Buy matched mosfets?

[Shike]

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]

Originally posted by Shike



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!

[es44]

If You don't want to make Your own matching, there's a few members here who have done the "hard work". here's one
Tarasque is quite reasonable and has fast delivery.

Best regards
Ebbe

[pinial26]

i had take matched fet's to Tarasque and to Landoctor

very serious work ,with fast shipping

[jackinnj]

Originally posted by Shike
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.

[jupiterjune]

Or is there an "easy" way of doing it in terms of supplying power for testing, etc?

You could always build the PS for the amp first and use it to supply the power for the mosfet testing!

JJ

[jackinnj]

I use an old Crown amplifier with a variac as the test power supply. Just use an LM317 as a current limiter -- and test all your devices at the same ambient temperature and for the same period of time.

[Shike]

Thanks guys, you've all been great help. I'm going to take the leap