Konniciwa,
No, you got it wrong way around.
Sorry? I seem to miss your point. What has random noise to do with this?
Do me a favour, PLEASE. Read Self's bloody book and articles.
It saves me miles of explaining and his Book really should be a standard on everyones shelfs (if only to understand why making amplifiers the usual way is usually a bad idea). You can have my one if you put cover price plus shipping to a childrens charity (I learned everything to learn from it ages ago).
Sayonara
millwood said:
No, you got it wrong way around.
millwood said:
If so, why don't we all inject identical random noise on our amplifier's input and feedback ends and our $10 boombox will sound as nice as our Krell / or whatever of your favorite brands,
Sorry? I seem to miss your point. What has random noise to do with this?
millwood said:
Do me a favour, PLEASE. Read Self's bloody book and articles.
It saves me miles of explaining and his Book really should be a standard on everyones shelfs (if only to understand why making amplifiers the usual way is usually a bad idea). You can have my one if you put cover price plus shipping to a childrens charity (I learned everything to learn from it ages ago).
Sayonara
Konnnichiwa,
Thanks for reminding me. I could have otherwise forgotten (sarkasm alert for non europeans).
!!!???? You NEED TO ASK????
It is a signal (actually AC or DC, but we are talking AC here) that is different from the "reference" (usually the negative rail) and common to both inputs. Any such signal will have any number of effects if applied to a LTP (Long tailed Pair) stage.
These have been documented for ages and ages since around the 1950 or was that the 1590 - ahhm, no, no electronics then, so 1950's it is (I do have problems with ancient history - too much of it to keep current - sorry).
Of course, my "mistake" is not to treat the "Op-Amp" (monolithic or dicrete) as black box, but as a circuit usually composed usually out of LTP, VAS & CAS with megatons of loop feedback....
Sayonara
BTW, for the uninitated, LTP = Long Tailed Pair, VAS = Voltage Amplification Stage, CAS = Current Amplification Stage
millwood said:
Thanks for reminding me. I could have otherwise forgotten (sarkasm alert for non europeans).
millwood said:
!!!???? You NEED TO ASK????
It is a signal (actually AC or DC, but we are talking AC here) that is different from the "reference" (usually the negative rail) and common to both inputs. Any such signal will have any number of effects if applied to a LTP (Long tailed Pair) stage.
These have been documented for ages and ages since around the 1950 or was that the 1590 - ahhm, no, no electronics then, so 1950's it is (I do have problems with ancient history - too much of it to keep current - sorry).
Of course, my "mistake" is not to treat the "Op-Amp" (monolithic or dicrete) as black box, but as a circuit usually composed usually out of LTP, VAS & CAS with megatons of loop feedback....
Sayonara
BTW, for the uninitated, LTP = Long Tailed Pair, VAS = Voltage Amplification Stage, CAS = Current Amplification Stage
Kuei Yang Wang said:
Thanks for that.
So a common mode signal is one that is present on both inputs of an opamp.
And for a non-inverting opamp, both inputs have the same signal (which is the input signal). to which I said earlier
.
And for an inverting opamp, there is no common mode signal (both ends are AC grounded - unless you consider the ground as a signal source). to which I said earlier
.
and you had stated earlier:
questions:
1) why was my understanding not consistent with your statements?
2) why is having common signals on both inputs better than NOT having common signals on both inputs?
I fully expect that you can explain this to us all without resorting having us read a book,
Konnichiwa,
Bludie quotes.... Lets do it olde style....
> So a common mode signal is one that is present on both
> inputs of an opamp.
AND is different from the "reference" primarily in AC terms.
> And for a non-inverting opamp, both inputs have the same
> signal (which is the input signal). to which I said earlier quote:
> having a common mode signal on both inputs
Yes.
> And for an inverting opamp, there is no common mode
> signal (both ends are AC grounded - unless you consider
> the ground as a signal source).
Not quite - the positive input is (AC) ground and becomes the "reference" input for the feedback system. The inverting input will be FORCED by the feedback to follow the non-inverting input, whch has no AC voltage.
> to which I said earlier quote: having a common mode signal on
> both inputs
And I said - NO. You MAY have forgotten to insert the key word "NO", or you may have the "common mode" definition wrong (a Common Mode signal BY DEFINITION exists on both inputs).
Yet you claim an (AC) common mode signal exists for the two inputs of the Op-Amp's in inverting mode, based on your writing. And I cannot agree with that, sorry. It is wrong.
