Function of Output Inductor

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#81
traderbam said:
I certainly have never claimed to be an expert on data compression formats. Should I be?

Perhaps you'll do me and others a favour and explain your improved Zobel for NS's circuit? I'll suspend disbelief, on this occasion, and assume you have something to teach me.
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Winrar is just as common as winzip. No need to be an expert. Just use it.

As for Zobel, I'm not going to teach you anything as long as you keep trolling here. Besides, it's soooooo basic.
 
#82
Re: Re: Re: Zőbel

Edmond Stuart said:

As I said before, that character (o-umlaut) will not correctly displayed on every PC/monitor.
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On my monitor it looked like the hungarian long version of the vowel written as a german umlaut o. Don't know if that was right or not, but that's why I said hungarian origin.

Anyhow, you have convinced me that, in order to avoid confusion, we should call this chap Zobel, or even better, Dr. Zobel (are you listening too, Ovidiu?)
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I think we should. Had he been an immigrant who used to americanize his name to avoid problems, then I agree it would be appropriate to use the original spelling when referring to him, but since he was born in the USA and used that spelling, I don't think one should do otherwise.

So shall we go on the next confusion then? Should it be called a Zobel filter or a Boucherot cell? It is often pointed out in the literature that these are different names for the same thing. So are they, and if so, which of the two guys should we attribute it to? 🙂

The wiki article on Zobel filters however seems to suggest that the term Boucherot cell should only be used, if at all, for certain specific implementations of the filter in the context of loudspeakers.
 
#83
Zobel

Hi Eva,

Thank you for the sims. Could you do me a favor and repeat the sims, now, without Rsn and Cns, a cap of 11nF across RL and 8 Ohm across the coil, please?

Cheers.

edit: Writing my previous posts, I have, admittedly, overlooked Rsn and Cns, which were a bit drawn out of focus. My apologies for creating confusion (if any).
 
#84
Re: Re: Function of Output Inductor

PMA said:


The output inductor helps compromised designs, whose parameters are achieved by high amount of global negative feedback, to stay stable when output connected to complex load. It is a necessary bandaid to keep such circuits working, not oscillating.
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This is completely wrong. Even designs without negative feedback can get into trouble if not properly isolated from a capacitive load.

Bob
 
#85
Christer said:
While I have no opinion whether coils are audible or not, I try to keep a bit of open mind in such issues and I don't mind exercises of hypothetical reasoning. So, if we assume the ouput coil is audible, can we imagine an explanation that might explain it? So let's speculate a bit instead of just dismissing it by adding inductances etc. If for no other reason, so at least just for the fun of it. 🙂

Tradebarm has already brought up the things that came to my mind too:

1. The coil and the speaker wire have different physical locations, so the explanation might lie there rather than in the inductance per se. As Traderbam said, what about the magnetic field of the coil affecting the small signal circuitry? Since the current dependes on the speaker impedance, the output current may have quite a different spectrum than the output voltage, so if the current induces a voltage in the feedback loop, for instance, perhaps that might distort at least the frequecy response of the amp? What happens if we add the coil just at the output connector instead of on the PCB, for instance? Would John still hear it?

Then, what about the other way around, ie. the coil picking up a field? In a class AB amp, the supply currents are heavily distored. We already know this can affect the circuit by inductive coupling with a bad PCB layout. Well, a coil is much better at picking up magnetic fields than a PCB track is. On the other hand, if this is the case, I suppose it should show up clearly already when testing with a single sine wave.

2. Assume it has something to do with high frequencies, like RFI, slight damped oscillation tendencies of the amp under certain load conditions or maybe back EMF from the speakers can cause fast rising edges with a HF spectrum? Whatever the reason for the HF, maybe we have to think transmission lines here, so we have to consider impedance matching of inner wiring, connectors speaker cable etc. Then perhaps the coil could make thing worse sometimes?

Yes, I know this is mostly very speculative, but if a phenomenon possibly exists, it usually requires quite a bit of speculation and creativity to figure out if it actually exists and why.
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These are all very good points. We don't necessarily know that audibility of the coil is a result of a frequency response deviation caused merely by its inductance in the line. As you point out, its audibility could be caused by the magnetic field that it is radiating while passing the large speaker currents (although one would expect an appropriate frequency response test or distortion test to pick something up as a result of such an interaction). Or, as you point out, it could be the coil picking up something, although again we would think that such might be evident in some measurement. It is all indeed perplexing, but the middle road is to assume that large values of inductance can be audible, so keep them as small and well-behaved as possible, but also recognize that a small amount of inductance is prudent for stability into the unknown environment of the real world. I would not be the least surprized if some audible stuff from some high-end amplifiers originates from burst parasitic oscillations occurring as a result of well-intentioned but misguided high-end design practices.

It would certainly be interesting if someone did a coil audibility listening test where the coil was placed in the line at the louspeaker end, where emission and pickup interactions with the electronics of the amplifier would be much less likely.

Cheers,
Bob
 
#86
Re: Re: Re: Zőbel

Edmond Stuart said:

Anyhow, you have convinced me that, in order to avoid confusion, we should call this chap Zobel, or even better, Dr. Zobel (are you listening too, Ovidiu?)
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I was taught german in the 60's when the alphabet was still full of gothic characters (umlaut wovels, scharfes S) and the transition to oe ue etc... was in progress. To me, correct is Zoebel, Goedel, Zuerich but I understand that languages are evolving and simplifying in time. I guess all forms are correct and even google doesn't seem to care about the syntax in the search, returning both. Interesting enough, Analog Devices is using Zoebel in the application note.
 
