Question about V & A in power supply

mossen · 16th October 2011, 05:20 AM

Hi. I'm planning to build a simple LM1875 amp. It will be my first one. If I use a power supply that can provide 15V at 2A, is this the ultimately same as one that can provide 30V at 1A?

Thanks
mossen

sofaspud · 16th October 2011, 06:57 AM

They're both 30VA, so if by "same" you mean power output the answer is yes.
But you probably want a little more power to run your LM1875.

Mooly · 16th October 2011, 07:27 AM

If it is a single PSU of just 15 volts (single as in not a split rail of -/+15) then that means the LM1875 can only swing a theoretical -/+ 7.5 volts across a load.

For an 8 ohm load that equates to only around 5.3 volts RMS giving a power of 3.5 watts RMS. Factor in losses in the IC and your nearer 3 watts or less.

For the 30 volts supply the power goes up to nearer 14 watts RMS.

So although your 15 volt 2 amp supply may seem equivalent to a 30v 1 amp supply the problem is that you can't put that "power" down across the load.

mossen · 16th October 2011, 06:00 PM

Thanks Mooly, for that explanation. Makes sense!

16th October 2011, 05:20 AM	#1
mossen diyAudio Member Join Date: Apr 2011	Question about V & A in power supply Hi. I'm planning to build a simple LM1875 amp. It will be my first one. If I use a power supply that can provide 15V at 2A, is this the ultimately same as one that can provide 30V at 1A? Thanks mossen

16th October 2011, 06:57 AM	#2
sofaspud diyAudio Member Join Date: Nov 2005 Location: San Antonio TX	They're both 30VA, so if by "same" you mean power output the answer is yes. But you probably want a little more power to run your LM1875. __________________ It is error only, and not truth, that shrinks from enquiry. - Thomas Paine

16th October 2011, 07:27 AM	#3
Mooly diyAudio Member Join Date: Sep 2007	If it is a single PSU of just 15 volts (single as in not a split rail of -/+15) then that means the LM1875 can only swing a theoretical -/+ 7.5 volts across a load. For an 8 ohm load that equates to only around 5.3 volts RMS giving a power of 3.5 watts RMS. Factor in losses in the IC and your nearer 3 watts or less. For the 30 volts supply the power goes up to nearer 14 watts RMS. So although your 15 volt 2 amp supply may seem equivalent to a 30v 1 amp supply the problem is that you can't put that "power" down across the load. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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16th October 2011, 06:00 PM	#4
mossen diyAudio Member Join Date: Apr 2011	Thanks Mooly, for that explanation. Makes sense!

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