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 29th May 2010, 07:30 AM #7961 meanman1964   diyAudio Member     Join Date: Oct 2006 Location: Belgium the land of chocolate How critical are the values of the 220µF caps can I use 470µF?
juma
diyAudio Member

Join Date: Nov 2005
Location: Berlin
Quote:
 Originally Posted by meanman1964 How critical are the values of the 220µF caps can I use 470µF?
22k and 220u have RC time constant of a bit less than 5 seconds - with 470u you'll have a bit more than 10 seconds.
The RC time value defines time needed to charge the cap to approximately 63% of the nominal voltage (kind of a slow start). Also, since this is capacitance multiplier, the cap value defines the resulting capacitance i.e. the ripple voltage in output DC voltage.

For example, with 10k and 220u (IRFP240, 4700uF on output, current draw = 1.2A) I get the following results:
- input DC voltage = 24V
- input ripple = 200mV peak
- output DC voltage = 20.2V
- output ripple = 1mV peak

Last edited by juma; 29th May 2010 at 08:13 AM.

 29th May 2010, 06:14 PM #7963 Nelson Pass   The one and only     Join Date: Mar 2001 It's probably easier to cascode the Jfets with some bipolar transistors.
meanman1964
diyAudio Member

Join Date: Oct 2006
Location: Belgium the land of chocolate
Quote:
 Originally Posted by Nelson Pass It's probably easier to cascode the Jfets with some bipolar transistors.
How?

Nelson Pass
The one and only

Join Date: Mar 2001
will do.

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 30th May 2010, 08:17 AM #7966 bobodioulasso   diyAudio Member     Join Date: May 2008 Larger heatsinks too.
 30th May 2010, 11:46 AM #7967 meanman1964   diyAudio Member     Join Date: Oct 2006 Location: Belgium the land of chocolate Thanks guys but I tried another solution.I've add 8 turn on my toroid and it's now a trannie of 2x18Vac
 30th May 2010, 11:59 AM #7968 jam   diyAudio Member     Join Date: May 2001 Location: Auburn, CA, USA Mr.Pass, Cascoding the jfet should reduce their non-linear capacitance would this lower the distortion and increase bandwidth to any significant amount to be beneficial if you were using lower voltage rails? Jam
 30th May 2010, 04:54 PM #7969 Nelson Pass   The one and only     Join Date: Mar 2001 Yes, but I don't expect it to be a significant improvement. Most of the capacitance issues are on the output stage.
 1st June 2010, 01:23 AM #7970 jam   diyAudio Member     Join Date: May 2001 Location: Auburn, CA, USA Thanks Mr. Pass. I have tried it and cannot hear a change. I guess leave it out if you don't need it. In keeping with Zen tradition...... Last edited by jam; 1st June 2010 at 01:28 AM.

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