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Old 27th March 2002, 04:01 AM   #1
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Question MOSFET outputs for an A-40?

I have most of the parts for an A-40 and plan on actually building the amp, but as always, I have been sidetracked by new technology. Having discovered this fabulous forum and read what I could on the Aleph's (This will be my next project), I began to wonder...

Can the IRFP 240's be used as the output devices for an A-40 amp? If so, how would I alter the A-40 circuit to drive them correctly, and make them work well?

I also wonder how different the 240's would sound vs. the Darlingtons?

Thanks for your comments.

Rodd Yamashita
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Old 27th March 2002, 07:12 AM   #2
FBJ is offline FBJ  United States
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There a mod for the Pass A40 to change the output BJTs to mosfets in one of the TAA back issuses. It's late and I have to get up early but I will get the issuse number for you tomorrow. And if I can work my CAD program and figure out how to post a drawing I will do that.
Also off the top of my head, I remember Mr. Pass responding to that article about the Mosfet used may not be higher wattage enough for the heat disspation. And the ones he recommended are the higher wattage types. Can't remember the part numbers but I noticed some for sell in the for trade section at this site.
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Old 27th March 2002, 07:58 AM   #3
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Default AA 3/87

FBJ,

Thanks for your reply.

I know that article. It was a letter from Randolph Vikan called "EZFET" from AA 3/87. The thing is that I'm sure that FET technology has come a long way since 1987. I know that the Aleph outputs are single ended. What I'm wondering is what would be a more up-to-date version of converting an A-40 to an FET output, with possibly IRFP 240's and it's complement what ever that may be.

Your right, Mr. Pass responded with a warning on the wattage of the 2SK134 and 2SJ49.

Rodd Yamashita
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Old 27th March 2002, 02:32 PM   #4
FBJ is offline FBJ  United States
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It's great to meet a fellow TAA-er or aX-er now. But I agree with you. The IRF mosfets may have higher gate capacitance but should work though I haven't tried this.
But Mr. Pass usually criuses in this forums around lunch time where I lived I'm should he will have some ideas.
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Old 27th March 2002, 06:40 PM   #5
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Norm Thagard did an excellent job updating the
A40 with MOSFETs, in TAA (now Audio Express) and
I recommend checking it out.

One of these days, I'll get around to the same sort
of project, trying to make it simpler than Norm's
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Old 27th March 2002, 08:14 PM   #6
FBJ is offline FBJ  United States
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Mr. Pass is right, the Thagard M-40 looks to be a more up to date design for a Mosfet output stage for the A-40.
But again if I remember correct the transistor pack, AH5020J (or the NPD5566) used in the design is very hard to find. And I know there is a source for the AH5020J at www.borbelyaudio.com.
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Old 7th March 2007, 01:08 PM   #7
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Default Updated A40

Quote:
Originally posted by Nelson Pass
Norm Thagard did an excellent job updating the
A40 with MOSFETs, in TAA (now Audio Express) and
I recommend checking it out.

One of these days, I'll get around to the same sort
of project, trying to make it simpler than Norm's

Any news for us on your progress Mr. Pass?
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Old 7th March 2007, 02:10 PM   #8
mlloyd1 is offline mlloyd1  United States
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Default Re: Updated A40

i can imagine " ... one of these days ... " means "it will be a while, so don't watch for it daily. practice on some other projects in the meantime"



mlloyd1

Quote:
Originally posted by gpsmithii
Any news for us on your progress Mr. Pass?
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Old 7th March 2007, 04:32 PM   #9
MikeW is offline MikeW  United States
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Here is a version
Attached Files
File Type: pdf 2-11-05 amp_schematic.pdf (48.8 KB, 348 views)
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Old 7th March 2007, 04:34 PM   #10
MikeW is offline MikeW  United States
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Attached Files
File Type: pdf 2-11-05 amp_layout.pdf (67.6 KB, 176 views)
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