> 1) why was my understanding not consistent with your
> statements?
See above.
> 2) why is having common signals on both inputs better
> than NOT having common signals on both inputs?
You make no sense. Common Mode Signals are COMMON to both inputs ALL THE TIME.
As to why is having NO common mode signal (my claim - please re-read what I wrote) is better than having one - isn't it BLINDINGLY OBVIOUS? The CM signal will bleed heavily distorted into the rest of the amplifier circuit.
> I fully expect that you can explain this to us all without
> resorting having us read a book,
I fully expect that you AT THE VERY LEAST exhaust the generically availabe sources on a topic before bothering me.
I guess that leaves us at an impasse? I expect you to inform yourself if you wish to talk as "INFORMED" participant (you may participate as admitted ignoramus as much as you like BTW).
You expect me to teach you for FREE what you omited to study and which is widely and readily available.
I THINK NOT. I am happy to comment on "what works", but I do not run on-line EE101 and 201 courses, sorry. This well's winch creeks on that stuff.
Sayonara
Bludie quotes.... Lets do it olde style....
> So a common mode signal is one that is present on both
> inputs of an opamp.
AND is different from the "reference" primarily in AC terms.
> And for a non-inverting opamp, both inputs have the same
> signal (which is the input signal). to which I said earlier quote:
> having a common mode signal on both inputs
Yes.
> And for an inverting opamp, there is no common mode
> signal (both ends are AC grounded - unless you consider
> the ground as a signal source).
Not quite - the positive input is (AC) ground and becomes the "reference" input for the feedback system. The inverting input will be FORCED by the feedback to follow the non-inverting input, whch has no AC voltage.
> to which I said earlier quote: having a common mode signal on
> both inputs
And I said - NO. You MAY have forgotten to insert the key word "NO", or you may have the "common mode" definition wrong (a Common Mode signal BY DEFINITION exists on both inputs).
Yet you claim an (AC) common mode signal exists for the two inputs of the Op-Amp's in inverting mode, based on your writing. And I cannot agree with that, sorry. It is wrong.
> 1) why was my understanding not consistent with your
> statements?
See above.
> 2) why is having common signals on both inputs better
> than NOT having common signals on both inputs?
You make no sense. Common Mode Signals are COMMON to both inputs ALL THE TIME.
As to why is having NO common mode signal (my claim - please re-read what I wrote) is better than having one - isn't it BLINDINGLY OBVIOUS? The CM signal will bleed heavily distorted into the rest of the amplifier circuit.
> I fully expect that you can explain this to us all without
> resorting having us read a book,
I fully expect that you AT THE VERY LEAST exhaust the generically availabe sources on a topic before bothering me.
I guess that leaves us at an impasse? I expect you to inform yourself if you wish to talk as "INFORMED" participant (you may participate as admitted ignoramus as much as you like BTW).
You expect me to teach you for FREE what you omited to study and which is widely and readily available.
I THINK NOT. I am happy to comment on "what works", but I do not run on-line EE101 and 201 courses, sorry. This well's winch creeks on that stuff.
Sayonara
Kuei Yang Wang said:
No, I wasn't expecting you being such a bad teacher,
I mistakenly thought that you said an non-inverting design is better. My bad. and appologies.
I figured out what went wrong in the above exchange. Your argument is essentially that as long as CMRR isn't infinite, any common mode signal (presenting on both inputs) will be amplified by the amp and be presented at the output.
an inverting design doesn't have a common mode signal (unless you consider ground being a singal source);
a non-inverting design has a common mode signal (the input signal itself).
and it beats me on two things:
1) why is having a common mode signal which is identical to your input signal not desirable?
2) maybe you are the exception but how many of us can hear a -120db signal?
I cannot.
BTW, have you thought about taken the audio challenge posted recent at the other form? the prize is $10K, too little for you I suppose?
Konnichiwa,
No, my point was that inverting designs are "better" (in the way Winnie the Poo considers "better") and in certain (most) applications more apropriate.
If you still don't got it - RTFB (Read The ******** Books).
Come on, this EE101 stuff.....
Such a blanket statement (first, where does you "120db" figure originate, second, once you have adjusted it to reality - have you cionsidered "nonharmonic" distortion mechanisms?
