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Old 1st April 2011, 06:45 PM   #1
knutn is offline knutn  Norway
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Default All MOSFET Amp - with improvement potential?

I am planning to build the MOSFET amp attached, but I would like to replace the VAS transistors IRF610/9610 with better types, preferably MOSFETs. I have tried to find low cap, high wattage types without any luck. I also intend to run this amp without global feedback. Any suggestions?
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Old 1st April 2011, 07:00 PM   #2
lineup is offline lineup  Sweden
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I only know IRF510/9510 is a bit lower capacitance.
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Old 1st April 2011, 07:39 PM   #3
lineup is offline lineup  Sweden
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What voltage supply?
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Old 1st April 2011, 09:10 PM   #4
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Nothing wrong wit hthe 240/9240 combo in the schematic.

I have done numerous designs using those MOSFETs and they all sound good.
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Old 2nd April 2011, 12:53 AM   #5
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by knutn View Post
I am planning to build the MOSFET amp attached, but I would like to replace the VAS transistors IRF610/9610 with better types, preferably MOSFETs. I have tried to find low cap, high wattage types without any luck.
I forget where this circuit is from, but are you sure it is good? It looks like the designer wanted a symmetrical circuit while the mosfet is less complementary than bipolar?

And what do you mean with "without any luck"?. How about 2SK213-216/2SJ76-79? These are lateral mosfets not vertical like the IRF.

I have found in many amps using the IRF610/9610 that the mosfet is the limiting factor. Luckily the MOSFET used in the JLH 80W is a lateral one (tho the IRF also fits there)...

About IRF510 (as per Lineup suggestion), I'm aware that there are many manufacturers but from my experiment/observation/search, the IRF610 is the best (soundwise), not IRF510. For higher power IRF530 is my favorite.
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Old 2nd April 2011, 06:02 AM   #6
lineup is offline lineup  Sweden
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Here is another take on ALL MOSFET.
+21/-21 Volt. Gives max 14 Watt.
Shows very good figures.
Now, I do not know how to test for noise.
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Old 2nd April 2011, 06:10 AM   #7
lineup is offline lineup  Sweden
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Originally Posted by Jay View Post
About IRF510 (as per Lineup suggestion), I'm aware that there are many manufacturers but from my experiment/observation/search, the IRF610 is the best (soundwise), not IRF510. For higher power IRF530 is my favorite.
IRF610 has somewhat higher RDSon than IRF510.
Maybe that's why it is more popular.
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Old 2nd April 2011, 09:44 AM   #8
knutn is offline knutn  Norway
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Thank you for your replies. I forgot to say I have a 2x18V 500 VA transformer and two quite large heatsinks, so I am planning to run it in Class A, about 25 W into 8 ohms. This makes it possible to not have feedback from the output, but from the VAS instead. the design is my own, the symmetrical input is maybe not necessary...
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Old 2nd April 2011, 05:43 PM   #9
Jay is offline Jay  Indonesia
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Originally Posted by knutn View Post
Thank you for your replies. I forgot to say I have a 2x18V 500 VA transformer and two quite large heatsinks, so I am planning to run it in Class A, about 25 W into 8 ohms. This makes it possible to not have feedback from the output, but from the VAS instead. the design is my own, the symmetrical input is maybe not necessary...
The circuit topology is imo "tailored" towards class-B. For class-A, we already "have" Pass Labs' F4 which is also about 25W into 8 ohm, using similar components as yours. Of course, it can be more fun to have own design regardless of quality. But isn't it better to follow the proven track? What I mean is, if you ask for expert's help here, they may suggest you to change your amp into something that is completely different.
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Old 2nd April 2011, 06:04 PM   #10
knutn is offline knutn  Norway
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Originally Posted by Jay View Post
The circuit topology is imo "tailored" towards class-B. For class-A, we already "have" Pass Labs' F4 which is also about 25W into 8 ohm, using similar components as yours. Of course, it can be more fun to have own design regardless of quality. But isn't it better to follow the proven track? What I mean is, if you ask for expert's help here, they may suggest you to change your amp into something that is completely different.
Yes, F4 is a nice amp, but I need voltage amplification. and I like your proposal of 2SK213-216/2SJ76-79. I have looked at their data sheets, and these transistors seem promising. But do they sound better than the IRF's?
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