A MOSFET power amp schematic - what do you think?

Doug Kim · 22nd April 2011, 11:43 PM

Hi all,

I have attached a schematic of power amp based on MOSFET output tr. It is very similar to Hafler XL 280.
http://www.hafler.com/techsupport/pd...80_amp_man.pdf

Whoever designed it, I got PCB boards from my friend in Korea, so I am thinking of starting to gather parts. K389/J109 are quite hard to get though.

What do you think about the circuit? Will it be worth bothering to gather parts?

Doug

Doug Kim · 22nd April 2011, 11:45 PM

I cannot find my attachment, this link might work.
http://www.e-audioclub.com/board/fil...K-II-60W-2.pdf

Ian Finch · 23rd April 2011, 11:28 AM

Starting at the input, are you certain of values like R14 (1k) earthing the signal? Hafler, at least, is using a more likely 47k.

jaycee · 23rd April 2011, 02:04 PM

1K input impedance is far too low. Try 22-47K. A 1nF capacitor for the lowpass filter is also a bit extreme, 330-470pF should be better.

Personally I am never a fan of driving the MOSFETs from the VAS. I'd add a driver stage.

22nd April 2011, 11:43 PM	#1
Doug Kim diyAudio Member Join Date: Apr 2008	A MOSFET power amp schematic - what do you think? Hi all, I have attached a schematic of power amp based on MOSFET output tr. It is very similar to Hafler XL 280. http://www.hafler.com/techsupport/pd...80_amp_man.pdf Whoever designed it, I got PCB boards from my friend in Korea, so I am thinking of starting to gather parts. K389/J109 are quite hard to get though. What do you think about the circuit? Will it be worth bothering to gather parts? Doug

23rd April 2011, 11:28 AM	#3
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	Starting at the input, are you certain of values like R14 (1k) earthing the signal? Hafler, at least, is using a more likely 47k. __________________ regards

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22nd April 2011, 11:45 PM	#2
Doug Kim diyAudio Member Join Date: Apr 2008	I cannot find my attachment, this link might work. http://www.e-audioclub.com/board/fil...K-II-60W-2.pdf

23rd April 2011, 02:04 PM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	1K input impedance is far too low. Try 22-47K. A 1nF capacitor for the lowpass filter is also a bit extreme, 330-470pF should be better. Personally I am never a fan of driving the MOSFETs from the VAS. I'd add a driver stage.

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