appear to be research or the desire to learn anything, not even what the competition is doing! :whazzat:
Your competition would probably like to thank you for moving the topic in the direction of his products. He is shy about using the forum to promote his work and I am sure he appreciates you using the forum to share the spotlight with his products as well as yours. It was the act of a gentleman and I tip my hat to your generosity!
You are, if not a gentleman and a scholar, surely a gentleman.
Please give me the opportunity to retire for the evening. You are providing so much fun for me that I could go on all night. I know you have amps to build and I have taken up way to much of your time. Such indulgences will make me very unpopular with your customers and I ask their forgiveness.
Thanks for playing,
Fred, who must go to bed.
* Mark Twain quote |
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| Da5id4Vz |
| quote: | | all these problems could be swept under the table with a simple output trannie... |
McInClone! |
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| andy_c |
| quote: | Originally posted by Jocko Homo
(...) 2.) Using the example of a CFP output that D.Self refers to is really disingenuous here. Those stinking things oscillate if you look at them wrong. (...) |
At VHF though? I'd expect the local loop instability of the CFP to be at a much lower frequency than VHF, a few MHz maybe. IOW that a VHF instability is most likely a parasitic rather than loop-related.
I didn't intend to be misleading with this. |
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| Jocko Homo |
I'm just trying to be fair and biased.
I always had troubles with those in the 2-5 MHz range......just like most any other putput stage.
Yeah......VHF......I doubt many output transistors would work in a 6 meter transmitter.
Jocko |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
Fred, who must go to bed.
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I'm off to sleep too. I hope it won't be (N)obel I'll be dreaming of;) |
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| Fred Dieckmann |
| quote: | Originally posted by Peter Daniel
You are not suggesting there is zobel in this picture?
PS: I believe you misquoted me at least in one case. Nice to see your little amp, but there is still much room for improvement in that board. |
This not my amp! i would have been proud to have designed it though. I believe the network might have been removed to show the rest of the board more clearly......... the other pictures of his amps appear to have the Zoble. Sorry for any confusion. Why don't you call RSN and ask him. Again, please tell him I sent you. I could be completely wrong of course. It may have been a clever ruse to throw the audio spys off the scent. I am glad to hear there is room for improvement. It was sufficient enough of a design, to reportably sound better than one of your amps and with much less of an investment, but I haven't heard either and so will only pass on the report to me. Maybe they were using the wrong speaker cables..........
I really must go to bed before the laughter wakes my wife up. |
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| fdegrove |
Hi,
| quote: | | I'm off to sleep too. I hope it won't be (N)obel I'll be dreaming of |
That would be a (N)ightmare...
It could be worse though...just don't look at Phred's new avatar for too long before jumping into bed...;)
Night guys,;) |
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| Christer |
| quote: | Originally posted by fdegrove
If it were me I'd take a gamble and play the same game the software publishers play; use Joe Consumer as a test bed, but only after I'd gain enough confidence in my product though.
Come to think of it, all these problems could be swept under the table with a simple output trannie...Mucho better than all Nobels and Zobels combined.
|
Yes, learn from Bill. Let the customers pay a hefty price to be
beta testers and then when the bugs (perhaps a lacking
Zobel filter) show up, release an upgrade package at another
hefty price. ;) |
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| platenspeler |
Hi,
I built the following amp (call it Geenkloon) two years ago and designed it and built it with Zobel. Hoewever for the second amp I missed the 22nF cap at the time and decided not to use the Zobel in the second amp for a while (and forgot about it later).
It turned out that during this period I did not need it, and I must say I never noticed a remarkable difference between the channels too. I more or less decided to go for a minimal clone next time. Even the 22uF cap should disappear.
Last week I opened up both boxes and changed the attenuator for another type. When connecting the amps again one channel was definitely instable (I reached the power switch in time to save the speaker). Of course I thought I made a mistake in the components just changed and even changed back to the old switch. After an hour or so decided to find another cap and connect the zobel since everything else was the same.