And have you ever considered the CMRR of Op-Amp's past DC? It makes for interesting Graphs. The closed loop CMRR for the rather "wideband" and "audio grade" OPA604 drops below 90db @ 10KHz. Now this matters not much, unless you have a lot of noise (from delta signa converters?) creeping in above say 100KHz where the CMRR is only a little above 60db.
And I notice the NE 5532 is not even charaterised for CMRR vs. Frequency. You may perpetuate the myth of the dstortion free op-amp, except under noiseload conditions things still look way dire.... Of course, that is not "THD & N", it's just ALL nonlinearities lumped - no more "cherry picking....
No, not particulary, primarily because all this challenge business is statistically so rank, it makes 2 Week old rotten fish smell sweet, but secondly because I was not aware of such.
Now, if I can define the audition process and the statistics such as to even out the likelyhood of type 1 and type 2 errors for small audible differences, I'll have no need to even be involved in first place anyway, as my own contribution (even with the hearing of a Vampire Bat) would be infinitisimal, the first and foremost point of entrance for statistics anyway.
So please, do yourself a favour, try studying the subject AT THE VERY LEAST to the limits documented by "objectivist" contibutors and then also study physio/psychoacoustocs to a level of reasonable competence. Combining both fully "objectivist" branches of science gives interesting inshighst, add o this a little understanding of dynamic systems (electronic or not) and you may go far, assuming you wish to.
It all boils down back to doing your homework, instead of substituting assumptions of others for your own knowledge.... Hence I usually try to avoid teaching my own prejudices and views to other and instead expect them to go and find their own darn answers, if they really want answeres (as opposed to re-inforcement of a position already held)....
Sayonara
No, my point was that inverting designs are "better" (in the way Winnie the Poo considers "better") and in certain (most) applications more apropriate.
If you still don't got it - RTFB (Read The ******** Books).
Come on, this EE101 stuff.....
Such a blanket statement (first, where does you "120db" figure originate, second, once you have adjusted it to reality - have you cionsidered "nonharmonic" distortion mechanisms?
And have you ever considered the CMRR of Op-Amp's past DC? It makes for interesting Graphs. The closed loop CMRR for the rather "wideband" and "audio grade" OPA604 drops below 90db @ 10KHz. Now this matters not much, unless you have a lot of noise (from delta signa converters?) creeping in above say 100KHz where the CMRR is only a little above 60db.
And I notice the NE 5532 is not even charaterised for CMRR vs. Frequency. You may perpetuate the myth of the dstortion free op-amp, except under noiseload conditions things still look way dire.... Of course, that is not "THD & N", it's just ALL nonlinearities lumped - no more "cherry picking....
No, not particulary, primarily because all this challenge business is statistically so rank, it makes 2 Week old rotten fish smell sweet, but secondly because I was not aware of such.
Now, if I can define the audition process and the statistics such as to even out the likelyhood of type 1 and type 2 errors for small audible differences, I'll have no need to even be involved in first place anyway, as my own contribution (even with the hearing of a Vampire Bat) would be infinitisimal, the first and foremost point of entrance for statistics anyway.
So please, do yourself a favour, try studying the subject AT THE VERY LEAST to the limits documented by "objectivist" contibutors and then also study physio/psychoacoustocs to a level of reasonable competence. Combining both fully "objectivist" branches of science gives interesting inshighst, add o this a little understanding of dynamic systems (electronic or not) and you may go far, assuming you wish to.
It all boils down back to doing your homework, instead of substituting assumptions of others for your own knowledge.... Hence I usually try to avoid teaching my own prejudices and views to other and instead expect them to go and find their own darn answers, if they really want answeres (as opposed to re-inforcement of a position already held)....
Sayonara
Kuei Yang Wang said:
Come on, Mr. Sayonara. It is so EE101 stuff and you still ask questions about it?
No more free education of you on this forum OK. Go read the ******** book!
This is turning into such a useless discussion.
BTW, I laughed so hard when you had to rely on alpha and beta to get yourself out of a challenge. that's so classic Mr. Sayonara.
millwood said:
Come on, Mr. Sayonara. It is so EE101 stuff and you still ask questions about it?
No more free education of you on this forum OK. Go read the ******** book!
This is turning into such a useless discussion.
BTW, I laughed so hard when you had to rely on alpha and beta to get yourself out of a challenge. that's so classic Mr. Sayonara.
