F5X -- the EUVL Approach - Page 80 - diyAudio
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Old 27th November 2012, 02:08 PM   #791
EUVL is offline EUVL  Europe
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Firstly I do not see higher distortion for 3rd and 5th with any of the measurements, within the measurement repeatability.
You always have to look at numbers below -120dB with care.

What you see here is also closed loop distortion.
Maybe you should read what John Curl or Charles Hansen says about open loop linearity.

e.g. http://www.diyaudio.com/forums/solid...int.html?pp=50

Of course we'll then end up in the endless discussion about ho wmuch feedback is good or bad.
As I said in post#1, 100 ways to skin a cat.
I only intend to show you how I want to do it.

If you believe in numbers, then use opamp, or even Class D.
But then you ar ein the wrong forum.


Patrick
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Old 27th November 2012, 07:14 PM   #792
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Originally Posted by EUVL View Post

Thanks to dave for all the experimental work.
My pleasure Patrick.

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Originally Posted by buzzforb View Post
In fact, while the corrected graphs fets are slightly higher in distortion, their harmonic distribution looks better to me. what is your opinion on this EUVL. Is the lower overall distortion worth the higher harmonics. I know this applies only to SE input.
The first graph deserves a little more explanation - That measurement was taken many moons ago when there was a noise issue on the bench from a florescent light. The low level, non-harmonic peaks are an artifact of the noise. And as Patrick points out, well below -120dB down. I was just a bit too preoccupied to convert it back to grounded x to re-measure now that the noise issue is solved.

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Old 27th November 2012, 07:45 PM   #793
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They all look great. I was mainly pointing out that the nonmatched devices were very close in performance to the matched. Encouragement for those who do not get in on that particular pool of fets. Of course all this distortion is at vanishing levels and way below other amps i have listened to that sound great. I kinda like a little dirt in my music.
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Old 28th November 2012, 02:43 AM   #794
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> I kinda like a little dirt in my music.

I don't like to use MSG when I cook.


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Old 28th November 2012, 08:37 AM   #795
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Originally Posted by EUVL View Post
Further to the discussion in post #783, we have done more work on the compensation method and are ready to publish.
so what exactly is your "compensation method" and how is it applied/calculated for a given Vgs offset?
I know I can shift the Vgs by changing by changing the value orf the source resistor, but I seem to remember that you told me that was "cheating"
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Old 28th November 2012, 12:05 PM   #796
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It is a bit more complicated than that.

You do change the source resistor value, but in doing so you also change the drain resistor value of the 1st stage.
If you combine both effects, you can recalculate the open loop gain of the top & bottom halves to rebalance them.
And we have an excel sheet designed precisely for that.

But since all Batch 1 &2 subscribers (will) have perfectly matched sets,
and the balanced mode will also sort it out for independent builders with only NNNN PPPP match,
there is right now no real incentive for publication.

We shall publish when it becomes interesting, e.g. when all the NNNNPPPP sets have been used up.

Call me evil if you wish ......



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Old 28th November 2012, 01:40 PM   #797
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Msg sucks. Salt and peppa, I like
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Old 11th December 2012, 10:27 AM   #798
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Thanks to Jan Didden's generosity, he has put my second article for Linear Audio online for free download :

http://www.linearaudio.net/images/st...%20PK%20lr.pdf

This is based on the thermal design of the F5X power amplifier case.
Since the article was written, we have done more analytical work, and wish to publish two further supplements.


Patrick

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Attached Files
File Type: pdf Optimum Pitch.pdf (372.2 KB, 164 views)
File Type: pdf The Myth of Heat Spreaders.pdf (99.6 KB, 173 views)
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Old 12th December 2012, 04:54 PM   #799
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Hi Patrick,

interesting article. Ive gone through this a few times building class-A power amps. One thing I don't understand is the big difference between the K/W given for Kapton insulators from Fisher (0,07) and the value you calculate (0,44). See the data sheet below.
For my last few amps Ive used the Kapton insulators and was quite satisfied. I think I even measured some temperatures not that far off the specs.

William

http://www.hifituning24.de/downloads/kapton.pdf
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Old 12th December 2012, 05:22 PM   #800
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Hello William,
im using those Kaptons too for years with best results.
My specs say
Waermeleitfaehigkeit 0,45 W/mK
Waermewiderstand 0,15 K/W .

Btw,
while youre sitting in germany,
if you want to get them @ a way better price, just PM.
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