As Paul Harvy says............
And now..... the rest of the story.
From the same LM3875 data sheet:
"External Components Description
(Figure 1 and Figure 2)
Components Functional Description
1. RIN Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.
2. RA Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.
3. CA Provides bias filtering.
4. C Provides AC coupling at the input and output of the amplifier for single supply operation.
5. RB Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load upon power-down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.
6. *CC Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of the output transistor. The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps.
*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function
description.
Components Functional Description
7. Ri Inverting input resistance to provide AC Gain in conjunction with Rf1.
8. *Ci Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
fc = 1/(2π Ri Ci).
9. Rf1 Feedback resistance to provide AC Gain in conjunction with Ri.
10. *Rf2 At higher frequencies feedback resistance works with Cf to provide lower AC Gain in conjunction with Rf1 and Ri. A high frequency pole (lowpass roll-off) exists at:
fc = [Rf1 Rf2] (s + 1/Rf2 Cf]/[(Rf1 + Rf2) (s + 1/Cf (Rf1 +Rf2))].
11. *Cf Compensation capacitor that works with Rf1 and Rf2 to reduce the AC Gain at higher frequencies.
12. *RSN Works with CSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.
13. *CSN Works with RSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations. fc = 1/(2πRSN CSN).
14. *L Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low frequencies to short out R and pass audio signals to the load.
15. *R
16. CS Provides power supply filtering and bypassing.
*Optional components dependent upon specific design requirements. Refer to the Application Information section for more information.
Attached image below
FIGURE 2. Typical Single Supply Audio Amplifier Application Circuit
The optional external components shown in Figure 2 and described above are applicable in both single and split voltage supply
configurations."
Please read the WHOLE data sheet, there is more on stability and layout.
And now..... the rest of the story.
From the same LM3875 data sheet:
"External Components Description
(Figure 1 and Figure 2)
Components Functional Description
1. RIN Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.
2. RA Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.
3. CA Provides bias filtering.
4. C Provides AC coupling at the input and output of the amplifier for single supply operation.
5. RB Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load upon power-down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.
6. *CC Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of the output transistor. The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps.
*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function
description.
Components Functional Description
7. Ri Inverting input resistance to provide AC Gain in conjunction with Rf1.
8. *Ci Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
fc = 1/(2π Ri Ci).
9. Rf1 Feedback resistance to provide AC Gain in conjunction with Ri.
10. *Rf2 At higher frequencies feedback resistance works with Cf to provide lower AC Gain in conjunction with Rf1 and Ri. A high frequency pole (lowpass roll-off) exists at:
fc = [Rf1 Rf2] (s + 1/Rf2 Cf]/[(Rf1 + Rf2) (s + 1/Cf (Rf1 +Rf2))].
11. *Cf Compensation capacitor that works with Rf1 and Rf2 to reduce the AC Gain at higher frequencies.
12. *RSN Works with CSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.
13. *CSN Works with RSN to stabilize the output stage by creating a pole that eliminates high frequency oscillations. fc = 1/(2πRSN CSN).
14. *L Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low frequencies to short out R and pass audio signals to the load.
15. *R
16. CS Provides power supply filtering and bypassing.
*Optional components dependent upon specific design requirements. Refer to the Application Information section for more information.
Attached image below
FIGURE 2. Typical Single Supply Audio Amplifier Application Circuit
The optional external components shown in Figure 2 and described above are applicable in both single and split voltage supply
configurations."
Please read the WHOLE data sheet, there is more on stability and layout.
Attachments
OMG, again a repetition of that datasheet. We can read and we can see the Typical application WITHOUT Zobel and we know it can oscillate and we know you can add optional components like a Zobel.
We know, all people know on the forum, even the tube guys started using Zobels afraid of having oscillations. I added a Zobel in my TV intimidated by the horror stories about oscillations of the picture tube. My bicycle has a Zobel too to avoid fluctuations and ringing of the lightbulb.
Please Sy, please.
We know, all people know on the forum, even the tube guys started using Zobels afraid of having oscillations. I added a Zobel in my TV intimidated by the horror stories about oscillations of the picture tube. My bicycle has a Zobel too to avoid fluctuations and ringing of the lightbulb.
Please Sy, please.
"BTW, who was or is Mr. Zobel? Anybody who knows?"
was a Mr. Dr. Zobel at Bell Labs according to http://www.rane.com/par-z.html
Jean-Paul if you can´t stand it, why do you want to close the thread? you always have the option to stay out.
was a Mr. Dr. Zobel at Bell Labs according to http://www.rane.com/par-z.html
Jean-Paul if you can´t stand it, why do you want to close the thread? you always have the option to stay out.
Re: Re: Oh we've come out of hiding eh?
This is the most disingenuous thing I have even seen you do. Pick out one figure and conveniently ignore the rest of the data sheet. Are you trying to KEEP members from understanding some basic amplifier design issues. At least you have let go of me and are dragging yourself through the mud. Do you really think this is wise? I really don't understand what you are trying to accomplish. Would you tell us please?
Will the moderators please split the thread so we can explore this topic which is off topic for this thread?
