F5 power amplifier - Page 149

zinsula · 24th July 2008, 07:48 PM

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

EUVL · 24th July 2008, 09:09 PM

> 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

EUVL · 24th July 2008, 09:15 PM

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

Nelson Pass · 24th July 2008, 10:15 PM

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.

MEH · 25th July 2008, 12:30 AM

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?

Magura · 25th July 2008, 01:04 AM

Transconductance.

Magura

jacco vermeulen · 25th July 2008, 01:37 AM

2 in parallel have both comparable transconductance and capacitance numbers.

Zen Mod · 25th July 2008, 01:39 AM

Quote:

Originally posted by jacco vermeulen
2 in parallel have both comparable transconductance and capacitance numbers.

two Pussycats

Magura · 25th July 2008, 01:42 AM

Quote:

Originally posted by jacco vermeulen
2 in parallel have both comparable transconductance and capacitance numbers.

Go to sleep!

Magura

jacco vermeulen · 25th July 2008, 01:44 AM

You check the transconductance number of the IRF P-channel before you do.

25th July 2008, 01:04 AM	#1486
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Transconductance. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

25th July 2008, 01:37 AM	#1487
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	2 in parallel have both comparable transconductance and capacitance numbers. __________________ Not so much,.......if it says "ZM" in the corner.

25th July 2008, 01:44 AM	#1490
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	You check the transconductance number of the IRF P-channel before you do. __________________ Not so much,.......if it says "ZM" in the corner.

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24th July 2008, 07:48 PM	#1481
zinsula diyAudio Member Join Date: Mar 2004	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

24th July 2008, 09:09 PM	#1482
EUVL diyAudio Member Join Date: Oct 2003	> 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

24th July 2008, 09:15 PM	#1483
EUVL diyAudio Member Join Date: Oct 2003	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

24th July 2008, 10:15 PM	#1484
Nelson Pass The one and only Join Date: Mar 2001	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.

25th July 2008, 12:30 AM	#1485
MEH diyAudio Member Join Date: Feb 2007	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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