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Old 26th March 2013, 08:49 PM   #341
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Douglas,
You really would think that if an invention had a commercial application you would want the patent to be found so that it would not be infringed upon. The cost to protect or attempt to disqualify a patent is expensive and obfuscation seems silly on the face or it, unless of course you are a patent lawyer and then job security could be an end result!
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Old 26th March 2013, 09:13 PM   #342
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Originally Posted by DouglasSelf View Post
It has been pointed out several times now that so far as anyone knows, the original inventor was Kunio Seki, in 1978; see US Patent 4,145,666 assigned to Hitachi. Unlike some people, I have never at any point claimed I invented it, re-invented it, popularised it, or done anything with it except use the information passed on to me by Peter Baxandall. I may however be the only person in this discussion who has actually made money out of it.

_____

I was not quibbling about who invented that which we now know as TMC, nor was I suggesting you claimed to invent it. It is indeed a shame that the Hitachi circuit went essentially unknown for such a long time. I only learned about it from Edmond, here. I wish I had known about it decades ago. I said that you were late to the party because you apparently did not involve yourself with it until after the detailed discussions that took place here quite awhile back. Indeed, in five editions of your book you never mentioned this technique that you subsequently described as so powerful in the Linear Audio article you wrote in late 2010. I'm guessing that if Edmond had not brought it up here, to this day you would not be touting its value. Ditto for me.

___

In your 600 page book, you only referenced my work five times.

I should have mentioned you in Chapter 3, where I evolved the old simple standard-bearing amplifier circuit with obvious engineering refinements into largely that which you call Blameless. That basic amplifier and its straightforward refinements has been around pretty much since the dawn of silicon transistors, but you poineered the systematic dissection of its sources of distortion. I just described its evolution with a different style so I could help those less experienced understand the circuit design techniques and use that basic amplifier as a launching pad for more sophisticated amplifiers. I think that one of your most important contributions is in the understanding of output stage static crossover distortion, and in chapter 10 on output stages I referenced you numerous times, and those references were well deserved.

______________

(For those not in the know, this diagram shows the very large currents that can be drawn by a loudspeaker if you hit it with a carefully designed set of pulses)
I gather that you published your version in 1983. I am not aware of this publication; perhaps you could enlighten us.

My diagram was directly inspired by the well-known but fallacious paper by Otala et al: "Peak Current Requirement of Commercial Loudspeaker Systems" JAES Volume 35 Issue 6 pp455-462; June 1987. It is of course of little more than curiosity value as the irregular square waves that are required to show the effect do not exist in music.

My diagram first appeared in the very collectable Second edition of Audio Power Amplifier Design, in 2000. That is a long time to harbouri a grievance.

______

I don't understand how you could be unaware of that diagram or my paper in which it was published. You reference that very same paper in that same chapter at a later point (my paper on Interface Intermodulation Distortion). I own fully 3 editions of your excellent book, but not editions 2 and 3. I hope you will reference it properly in your sixth edition.

Cheers,
Bob
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Old 26th March 2013, 10:08 PM   #343
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Originally Posted by DouglasSelf View Post
The shunt capacitors have been found to be effective with both an EF-VAS (with added emitter-follower) and a bootstrapped cascode VAS, in large quantity production over many years.
Doug, may I ask if these cb capacitors on the drivers were on an amp where the output devices were connected via twisted leads rather than soldered directly to the PCB?

My contention is that if the layout is rigorously controlled, including the connections to the outputs, (no long evil twisted leads) it is possible to do without them.
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Old 26th March 2013, 10:12 PM   #344
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Originally Posted by Waly View Post
Very considerate, Edmond . But why would anybody expect anything better from you?

True!
Then again Edmond has always been a bit of an ***.
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Old 26th March 2013, 10:29 PM   #345
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We need to simplify as much as possible .. not add complexity which will make things further from real life .. especially if good practice can get rid of certain evils.
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Originally Posted by Edmond Stuart View Post
Are we on cross purposes here? I only made this suggestion in oder to find out why some implementations of Cherry's amp were unstable.
Not at all. This is exactly what I'm trying to simulate.

My contention is that for output devices on sensible PCB layouts without evil 6" connections, the 33p collector/base caps on the devices that Cherry uses are redundant .. as are heretical variations of pure Cherry like TMC

Of course as a beach bum, relying on experience from more than 2 decades ago, I'm on very shaky ground in this august company.

On the subject on evil twisted 6" leads, isn't there a fair amount of coupling capacitance in addition to the inductance, mutual and otherwise of the leads.