Peter Daniel said:
This is the most disingenuous thing I have even seen you do. Pick out one figure and conveniently ignore the rest of the data sheet. Are you trying to KEEP members from understanding some basic amplifier design issues. At least you have let go of me and are dragging yourself through the mud. Do you really think this is wise? I really don't understand what you are trying to accomplish. Would you tell us please?
Will the moderators please split the thread so we can explore this topic which is off topic for this thread?
Re: As Paul Harvy says............
I can also read: "*Optional components dependent upon specific design requirements. Refer to the Application Information section for more information."
My experience show that they are not required in my application. You have no experience, as you've built only one amp.
EDIT: I would have post it in the other thread, but then it would be out of context. I leave it to moderators to use the most suitable approach.
Fred Dieckmann said:
I can also read: "*Optional components dependent upon specific design requirements. Refer to the Application Information section for more information."
My experience show that they are not required in my application. You have no experience, as you've built only one amp.
EDIT: I would have post it in the other thread, but then it would be out of context. I leave it to moderators to use the most suitable approach.
till said:
Whoops, that the info I linke to previously. I missed it said
anything about Zobel himself. Still, it says nothing about
what he did, but but, that's maybe not interesting anyway.
One point in closing the thread is that it is now suddenly
about Zobel filters, something which is already being
discussed in two other threds which are dedicated to that
topic.
"One point in closing the thread is that it is now suddenly
about Zobel filters,.."
Thats no reason for closing it, as the main topic is not finished.
Its a good reason for splitting it and clean it up. But this obviosly would be more work for the moderators. And me thinks they may have some interest in the main topic not discussed anymore.
O. J. Zobel, "Theory and Design of Uniform and Composite Electric Wave Filters",
Bell Tel. Sys. Tech. J., vol. 2, pp. 1-46 (1923 Jan).
from http://www.trueaudio.com/st_zobel.htm
about Zobel filters,.."
Thats no reason for closing it, as the main topic is not finished.
Its a good reason for splitting it and clean it up. But this obviosly would be more work for the moderators. And me thinks they may have some interest in the main topic not discussed anymore.
O. J. Zobel, "Theory and Design of Uniform and Composite Electric Wave Filters",
Bell Tel. Sys. Tech. J., vol. 2, pp. 1-46 (1923 Jan).
from http://www.trueaudio.com/st_zobel.htm
Re: Re: As Paul Harvy says............
There is a very big difference between doing empirical evaluation
on a limited number of load situation and doing a proper
theoretical worst-case analyses. Many have found that out
the hard way, both in electronics and other areas. I think that
is what Fred is trying to tell. One of the most famous cases
is a missing blank in a Fortran program that caused a
satellite to crash. But no big deal, that was only about a
billion dollars thrown in the trash can.
Peter Daniel said:
There is a very big difference between doing empirical evaluation
on a limited number of load situation and doing a proper
theoretical worst-case analyses. Many have found that out
the hard way, both in electronics and other areas. I think that
is what Fred is trying to tell. One of the most famous cases
is a missing blank in a Fortran program that caused a
satellite to crash. But no big deal, that was only about a
billion dollars thrown in the trash can.
Re: Re: Re: As Paul Harvy says............
I still feel I have the right to be able to do it my way, not according some guy on a forum I have never met before. Even if I have to learn it hard way.
Christer said:
There is a very big difference between doing empirical evaluation
on a limited number of load situation and doing a proper
theoretical worst-case analyses. Many have found that out
the hard way, both in electronics and other areas. I think that
is what Fred is trying to tell. One of the most famous cases
is a missing blank in a Fortran program that caused a
satellite to crash. But no big deal, that was only about a
billion dollars thrown in the trash can.
I still feel I have the right to be able to do it my way, not according some guy on a forum I have never met before. Even if I have to learn it hard way.
Moamps,
I am not sure I have understood… It is not a problem if there are a few ways in which Zobel works and a few posts back I just have wrote that.
My last post was intended just to inform what I have found to be the logic of the National's datasheet writer. It was just an effort to clarify “Read the datasheet!” hassle.
Recommendations found in the datasheets may and may not have something with the internal circuit, but I can not comment (or surmise) on this since none TDA2030 datasheet I have (4 pcs) shows what is inside.
Btw, as can be seen from your screenshot, it is claimed that the ineffectiveness of this network will deteriorate stability under an inductive load. True, the comment for the C7 (that is the Zobel cap) can be understood as it refers to either load but it also may refer to not load at all. If I recognized well, that is from the datasheet from 1998 and here the Typical Application circuit uses single supply. Note that in the datasheet from 2000, in which the Typical Application uses split supply (though it comprises the band limiting inside the feedback loop which certainly results in the nicer phase margin), has next comment for the situation in which this cap is smaller than recommended: “higher bandwidth”.
Pedja
I am not sure I have understood… It is not a problem if there are a few ways in which Zobel works and a few posts back I just have wrote that.
My last post was intended just to inform what I have found to be the logic of the National's datasheet writer. It was just an effort to clarify “Read the datasheet!” hassle.
