CFA Topology Audio Amplifiers

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#4,601
Might also be device dependent. 😕

90's Sanken - HK used 4.7R
21'st century 990 integrated amp with MJLxxxx/5-pair , same EF3 design ....
they used 2.2R//bead instead .

Edit - Sankens are higher Ft/hfe
On's are lower Ft/Hfe

OS
 
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#4,602
Dear Bob, keantoken, Bonsai, John, mcd99uk, manso, ostripper and all others,

thank you for so much hints and sharing your experience.
Next days will try one or more combinations of


  • additional R-C decoupling between the different driver stages.
  • shunt resistor VAS/GND
  • Cbc for drivers
It would be great, if this helps to improve the design.

BR, Toni
 
#4,605
mcd99uk said:
Toni,

Good luck. The more effort it takes to achieve the goal, the more satisfying it is.

I feel your pain. It has taken me literally months to get my latest creation stable and operating correctly.

Paul
Click to expand...

Yes .... I was "poopin' bricks" as NAF/Bimo prototyped my designs.
Add to this , NAF prototyped the "alien CFA" w/servo on top of this.

I thought my "goose was cooked" 😱😱 with so many "guesses" ... but things
actually worked better than the thermal/operating points simulated..
Thanks to this thread/DIYA in general , conception --> real world goes
smoothly.
Many thanks to the great minds/designs in this forum. 🙂

OS
 
#4,606
jcx said:
so LCR Capacitors - Capacitors and EMC filters are has beens?
Click to expand...

Mil spec alone is Not what you want for audio. Let me give just one very obvious reason to not use MIL SPEC parts --- they will all have ferrous metal steel leads (plated). This is to meet the pull strength test requirement. There are many trade secrets involved... such as an annealing processes and what its benefits are (adds cost). etc.

TH-RNMarsh
 
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#4,607
Bob Cordell said:
Finally, it is VERY important to recognize that the addition of the shunt R-C network to the output of the VAS is NOT part of the global compensation, and does not take the place of the Miller compensation. It is NOT lag compensation of the amplifier.
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I have simulated that amplifier some time ago, and the lead-lag at the VAS output is required because the Miller loop stability margins, as designed, are rather low. In this sense, the lead-lag cell can be considered as a Miller (local feedback) loop compensation.
 
#4,608
ostripper said:
Might also be device dependent. 😕

90's Sanken - HK used 4.7R
21'st century 990 integrated amp with MJLxxxx/5-pair , same EF3 design ....
they used 2.2R//bead instead .

Edit - Sankens are higher Ft/hfe
On's are lower Ft/Hfe

OS
Click to expand...

Its quit conceivable that the higher Ft devices would need greater value of base Rs to stabilize them in this topology. But, again doing that affects the peak current driving the base and its inderect affect on the sound. And Ls doesnt limit the base drive current except at highest freqs.

This is Exactly where engineering leaves off and HighEnd designers begin... such as john Curl. You change an R somewhere and listen to the affect. Then decide why and what is the best thing to do about it.

Building, modifying and listening is a necessary next step to optimizing for 'listening' performance while keeping it optimized for stability and other technical parameters.


Thx-RNMarsh
 
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#4,609
john curl said:
I find that quibbling between 10 ohms and 5 ohms as base stopper resistors is more political than practical. Of course, less is best, but not too small or problems will happen that can be almost random in nature and hard to protect against any other way. However, I agree that 10 ohms is the 'outside' value and 5 might be better.
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John,

Its not quibbling and its not political. Its solid engineering. You need to read the chapter in my book on thermal stability where the math illustrates the problem. It's a feedback circuit - DUH.

Cheers,
Bob
 
#4,610
RNMarsh said:
Mil spec alone is Not what you want for audio. Let me give just one very obvious reason to not use MIL SPEC parts --- they will all have ferrous metal steel leads (plated). This is to meet the pull strength test requirement. There are many trade secrets involved... such as an annealing processes and what its benefits are (adds cost). etc.

TH-RNMarsh
Click to expand...

Hi Richard,

This is a good point about ferrous metal steel leads. It brings up an interesting question, at least in my mind. If steel leads are bad for the sound, then does it follow that the use of ferrite beads is bad for the sound for the same reason?

Cheers,
Bob
 
#4,611
If you use them to stablize an amp at freq well above audio, then no. They dont develop any Z (Ls) at audio freq currents if you pick them correctly. At audio they are just wire.

In a cap or resistor, the audio current passes directly thru the ferrous material at all freqs setting up a nonlinear component in the current.... not just at the HF freq needed for stabilizing.

The higher the current the greater the distortion so maybe Ok in a preamp IPS but not driver or OPS of a power amp -- for a practical sized core.

Thats the short answer. Generally, speaking.

Thx-RNMarsh
 
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#4,613
most "steel leads" are steel core with heavy Cu overplating - most of the current is flowing in Cu just due to the resistivity advantage, often greater cross section by area is Cu too
and then at AC the higher permeability of Fe wire core of the "steel lead" will give greatly enhanced skin effect - the ferromagnetic wire core will expel the AC current - pushing more into the heavy Cu over plating



there are some special nonferrous leaded parts made for MRI application where multi Tesla level fields are being generated and require ppm uniformity
 
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#4,614
jcx said:
most "steel leads" are steel core with heavy Cu overplating - most of the current is flowing in Cu just due to the resistivity advantage, often greater cross section by area is Cu too
and then at AC the higher permeability of Fe wire core of the "steel lead" will give greatly enhanced skin effect - the ferromagnetic wire core will expel the AC current - pushing more into the heavy Cu over plating



there are some special nonferrous leaded parts made for MRI application where multi Tesla level fields are being generated and require ppm uniformity
Click to expand...

