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Old 24th July 2008, 07:48 PM   #1481
zinsula is offline zinsula  Switzerland
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Patrick's measurements are very intresting, thank you for the detailed presentation.

From the whole thing, it seems to me that the quite substantial lower transconductance of the P channels MOSFET's will not have major drawbacks because they have also a much higher Vgs threshold.
Therefore, the required higher JFET drain resistor of the upper halve does compensate for this.
Also shown clearly in Patrick's spreadsheet.

My thoughts on better complements here:
http://www.diyaudio.com/forums/showt...36#post1494636




As OT, what would be the consequence in a F4 when using MOSFET's with these transconductance differences? Very high K2?

Tino
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Old 24th July 2008, 09:09 PM   #1482
EUVL is offline EUVL  Europe
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> My thoughts on better complements here:

Tino,

You cannot get better complementaries than the Toshibas, IMHO !!
http://www.diyaudio.com/forums/showt...t=#post1507044



Also the spreadsheet I posted only shows gain balancing, but says nothing about 2nd and 3rd. I have another spreadsheet for that, which is 1.8MB and too complicated to explain. But there, it shows that the Toshibas give half the distortion as the Fairchilds when trimmed properly (to account for the Transconductance differences of the JFETs.)

Not that it is important, whether at 0.003% or 0.006%


Patrick


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Old 24th July 2008, 09:15 PM   #1483
EUVL is offline EUVL  Europe
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May I come back to my question a couple of pages before ?

http://www.diyaudio.com/forums/showt...32#post1567732

>> What would you suggest to flatten the small hump? Gate resistor to 22R does not seem to do much.
> What hump is that?
>> The second plot when the amp is loaded with a dummy speaker load (reactive, about 4 ohm).


Thanks,
Patrick

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Old 24th July 2008, 10:15 PM   #1484
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I don't know what reactance you have in the load, but you can
induce an arbitrary rolloff with capacitors across the 100 ohm
feedback resistors or at the input.
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Old 25th July 2008, 12:30 AM   #1485
MEH is offline MEH  United States
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Somebody please remind me again, for use in an F5 topology, what is the reason to choose the IRF or Fairchild MOSFETs over 2SK1530s and 2SJ201s?
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Old 25th July 2008, 01:04 AM   #1486
Magura is offline Magura  Denmark
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Transconductance.


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Old 25th July 2008, 01:37 AM   #1487
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2 in parallel have both comparable transconductance and capacitance numbers.
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Old 25th July 2008, 01:39 AM   #1488
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Quote:
Originally posted by jacco vermeulen
2 in parallel have both comparable transconductance and capacitance numbers.


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Old 25th July 2008, 01:42 AM   #1489
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Quote:
Originally posted by jacco vermeulen
2 in parallel have both comparable transconductance and capacitance numbers.

Go to sleep!


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Old 25th July 2008, 01:44 AM   #1490
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You check the transconductance number of the IRF P-channel before you do.
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