The zobel worked, quite to my surprise. I used the same speakers (B&W) I used for a longer time for my DIY projects and I used the same speaker cable (ordinary copper of 4 meters in length). The zobel is gonna stay in ..
Have a look at my project pages, to see I soldered everything of the amp except the attenuator on just a few square cm. Unfortunately I cannot go back to exactly the same amp since over the last two days I changed the caps for Black Gates. It sound great already.
Maarten
http://www.platenspeler.com/gainclone.html geenkloon project |
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| indoubt |
Currently in the process of building a GC. But my current setup uses braided catV cable for the tweeter after the (external) crossover filters.
From what is said earlier in this thread it seems that CATV cable is definitely a NONO with gainclones due to the high capacitance of the cable. Is this true or do I have a problem grasphing the real issue here.
And if yes what can I do to prevent oscillation? |
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| fdegrove |
Hi,
| quote: | | But my current setup uses braided catV cable for the tweeter after the (external) crossover filters. |
Those are passive filters?
| quote: | | From what is said earlier in this thread it seems that CATV cable is definitely a NONO with gainclones due to the high capacitance of the cable. |
That depends on the way the CAT5 is used. It sure isn't a problem on its own.
| quote: | | And if yes what can I do to prevent oscillation? |
If you're sure the amp oscillates and it's not due to a layout mistake in the amp itself, a zobel network can help as can using a less capacitive speakercable if that's the cause of it.
Cheers, ;) |
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| Peter Daniel |
| I'm sure you'll find the answer in posts I quoted previously. It seems like more effective than Zobel was a series resistor at the output (10 ohm or so) with few turns of wire over it. But don't loose your sleep over that issue. It may appear that your setup will be fine without any additional preventive measures.;) |
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| Fred Dieckmann |
CAT 5 is data cable not CATV coax. Some of the DIY designs using braided Category 5 are pretty capacitive. Read the data sheet for options for the LM3785. I believe the 2.7 ohm resistor with the 0.1uF cap across the output and possibly the 20K in series with 50pFcapacitor that goes in parallel with the 20K feedback network in addition, are the preferred solutions for amplifier instability when driving capacitive cables. These are very common circuits in amplifier designs. I really believe that this should make the Category 5 cable work fine. If you really want to be sure, look at the output of the amp while driving a 8 ohm power resistor through the cable in question with and without the additional RC circuits. The inductor with a parallel resistor, output networks are becoming rarer in new amplifier designs. I believe it was Nelson Pass who said he found the series resistor and capacitor network to ground at the output of an amp more effective than the inductor resistor combination.
Be careful about some of the vague advice on the forum ........ you never know what the qualifications of the poster are and there is plenty of bad advice. Read the data sheet and don't be afraid to try the things that the actual designers of the IC recommend. You are much more likely to get good advice from the data sheet than some of the stuff floating around of the web. |
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| chris ma |
I am with you one hundred percent there Fred. For the matter of filtering information same should go with news paper, TV news, books let alone the net. For example how do one can prove that the so called Nelson Pass here is the real Mr.Pass and even if he post all his qualifications, cerificates etc etc even those can be fake too..like stories of university certificates that people bought. Doctors practiced for years with faked certificates framed in their office... thinking more and more I should not even trust my father..such a sad situation we are living in ...
Any positive or good news lately?
Regards,
Chris |
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| Fred Dieckmann |
I am quite sure that the Mr. Pass on the forum is real deal. It wasn't fake identities (I can hear all of you laughing about me,of all people,mentioning that topic!) I was referring to, but unqualified claims of expertise of some posters.
Returning to the topic of Zobels and other output stability networks, the search engine found some post by Mr. Pass on the subject. The last one being the best I think.
http://www.diyaudio.com/forums/show...5854#post245854
Re: Revised Schematic
Originally posted by TucsonSean
Here is the revised schematic of my Bass Amp.
It looks very nice. I think you should consider some sort of
RC network to ground at the output to keep it stable with
the variety of loads you might see up at a few megaHertz.
http://www.diyaudio.com/forums/show...88205#post88205
The Aleph is exceptionally stable, and I have not encountered
a load which makes it oscillate. This is reflected by the
fact that the design doesn't bother with an RC load ("Zobel")
network at the output.
