My first designed amp

danuphonj · 2nd September 2011, 04:25 PM

Try it. Don't believe me.
I like its sound more than non inverting LM3875 and inverting LM3875.

I don't know why the simulation R7 = 53.5k but the real world R7 = 30k.

*** R7 must be 30k ***

samod · 2nd September 2011, 09:17 PM

Hello, maybe you to try so?

AndrewT · 3rd September 2011, 10:46 AM

The value of R7, the bias voltage applied to the FET gate, must be determined for each individual FET used.
The Vgs of FETs are all over the place. Test and measure every FET to allow a sensible prediction of the required bias voltage.
Or make a temporary connection with a VR and adjust the output voltage of the FET to a satisfactory operating point. Then replace the temp VR with a fixed R of equal value and re-check the FET output voltage..

3rd September 2011, 10:46 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The value of R7, the bias voltage applied to the FET gate, must be determined for each individual FET used. The Vgs of FETs are all over the place. Test and measure every FET to allow a sensible prediction of the required bias voltage. Or make a temporary connection with a VR and adjust the output voltage of the FET to a satisfactory operating point. Then replace the temp VR with a fixed R of equal value and re-check the FET output voltage.. __________________ regards Andrew T.

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