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-   -   All MOSFET Amp - with improvement potential? (http://www.diyaudio.com/forums/solid-state/186236-all-mosfet-amp-improvement-potential.html)

knutn 1st April 2011 06:45 PM

All MOSFET Amp - with improvement potential?
 
1 Attachment(s)
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?

lineup 1st April 2011 07:00 PM

I only know IRF510/9510 is a bit lower capacitance.

lineup 1st April 2011 07:39 PM

What voltage supply?

nigelwright7557 1st April 2011 09:10 PM

Nothing wrong wit hthe 240/9240 combo in the schematic.

I have done numerous designs using those MOSFETs and they all sound good.

Jay 2nd April 2011 12:53 AM

Quote:

Originally Posted by knutn (Post 2524421)
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.

lineup 2nd April 2011 06:02 AM

1 Attachment(s)
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.

lineup 2nd April 2011 06:10 AM

Quote:

Originally Posted by Jay (Post 2524732)
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.

knutn 2nd April 2011 09:44 AM

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...

Jay 2nd April 2011 05:43 PM

Quote:

Originally Posted by knutn (Post 2524939)
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.

knutn 2nd April 2011 06:04 PM

Quote:

Originally Posted by Jay (Post 2525248)
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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