Particularly since you have chosen to place an RC across the
load, I don't think you have anything to worry about.
The toroid making noise is more likely to be DC on the AC power
line, usually caused by lamp dimmers and other solid state
controls. If the noise goes away when you disconnect the
speaker, then it probably is DC at the output causing noise
with mismatched secondary windings.
http://www.diyaudio.com/forums/show...6968#post246968
Where's the RC output to ground network?
(Don't say I never told you so)
http://www.diyaudio.com/forums/show...89804#post89804
In addition to the bootstrapping mentioned above, this
amp seriously needs a few parts. (Did I just say that???)
1) Some sort of input resistance to prevent parasitic oscillation
with the source impedance. Happens all the time.
2) An output RC network to prevent oscillation with the load.
Also happens all the time
3) Flyback diodes across outputs - You never Know.
4) Decouple the V+ on the diff pair's current source to get
the ripple out unless your supply is regulated.
5) You will really need some adjustability on the bias.
4 diodes is never going to give you the exact value, and you'll
need better than that.
Do all these things and you won't be sorry.
Do all these things and you'll have an HK Citation 12.
http://www.diyaudio.com/forums/show...37874#post37874
The diodes protect against flyback voltages, and are a
hangover from the old days when V/I limiters were
used for protection. They don't hurt, though, so we leave
them on in case we encounter something really crude for
a load. Mosfet amps don't need them, so you only see them
on Bipolars.
The output coil and resistor are similarly hangovers from the
old days. They were in the original RCA manual, and most
designers use them because monkey-see-monkey-do.
I have never seen a case where they stabilized an unstable
amp, nor where their absence caused instability, and so I
don't use them.
By contrast, the RCA network to ground on the output is
standard and useful for feedback amps. Again, I don't tend
to use them, but I don't usually have enough feedback to
worry about. |
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| chris ma |
I am sorry Fred that I did not mean to imply Mr.Pass is fake here on the forum. It was just an example I used.. bad judgement on my part I guess..Not to be off topic again. I better shut up.
Regards,
Chris |
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| Pedja |
| quote: | Originally posted by Fred Dieckmann
(...)
Read the data sheet for options for the LM3785. I believe the 2.7 ohm resistor with the 0.1uF cap across the output and possibly the 20K in series with 50pFcapacitor that goes in parallel with the 20K feedback network in addition, are the preferred solutions for amplifier instability when driving capacitive cables.
(...) |
You are discussing the single supply application circuit. |
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| indoubt |
Thanks
The filter is passive
I will not go over one night of ice (unlike in my younger years, when ice was thick enough when you could get over without getting wet too much). I'l first try with resistors on the speaker terminals whether the amp is oscillating or with cheap loudspeakers, after that I will decide if and what measures need to be taken |
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| dimitri |
Dear PD,
I perfectly understand your uncertainty about Zobel network. Yes, you are right, bad layout or/and unproper caps could be also the origin of oscillation. Regarding layout there are crosstalk, rail induced disto (local decoupling caps) and the proper ground connection to main PSU caps. The solutions are well documented (Self). It is also generally accepted that Zobel network prevents the load to be too inductive. Otherwise Bateman in CapSound-II reported distortion, which was induced by Zobel network cap. So, if your amp will work with the same load (powered loudspeaker system), with the same wires, if you are 100% sure that the output clipping is totally avoided, and nobody can occasionally disconnect the load while amp is working - you can avoid Zobel network or experimented with resistor/cap value or place Zobel network (or even a simple resistor, which can be a part of the L-pad) near tweeter. By placing Zobel network near tweeter you prevent the Zobel cap from large voltage swing.
