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.
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.
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
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
Attachments
moamps said:
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
Hi:grataku said: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.
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
"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.
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.
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.
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.
On the other hand
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?
We really don't want to cut into your amp building time over an 'agree to disagree' type issue.
Peter Daniel said:
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?
We really don't want to cut into your amp building time over an 'agree to disagree' type issue.
Fred,
I'm already tired of your "brilliant" persistance. I'll do some search on my part. This is a first thread I found. I know there is much more, similar: http://www.diyaudio.com/forums/showthread.php?s=&postid=382347&highlight=#post382347
I'm already tired of your "brilliant" persistance. I'll do some search on my part. This is a first thread I found. I know there is much more, similar: http://www.diyaudio.com/forums/showthread.php?s=&postid=382347&highlight=#post382347
Fred,
If you want to play the game, I'm looking for posts like #23 in this thread: http://www.diyaudio.com/forums/showthread.php?s=&postid=387284&highlight=zobel#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.
If you want to play the game, I'm looking for posts like #23 in this thread: http://www.diyaudio.com/forums/showthread.php?s=&postid=387284&highlight=zobel#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.
#2279 in this http://www.diyaudio.com/forums/showthread.php?s=&postid=379186&highlight=#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
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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