MOSFET Quasi Complimentary ???

IIR · 25th August 2002, 02:43 AM

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!

mikek · 26th August 2002, 01:21 AM

...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......

Kilowatt · 26th August 2002, 02:37 AM

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.

Circlotron · 26th August 2002, 11:41 AM

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.

UrSv · 26th August 2002, 12:14 PM

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

Nelson Pass · 26th August 2002, 08:20 PM

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

carlmart · 26th August 2002, 09:43 PM

D. Self doesn't like FET or MOSFET at all, complementary or not.

Carlos

Kilowatt · 26th August 2002, 09:45 PM

And Slone loves them.

Nelson Pass · 26th August 2002, 11:31 PM

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.

hifidaddy · 27th August 2002, 07:19 PM

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

25th August 2002, 02:43 AM	#1
IIR diyAudio Member Join Date: Apr 2002	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!

26th August 2002, 02:37 AM	#3
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	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. __________________ - "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"

26th August 2002, 11:41 AM	#4
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	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.

26th August 2002, 09:45 PM	#8
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	And Slone loves them. __________________ - "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"

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26th August 2002, 01:21 AM	#2
mikek Account Disabled Join Date: May 2002	...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......

26th August 2002, 12:14 PM	#5
UrSv diyAudio Member Join Date: Jan 2002 Location: Sweden	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

26th August 2002, 08:20 PM	#6
Nelson Pass The one and only Join Date: Mar 2001	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

26th August 2002, 09:43 PM	#7
carlmart diyAudio Member Join Date: Mar 2001 Location: Brazil	D. Self doesn't like FET or MOSFET at all, complementary or not. Carlos

26th August 2002, 11:31 PM	#9
Nelson Pass The one and only Join Date: Mar 2001	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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