One short note regarding power ratio of Zobel network resistor. While it was mentioned in one magazine that only tiny portion of power is dissipated in such resistor, it becomes completely different once the amp being clipped. From my experience, I'd repaired at least half a dozen amps (home and pro) where the small power rating Zobel resistor was opened. There were no visual signs of burning/mechanical damage. Such amps behaved unpredictable and turned to instability/oscillation when I changed the load value, disconnect it, drive the amp above clipping or wait for a certain heating of output transistors. Thus I can recommend no less than 5W Zobel resistor rating for 100W amp. |
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| Fred Dieckmann |
The point about clipping is well taken. You can pretty well count on these small amps being driven into clipping from time to time. A 1 watt M.F. or 1 W metal oxide should work fine. The higher power resistor are more inductive. For 5 watt resistors you are very likely to wind up with a very inductive wirewound type if you are careful. Keep the leads short and mount by IC and not the binding post. NO WIREWOUNDS! Remember amps driven into clipping long enough tend to eat high frequency drivers.
"You are discussing the single supply application circuit."
No............ I'm not.:whazzat: The network is applicable to both single and split supply. From the DS (the source of much information about applications for the IC...... who knew?)
Reading from the data sheet..........
"The optional external components shown in Figure 2 and described above are applicable in both single and split voltage supply configurations."
Is there anybody who reads the data sheets?! This is getting depressing when people want all this insight into amp design when THEY WON'T READ THE DATA SHEETS AND WON'T BELIEVE THEM WHEN THEY DO.
I am really wondering if purchasing amp or kit that is already designed and fully tested (by someone who reads the data sheets and has good electronics knowledge and experience) might not be a better solution for beginners.
When you design something to be idiot proof they will come up with new and improved idiots. :smash: (HUMOR!) This is not aimed at any one individual but at a mindset that tends to seek the lowest common denominator based on questionable advisce. Make an effort and pick your advice carefully, based on the track record of the advisor and the qualifications of others who agree or disagree with the advice given ( like the guys who wrote the data sheet). |
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| Pedja |
In the single supply application circuit first you have the voltage divider from the supply/ground to the input. This brings some thoughts both about deteriorated PSR and problems in which the internal transistors can fall. Then you see Cc (220pF) between two inputs that… what does that can do? It filters possible hash? More needed in single supply application? Yes! Unfortunately this cap reduces the phase margin. Hence Cf-Rf2 that pushes back the phase. As a side effect, the chip is better protected from any HF hash coming with the signal, but generally, would you bet that the stability is as good as without all this? I am still adding and subtracting as the new stuff comes into my eye, but I can not escape the impression the Zobel is shown because of this.
(Check LM1875’s datasheet, in the single supply application it does not have the cap (Cc) between the inputs, corresponding cap (C2) goes to ground, and none of the other component is shown.)
As about the datasheet and reactive loading, there is not a single word about Zobel that solves reactive loading issues in the datasheet (chapter “Reactive loading”). Actually the 10R//0.7uH is what National recommends for driving loads of 0.2uF or higher (at 0.2uF it will ring but this yet does not meant it will oscillate). Obviously, they do not read carefully Nelson’s posts… Btw, how many of those with plan to drive anything like that?
In fact, when you “read the datasheet” you can not conclude that the Zobel has anything with loading! They say that the Zobel forms the pole that stabilizes the output stage thus preventing it from high frequency oscillations. Nothing about source(s) of these! Funny, I am prone to think that in the real life these sources are mainly not load related.
Pedja |
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| netgeek |
| quote: | Originally posted by Fred Dieckmann
...I am really wondering if purchasing amp or kit that is already designed and fully tested (by someone who reads the data sheets and has good electronics knowledge and experience) might not be a better solution for beginners.
When you design something to be idiot proof they will come up with new and improved idiots. :smash: (HUMOR!) |
It will no doubt cost more but should be well worth it in the long run to avoid the type of disappointment you see here frequently (e.g. "My amp runs REALLY hot". "Sound is distorted - what to do?", Fuses keep blowing", "Fried my tweeters", "My dog went bats**it - should I sell him?")..:) :rolleyes: ...
