F4 sweet spot...

Skorpio · 15th June 2010, 11:59 AM

I had read this nice article:
http://www.firstwatt.com/pdf/art_sweet_spot.pdf

It looks like replacing the two 10R resistors at the source of the input follower will enable you to reduce distorstion by 80%?

Is this usable for a DIYer without a distorsion analyser? I guess the sweetspot will not be the same point as minimum DC-offset?'

But you might have a option to try to listen to different settings of the pot....

Will 20R trimmer be a good starting point or perhaps 100R?

Nelson Pass · 16th June 2010, 12:32 AM

No, but you can trim the distortion a bit by replacing the
two resistors with a 20 ohm (or so) trim pot.

Skorpio · 17th June 2010, 06:16 AM

Ok, I should try...

The same might apply to the F4 output stage? The zero off-set level might not be the most optimal setting regarding distorsion?
I have build the F4 with single 50V supply, so could it be possible to tweek on the output also?
This might be 0.47 to 0.1 Ohm source resistors?

Nelson Pass · 17th June 2010, 08:31 PM

It's possible to tweak, but don't expect a lot of improvement.

15th June 2010, 11:59 AM	#1
Skorpio diyAudio Member Join Date: Mar 2004 Location: Denmark	F4 sweet spot... I had read this nice article: http://www.firstwatt.com/pdf/art_sweet_spot.pdf It looks like replacing the two 10R resistors at the source of the input follower will enable you to reduce distorstion by 80%? Is this usable for a DIYer without a distorsion analyser? I guess the sweetspot will not be the same point as minimum DC-offset?' But you might have a option to try to listen to different settings of the pot.... Will 20R trimmer be a good starting point or perhaps 100R?

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16th June 2010, 12:32 AM	#2
Nelson Pass The one and only Join Date: Mar 2001	No, but you can trim the distortion a bit by replacing the two resistors with a 20 ohm (or so) trim pot.

17th June 2010, 06:16 AM	#3
Skorpio diyAudio Member Join Date: Mar 2004 Location: Denmark	Ok, I should try... The same might apply to the F4 output stage? The zero off-set level might not be the most optimal setting regarding distorsion? I have build the F4 with single 50V supply, so could it be possible to tweek on the output also? This might be 0.47 to 0.1 Ohm source resistors?

17th June 2010, 08:31 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	It's possible to tweak, but don't expect a lot of improvement.

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