G-class with LM3886?

Elias · 24th February 2004, 05:01 PM

Hello!

Have you seen any G-class amplifiers realised using LM3886 amplifier chip? I'm building an active loudspeaker system with surrounds so I need efficient amplifiers to be able to cope with the heat from 12 channels. The one G-class amplifier I know is done with TDA7294 http://www.st.com/stonline/books/pdf/docs/1057.pdf but somehow I feel that LM3886 might perform equally well or even better since LM3886 seems to have better distortion graphs, open loop gain and PSRR.

Please share your wisdom

-Elias

subwo1 · 24th February 2004, 09:57 PM

It seems like it should work, but the TDA7294 has separate power pins for the input and driver stages. Though, class G should work best with discrete part amps because then the output transistors are the only parts which have to be affected by the variable voltage. But the TDA7294 seems to be an exception.

djk · 25th February 2004, 12:40 PM

http://164.195.100.11/netacgi/nph-Pa...&RS=PN/6304138

You need TIFF viewer, click on 'images'.

See fig.2, prior art, just what you need.

Elias · 27th February 2004, 08:44 AM

Thanks for the link, I've examined the patent. Yes, it shows the principle of operation of how to do G-class with chip amplifiers like LM3886, but like in all the patents they don't show any really working circuits. I don't think the presented configuration is stable if copied directly without any extra stabilising components (whatever those might be in this case). That's why I'm thinking more like a 'feedforward G-class chip amplifier' where the control for the higher supply voltage transistors is fed from the input and not from the output.

One performance limiting factor in G-class is the nonlinearities of the output conductance of the transistors, the same property wrehe the Early effect comes from. This might be an issue if G-class is realised with e.g. LM3886 where all the transistor stages are experiencing the voltage variations of the supply lines. In this regard, the TDA7294 (and likes) might perform better.

However, I can not be sure before I've build and measured a prototype, which is hopefully going to happen in coming weeks.

-Elias

24th February 2004, 05:01 PM	#1
Elias diyAudio Member Join Date: May 2003 Location: Where you live	G-class with LM3886? Hello! Have you seen any G-class amplifiers realised using LM3886 amplifier chip? I'm building an active loudspeaker system with surrounds so I need efficient amplifiers to be able to cope with the heat from 12 channels. The one G-class amplifier I know is done with TDA7294 http://www.st.com/stonline/books/pdf/docs/1057.pdf but somehow I feel that LM3886 might perform equally well or even better since LM3886 seems to have better distortion graphs, open loop gain and PSRR. Please share your wisdom -Elias

24th February 2004, 09:57 PM	#2
subwo1 diyAudio Member Join Date: Jan 2002 Location: North American Continent	It seems like it should work, but the TDA7294 has separate power pins for the input and driver stages. Though, class G should work best with discrete part amps because then the output transistors are the only parts which have to be affected by the variable voltage. But the TDA7294 seems to be an exception. __________________ USMPS http://groups.yahoo.com/group/switchmode/

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25th February 2004, 12:40 PM	#3
djk diyAudio Member Join Date: Feb 2001 Location: USA	http://164.195.100.11/netacgi/nph-Pa...&RS=PN/6304138 You need TIFF viewer, click on 'images'. See fig.2, prior art, just what you need.

27th February 2004, 08:44 AM	#4
Elias diyAudio Member Join Date: May 2003 Location: Where you live	Thanks for the link, I've examined the patent. Yes, it shows the principle of operation of how to do G-class with chip amplifiers like LM3886, but like in all the patents they don't show any really working circuits. I don't think the presented configuration is stable if copied directly without any extra stabilising components (whatever those might be in this case). That's why I'm thinking more like a 'feedforward G-class chip amplifier' where the control for the higher supply voltage transistors is fed from the input and not from the output. One performance limiting factor in G-class is the nonlinearities of the output conductance of the transistors, the same property wrehe the Early effect comes from. This might be an issue if G-class is realised with e.g. LM3886 where all the transistor stages are experiencing the voltage variations of the supply lines. In this regard, the TDA7294 (and likes) might perform better. However, I can not be sure before I've build and measured a prototype, which is hopefully going to happen in coming weeks. -Elias

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