The buffer has a gain of 'about' one for anything at pin5, + some offset. Short pin 5 to gnd and you still have some offset at pin 6.
I could probably come up with half a dozen ways to null it out, depending on the app circuit, but that's circuit design 101 so I won't tire you with it 😉
BTW I do understand George's feelings. I react differently, but I understand.
BTW2 You can't null out pin 5 and pin 6 at the same time, offset wise. That's physically impossible, with or without fb. Do you understand that?
Jan
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You do indeed. Null Pin 5 and I as indicated and you will get an offset on Pin 6, so it must be the buffer.
Already been there - even developed a servo that worked around the 844 and DC coupled both input and output, but you had to let it settle after connecting source. Tried servos that went back to Pin 3 "+" and also Pin 8 and effective made an 'automatic trimpot'. Even tried Lars Clausen RIAA on Tz and could make a simple and effective DC coupled phono. Good fun.
Two things:
1. Not sure about George's feelings and if he has any, here in Sydney he has upset a lot of people, and I mean a LOT of people.
2. If you were to know the full story, then what you 'understand' might change rather something near 180 degrees.
Should I tell the full story here? Maybe I finally should say a few words and leave it at that. We have two audio clubs here in Sydney and I am in good standing with both. George on the other hand belongs to just one. The other club does not want him. When about six months ago we were having discussions as to whether we should merge those two clubs, I made it clear I was in favour of that. I was then told in no uncertain terms that it would not happen, because the other club did not want a certain person in their club.
Jan, keep this in mind, I have just been contacted by others who are now reading this post etc, so what it happening here is is now public, and George isn't getting much support. George surely knows this and resents it. He resents me, not the other way round. I have never insulted George, I have always been cordial to him - many witnesses to that - I don't even swear or use cuss words, my tone is always moderate. People who are reading this (and they are) know me and what I say is true.
I would dearly like that merger to take place, I think it is for the better, for all concerned. It is the right thing IMO. I am a diplomat by nature (he doesn't even understand what the word means) and if that means if I take a hammering, so be it - it will be for the greater good. I am glad I don't have any huge ego and I can take a slap or two in the face, well, so be it. My friends will be behind me.
George is the one who has brought this to a head, it has been brewing for some time. He objecting to me being here is just a trigger. A few posts back he even slagged off his own (our) club's last meeting - I thought this was going too far. This exchange is certain to cause a bit of a storm here in Sydney, but maybe for the better and it was due to happen. And maybe George will learn to 'curb his enthusiasm'. His problems are not mine.
I will now promote the merger of the clubs more forcefully.
Cheers, Joe
PS: I actually feel somewhat relieved - figure that one out? 😀
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An externally hosted image should be here but it was not working when we last tested it.
I have now received several small batches of AD844 from a Chinese source on eBay and they are just fine.
eBay item number:271519352041
Cheers, Joe
Example:
The output amplifier's impedance is in series with the speaker's Z.
Represent that as an internal resistor/resistance (which we do when modeling speakers).
They are in series, are they not?
But inside the amplifier, that output impedance is driven by a voltage source, zero Ohm.
The speaker is grounded, zero Ohm.
Are they in series, are they in parallel, or are they both?
You surely know the answer, so I won't even tell you which one.
Nothing daft at all - why be so aggro then?
I don't understand the need for it.
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Joe. The fact that others are having difficulty with your unconventional arguments here, is not not unreasonable. Looking back over this thread, it does look like the last few days of discussion have revolved around your arguments.
George. You sound like a toddler who has had his rattle taken away from him. Get over it. It is the nature of open discussion, that the direction of the discourse will change over time.
George you started the slagging. Joe you didn't help. Both of you sound more like children than adults. Try reading your post as if you were the recipient before you hit the POST button.
Cheers
Warren
(with no ax to grind)
George. You sound like a toddler who has had his rattle taken away from him. Get over it. It is the nature of open discussion, that the direction of the discourse will change over time.
George you started the slagging. Joe you didn't help. Both of you sound more like children than adults. Try reading your post as if you were the recipient before you hit the POST button.
Cheers
Warren
(with no ax to grind)
You are right. Sad, but true. But you may not be interested, but then you are not in Sydney.