This is generally, true... plated in one or two metals usually. The reason for plating over steel is solderability.

I wouldnt assume the thickness is as great as needed to be of no concern/distortion. thus it is not as ideal as it could be but rather something in between. Its just as easy to find parts without steel leads so, although plating for solderability has some small spin-off benefit for audio, it would be better without the steel.


Thx-RNMarsh
 
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#4,615
Waly said:
I would appreciate if you could substantiate "very obvious reasons". There's none that I can think of, but then I'm already ready to learn something new, if it makes any solid engineering sense.
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Distortion generated by non-linear Z of ferrous metals. measured and discussed decades ago and here/there and many times/places before. Just run a current thru a non-linear material and see what you measure. Try it. Or, even bring ferrous metals 'near' a conductor with current passing thru it and see what you measure. It was first reported by Japanese in a published tech paper decades ago.


Thx-RNMarsh
 
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#4,616
Bob Cordell said:
These are very good and interesting points. The bandwidth issue also touches on the conflict between specs and sound. For example, if we were to bandlimit to, say 20kHz, we would be down 3dB at 20k and we would have to put it on the spec sheet. Even if that sounded better, how would the reader of the spec sheet react?

There is a parallel to this. It is soft clipping. Put an adaptive soft clipper in front of the amplifier (like the Klever Kippler) and all your concerns about clipping behavior are gone. The amp never ever clips. No nasties or recovery issues. But a soft clip will necessarily introduce distortion, albeit soft (third, typically). Those low-ppm THD numbers are way gone. Now you are looking at numbers like those of tube amps, like in the 0.1 to 1% range that you must put on the spec sheet. Many cringe when they see a 0.1% number for THD at 1kHz for a solid-state amplifier.

So we have the paradox. Oh well....

BTW, if we put the soft clip in front of the amp, we should still shoot for very good distortion numbers in the amp itself, especially in regard to nasties like primary and secondary crossover distortion.
Click to expand...
It's not a paradox, Bob.

It's the triumph of Marketing over the REAL requirements.

We should be doing much more Double Blind Listening Tests to find out what is REALLY important instead of agonising over whose virgins we should use to carve our Unobtainium caps. 😱

I've also been involved with a series of DBLT on soft clipping using a MUCH cruder circuit than your Klever Klipper. It was organised by KEF at one of the London AES conventions. And yes. It was the same people who could reliably tell the difference and the soft clipper was always preferred.
_______________

But there are far fewer DBLT on soft clipping than on Bandwidth Limitation. I hope to try your Klever Klipper sometime before the end of this Millenium.

For those who have never organised such tests (MUCH more difficult than you think), the first thing you find is that ALL self declared Golden Pinnae are deaf (ie give completely random results).

After much work, you may be lucky to find true golden pinnae and they are often people who profess no interest in our toys eg your girlfriend, wife or mother. They are the ones who give consistent results and if you want to make design decisions for better sound, you listen to them. 😱

For da pseudo self declared Golden Pinnae, you just tell them VERY LOUDLY that your stuff is all hand carved from solid BS or Unobtainium by virgins. 😀

PS I would still try for 1ppm 20kHz full power but would gladly sacrifice it for greater simplicity or stability in an amp. 🙂
 
#4,618
Clipping (hard or soft) is a non issue IMO. Just dont do it. Scale and match system componenets so it doesnt happen. It should be an accident if it clips and should not blow up if it did get accidently clipped.

How good can you make an amp sound while clipping isnt a worthy subject.... worthy if it involves circuit/speaker protection etal.

THx-RNMarsh
 
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#4,619
RNMarsh said:
Distortion generated by non-linear Z of ferrous metals. measured and discussed decades ago and here/there and many times/places before.
Click to expand...

Really? Citation please? Not about the non linear magnetic properties of ferrous materials, but about the impact of ferrous materials in electronic components? Where are the large variable magnetic fields required to drive the ferrous material in the terminals into nonlinearity coming from in Audio applications?

The very large array radio telescope at Soccoro, New Mexico, arguably the most sensitive installation ever build, uses MIL parts.
 
#4,620
Waly said:
Really? Citation please? Not about the non linear magnetic properties of ferrous materials, but about the impact of ferrous materials in electronic components? Where are the large variable magnetic fields required to drive the ferrous material in the terminals into nonlinearity coming from in Audio applications?

The very large array radio telescope at Soccoro, New Mexico, arguably the most sensitive installation ever build, uses MIL parts.
Click to expand...

Sorry, no time for that... telescope at Soccoro has nothing even remotely to do with this subject. Like I said, get out your test equipment and do some measurements if you cant find the info.

hey. I just sold a painting for >$100K and that it isnt relevant either.... but I'm taking my closest friends to dinner now.

Cheers

Thx-RNMarsh
 
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