Replacing the Mosfets of the Aleph 2

Hydesg · 14th March 2003, 09:21 PM

Hi

is it possible to replace the irf 244 mosfets in the aleph 2 with irf 250 ? anyone of you have done that ? did you guys notice any difference in sound ?

any other comments are most welcomed

Jay · 15th March 2003, 04:48 AM

Hi,

I use IRFP250 for my Aleph (Input capacitance around 2000pF, transconductance around 18 Siemens), and there will not be much difference in the sound quality using quite a similar MOSFET. But IRF250 has 3500pF (and 10 Siemens)!

I think Nelson Pass (and so am I) is more concerned with the input capacitance in choosing the IRF type. As far as I can remember, IRF244 has the lowest input capacitance in it's class.

Many people (due to the system they own) cannot appreciate the difference in high frequencies more than they appreciate low frequencies, so I don't know whether the high input capacitance (usually correspond to poor treble) will suit you or not.

Personally, I found that the high input capacitance is the biggest problem with MOSFET for an amplifier. I think this is because the MOSFET is mainly designed for other purposes like power switching, not for an amplifier.

Nelson Pass · 15th March 2003, 06:45 PM

An Aleph 2 has 12 times IRF240 per channel ( two banks of 6 ) as I recall. The IRF250 is a bigger chip, and I would suggest that if you use it, go with 2 banks of 4 devices, and you should get what you are looking for.

Coulomb · 20th March 2003, 05:45 PM

Quote:

Originally posted by Hydesg
Hi

is it possible to replace the irf 244 mosfets in the aleph 2 with irf 250 ? anyone of you have done that ? did you guys notice any difference in sound ?

any other comments are most welcomed

Here is a little spreadsheet with the important specs listed of IRF FET's. It also has some pricing on it for FET's used in Pass designs, the pricing is in Canadian Dollars. So that would mean lower US dollar prices would likely be applicable.

davesaudio · 22nd March 2003, 03:45 AM

nice table- reminds me why I don't shop at electrosonic
anymore...

got a little bag of IRF250 on eBay a while ago,
for when I need to PASS-ify myself

df · 26th March 2003, 01:55 PM

Here is another version of a mosfet spreadsheet. I focused the relation between capacitance and transconductance.

14th March 2003, 09:21 PM	#1
Hydesg diyAudio Member Join Date: Dec 2002 Location: Singapore	Replacing the Mosfets of the Aleph 2 Hi is it possible to replace the irf 244 mosfets in the aleph 2 with irf 250 ? anyone of you have done that ? did you guys notice any difference in sound ? any other comments are most welcomed

22nd March 2003, 03:45 AM	#5
davesaudio diyAudio Member Join Date: Feb 2003 Location: GTA	nice table- reminds me why I don't shop at electrosonic anymore... got a little bag of IRF250 on eBay a while ago, for when I need to PASS-ify myself __________________ intentionally blank

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15th March 2003, 04:48 AM	#2
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	Hi, I use IRFP250 for my Aleph (Input capacitance around 2000pF, transconductance around 18 Siemens), and there will not be much difference in the sound quality using quite a similar MOSFET. But IRF250 has 3500pF (and 10 Siemens)! I think Nelson Pass (and so am I) is more concerned with the input capacitance in choosing the IRF type. As far as I can remember, IRF244 has the lowest input capacitance in it's class. Many people (due to the system they own) cannot appreciate the difference in high frequencies more than they appreciate low frequencies, so I don't know whether the high input capacitance (usually correspond to poor treble) will suit you or not. Personally, I found that the high input capacitance is the biggest problem with MOSFET for an amplifier. I think this is because the MOSFET is mainly designed for other purposes like power switching, not for an amplifier.

15th March 2003, 06:45 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	An Aleph 2 has 12 times IRF240 per channel ( two banks of 6 ) as I recall. The IRF250 is a bigger chip, and I would suggest that if you use it, go with 2 banks of 4 devices, and you should get what you are looking for.

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