PS: Love your wines though. 🙂
Hi Jan
Take a pot, drive it from a voltage source, then set the wiper to the middle. That is effectively two resistors. Are they in series or are they in parallel? The total Z at the wiper will be seen as half the value of the pot. Yet inside that pot we know they are in series.
So, all depends on how you look at it. Nothing earth shattering about it. Just Thevenin.
If the load on the wiper is very high and it becomes a current source going into the wiper, then analyse what it does - and then everything I have said falls into place. It is not so much what we see, but how we see.
Maybe because I come from a different discipline than others, that I see it from a different viewpoint? Then my language becomes less formal and less approved? I am open to Gotcha moments? Oh well, so be it. Don't have the ego to be bruised that much.
My background is loudspeaker design first and decided I need to know more about amplifiers. The interface, between speakers and amplifiers, is less well understood. I have a fascination with driving speakers from current sources and getting pseudo-current drive from voltage sources. This has opened up a lot of new things, new and less formal way of looking at things.
-----
George knows I have several collaborators on this. One is Morris Swift.
I mention Morris' name because of what I am about to type: if what I said early seemed crazy, then how about this example (several loudspeaker designers can verify the truthfulness):
The example, calculate a single driver and the required volume to achieve Q=0.707 (Butterworth). Now imagine being able to drive that box alignment from any source impedance and still have a 2nd order Butterworth alignment locked in. Impossible? Seemingly impossible, after all, that alignment needs to see a voltage source at all times - or 'Re' erodes and the rest falls apart (becomes Chebyshev is the term we use).
But I can assure you that it could be done - and has been done.
Daft? Seems daft - until it is shown how it is done. And then you say "Of course, I just didn't see it."
C'est la vie.
Yep, a 2nd order Butterworth alignment that does not see a voltage source and yet tracks as a 2nd order mechanical filter slope.
If that is amazing, there more. Since Neville Thiele realised that electrical filter theory has an mechanical equivalence, then we reversed thought it again, the other way - and we were able to come up with crossovers that can also be driven independently of a voltage source. The filters track properly and can be driven from any source impedance, even infinity. So one understanding led to another. I predict this will have a large influence on the future of loudspeaker design.
So when I made that Tz comment - it was an observation I made and I believe a correct one; then it is because of being guided by that principle: That one understanding can lead to another understanding - and a surprising one at that.
Cheers, Joe
.
Take a pot, drive it from a voltage source, then set the wiper to the middle. That is effectively two resistors. Are they in series or are they in parallel? The total Z at the wiper will be seen as half the value of the pot. Yet inside that pot we know they are in series.
So, all depends on how you look at it. Nothing earth shattering about it. Just Thevenin.
If the load on the wiper is very high and it becomes a current source going into the wiper, then analyse what it does - and then everything I have said falls into place. It is not so much what we see, but how we see.
Maybe because I come from a different discipline than others, that I see it from a different viewpoint? Then my language becomes less formal and less approved? I am open to Gotcha moments? Oh well, so be it. Don't have the ego to be bruised that much.
My background is loudspeaker design first and decided I need to know more about amplifiers. The interface, between speakers and amplifiers, is less well understood. I have a fascination with driving speakers from current sources and getting pseudo-current drive from voltage sources. This has opened up a lot of new things, new and less formal way of looking at things.
-----
George knows I have several collaborators on this. One is Morris Swift.
I mention Morris' name because of what I am about to type: if what I said early seemed crazy, then how about this example (several loudspeaker designers can verify the truthfulness):
The example, calculate a single driver and the required volume to achieve Q=0.707 (Butterworth). Now imagine being able to drive that box alignment from any source impedance and still have a 2nd order Butterworth alignment locked in. Impossible? Seemingly impossible, after all, that alignment needs to see a voltage source at all times - or 'Re' erodes and the rest falls apart (becomes Chebyshev is the term we use).
But I can assure you that it could be done - and has been done.
Daft? Seems daft - until it is shown how it is done. And then you say "Of course, I just didn't see it."
C'est la vie.
Yep, a 2nd order Butterworth alignment that does not see a voltage source and yet tracks as a 2nd order mechanical filter slope.