#88
Re: Re: Re: Re: Zőbel

Christer said:
The wiki article on Zobel filters however seems to suggest that the term Boucherot cell should only be used, if at all, for certain specific implementations of the filter in the context of loudspeakers.
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Hi Christer,

Indeed, another point of confusion. As for Boucherot cells, wikipedia describes them as RC networks and it's purpose is to keep the load at HF at the same resistive level as the nominal load (many times applied to tube amps, btw)

A Zobel network however, serves two purposes: keeping the load constant (and resistive) and block RFI from outside.

So, the info from wiki is not always as consistent as it should be.

Cheers,
Edmond.
 
#89
Re: Re: Re: Re: Zőbel

syn08 said:


I was taught german in the 60's when the alphabet was still full of gothic characters (umlaut wovels, scharfes S) and the transition to oe ue etc... was in progress. To me, correct is Zoebel, Goedel, Zuerich but I understand that languages are evolving and simplifying in time. I guess all forms are correct and even google doesn't seem to care about the syntax in the search, returning both. Interesting enough, Analog Devices is using Zoebel in the application note.
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Yes, but the question is not about transliteration but about what his name actually was. In the cases of Goedel and Zuerich it is perfectly correct as transcriptions into english, since those names are spelled with umlaut in original. But is there any evidence that Zobel should have umlauts in the name? There are only 69 people with that name in Germany
http://www.verwandt.de/karten/absolut/z%C3%B6bel.html
while there are 11504 with the name Zobel
http://www.verwandt.de/karten/absolut/zobel.html
Googling for hungarian language pages seems not to find anything byt Zobel and Zo'bel (deliberaty slightly wrong to assure readability).

It seems thus most likely that even Otto J Zobels ancestors did spell their name with just an "o" before emigrating the USA.

Maybe there is something about his origins in this link?
http://genforum.genealogy.com/zobel/
 
#90
Re: Re: Re: Re: Re: Zőbel

Edmond Stuart said:



So, the info from wiki is not always as consistent as it should be.
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Absolutely. Wiki is probably more reliable than most internet pages, but not to be trusted. My point was rather that wiki is the only place so far where I have seen both terms mentioned but not as quite the same thing. Everywhere else I have seen it, they have been claimed as alternate names for the same thing.

Anyway, it seem very few people use the term Boucherot cell, so there is probably not much confusion in practice.
 
#95
Oh Edmond,
Don't lower yourself to character assassination. I criticized the design of your "ultimate amplifier" or what ever it was called - that was over a year ago, wasn't it? Is that what this is about? Get over it, life's too short.

You made a late appearance in this thread and posted your opinion that the NS Zobel circuit that Lineup posted was badly designed (and you said almost all Zobels are badly designed). You then gave a new resistor value and said a capacitor should be put in parallel with the speaker output. I am unfamilar with the scheme you proposed and cannot understand what benefit it would give. So I asked you to explain it for me and Lineup and anyone else who is following this thread.

You don't want to go to the trouble for some reason, that's fine.
I don't have that Cherry article, please send it to me and I'll have a look.
 
#96
traderbam said:
Oh Edmond,
Don't lower yourself to character assassination. I criticized the design of your "ultimate amplifier" or what ever it was called - that was over a year ago, wasn't it? Is that what this is about? Get over it, life's too short.
..............
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First, please don't be so pathetic.
Second, read this post again:
http://www.diyaudio.com/forums/showthread.php?postid=1553827#post1553827
Third, not only your comment on the PGP amp was below all standards, also on other topics, like Ovidiu's view on EC and my NFB OPS.

As for Cherry's article, if you don't have a copy, one more reason to keep your mouth shut.
 
#97
Edmond Stuart said:
Hi Lineup,

As usual, most published Zoebel networks are wrong, including this one from NS.
If the load is 8 Ohm, then the R across the coil should also be 8 Ohm.
Furthermore, a parallel cap across the load is missing.
With 0.7uH and 8 Ohm the correct value is ~11nF.

Cheers,
Edmond.

PS: Zoebel rules!
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I disagree. I've got some Neville Thiele articles where he describes the component values for a couple of load isolations/HF terminating networks designed to present a constant (with frequency) load impedance to the amplifier for both 4 and 8 ohms. One is just as the NS design and the other has just a parallel cap across the speaker terminals. The inductances are huge (14uH/8R, 6uH/4R) and the constant impedance thingie only works with a resistive load!

I never use his values for even attempt to fudge them to approximate a constant load impedance to the amp. The only thing the output network has to do IMHO is to isolate any capacitive load to a sufficient degree with a well dampened inductor and provide a low impedance termination at HF. Works well for me and the squarewave response is infinitely better too! 😀

Cheers,
Glen
 
#98
Using just a capacitor after the zobel was interesting but if you parallell the output with a small inductor (like a short circuit) there will be impedance peaks as seen from the amplifier. This might not be a problem though depending on the amp...

Using R+C before a L//R network will have controlled impedance even when the output is parallelled with a resonant circuit. It seems R+C after L//R works too with some differences. I wonder which one is best though. I've seen both used.
 
#99
Time Out, Please!

Gentlemen, please do a break! All those who write is ENGLISH for me! You put me in doubt. What recommend finally all of you? To use or not inductor in the output of my amp? It is obvious that your views differ. It is also clear that exists - for some time, as well as in other threads too - a dispute between some members who have a higher knowledge level from us the common mortal. Thus, with the slightest opportunity, they exploit a simple query from a member, to start a new battle. This puts me into suspicions that something else exists in reality behind all this. From that I understand, "caesar148" who started this thread, he is confused at the moment. Or he is also playing the game from the start?

With humility
Fotios
 
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