C'mon Fred - jump in there and offer a kit!!!...:) I'll bet you'd really enjoy the constant interchange and contact it would provide with newbies!... :rolleyes:
Regards,
Bill |
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| chris ma |
IMHO, the BrainGT Kit has provide newbies like myself a very good starting point in the DIY audio route. When I read any problems and solutions regarding the kit I can relate to it and take advantage learn from others success and mistakes. Without this kit and assuming with the same number of people building the chip amps I am sure there would have been a lot more newbies questions and problems postings. And some might not even dare to take the first step of this DIY garden path. Thanks to Brain and Peter, and certainly thanks to Fred we all benefit from this kit project. Like the governments we need the opposition parties to keep the country stay on the right course. They agrue in the government and the citizen reap the benefits.
Regards,
Chris |
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| Fred Dieckmann |
"C'mon Fred - jump in there and offer a kit!!!"
Let the punishment fit the crime! I'll have nightmares for a month. :smash:
Keep the dog........ somebody needs to know how to recognize when the amp's misbehavin' :snoopy: |
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| Fred Dieckmann |
| quote: | Originally posted by Pedja
In the single supply application circuit first you have the voltage divider from the supply/ground to the input. This brings some thoughts both about deteriorated PSR and problems in which the internal transistors can fall. Then you see Cc (220pF) between two inputs that… what does that can do? It filters possible hash? More needed in single supply application? Yes! Unfortunately this cap reduces the phase margin. Hence Cf-Rf2 that pushes back the phase. As a side effect, the chip is better protected from any HF hash coming with the signal, but generally, would you bet that the stability is as good as without all this? I am still adding and subtracting as the new stuff comes into my eye, but I can not escape the impression the Zobel is shown because of this.
(Check LM1875’s datasheet, in the single supply application it does not have the cap (Cc) between the inputs, corresponding cap (C2) goes to ground, and none of the other component is shown.)
As about the datasheet and reactive loading, there is not a single word about Zobel that solves reactive loading issues in the datasheet (chapter “Reactive loading”). Actually the 10R//0.7uH is what National recommends for driving loads of 0.2uF or higher (at 0.2uF it will ring but this yet does not meant it will oscillate). Obviously, they do not read carefully Nelson’s posts… Btw, how many of those with plan to drive anything like that?
In fact, when you “read the datasheet” you can not conclude that the Zobel has anything with loading! They say that the Zobel forms the pole that stabilizes the output stage thus preventing it from high frequency oscillations. Nothing about source(s) of these! Funny, I am prone to think that in the real life these sources are mainly not load related.
Pedja |
Try reading the data sheet as written instead of analyzing it for subtext. The falling open loop gain with increasing frequency makes the output impedance look inductive. Most speaker cable provide a capacitive load. Inductance and capacitance resonate at some frequency. The Zoble network has a capacitor value chosen to put the resonance at a low enough frequency for the amp to have good phase margin and the series resistor provides damping so there is no ringing at this resonant frequency and provides a resistive impedance as the frequency increases past the point where the capacitors impedance becomes less than the resistance.
I don't see the big confusion why a single supply amps compensation should be different from with split supplies. The impedance from ground to the negative supply is less that of the cap in the Zobel network by the ratio of the filter cap value over the Zobel cap value. The impedance of the negative supply cap is many orders of magnitude lower than that of the Zobel cap. At the frequency range we are interested in with stability issues, the negative supply is very closely couple to AC ground by the filter and bypass cap and can be considered AC ground. This assumes a good low inductance layout and filter caps that have not gone inductive much below several hundred kHz. A lot of electrolytic filter caps have is why the 0.1uF filter caps. If you are going to leave the bypass caps out the choice of the filter cap is very important and the reason for filter caps of 1000 uF and smaller being used when no 0.1 uF caps are added. I am very reluctant to put a cap across the inputs to the op amp and would recommend an RC input filter (C to ground) to keep RF out of the input. |
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| janneman |
Amen!
Jan Didden |
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| Pedja |
| quote: | Originally posted by Fred Dieckmann
Try reading the data sheet as written instead of analyzing it for subtext. The falling open loop gain with increasing frequency makes the output impedance look inductive. Most speaker cable provide a capacitive load. Inductance and capacitance resonate at some frequency. The Zoble network has a capacitor value chosen to put the resonance at a low enough frequency for the amp to have good phase margin and the series resistor provides damping so there is no ringing at this resonant frequency and provides a resistive impedance as the frequency increases past the point where the capacitors impedance becomes less than the resistance.