If that is amazing, there more. Since Neville Thiele realised that electrical filter theory has an mechanical equivalence, then we reversed thought it again, the other way - and we were able to come up with crossovers that can also be driven independently of a voltage source. The filters track properly and can be driven from any source impedance, even infinity. So one understanding led to another. I predict this will have a large influence on the future of loudspeaker design.
So when I made that Tz comment - it was an observation I made and I believe a correct one; then it is because of being guided by that principle: That one understanding can lead to another understanding - and a surprising one at that.
Cheers, Joe
.
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Warren seeing you've now chimed in! I didn't start slagging him, no rattle taken away. He misquoted me at first and would not acknowledge it after I corrected him. http://www.diyaudio.com/forums/digital-source/227677-using-ad844-i-v-55.html#post4412172 instead quoting me again saying "Guys, it is NOT !!!"
Your posting history may explain things a bit more clearly to others that are interested, I can't see why.
http://www.diyaudio.com/forums/search.php?searchid=10398773
Strange that your only other three posts on diyAudio since 2011 are all gee ups on Joe's Elsinore speakers and JLTI amplifier.
Maybe no axe to grind, but definitely something else being sharpened.
Now can we please get back on topic "Using the AD844 as a zero feedback I/V" I'm sure members are sick of this s**t
Cheers George
Fair enough synopsis. Nobody is entirely innocent.
George, I disagree, it is very much about the nature Tz.
Can we have a bit less aggro here, a little bit less ego? It's not too much to ask for.
Cheers, Joe
PS: I don't mind being described as unconventional, but I deny being a heretic.
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Joe are you so dense? You draw two resistors in //, both end connected together and you go off about 'series'? If you think they are in series, draw them in series, NOT //! Get a grip man!
About those group and who wants who: there are lots of forums that do NOT accept anyone who likes facts and figures. So I am not at all impressed to know who does and who doesn't want George as a member and who does or does not want you as a member.
Finally, I support that post saying keep your dirty laundry to yourself.
Jan
Hi,
feeding a dynamic speaker (CB, hence 2nd order) from a current source instead of a voltage source doesn't change the order of that 'mechanical filter'.
What changes is the damping, expressed by the Q-factor and in the following the whole transfer function H changes.
The damping is lost with current drive.
As such any alignment -Buterworth of course included- must change towards a higher Q alignment of still second order.
The pot example is off imho.
As I already remarked in reply to the bepictured post You can't simply change the position and the kind of source and tell us it were all the same.
What You call series apperas in fact as pure, clean, doubtless parallel connection.
jauu
Calvin
ps. if Anybody in Sydney is interested in Your dirty laundry, please molest the readers of the Sidney Tribune or any other local cheesy print media.
Congrats btw, for sinking the niveau 'down under'
feeding a dynamic speaker (CB, hence 2nd order) from a current source instead of a voltage source doesn't change the order of that 'mechanical filter'.
What changes is the damping, expressed by the Q-factor and in the following the whole transfer function H changes.
The damping is lost with current drive.
As such any alignment -Buterworth of course included- must change towards a higher Q alignment of still second order.
The pot example is off imho.
As I already remarked in reply to the bepictured post You can't simply change the position and the kind of source and tell us it were all the same.
What You call series apperas in fact as pure, clean, doubtless parallel connection.
jauu
Calvin
ps. if Anybody in Sydney is interested in Your dirty laundry, please molest the readers of the Sidney Tribune or any other local cheesy print media.
Congrats btw, for sinking the niveau 'down under'
Jan, smile - you don't sound too happy. Who is carrying on now?
It's a free world - at least it was last time I looked. I never demanded that everybody agree 100% with me, only to afford other's respect, even if they don't agree - and sometimes instead of mental laziness, make an effort to try see the other person's view rather than find an opportunity for shirt fronting. A bit more open-mindedness wouldn't go astray either.
Sometimes a bit of humour wouldn't go amiss. Covers a lot of sins.
Cheers, Joe
PS: To Aussie guys here, betcha Jan has never heard of shirt fronting. 😀
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I am not John Howard and I have a policy that maybe you might adopt as well. I always apologise.
If I offended you, you have my apologies and all I can assure you is that I had no intention of misquoting you - no reason at all.
