24-0-24-5 transformer for LM3875

danielnaveen · 12th December 2007, 09:49 AM

Hi,
I have a transformer with 24 - 0 - 24 - 5 volt secondaries which came of a DPA amplifier. Can i mask the 5 volt out and use it to power a LM3875 based amp?

Thank You

AndrewT · 12th December 2007, 10:47 AM

Hi,
yes, you can insulate the the 5V tapping and just ignore it.

Is the 5V tapping connected to the others or a separate winding?

Are the 24V tappings connected together or separate windings?

If they are connected you have a centre tapped secondary and must use a single rectifier to generate your +-V for the chipamp.
This is different from many of the chipamp PSU schematics, but all of them can be made to work with a centre tapped transformer.

danielnaveen · 12th December 2007, 02:27 PM

Thank you for the reply,
The taps are connected together so i guess i'll have to use a single rectifier, will a 6amp rectifier to enough to power the amp and will a GBU802 rectifier work with a 50Hz AC power supply?

Daniel

AndrewT · 12th December 2007, 03:09 PM

Hi,
the current rating of the rectifier is closely bound to the value of the smoothing capacitance after it.
If you go for typical 4.7mF to 10mF then 6A seems about right.
You may even get away with 1n5402 diodes which have a 3A rating.

If you were to go with +-20mF then 12A to 25A would probably be more suitable.

Leolabs · 14th December 2007, 01:20 AM

How many VA of your transformer???

danielnaveen · 14th December 2007, 12:22 PM

its 200VA

Leolabs · 14th December 2007, 01:28 PM

Wow.Plenty power for the LM3875.But the voltage is a bit high for it to drive a 4 ohms load.

danielnaveen · 16th December 2007, 07:55 AM

Quote:

Originally posted by Leolabs
Wow.Plenty power for the LM3875.But the voltage is a bit high for it to drive a 4 ohms load.

I know but it should be alright with my modified PSB alpha's

12th December 2007, 09:49 AM	#1
danielnaveen diyAudio Member Join Date: Oct 2006	24-0-24-5 transformer for LM3875 Hi, I have a transformer with 24 - 0 - 24 - 5 volt secondaries which came of a DPA amplifier. Can i mask the 5 volt out and use it to power a LM3875 based amp? Thank You

12th December 2007, 10:47 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, yes, you can insulate the the 5V tapping and just ignore it. Is the 5V tapping connected to the others or a separate winding? Are the 24V tappings connected together or separate windings? If they are connected you have a centre tapped secondary and must use a single rectifier to generate your +-V for the chipamp. This is different from many of the chipamp PSU schematics, but all of them can be made to work with a centre tapped transformer. __________________ regards Andrew T.

12th December 2007, 03:09 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, the current rating of the rectifier is closely bound to the value of the smoothing capacitance after it. If you go for typical 4.7mF to 10mF then 6A seems about right. You may even get away with 1n5402 diodes which have a 3A rating. If you were to go with +-20mF then 12A to 25A would probably be more suitable. __________________ regards Andrew T.

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12th December 2007, 02:27 PM	#3
danielnaveen diyAudio Member Join Date: Oct 2006	Thank you for the reply, The taps are connected together so i guess i'll have to use a single rectifier, will a 6amp rectifier to enough to power the amp and will a GBU802 rectifier work with a 50Hz AC power supply? Daniel

14th December 2007, 01:20 AM	#5
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	How many VA of your transformer???

14th December 2007, 12:22 PM	#6
danielnaveen diyAudio Member Join Date: Oct 2006	its 200VA

14th December 2007, 01:28 PM	#7
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Wow.Plenty power for the LM3875.But the voltage is a bit high for it to drive a 4 ohms load.

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