Hi millwood
Check out Douglas Self's web site and then bookmark it!!!!!!!
http://www.dself.dsl.pipex.com/ampins/ampins.htm
Perhaps more specifically the page: Distortion In Power Amplifiers
http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm
Joe R.
Joe Rasmussen said:
thanks for the link.
here is what it says about common mode distortion:
the discussion about thermal distortion is also quite interesting. He essentially said that for discrete devices, it is unlikely we will see thermal distortion above 10hz due to large thermal inertia. I remember reading from another thread where another author said that thermal distortion can be upto 10KHz.
I looked at the data sheet for the LM3857 yesterday, IIRW the CMRR is about 40dB at higher audio freqs. That means that a common mode signal of say 100mV generates up to 1mV of CM error that is amplified and appears at the output. Wouldn't that be significant? I think I am with KYW here.
Jan Didden
Jan Didden
millwood said:
Put that man in room 101 with Naim-driven Bose Acoustimess speakers at full blast.
the schoolbook transfer of an opamp is
Vo = Aol (Vp - Vn)
with Aol likely being some ugly non-linear coeffient.
if you stay in school a day longer than that, the equation becomes
Vo = Aol (Vp - Vn) + Acm (Vp + Vn)
with Acm another nasty non-linear thingy.
I sort of admire T's patience in this ...
What Do the Common Mode Folk Say?
Using inverting mode for op amp circuits is recommended by very good op amp applications guys that know what they are talking about. Relying of Mr. Self opinions on amplifiers is usually a pretty good indication you're on the wrong side in my experience.
John Curl designed with an inverting topology for the JC-2 about a quarter of century ago. Nelson Pass's Aleph X designs use an inverting topology. The reason most amps do not use an inverting topology is the input impedance must be lower the 100K ohms that everyone seems to use. It is a better topology and for reasons including some independent of signal level.
It appears to me that difference between the DIY God of Thunder's stance and that of the non inverting crowd is, as Mark Twain put it, "the difference between the lightning and the lightning bug.
http://www.geocities.com/Hollywood/Hills/6396/optimist.wav
You're out of the woods,
you're out of the dark,
you're out of the night.
Step into the sun,
step into the light,
then open your eyes
Using inverting mode for op amp circuits is recommended by very good op amp applications guys that know what they are talking about. Relying of Mr. Self opinions on amplifiers is usually a pretty good indication you're on the wrong side in my experience.
John Curl designed with an inverting topology for the JC-2 about a quarter of century ago. Nelson Pass's Aleph X designs use an inverting topology. The reason most amps do not use an inverting topology is the input impedance must be lower the 100K ohms that everyone seems to use. It is a better topology and for reasons including some independent of signal level.
It appears to me that difference between the DIY God of Thunder's stance and that of the non inverting crowd is, as Mark Twain put it, "the difference between the lightning and the lightning bug.
http://www.geocities.com/Hollywood/Hills/6396/optimist.wav
You're out of the woods,
you're out of the dark,
you're out of the night.
Step into the sun,
step into the light,
then open your eyes
Attachments
Cancelled at the output???
No. Read what I wrote.
(
Kuei, with a concept like CM/CMRR apparently not belonging to common electronics knowledge anymore (*) I smell an opportunity for a new amplifier brand and matching Marketing Campaign.
(*) I wonder when they'll start forgetting about Miller.
)
No. Read what I wrote.
(
Kuei, with a concept like CM/CMRR apparently not belonging to common electronics knowledge anymore (*) I smell an opportunity for a new amplifier brand and matching Marketing Campaign.
(*) I wonder when they'll start forgetting about Miller.
)
jh6you said:
Am I wright? Two signal voltages of the same phase, frequency and amplitude applied to two inputs.
yes.
Ideally, they are cancelled at the output, to zero.
yes you are. But none of us live in that ideal world,
take numbers for example. Suppose you have a less than ideal opamp, and its differential gain is -20x (the inverting gainclone is in the ballpark), and CMRR of 40db (at 50Khz I think). and you apply two voltages, 10v (at the inverting end) and -11v at the non-inverting end).
the common mode signal (10v) will be amplified by the model at -40db of its differential gain. that is 20x/100x (40db is 100x)=0.2x.
so the end result is 1v (the differential signal)x20x+10v (the common mode signal)x0.2x=22v, vs. 20v of an ideal opamp.
now, which one of us has built a gain clone with 10v 50khz common mode signal applied to both ends?
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