Alpha Nirvana 39w 8ohm Class A Amp

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#3,821
I'm pretty new to all this measurement stuff @andyr . I really am reliant on experts like yourself to help guide noobs like myself with this stuff. I'm just going off what others have suggested. I do think matching FETs (if needed) at operating temp does help ensure the best matches as I found that the Vgs matching measurements are different for MOSFETs at room temperature vs operating temperature (maybe slightly different slopes of Vgs vs temp). Although, with that said, the difference is pretty minimal overall (a few % at most). It is clear and repeatable that power FETS matched at 50°C are not the same "match" at room temp, even if it's not that significant of deviation. I've only been matching power MOSFETs N to N and P to P, not N to P.

I suspect there's not much advantage of measuring the smaller BJT's at operating temp vs room temp as you point out, however, I'm open to input from experts like yourself. Mostly, I just wanted to share how I have been matching power MOSFETs at temperature using the hot plate technique so others can give it a try.

I guess I should also say for clarity that the AN39 doesn't need matched power MOSFETs at all due to only using a single N and single P per channel, so matching power FETs for AN39 is not value added as far as I understand.
 
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#3,826
birdbox said:
I'm pretty new to all this measurement stuff @andyr . I really am reliant on experts like yourself to help guide noobs like myself with this stuff. I'm just going off what others have suggested. I do think matching FETs (if needed) at operating temp does help ensure the best matches as I found that the Vgs matching measurements are different for MOSFETs at room temperature vs operating temperature (maybe slightly different slopes of Vgs vs temp). Although, with that said, the difference is pretty minimal overall (a few % at most). It is clear and repeatable that power FETS matched at 50°C are not the same "match" at room temp, even if it's not that significant of deviation. I've only been matching power MOSFETs N to N and P to P, not N to P.

I suspect there's not much advantage of measuring the smaller BJT's at operating temp vs room temp as you point out, however, I'm open to input from experts like yourself. Mostly, I just wanted to share how I have been matching power MOSFETs at temperature using the hot plate technique so others can give it a try.

I guess I should also say for clarity that the AN39 doesn't need matched power MOSFETs at all due to only using a single N and single P per channel, so matching power FETs for AN39 is not value added as far as I understand.
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You seem to have misconstrued me as an 'expert', bb! 😀

Thank you for explaining that matching readings at a lower temp ... doesn't hold true for the higher, amp-operating temperature. I suspect I will never be going to your extent, though. 🙁
 
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