LM3876 and 4-ohm drivers

astrodog · 28th June 2008, 11:03 AM

I am building a Silicon Chip kit with the LM3876 chips - I'd lke to use a pair of car speakers (I have spares) if possible. An addition in the kit mentions using supply rails at +/- 28V for this.
If I use an 18+18 VAC transformer - should this give me the +/- 28V.

Given these speakers will be in my observatory - quite small, used late at night - so quite low volume - should using this chip with 4-ohm loads be a problem??

TIA

Lee

Nuuk · 28th June 2008, 11:08 AM

That should be fine Lee.

AndrewT · 28th June 2008, 11:09 AM

the 18Vac transformer should be about right.

astrodog · 28th June 2008, 11:38 AM

Thanks for the advice guys - my plan, at least initially is to use my iPod or laptop as source - should I expect to have to use a preamp??

Nuuk · 28th June 2008, 11:44 AM

Expect the possibility!

I don't wish to be offensive but you say that you are going to play MP3 files into car speakers, so I don't know if quality is an issue here. If not, you shouldn't need a pre.

astrodog · 28th June 2008, 12:08 PM

If I could reliably pick a 256kbps MP3 from CD I wouldn't play them! I'll see how it all sounds and tinker from there.....

astrodog · 30th June 2008, 11:26 AM

Music!!

My amp (one channel so far) produced some music! Stoked! Small amount of hum also - although so far I've not bothered with trying to minimise this with star grounding etc.
It sounded surprisingly good, considering I had the amp board connected to a bare, cheapo, paper-cone woofer alone, without any crossover/filter....

The hum I had completely disappeared upon shorting the inputs, or connecting an ipod - is this hum then due to ground loops??

AndrewT · 30th June 2008, 11:34 AM

Quote:

Originally posted by astrodog
The hum I had completely disappeared upon shorting the inputs, or connecting an ipod - is this hum then due to ground loops??

was the input open circuit when the hum was detectable?

astrodog · 30th June 2008, 12:05 PM

Yes - hum only heard when input open circuit.

AndrewT · 30th June 2008, 12:13 PM

open circuit input is not a normal operating condition.
Ignore this.

28th June 2008, 11:03 AM	#1
astrodog diyAudio Member Join Date: Jun 2008	LM3876 and 4-ohm drivers I am building a Silicon Chip kit with the LM3876 chips - I'd lke to use a pair of car speakers (I have spares) if possible. An addition in the kit mentions using supply rails at +/- 28V for this. If I use an 18+18 VAC transformer - should this give me the +/- 28V. Given these speakers will be in my observatory - quite small, used late at night - so quite low volume - should using this chip with 4-ohm loads be a problem?? TIA Lee

28th June 2008, 11:08 AM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	That should be fine Lee. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

28th June 2008, 11:44 AM	#5
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Expect the possibility! I don't wish to be offensive but you say that you are going to play MP3 files into car speakers, so I don't know if quality is an issue here. If not, you shouldn't need a pre. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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28th June 2008, 11:09 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the 18Vac transformer should be about right.

28th June 2008, 11:38 AM	#4
astrodog diyAudio Member Join Date: Jun 2008	Thanks for the advice guys - my plan, at least initially is to use my iPod or laptop as source - should I expect to have to use a preamp??

28th June 2008, 12:08 PM	#6
astrodog diyAudio Member Join Date: Jun 2008	If I could reliably pick a 256kbps MP3 from CD I wouldn't play them! I'll see how it all sounds and tinker from there.....

30th June 2008, 11:26 AM	#7
astrodog diyAudio Member Join Date: Jun 2008	Music!! My amp (one channel so far) produced some music! Stoked! Small amount of hum also - although so far I've not bothered with trying to minimise this with star grounding etc. It sounded surprisingly good, considering I had the amp board connected to a bare, cheapo, paper-cone woofer alone, without any crossover/filter.... The hum I had completely disappeared upon shorting the inputs, or connecting an ipod - is this hum then due to ground loops??

30th June 2008, 12:05 PM	#9
astrodog diyAudio Member Join Date: Jun 2008	Yes - hum only heard when input open circuit.

30th June 2008, 12:13 PM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	open circuit input is not a normal operating condition. Ignore this.

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