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Old 14th March 2003, 09:21 PM   #1
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Default 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
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Old 15th March 2003, 04:48 AM   #2
Jay is offline Jay  Indonesia
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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.
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Old 15th March 2003, 06:45 PM   #3
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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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Old 20th March 2003, 05:45 PM   #4
Coulomb is offline Coulomb  England
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Default Re: Replacing the Mosfets of the Aleph 2

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.
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File Type: zip irf fets.zip (6.4 KB, 208 views)
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Old 22nd March 2003, 03:45 AM   #5
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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
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Old 26th March 2003, 01:55 PM   #6
df is offline df  Switzerland
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Smile another spreadsheet

Here is another version of a mosfet spreadsheet. I focused the relation between capacitance and transconductance.
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File Type: zip mosfet.zip (3.8 KB, 137 views)
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