It might help to consult someone with the appropriate expertise. The problem isn't a statistical one.
You can use a higher absolute value of output negative resistance than that to improve the electrical damping of the loudspeaker. However the problem which arises is that voice coil inductance Le is going to have a peaky resonance with capacitor Ces of the motional impedance. Le can be compensated but only partly due to its non constant value with frequency and inside the gap. This is the main problem in servo drivers based on a bridge to sense the velocity of the cone.
Petr1951 said:
The aim of global negative feedback of an amplifier is to maintain its output voltage independent of its load even if this load acts as an Electromotive Force generator. Remember that in a loudspeaker, the (Back-)EMF always in series with voice coil resistance Re.
Back-EMF is not a problem for a GNFB amplifier.
Do I need to ask for evidence/data first? Or can I conclude, right away, this is subjective crapola.
company performance can be objectively tracked - sales numbers, revenue, margins
relation to technical performance in high end audio may be weak...
...Halcro has closed - so the combo of tech specs And visual impact/"story" didn't seem to survive the currents of Fashion - are we supposed to take a lesson on the audible character of error correction amps from this?
relation to technical performance in high end audio may be weak...
...Halcro has closed - so the combo of tech specs And visual impact/"story" didn't seem to survive the currents of Fashion - are we supposed to take a lesson on the audible character of error correction amps from this?
Last edited:
yes one of the condtions for "all amplifiers sound alike" is linear operation - within respective design limits, approrate signal and load combos
and yes there are unreasonable signals and loads - and they can be designed for if you want to spend the money
you could make a case for "audio taste" in clipping, rail collapse, output protection...
but so far those arguments haven't been put to the front in this thread - the main claim seems be CFA is distiguishible from VFA in linear operation, both designed to work with below -80 dB distortion
and yes there are unreasonable signals and loads - and they can be designed for if you want to spend the money
you could make a case for "audio taste" in clipping, rail collapse, output protection...
but so far those arguments haven't been put to the front in this thread - the main claim seems be CFA is distiguishible from VFA in linear operation, both designed to work with below -80 dB distortion
Last edited:
Waly (4323)
Do I need to ask for evidence/data first? Or can I conclude, right away, this is subjective crapola.
Dear Waly! I in no way not going to dispute your personal opinion of your book about the harm of negative impedance for audio amplifiers.
Number of people make my amplifier is growing every day. And growing number of enthusiastic reviews. And your opinion will remain your personal opinion.
Speaker impedance conductors allowing the skin effect and proximity effect conductors is about 0.2 ohms. Throw resistance inductance crossover. This is roughly the same 0.2 ohms. Here you are almost 0.4 Ohm which additionally between the amplifier and speaker system.
Negative output impedance compensates the distortion caused by the response (back EMF) due to the voltage drop across the speaker wires and crossover elements
Best regards
Petr
Do I need to ask for evidence/data first? Or can I conclude, right away, this is subjective crapola.
Dear Waly! I in no way not going to dispute your personal opinion of your book about the harm of negative impedance for audio amplifiers.
Number of people make my amplifier is growing every day. And growing number of enthusiastic reviews. And your opinion will remain your personal opinion.
Speaker impedance conductors allowing the skin effect and proximity effect conductors is about 0.2 ohms. Throw resistance inductance crossover. This is roughly the same 0.2 ohms. Here you are almost 0.4 Ohm which additionally between the amplifier and speaker system.
Negative output impedance compensates the distortion caused by the response (back EMF) due to the voltage drop across the speaker wires and crossover elements
Best regards
Petr
jcx (4325)
but so far those arguments haven't been put to the front in this thread - the main claim seems be CFA is distiguishible from VFA in linear operation, both designed to work with below -80 dB distortion
VAS distortion without NFB can be reduced to 0.00003% (-130dB)!!! using VAS-clone (backup)
For this it is necessary to bring the output voltage VAS-clone of the input voltage and to subtract it from the input voltage. The error signal is used as the predistortion signal in the main channel VAS and thus minimizes the distortion. This mechanism acts much more efficient than traditional NFB.
