how does a LEF (load effect free) amplifier work?

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[IDC]Dragon

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Joined 2008
#1
I found some interesting whitepapers from Carlos Cadeias:

Candeias Engineering
http://www.aqvox.de/LEF_Amp_en.pdf

It claims that this "LEF" removes all present day amp disadvantages, wonderful, isn't it? It is probably in the nature of whitepapers to stay vague.

My question is: what is behind that claim? How does it really work, has anybody seen such a design or a schematic of it? Did the concept perhaps exist before, under a different name?
I'd be interested in building such a thing!

He goes one step further, joining a DAC into the circuit, which he then calls a DAPC:
Candeias Engineering
(That'll be my holy grail. I'm phantasizing about active speakers, each chassis driven by such, and a DSP unit for crossover and time correction.)

Jörg
 
#2
What is behind that claim is likely marketing and mis-iformation.

Claims and design approaches like this are often ituitively appealing, but usually don't work as advertized because the real world is cruel.

His starting generalizations about TIM and NFB demonstrate that he is probably not a sophisticated designer.

I would wager that if someone wants an amplifier without NFB, then the Ayre MXR probably blows away anything this guy has. The MXR does not have LEF, but it does have very good engineering and attention to detail.

Although the correlation between conventional bench tests and sound quality is sometimes disappointing, that is no reason to throw out any expectation of good objective performance from a design with such lofty quasi-technical claims (my gosh, he uses the term floating cascode). What I'm saying here is that if his techniques work as claimed, he should be able to show very good measured performance even if he does not believe there is strong correlation with sound quality.

He is certainly entitled to protect his potentially innovative ideas by being a bit vague in his description, but there is no reason why he cannot quote some performance to demonstrate that his claims of extraordinary linearity and load invariance are valid.

Cheers,
Bob
 
#4
Their CC80 module report makes me think that they have encapsulated an op-amp for gain, another for a servo, a discrete output stage, and a couple of three terminal regulators !!!

(Oh cynical me)
 
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#5
Bob Cordell said:
What is behind that claim is likely marketing and mis-iformation.

Claims and design approaches like this are often ituitively appealing, but usually don't work as advertized because the real world is cruel.
Click to expand...

I agree, I remember few years ago when still in college as student, I try to make this "DIGITAL TO ANALOG POWER CONVERTER". Inspired by LEF that time, but after studying more about loudspeaker, I think that if LEF is realized, it is not the best way in driving loudspeakers. It is good in driving motors and others that has dynamic impedance but not loudspeakers. I am now using my digital to power converter to drive my PCB drilling motor. Speaker need load effect management, not free.
Just like when we using output transformer, it help to dissipate any low freq speaker displacement to keep it in better linearity, or when we using positive feedback for better bass response, and more.
 
#7
cloning of this LEF topology is not really difficult for the right engineers after read this:
http://www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
LEF means "Load Effect Free" that means, instead the "signal transistor" a second power transistor fed the load. The current comes from the collector (instead from the emitter) from the power transistor. For me this is basicly a Sziklai-Darlington instead a normal darlington (either single ended or push pull, both appropriate to design preamp line stages and power amp stages) e. g. like this one
Sziklai - Complementary Feedback Power Amp Output
check out this terms by google to get more informations:
"complementary Sziklai output" (Sziklai, Sziklai-darlington, CFP, current feedback pair or compound darlington)

here on diyaudio are also this threads to Candeias LEF topology:
1) http://www.diyaudio.com/forums/pass-labs/5808-cec-amp71.html
2) http://www.diyaudio.com/forums/solid-state/127182-lef-load-effect-free-amplifier-technology.html

In case of power amps a similar topology was released from Abacus Rieder (Germany) and Nelson Pass (Stasis series have a look to above link number 1). About circuit topology from Abacus Rieder I find only papers in German, not in english - sorry
Abacus Rieder 60-120 Service

If you read the last section of the german pdf file about
http://www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
"Leonardo Da Vinci und die LEF Schaltung"
(Leonardo Da Vinci and the LEF circuit topology) you can easy create your LEF circuit (for english version read patent's pending paper
"Avoiding a Mistake instead of correcting a Mistake"
about the URL at bottom.

Nevertheless I need a circuit from CEC's LEF integrated amp 3300 (AMP3300R) to create interfaces for connect of an external (outdoor) power supply
http://www.diyaudio.com/forums/soli...3300-amp5300r-lef-class-schematic-wanted.html
 
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#10
Is it possible this a current-dumping type amplifier?

Maybe two output stages, one class A for HF and details and the other a power AB stage for bass?

After hearing "load-effect free" I thought of an amplifier with negative output impedance.

- keantoken
 
#12
#15
Bob Cordell said:
What is behind that claim is likely marketing and mis-iformation.

Claims and design approaches like this are often ituitively appealing, but usually don't work as advertized because the real world is cruel.

His starting generalizations about TIM and NFB demonstrate that he is probably not a sophisticated designer.

I would wager that if someone wants an amplifier without NFB, then the Ayre MXR probably blows away anything this guy has. The MXR does not have LEF, but it does have very good engineering and attention to detail.

Although the correlation between conventional bench tests and sound quality is sometimes disappointing, that is no reason to throw out any expectation of good objective performance from a design with such lofty quasi-technical claims (my gosh, he uses the term floating cascode). What I'm saying here is that if his techniques work as claimed, he should be able to show very good measured performance even if he does not believe there is strong correlation with sound quality.

He is certainly entitled to protect his potentially innovative ideas by being a bit vague in his description, but there is no reason why he cannot quote some performance to demonstrate that his claims of extraordinary linearity and load invariance are valid.

Cheers,
Bob
Click to expand...
check out the URL's by post #12 under
http://www.diyaudio.com/forums/pass-labs/5808-cec-amp71-2.html
 
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