Now since you have seemed to go out of your way to shirt front me so many times, may I ask for a similar concession from you?
Cheers, Joe
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Hi,
I´d like to be more precise on the damping issue:
The simplified electrical model after Thiele and Small lists four components:
- the resistance of the electromagnetical damping
- the resistance of the mechanical damping
- the dynamic mass
- the mechnaical compliance
All four appear in series connection, fed by voltage source with a generator impedance of Rg.
The electromagnetical damping formula reads: (BL)²/[(Rg+Re)xSd²]
If Rg now becomes very high, as its a mark of current sources, the complete term decreases, eventually becoming 0 for RG-->oo
With current steering, the driver looses the electromagnetical component of the damping.
The mechanical damping still applies.
The combined damping is lower and the Q t of the driver rises.
jauu
Calvin
I´d like to be more precise on the damping issue:
The simplified electrical model after Thiele and Small lists four components:
- the resistance of the electromagnetical damping
- the resistance of the mechanical damping
- the dynamic mass
- the mechnaical compliance
All four appear in series connection, fed by voltage source with a generator impedance of Rg.
The electromagnetical damping formula reads: (BL)²/[(Rg+Re)xSd²]
If Rg now becomes very high, as its a mark of current sources, the complete term decreases, eventually becoming 0 for RG-->oo
With current steering, the driver looses the electromagnetical component of the damping.
The mechanical damping still applies.
The combined damping is lower and the Q t of the driver rises.
jauu
Calvin
Indeed, all this is well established, right down here in Sydney.
Ahhh...
If you are happy with that and do nothing, then it certainly will. But if you understand current driving (steering), then there is something you can do. Look at the impedance that defines Qts of the driver, what causes it? It is something called 'motional EMF' - know how to deal with that while driving it with current and a technique can be developed that counters it. Not just counters it, but neutralises it.
BTW, this is Sydney, Australia and this is our city that originated Thiele-Small Parameters at The Sydney University and I used to live next to it.
But I only used this as example and really have to be careful to relate this to Tz and not be off topic.
Not many amplifier designers look at 'current steering' loudspeakers - yet there really is something beneficial in doing so. It opens your eyes.
Even distortion profiles change. Both for the amplifier and also for the speaker. Speakers are 'quieter' when in current drive (yes, that is not a conventional expression I know). Now I may get another Gotcha! moment out of that. But it is still a statement of fact. Instead they could ask what I mean.
Cheers, Joe
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Hi,
I just noted, that You can´t simply replace voltage drive of a speaker by current drive, without taking additional measurements, like filtering (NIC-Filters e.g).
It´d result amongst others in a different amplitude response.
No more, no less.
What results are possible with current steering of dynamic drivers, implemented under due consideration of the specialties of that technique, may well be debated in another thread.
jauu
Calvin
ps: Your local pride on a city(!) and Your nitpicking on an obvious typo can only be regarded ridicolous at best.
I just noted, that You can´t simply replace voltage drive of a speaker by current drive, without taking additional measurements, like filtering (NIC-Filters e.g).
It´d result amongst others in a different amplitude response.
No more, no less.
What results are possible with current steering of dynamic drivers, implemented under due consideration of the specialties of that technique, may well be debated in another thread.
jauu
Calvin
ps: Your local pride on a city(!) and Your nitpicking on an obvious typo can only be regarded ridicolous at best.
I agree about topic.
What typo? I wasn't aware I was nitpicking a typo???
Ridicolous? Is that a new word? You don't know about Sydney? Are you always so condescending about other people and where they come from? That's an odd attitude. Please can we stop this.... sigh.
FYI, Sydney is where Neville Thiele and Richard Small devised the Thiele-Small Parameters - that's a big deal to a lot of us.
BTW, I was born in Copenhagen, Denmark. So there !!!
Cheers, Joe
What typo? I wasn't aware I was nitpicking a typo???
Ridicolous? Is that a new word? You don't know about Sydney? Are you always so condescending about other people and where they come from? That's an odd attitude. Please can we stop this.... sigh.
FYI, Sydney is where Neville Thiele and Richard Small devised the Thiele-Small Parameters - that's a big deal to a lot of us.
BTW, I was born in Copenhagen, Denmark. So there !!!
Cheers, Joe