http://s020.radikal.ru/i715/1401/6d/f52c6e5786c1.png
best regards
Petr
but so far those arguments haven't been put to the front in this thread - the main claim seems be CFA is distiguishible from VFA in linear operation, both designed to work with below -80 dB distortion
VAS distortion without NFB can be reduced to 0.00003% (-130dB)!!! using VAS-clone (backup)
For this it is necessary to bring the output voltage VAS-clone of the input voltage and to subtract it from the input voltage. The error signal is used as the predistortion signal in the main channel VAS and thus minimizes the distortion. This mechanism acts much more efficient than traditional NFB.
http://s020.radikal.ru/i715/1401/6d/f52c6e5786c1.png
best regards
Petr
All who are interested in the problem I described with THD at amp vs at speaker end of 20 feet of zip cord......combined with motional feedback and the like -- Buy the book by Esa Merilainen. Current-Driving of Loudspeakers. Eliminating Major Distortion and interference Effects by the Physically Correct Operation method. 340 pages. Yr 2010.
Thx-RNMarsh
Thx-RNMarsh
RNMarsh (4328)
Current-Driving of Loudspeakers. Eliminating Major Distortion and interference Effects by the Physically Correct Operation method. 340 pages. Yr 2010.
it all started here with this publication:
Distortion Reduction in Moving-CoilLoudspeaker Systems Using Current-Drive Technology*
P. G. L. MILLS** AND M. O. J. HAWKSFORD
University of Essex, Wivenhoe Park, Colchester, Essex, C04 3SQ, UK
J.AudioEng.Soc.,Vol_.37,No.3,1989 March
This has been a long way, and many have realized that it is a dead-end destination
best regards
Petr
Current-Driving of Loudspeakers. Eliminating Major Distortion and interference Effects by the Physically Correct Operation method. 340 pages. Yr 2010.
it all started here with this publication:
Distortion Reduction in Moving-CoilLoudspeaker Systems Using Current-Drive Technology*
P. G. L. MILLS** AND M. O. J. HAWKSFORD
University of Essex, Wivenhoe Park, Colchester, Essex, C04 3SQ, UK
J.AudioEng.Soc.,Vol_.37,No.3,1989 March
This has been a long way, and many have realized that it is a dead-end destination
best regards
Petr
RNMarsh,
Following your post in the Blowtorch thread I found this note by the author you mentioned for current drive for loudspeakers. Perhaps this is one of the things that answers some of the question about why some prefer the cfa over the vfa topology? I got this from EDN Network. This was a comment to another person following an article about the current driven loudspeaker.
Loudspeaker operation: The superiority of current drive over voltage drive | EDN
Esa Merilainen
In current-output (transconductance) amplifiers, the feedback represents the current flowing through the load and thus increases the output impedance while reducing distortion similarly as with voltage feedback. The two forms of feedback can also be mixed to adjust the output impedance.
Yes, for a given load impedance and signal level, current-drive needs some extra voltage margin especially with highly complex loads; but on the other hand, the peak current demand is correspondingly lower and precisely known.
Applying pure current-drive for existing voltage speakers is not so advisable due to frequency response alteration. Speakers naturally have to be designed for the concept, preferably beginning from the drivers.
Following your post in the Blowtorch thread I found this note by the author you mentioned for current drive for loudspeakers. Perhaps this is one of the things that answers some of the question about why some prefer the cfa over the vfa topology? I got this from EDN Network. This was a comment to another person following an article about the current driven loudspeaker.
Loudspeaker operation: The superiority of current drive over voltage drive | EDN
Esa Merilainen
In current-output (transconductance) amplifiers, the feedback represents the current flowing through the load and thus increases the output impedance while reducing distortion similarly as with voltage feedback. The two forms of feedback can also be mixed to adjust the output impedance.
Yes, for a given load impedance and signal level, current-drive needs some extra voltage margin especially with highly complex loads; but on the other hand, the peak current demand is correspondingly lower and precisely known.
Applying pure current-drive for existing voltage speakers is not so advisable due to frequency response alteration. Speakers naturally have to be designed for the concept, preferably beginning from the drivers.
