LM3886 on +/-42V

diarav · 11th April 2006, 12:03 PM

Hi,
I purchased a 30-0-30 V Transformer to build the PSU and power the LM3886 power amp (yet to build) and now I realise that the output DC voltage will be 1.414 x 30 = ~ 42V. The LM3886 datasheet shows maximum rated input voltage to be |V+|+|V-| = 84 V which comes very close.
Has anyone tried to use the LM3886 at the voltage of +/- 42V ? Or should I cut of the voltage at about 35V?

Thanks in advance
Din

edl · 11th April 2006, 12:20 PM

Hi,

That's so risky. Mains can vary +10%, and then the rails will be 45-47V.
Anyway +/-42V is already too much!

You could try an STK IC.

jaudio · 11th April 2006, 12:25 PM

running the lm3886 at +-50V

Do a search for max supply voltage. A few people run lm3886 amp with +/- 42.

diarav · 11th April 2006, 01:28 PM

Thanks for your responses.

Looks like it is safe to use the 3886 at about +/- 35V. Would it be safe to use a 35V zener diode? I am not very keen on spending more on regulator ICs if not really required.

Moderator:
Not sure if this post now belongs to the power supplies area.

Rgds
Din

SteveMajerus · 11th April 2006, 01:35 PM

Our, just use an extra bridge (or even two!) on each channel...that will knock it down another 1.5 to 3 volts...

Bazukaz · 11th April 2006, 01:44 PM

If you would put 5 bridges in series you would end with ~35V dc.
Maybe its better to unwind some secondary windings , if you don't mind disassembling the trafo.It would be more rational.

diarav · 11th April 2006, 01:48 PM

SteveMajerus:
Are you suggesting something as attached? (Sorry for the crude drawing, I used Microsoft PaintBrush).

pinkmouse · 11th April 2006, 01:51 PM

My LM4780 is running quite happily on 42V rails. You do need big heatsinks, and pay attention to thermal coupling as it does run fairly warm. It also sounds nicer than when it was running on lower rails.

Bazukaz · 11th April 2006, 02:00 PM

It may run for few years at higher rails , but may fail one day if mains voltage rises for 10%.
Also , Spike protection will surely activate when listening at highest levels , because the ICs internal power dissipation will be exceeded.
For 4 ohm loads , one should use ~30Vdc , and for 8 ohms 36V is ok.

Diarav : you got the idea right...

demogorgon · 11th April 2006, 02:06 PM

I'v run the lm3886 on 50V rails, and it played, but was severely unstable, and when i pulled out a phonoplug, the chip blew.

i have altso tested the chips at 45-46V, and it ran without any problems at all. so in conclution, running the chips at maximum reccomended voltage, is not a problem. if you view the datasheet it altso says that maximum voltage the chip can handle in a non-playing envirement is 94 or 92V if i remember correct, and that allows for some margines. remember when power is pulled through your transformer voltages will sag.

-Marius

11th April 2006, 12:03 PM	#1
diarav diyAudio Member Join Date: Dec 2004 Location: Bangalore India	LM3886 on +/-42V Hi, I purchased a 30-0-30 V Transformer to build the PSU and power the LM3886 power amp (yet to build) and now I realise that the output DC voltage will be 1.414 x 30 = ~ 42V. The LM3886 datasheet shows maximum rated input voltage to be \|V+\|+\|V-\| = 84 V which comes very close. Has anyone tried to use the LM3886 at the voltage of +/- 42V ? Or should I cut of the voltage at about 35V? Thanks in advance Din

11th April 2006, 01:51 PM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	My LM4780 is running quite happily on 42V rails. You do need big heatsinks, and pay attention to thermal coupling as it does run fairly warm. It also sounds nicer than when it was running on lower rails. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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11th April 2006, 12:20 PM	#2
edl diyAudio Member Join Date: Oct 2004	Hi, That's so risky. Mains can vary +10%, and then the rails will be 45-47V. Anyway +/-42V is already too much! You could try an STK IC.

11th April 2006, 12:25 PM	#3
jaudio diyAudio Member Join Date: Oct 2004	running the lm3886 at +-50V Do a search for max supply voltage. A few people run lm3886 amp with +/- 42.

11th April 2006, 01:28 PM	#4
diarav diyAudio Member Join Date: Dec 2004 Location: Bangalore India	Thanks for your responses. Looks like it is safe to use the 3886 at about +/- 35V. Would it be safe to use a 35V zener diode? I am not very keen on spending more on regulator ICs if not really required. Moderator: Not sure if this post now belongs to the power supplies area. Rgds Din

11th April 2006, 01:35 PM	#5
SteveMajerus diyAudio Member Join Date: Sep 2004 Location: Cleveland, OH	Our, just use an extra bridge (or even two!) on each channel...that will knock it down another 1.5 to 3 volts...

11th April 2006, 01:44 PM	#6
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	If you would put 5 bridges in series you would end with ~35V dc. Maybe its better to unwind some secondary windings , if you don't mind disassembling the trafo.It would be more rational.

11th April 2006, 02:00 PM	#9
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	It may run for few years at higher rails , but may fail one day if mains voltage rises for 10%. Also , Spike protection will surely activate when listening at highest levels , because the ICs internal power dissipation will be exceeded. For 4 ohm loads , one should use ~30Vdc , and for 8 ohms 36V is ok. Diarav : you got the idea right...

11th April 2006, 02:06 PM	#10
demogorgon diyAudio Member Join Date: Jul 2004 Location: Behind you.	I'v run the lm3886 on 50V rails, and it played, but was severely unstable, and when i pulled out a phonoplug, the chip blew. i have altso tested the chips at 45-46V, and it ran without any problems at all. so in conclution, running the chips at maximum reccomended voltage, is not a problem. if you view the datasheet it altso says that maximum voltage the chip can handle in a non-playing envirement is 94 or 92V if i remember correct, and that allows for some margines. remember when power is pulled through your transformer voltages will sag. -Marius

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