MOSFET Quasi Complimentary ??? - diyAudio
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Old 25th August 2002, 02:43 AM   #1
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Default MOSFET Quasi Complimentary ???

Could someone please explain how a MOSFET quasi complementary output stage (all N-channel FETS) really works? Kind like the one off www.aussieamplifiers.com

Are the high-side FETs operating as source followers (for the postive side) while the low-side FETS acting like transconductance amps (for the negative side)? Please help!
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Old 26th August 2002, 01:21 AM   #2
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...get a-hold of douglas self's 'audio power amplifier handbook'...third edition......
In brief, quasi-complementary MOSFET output stages are sub-optimal in nearly all respects......
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Old 26th August 2002, 02:37 AM   #3
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Unless of course you (for some reason or other) need to use devices that have no compliment.

Randy Slone's "High Power Audio Amplifier Construction Manual also explains how they work.
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Old 26th August 2002, 11:41 AM   #4
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Default N-channels rule!

Look in any catalogue and you will find seriously big N-channel Hexfets and IGBT's. Big enough to need bolts to attach the conductors. In contrast, P-channel devices wimp out comparitively early on the buahahaha scale. Super duper sized amplifiers (not necessarily audio) may well need to use a pair of N-channel devices for this reason.

GP.
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Old 26th August 2002, 12:14 PM   #5
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The abundance of big N-channel FETs and lack of P-channel FETs could also be because the biggest ones are designed for switching which means no P-channel needed...hence no complimentary.

/UrSv
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Old 26th August 2002, 08:20 PM   #6
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If you need an example of a quasi-comp Mosfet output
stage, you can check out the 60 watt Mosfet upgrade on
an HK Citation 12 at www.passdiy.com

Sounds tho, like D. Self doesn't like quasi-comp Mosfets
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Old 26th August 2002, 09:43 PM   #7
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D. Self doesn't like FET or MOSFET at all, complementary or not.


Carlos
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Old 26th August 2002, 09:45 PM   #8
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And Slone loves them.
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Old 26th August 2002, 11:31 PM   #9
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I like to be agnostic about it, and I've made plenty of
money with both.

Bipolar are great if you are trying to get decent distortion
with a low bias AB amp. Home theater stuff is a good example.

Mosfets are the choice if you have high voltages and power,
or if you want simple Class A circuits. In general, they tend
to be easier to design with if you can afford lots of bias.
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Old 27th August 2002, 07:19 PM   #10
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Default Here is a quasi-comp Mosfet power amp

Hi,

I just browsed my MJ mag articles and found a kaneda Power amp from 1999, which has both N-type Mosfets in the output stage. Though he drives them rather symmetrically, in my opinion.

regards,
Hartmut
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