The problem is as kindhornman says is no modern speakers are designed for current drive. Most will give really wonky results if current driven.
That's not to say, there are no advantages though they are only available if speaker & amp are designed as a whole. And pure current drive is actually quite a poor way to get these advantages.
I posted this in another forum.
>For what it is worth, I think this is impossible. It seems to violate the cause and effect principle. How could the amplifier "know" what the speaker is up to ? Short of sensing the actual motion of the drivers or the actual sound... this has to be sort of by guess and by golly, it seems to me.
It is entirely possible for an "amplifier" to know what the speaker is doing.
It needs to sense the speaker current. An amp which twiddled its Output Z using both current & voltage feedback does this. Speakers act as accurate microphones (sense the actual sound) if operated into Low Z.
See "Loudspeakers as Microphones" - Peter Baxandall special lecture London AES (early 80s, late 70s?)
If operated into High Z, then the voltage at the terminals is a measure of cone velocity.
Both these mechanisms obey superposition & Thevenin so if you're clever, you can look at this while the amp is giving zillion volts and amps to the speaker. But non est tantum facile.
There are several tried & tested methods of using this "controlled output Z" or "current + voltage feedback" or "actual sound & motion feedback" (different descriptions of the same thing) if you incorporate the amplifier design in the speaker. Some of these are in the zanier incarnations of my Powered Integrated Super Sub technology.
The simplest is the negative output R that Fons mentions.
More sophisticated but similar (??!) is ACE technology by Erik Stahl which was used by Audio Pro, Sweden for subs. Unfortunately, since he left, there isn't anyone there who understands it. Anyone have a contact for Erik? Or a clean copy of his original AES preprint?
These methods have the distortion reduction and dynamic overload protection features discussed in Mills & Hawksford. However, they are badly affected by heating of the voice coil.
David Birt (?) did an excellent IoA paper at Windermere where he arranged speaker and amp in a bridge so he could measure and compensate for heating on the fly. Anyone have an email for him?
These are the most elegant methods and they can be analysed from many viewpoints. Some of these viewpoints don't show up the distortion reduction advantages clearly.
I'm contemptous of methods which rely on extra transducers or extra windings (like Mills) or zillion point DSP EQ especially if they don't give ALL the advantages of the elegant methods.
A brute force zillion point approach possible today is measure accurately speaker Z (not that easy) and tailor the output of a High Z amp to suit. This would give some but not all the advantages of the above systems cos it wouldn't "know" what the speaker is up to.
It is entirely possible for an "amplifier" to know what the speaker is doing.
It needs to sense the speaker current. An amp which twiddled its Output Z using both current & voltage feedback does this. Speakers act as accurate microphones (sense the actual sound) if operated into Low Z.
See "Loudspeakers as Microphones" - Peter Baxandall special lecture London AES (early 80s, late 70s?)
If operated into High Z, then the voltage at the terminals is a measure of cone velocity.
Both these mechanisms obey superposition & Thevenin so if you're clever, you can look at this while the amp is giving zillion volts and amps to the speaker. But non est tantum facile.
There are several tried & tested methods of using this "controlled output Z" or "current + voltage feedback" or "actual sound & motion feedback" (different descriptions of the same thing) if you incorporate the amplifier design in the speaker. Some of these are in the zanier incarnations of my Powered Integrated Super Sub technology.
The simplest is the negative output R that Fons mentions.
More sophisticated but similar (??!) is ACE technology by Erik Stahl which was used by Audio Pro, Sweden for subs. Unfortunately, since he left, there isn't anyone there who understands it. Anyone have a contact for Erik? Or a clean copy of his original AES preprint?
These methods have the distortion reduction and dynamic overload protection features discussed in Mills & Hawksford. However, they are badly affected by heating of the voice coil.
David Birt (?) did an excellent IoA paper at Windermere where he arranged speaker and amp in a bridge so he could measure and compensate for heating on the fly. Anyone have an email for him?
These are the most elegant methods and they can be analysed from many viewpoints. Some of these viewpoints don't show up the distortion reduction advantages clearly.