Recommendations found in the datasheets may and may not have something with the internal circuit, but I can not comment (or surmise) on this since none TDA2030 datasheet I have (4 pcs) shows what is inside.
Btw, as can be seen from your screenshot, it is claimed that the ineffectiveness of this network will deteriorate stability under an inductive load. True, the comment for the C7 (that is the Zobel cap) can be understood as it refers to either load but it also may refer to not load at all. If I recognized well, that is from the datasheet from 1998 and here the Typical Application circuit uses single supply. Note that in the datasheet from 2000, in which the Typical Application uses split supply (though it comprises the band limiting inside the feedback loop which certainly results in the nicer phase margin), has next comment for the situation in which this cap is smaller than recommended: “higher bandwidth”.
Pedja
Hi,
Sorry but that's just not true.
This is precisely what Fred and others have been trying to put across, you can have a very stable amp and still run into trouble given extreme circumstances.
Heck Peter, you should even recall the trouble someone had with a certain speaker cable and a transformer coupled tube amp not too long ago....
Not that a Zobel network behind the OPT could have saved that one IMO but still...
Better safe than sorry?
At the end of the day it's up to you to include it or not, it doesn't cost an arm and a leg and hey, you can always include a switch. If you gain enough market confidence you could eventually leave it out of the production units, no? Not that I would but I suppose you catch my drift, right?
Just my two lousy cents,
Sorry but that's just not true.
This is precisely what Fred and others have been trying to put across, you can have a very stable amp and still run into trouble given extreme circumstances.
Heck Peter, you should even recall the trouble someone had with a certain speaker cable and a transformer coupled tube amp not too long ago....
Not that a Zobel network behind the OPT could have saved that one IMO but still...
Better safe than sorry?
At the end of the day it's up to you to include it or not, it doesn't cost an arm and a leg and hey, you can always include a switch. If you gain enough market confidence you could eventually leave it out of the production units, no? Not that I would but I suppose you catch my drift, right?
Just my two lousy cents,
Peter Daniel said:If I encounter a single case when Zobel is required, THEN I will include a switch. Everybody on a forum will know about it too.
Yes, but what if it is too late? What's you budget for refunds
for customers blown amps and speakers? No, I am not asking
you to reveal business secrets, just make you ask yourself
that question.
fdegrove said:Hi,
From a business POV that is akin to commercial suicide if you don't mind me saying so...
Let's see if I can come up with a consultant at a reasonable fee for you...
Cheers,
I think we are all speaking for deaf ears. Maybe it's better to
just let him find out the hard way. If he's lucky he get no
problems. If not, he might get himself into deep trouble.
Too bad. He seems to be a nice bloke.
Hi,
Christer,
Since everyone's going OT these days I'll have a little fun too:
Lesson in Dutch/Flemish #1:
Tot dovemans oren spreken.
Lesson in Dutch/Flemish #2:
Philosophical conclusion of the above:
Wat helpen kaars en bril als de uil niet zienen wil.
(Old flemish popular expression).
If you manage to guess it right you'll notice the etymological closeness of the European languages...Have fun.
Cheers,
P.S. Only trying to help, Peter...by no means patronizing you...Although I'd dare...
Christer,
Since everyone's going OT these days I'll have a little fun too:
Lesson in Dutch/Flemish #1:
Tot dovemans oren spreken.
Lesson in Dutch/Flemish #2:
Philosophical conclusion of the above:
Wat helpen kaars en bril als de uil niet zienen wil.
(Old flemish popular expression).
If you manage to guess it right you'll notice the etymological closeness of the European languages...Have fun.
Cheers,
P.S. Only trying to help, Peter...by no means patronizing you...Although I'd dare...
Christer said:
Perhaps Christer has hit upon the "real problem". National wants to provide guidance for potential designers so they know what to expect - and to help them take care of the unexpected. I'll bet that many of the parts from the "recommended" (i.e. application note) schematic can be deleted in *many* applications - but we're talking about a "general purpose" and "unknown environment" in the case of DIY gainclones aren't we? I'd get alot of satisfaction as a DIY-guy if I had a PCB which included layout options for ALL of the app-note components and I only used 1/2 of them (with the rest unpopulated) - but ONLY if it was because I *understood* the circuit, had *tested* the parameters, and finally determined that MY application could do without some of the components - OR - that I'd done enough work (and the math, and the testing) to figure out how to optimise the values for MY application.
Given that the majority of hobbyists either lack the skills and/or the test equipment to make such determinations - Fred is ABSOLUTELY RIGHT in calling for the minimum of safeguards required to ensure that MOST applications will work reasonably (and safely). Why are we still bashing this subject? It's the responsibilty of those who know to look out for the interests of those that don't know - and that's exactly what Fred is doing. He should be thanked - and so should Peter - and so should PA - and so should anybody else who has gone to the trouble of thinking about, building something and trying to share it with the community.
I hope all of this discussion has served to enlighten the non-technical DIYers rather than frighten them off......
All the best,
Bill
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