What can I do with these MOSFETs?

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Jay

Banned
Joined 2003
That's N-channel mosfet for switching. How many transistors do you have? With only 4 transistors you cannot parallel them to get high power amp, unless you purchase another 4 P-channel mosfets.

Those mosfets have 5000pF of input capacitance. That's not a good thing, especially if you have to build class-B amp (to get high power). Search for Pass' modified Citation 12. It uses 2 N-channel mosfets per channel. I think it is 50W I'm not sure. If you have 12 mosfets you can build Quasi Amp (search in this forum). It depends on one's standard but to me such mosfet can never sound good enough in class-B.

Class-A is low in power but the sound quality is a good compensation. You can get relatively higher power using Aleph current source such as in Aleph J amplifier. But your heatsink may be too small for the heat.
 
antiquekid3

antiquekid3

Member
Joined 2010
Yeah, I only have those four. But I like that Mini-MOSFET amp. I might try putting that circuit together once I get a big 'ole 40V power supply. Any suggestions for that?

Thanks for the great suggestions! I've got a lot of projects right now (and a new one today; more on that later), but I have quite a bit of time ahead of me to work on some more amps.

Kyle
 
djk

djk

R.I.P
Joined 2001
" is under use of the PS (much lower power than the original). This is because the gate drive needs to be at least 8 to 10V higher than the main supply rails"

Is 10W 'much lower'? It's less than 0.8dB lower than the rated 60W of the original Citation.

In fact, since he doesn't have the Citation ±42V supply, he can build something more robust. Pass himself suggested using a high voltage tier for the front-end. The MTM55N10 is a 250W device (the IRF part was only 150W), so a 100W/8R stereo amplifier could be built with the four MTM55N10 and the heatsink he has.
 
infinia

infinia

Member
Joined 2005
"Because the transconductance is low compared to bipolars, there is significant loss in maximum power for a follower unless the source voltage can deliver several more volts than the supply to the output transistor, resulting in either lower efficiency, or the use of tiered power supplies to feed the amplifier's front end several more volts than the output stage." N Pass​

Yes higher voltage drive is advised to realise the most power output for a given PS. Without tiered power supplies efficiency suffers esp for lower voltage power rails.
 
djk

djk

R.I.P
Joined 2001
"You know, it is NOT the transconductance ! It is the THRESHOLD VOLTAGE that causes the losses. "

On these FETs you're correct. On lateral types (Hitachi) the gate loss is about 1A/1V, plus the I^2R Rds on loss (can be ignored on these MTM55N10).
 
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