I'm contemptous of methods which rely on extra transducers or extra windings (like Mills) or zillion point DSP EQ especially if they don't give ALL the advantages of the elegant methods.
A brute force zillion point approach possible today is measure accurately speaker Z (not that easy) and tailor the output of a High Z amp to suit. This would give some but not all the advantages of the above systems cos it wouldn't "know" what the speaker is up to.
In fact, I (or anyone else) dunno know how to design dynamic speakers for good performance with current drive. Rice & Kellog, who invented the speaker as we know it, had much more insight than the Thiele-Small pseudo gurus today.
But it is theoretically possible to design an electrostatic speaker for good performance with current drive.
___________________________
As a speaker designer, I expect my speakers to be used with high quality cables and flat response 0R impedance amps. I hate it when unwashed amp designers try to 'improve' on my designs. Petri's negative 0R2 is probably innocuous. The 1R presented by many tube amps is starting to get dodgy.
BTW, Carver's successful Stereophile Challenge proved 2 things .. not one.
- it is possible to hear differences between amps that might lead to a preference.
- it is possible for one versed in the art to replicate these preferred differences with entirely different technology & topology. With respect to Mr. Cordell, I don't think anyone on this forum is sufficiently versed 😱
ALL. Please don't indulge in more "Yus guys are all idiots & deaf" exchanges with those who persist. Just report them to the moderators. 🙂
Last edited:
Let's stick with the CFA stuff guys.
Should I open up a current drive loudspeaker thread? ( remember,that's how this one started as well! )
🙂
Should I open up a current drive loudspeaker thread? ( remember,that's how this one started as well! )
🙂
I fear you should, there seems to be far too many people here who don't understand the difference between CFA amps and amps with a high output impedance (current drive).
I was foolish enough to buy the Finn's book on current driving of speakers. 10% sense culled from Malcolm Hawksford's work, + 90% nonsense, comprising pseudo-science, poor-quality amplifier designs, and ranting!
(I donated the useless book to the local Oxfam charity shop)
Because, formely, the amps called CFAs were those where it was the output current which was the value controlled by the feedback.
As CFA now means an amp with a low impedance inverting input, how do you call the concept underlying in the initial term ?
It would be interesting to see you detailing your arguments against Merilainen's book in the new thread opened by Bonsai :
http://www.diyaudio.com/forums/solid-state/250272-current-drive-loudspeakers.html#post3798772
Yes, lot of confusion here about CFA = current drive output or CFA must be a VFA (mixing internal amplifier topology up with canonical feedback topology)
But, let's leave it at that least we sink once again into a long worthless exchange.
😉
But, let's leave it at that least we sink once again into a long worthless exchange.
😉
First rule of statistics is to ask the statistician first.😉 Then you know what data you need.
Waste of your time to collect lots of worthless data and then a waste of the statistician's time to try to extract information that isn't in the data.
A pattern is already obvious. xFA believers report that xFAs sound better, when they know what "should" sound better. That is almost certainly a real pattern.
What would be useful is the answer to a different question.
If your statistician can see the true answer to that then please post his analysis, I'd love to learn his methods.
I don't know where you will obtain your "thousands" from.
Meta-analysis is essentially confined to data, usually peer reviewed, that is not "stacked".
I have not yet seen even one audibility test here that meets the basic minimum to qualify for a competent journal, but I live in hope.
Best wishes
David
I agree. Many times people take things and go off on a tangent with it. I thought it would be obvious that as we are designing amps here and CFA in particualr, that the amp must interface with the load in the best way - which means lowest distortion. Is this the best way to get lowest distortion thru the System?
Might make a good new thread to develop amps which interface better for best over-all results. Rather than amps which just measure well in isolation without real world I/O conditions.
So back to CFA --- lets try various simi-real speaker loads also with the SIM's and see what develops. Several models of speakers exist which can be used and whole XO/Spkr circuits can be used. I have a pair of new Quads .. how does the OPS we have developed so far with CFA handle that load? Others? Is there a universal OPS that keeps distortion at its lowest with any and all speaker and XO types? Or are there two... one for electrostatics and one for dynamic loads? And, are the SOA protection different?
Thx-RNMarsh
Last edited: