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Old 12th December 2012, 06:45 PM   #801
EUVL is offline EUVL  Europe
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If you read the data from Fischer a bit further down you see :

Thermal resistance: 0,07 K/W .....
Thermal conductivity: 0,45 W/mK

0.45 W/mK is the material constant.
0.07 K/W refers to that particular insulator with a specific surface geometry.

Rth Kapton Bulk = 0.45 x 0.00005 / (0.024 x 0.021) = 0.045 K/W for a TO247 Insulator.

But this is the resistance of the bulk material itself.
On top of that you need to add the Thermaphase conductive layer on both sides.
What that is precisely and how to arrive at the 0.32 extra resistance is not explained by Fischer.
I presume you then do not need to add grease with that stuff already coated.

I am still using Kerafol.
You only need to measure temperature difference between MOSFET case and heat sink with the same device dissipating the same heat
to figure out which is better and by how much.

As I mentioned elsewhere before, the thermal prediction for my AX100 agrees with measurement to <2C, over the total thermal chain.
And no, I don't have share at Kerafol.


Patrick
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Last edited by EUVL; 12th December 2012 at 06:49 PM.
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Old 12th December 2012, 06:56 PM   #802
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Quote:
Originally Posted by EUVL View Post
And no, I don't have share at Kerafol.
As i do with Fischer
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Old 27th March 2013, 02:46 AM   #803
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Other then long cable runs, what is the point behind balanced pre amps and power amps. If that is the only reasoning what is considered a long run for either a f5 or f5x, or even a f5t. I don't know if this question should be else where if so it may be moved, sorry for any hijacking of this thread.
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Old 27th March 2013, 05:27 AM   #804
EUVL is offline EUVL  Europe
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There are many white papers around from Nelson, Charles Hansen, etc about balanced amplifiers vs single ended.
Why not search in Google for a more balanced opinion ?

I build balanced for lower harmonic distortions.
But that is my personal choice.


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Old 28th March 2013, 03:09 AM   #805
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Quote:
Originally Posted by EUVL View Post
Why not search in Google for a more balanced opinion ?


Patrick
Is that a play on words,
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Old 28th March 2013, 06:26 AM   #806
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Use "neutral opinion" if you like.


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Old 3rd April 2013, 08:00 PM   #807
NicMac is offline NicMac  Italy
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Patrick,

While studying the history of source generation in the context of the F5 amp I came over this post in the F5 thread where you present your build F5X (for the first time?).

You say:
"Circuit is similar to the balanced version posted by Tino.
Rails are +/- 16V, total bias 4A.
JFETs are matched 2SK170BL/2SJ74BL running at 5mA.
Output MOSFETS are 2SK1530/2SJ201.
Source resistor 0R22 & 0R18 respectively."

Would that mean that you were biasing the K1530/J201 differently to make the devices track better and why did you give it up later?

Nic
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Old 3rd April 2013, 09:05 PM   #808
EUVL is offline EUVL  Europe
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It meant that I was using a different way than in the public version to take care of the different Yfs of the JFETs.
The public version is much easier to understand and hence to build.
The end results are, at least in theory, the same, i.e. open loop gain balancing between top & bottom halves.


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Old 3rd April 2013, 10:26 PM   #809
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Thanks Patrick - I'm learning and that is important (for me)

>It meant that I was using a different way than in the public version to take care of the different Yfs of the JFETs.

Essentially you are compensating the non-complementarity of the K170/J74 FETs using different source degeneration for the K1530/J201. In the later public version this is replaced by differential degeneration directly on the JFET's (typically 10R/15.1R). Correct?

>The public version is much easier to understand and hence to build.

I disagree. It is generally easier to build that to understand. Anyway, the use of different MOSFET source resistors is not really that easy to understand without an explanation, but then again I may be a very dumb audio DIY'er

>The end results are, at least in theory, the same, i.e. open loop gain balancing between top & bottom halves.

I'm very happy to hear that
It seem that a proper source R choice is a reliable way to compensate off-sets in both JFET and MOSFET complementarity.

Cheers,

Nic


P.S. Out of complete ignorance with respect to audio terminology: does "top & bottom" effectively equal "front-end & output-stage" ?
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Old 3rd April 2013, 10:33 PM   #810
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Top & bottom means +ve rail and -ve rail halves.
The use of different source resistor values have already been mentioned once when we discussed poor NN-PP match before.
You need to calculate the total open loop gain from front to end (in this case only 2 stages).
Changing one resistor values will force other changes to occur simultaneously.
And that has to be taken into account.

That applies to the first order effects (one assume the FETs to be linear).
When you take higher orders into account, it becomes more complex.

Writing some equations will help you to figure it out.
Or learn to use Spice and play with the model.


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