I don't see the big confusion why a single supply amps compensation should be different from with split supplies. The impedance from ground to the negative supply is less that of the cap in the Zobel network by the ratio of the filter cap value over the Zobel cap value. The impedance of the negative supply cap is many orders of magnitude lower than that of the Zobel cap. At the frequency range we are interested in with stability issues, the negative supply is very closely couple to AC ground by the filter and bypass cap and can be considered AC ground. This assumes a good low inductance layout and filter caps that have not gone inductive much below several hundred kHz. A lot of electrolytic filter caps have is why the 0.1uF filter caps. If you are going to leave the bypass caps out the choice of the filter cap is very important and the reason for filter caps of 1000 uF and smaller being used when no 0.1 uF caps are added. I am very reluctant to put a cap across the inputs to the op amp and would recommend an RC input filter (C to ground) to keep RF out of the input. |
No, you read the datasheet instead of screaming to others to read the datasheet.
There is no Zobel suggested in the datasheet to solve the capacitive loading issues!
Are we reading the same datasheet?
And this still does not have anything with what you or I think about Zobel. Yes, of course it will make capacitive loads easier acceptable. It won’t make miracles yet. And there are a few mechanisms the Zobel works. I mean, works sometimes. But there is nothing in the datasheet about it. Or you maybe have the different datasheet?
As about the decoupling of inductive impedance raise (amp’s ouput) and capacitive impedance fall (cable) to prevent resulting peak, normal way of solving this is usage of series resistances, not of Zobel. Or you already started to use Zobel in, say, supply regulators?
If you check Rod Elliot’s article about speaker cable impedance, you might find Zobel both able to compensate inductive and not capacitive load, as well as (put at the amp’s output) being nicely useless to protect amp’s stability under some real loads.
http://sound.westhost.com/cable-z.htm
In fact, a capacitive reactance is not supposed to be compensated by series RC network in parallel, but parallel RL network in series. Just as per LM3875 datasheet, chapter “Reactive Loading”. No subtext, no hidden catch, just the chapter “Reactive Loading”, LM3875’s datasheet, page 13.
And among all the “read the datasheet” noise you brought, I just do not understand your statement about your reluctance about something. Instead of reluctance, think again about that single supply application. Afterward, you might be reluctant or not, won’t change much. I anyway do use the passive RC LPF at the input.
Pedja |
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| Fred Dieckmann |
A reactive load of 0.22 uF is much higher than any speaker cable load that one is likely to encounter. It fact you are talking about a capacitance that is twice the value of the recommended capacitance in the Zobel network shown in the data sheet. In fact, for a 20 foot speaker cable that comes out to 11,000 pF per foot! I believe the use of a damped inductor is for capacitance approaching or exceeding the value in the Zobel shown in the data sheet. I believe that capacitive loads in the range of 10 to 100 pF are more typical and even 100 pF per foot would be a pretty high capacitance. A 20 foot cable with 2000 pF would be 50 times less capacitance and the Zobel will pretty much determine the resonant frequency. It is interesting that LR network looks like 10 ohms at very high frequencies and the load on the amp would be 10 ohms in series with 0.22 uF and in the neighbor hood of 0.1 uFand 2.7 ohms and not an order of magnitude removed.
I will be more specific this time. Follow the recommended network values in the data sheet. Those of you putting schematics for these amps on the web and selling kits should be aware of what kind of loads these amps are going to drive and understand damped RCL circuits. You had better be measuring this stuff as well. You can get a meter for less than $100 that will measure capacitance. Flogging the amp with a 100 MHz scope with a variety of resistive loads (2 to 20 ohms perhaps) in parallel with capacitance to represent speaker cable loading as required. This would be the least I would expect from someone selling kits while claiming to have a feel for what makes a stable amp. Of course I expect them to listen to extensively it as well........
In the general scheme of amplifier design, this level of knowledge and effort is the equivalent of wading in ankle deep on the journey to becoming a full immersion baptized amp designer. And by the same analogy, I believe that Mr. Pass and Mr. Curl can walk on water. I bet both of them would confess to having to swim to shore a few times on the way to that level. |
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| janneman |
Fred,
Only 391 words. ;) And I fully agree with every single one. It was about time someone spelled out the responsibility of those selling those kits to the unsuspecting.
Jan Didden |
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| Pedja |
| quote: | Originally posted by Fred Dieckmann
A reactive load of 0.22 uF is much higher than any speaker cable load that one is likely to encounter. It fact you are talking about a capacitance that is twice the value of the recommended capacitance in the Zobel network shown in the data sheet. |
Now just be that smart and “note” that this capacitance (which is not something "I am talking about"!) is about 1000 times the value of the cap between the inputs.
:hypno2:
I mean if it is for the nonsense...
| quote: | I believe that capacitive loads in the range of 10 to 100 pF are more typical and even 100 pF per foot would be a pretty high capacitance.
(…) |
Do me/us a favor, read the article I have linked previously, you will find there some real cable/speaker loads and their consequences. Zobel at the amp’s output included all the time.
| quote: | | I believe the use of a damped inductor is for capacitance approaching or exceeding the value in the Zobel shown in the data sheet. |
You do not have to believe in anything, in the datasheet you have precise info what the damped inductor is for! Madre mia! “Read the datasheet!” Screen shot attached in the post before your post! Duh!
Now, for the sake of the peace in the house let me skip the paragraph with your advices and let me give my last try to help you. None have told it is the 0.2uF something that should be driven. It is clamed that the LM3875 will be stable as long as the amount of direct capacitive load does not exceed 0.2uF. By the other words, as long as you do not deal with PA systems, LM3875 is, per datasheet, claimed to be able to cope with the capacitive load. “Read the datasheet!”
RC Zobel network is not the circuit intended to correct a capacitive load. Almost entirely the opposite, it corrects inductive loads. You have been warned a few posts earlier by andy_c who has quoted Self. Anyone who even slightly dealt with loud speaker design knows that the Zobel is used to correct an inductive part of the impedance. Zobel for beginners here (small warning: you will learn here there is also RL Zobel which do can compensate for the capacitive impedance, but you better leave this for the future so do not confuse yourself with it at this stage):
http://www.reed-electronics.com/edn...22195/26di3.htm
So, what you have to learn is:
1. As long as you do not read/understand/are not interested for the datasheets, do not scream to others to read the datasheets! In the LM3875 there is no Zobel suggested to protect the amp under the capacitive loading.
2. Do not waste the bandwidth hunting others about the “lack of understanding” of the circuits, you alone yet do not know what the Zobel is for!
Pedja
(Jan in the background: “You’ll tell him again Fred, you’ll tell him, would you…”) |
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| 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 |
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| Fred Dieckmann |
"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. |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
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. |
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. |
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| Fred Dieckmann |
"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.
:Popworm: :smash: :whazzat: |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
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.
:Popworm: :smash: :whazzat: |
Slowly, I'm beginning to grasp the real reason for your Zobel crusade. A bit too late though. |
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| Pedja |
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. |
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| jean-paul |
| quote: | | He doesn't need to use the forum in search of customers or to build a cult following. |
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... |
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| peranders |
| quote: | Originally posted by Fred Dieckmann
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 |
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?
Since I don't know everything Fred, who is the Gainclone builder you are talking about? Is it Jeff Rowlands? |
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| jean-paul |
| quote: | | Fred, I didn't like PD's gainclone either 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) |
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. |
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| peranders |
| quote: | Originally posted by Fred Dieckmann
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. |
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.
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. |
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| Fred Dieckmann |
"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. |
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| Fred Dieckmann |
"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! |
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| moamps |
Try SGS
for TDA2030: |
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| Peter Daniel |
| quote: | Originally posted by Fred Dieckmann
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. |
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. |
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| Christer |
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 | | | |