I fully understand that DIY stuff may require evil twisted or ribbon 6" leads but I feel a commercial design should have the PCB fully define any paths .. and hence remove the need for 33p collector/base caps on drivers or even TMC.
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Old 27th March 2013, 12:03 AM   #346
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Default EF vs CFP

If I may return to the original thread ..

In Figs 5.39 & 5.40 of the 4th edition, Doug shows what happens at low power between EFII and CFP. He shows that CFP output stages may exhibit the evils of crossover distortion to a greater extent.

This is certainly worth further real life investigation. I've seen some evidence of this myself, but 20+ yrs ago, I couldn't measure THD to that precision at those levels.
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Old 27th March 2013, 03:43 AM   #347
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Originally Posted by kgrlee View Post
If I may return to the original thread ..
Amen
Quote:
In Figs 5.39 & 5.40 of the 4th edition, Doug shows what happens at low power between EFII and CFP. He shows that CFP output stages may exhibit the evils of crossover distortion to a greater extent.

This is certainly worth further real life investigation. I've seen some evidence of this myself...
This is my impression also.
Can someone reference the pics to the 5th edition?

Best wishes
David
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Old 27th March 2013, 02:02 PM   #348
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Originally Posted by kgrlee View Post
Not at all. This is exactly what I'm trying to simulate.

My contention is that for output devices on sensible PCB layouts without evil 6" connections, the 33p collector/base caps on the devices that Cherry uses are redundant .. as are heretical variations of pure Cherry like TMC

Of course as a beach bum, relying on experience from more than 2 decades ago, I'm on very shaky ground in this august company.

On the subject on evil twisted 6" leads, isn't there a fair amount of coupling capacitance in addition to the inductance, mutual and otherwise of the leads.
I believe that, compared to the capacitances of the O/P devices itself, the coupling capacitance between the leads is of little influence. Cbe is a few nF!

Quote:
I fully understand that DIY stuff may require evil twisted or ribbon 6" leads but I feel a commercial design should have the PCB fully define any paths .. and hence remove the need for 33p collector/base caps on drivers or even TMC.
Short story: If you omit the 33p caps, things get much more complicated.

Long story: In case of Miller output inclusive compensation (MOC), we are dealing with a (relative) high output impedance of the TIS. Tied to the drivers, which also exhibit a high (input) impedance, the resulting impedance is high too. The overall gain as well as the Miller loop gain strongly depends on this (the higher the impedance, the higher the gain). But we have little control over it, as it's defined by the parasitic capacitances of the trannies, Early effect, stray capacitance and stray inductance. IOW, it's a rather unpredictable and ill defined affair. At about 10MHz, being approximately the ULGF of the Miller loop, this means trouble. To get rid of this unpredictable behavior, just overrule the aforementioned impedance by a lower and better defined one. That are the two 33p caps for. Now you get (about) 6dB/oct roll-off and the Miller loop will be (more) stable.

That being the case, these caps are certainly not 'redundant'. Even which shortest possible leads to the O/P devices, I wouldn't omit these caps.

Cheers,
E.
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Old 27th March 2013, 02:46 PM   #349
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Quote:
Originally Posted by kgrlee View Post
If I may return to the original thread ..

In Figs 5.39 & 5.40 of the 4th edition, Doug shows what happens at low power between EFII and CFP. He shows that CFP output stages may exhibit the evils of crossover distortion to a greater extent.

This is certainly worth further real life investigation. I've seen some evidence of this myself, but 20+ yrs ago, I couldn't measure THD to that precision at those levels.
As my experience.
If you use TMC compensation. EFII is more linear.
If you use normal miller compensation. CFP is more linear.

Why?

Because CFP has strong local voltage negative feedback to ensure high linearity when it is driven by voltage source.
On contrast, EFII has high linearity when it is driven by current source.

When you use TMC compensation, most of time(Low Freq.) the output stage is included in miller compensation. Then you can look VAS as a current source. EFII is more suitable for this job.
When you use normal miller compensation, the strong local nagetive feedback on VAS make it more like a voltage source. CFP does well in this case.

Last edited by jxdking; 27th March 2013 at 03:06 PM.
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Old 27th March 2013, 04:36 PM   #350
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Originally Posted by kgrlee View Post
If I may return to the original thread ..

In Figs 5.39 & 5.40 of the 4th edition, Doug shows what happens at low power between EFII and CFP. He shows that CFP output stages may exhibit the evils of crossover distortion to a greater extent.

This is certainly worth further real life investigation. I've seen some evidence of this myself, but 20+ yrs ago, I couldn't measure THD to that precision at those levels.
I believe this is true, and is one of the reasons I do not recommend the use of CFP output stages, as explained in chapter 5 (5.4) of my book.

Cheers,
Bob
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