Buy matched mosfets?

Shike

Member
2007-06-30 6:01 am
Hey everyone,

I'm really new to the DIY amplifier community, the max I've ever done was a simple cmoy. I'm really interested in building an Aleph 5 amp . . . but one thing is really keeping me from taking the leap. Mosfet matching. I don't have a lot of equipment in terms of power supplies or the like for extensive testing. Is there a place where I could buy matched ones from the git and go in the US? Or is there an "easy" way of doing it in terms of supplying power for testing, etc?

Thanks for your time,

-Drew
 

Babowana

Formerly "jh6you". R.I.P.
2006-07-13 4:23 pm
www.aheadamp.com
Shike said:
Or is there an "easy" way of doing it in terms of supplying power for testing, etc?




I usually measure the threshold Vgs for matching, following
the attached method. As the MOSFETs have quite similar
forward transconductance curves, I match for the same threshold
Vgs (within 0.01V deviation) only. I did the same way of
matching for my recent F4 firstwatt amp.

You could get the supply voltages from any power amp.

Good luck!


:darkside:
 

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Shike said:
Mosfet matching. I don't have a lot of equipment in terms of power supplies or the like for extensive testing. Is there a place where I could buy matched ones from the git and go in the US? Or is there an "easy" way of doing it in terms of supplying power for testing, etc?
-Drew


You can make a constant current source with an LM317 -- see National Semi's product folder -- for 200 mA use a 6.25 ohm resistor.

If you get the devices with the same lot number chances are very good that transconductance and device capacitance will be highly correlated. Several years ago I sat down and matched a hundred N and P channel devices and then did a linear regression of these parameters. I don't want to speak for the MOSFET oracle, but I believe that he has opined similarly.

Aside from the elimination of load-hogging, with matched devices of any stripe you'll find that the THD% is reduced by a few thousandths of a percent.


Landoctor matches his devices (I do my own) to 1mV at 200 ma or 400 ma -- and 40 degrees C.