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Old 21st July 2007, 05:26 AM   #1
dovganj is offline dovganj  Argentina
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Default Dual supply for LM1875 split supply

Hello people there. I've just bought the stuff neccesary to assemble two LM1875 split suply and fit a stereo amp. I got evr'ything but the supply.
I guess I need a dual supply, but I have no idea about how to assemble it. I can't find any diagrams of it, and I know that supply is the most important thing to make an amp work.
I'll use two 10W speakers, so I guess the source has to be a +20/-20 V, 1A, but nothing else.
Has anyone fitted that kind of supply for the LM1875? Can you show me diagrams, datasheets, pictures or whatever?

Tank you very much,

Alexis.
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Old 21st July 2007, 06:42 AM   #2
Danko is offline Danko  Hungary
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Here it is: Click the image to open in full size.
The image is linked from http://sound.westhost.com/project72.htm , where a LM1875 based amplifier is described.

Did you think something like that?
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Old 21st July 2007, 07:04 PM   #3
dovganj is offline dovganj  Argentina
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Yes, that's right what I mean, but I can't see any diodes in the diagram, and... why is the fuse bofore the transformer?

The diagram is clear, but, is there any fascimiliar sheet for the printed circiut?

Thank you very much.

Alexis.
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Old 21st July 2007, 09:15 PM   #4
Danko is offline Danko  Hungary
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The diodes are in "BR1". That's a diode bridge.

That fuse is there, to protect the transformer and the mains network from overloading, shirt circuit.
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Old 21st July 2007, 11:32 PM   #5
dovganj is offline dovganj  Argentina
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Ok, thank you. I'll buy all the stuff, assemble and test the supply.
I'll post the evolution of project and future doubts and troubles, and, once I have the full gainclone ready and working, I'll post the experience for those who (as I do now) need some help.
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Old 22nd July 2007, 07:40 AM   #6
Danko is offline Danko  Hungary
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Be careful at the primary side of the transformer! There are lethal voltages, that can kill you in a moment, if you touch at the wrong part!!
Also be areful at the secondary-side. 20-30V is not as dangerous as 230V, but touching a capacitor, charged to 25V could be "surprise".

Good luck on the project!
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Old 22nd July 2007, 04:53 PM   #7
dovganj is offline dovganj  Argentina
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Once, I reeplaced a capacitor of my PCs monitor. It was a big one, I do not remember how big, and I touched the burned one with my thongue. It was strong, belive me.
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Old 23rd July 2007, 06:43 AM   #8
dovganj is offline dovganj  Argentina
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The PCB for split provided by National in the datasheet of LM1875 has a mistake, there's a 1000 uF cap with not specified position. Should I put - in the V- track?

The one I'm reffering to is bellow the chip in the picture:

http://petrovich.nutus.com.ar/Split ... corregido.jpg

Also, I made a new PCB with Photoshop, fited to a 36x36 holes multi-purpose grid. It will be here in next post, availabe for whose don't want to print a special PCB (which can be a little expensive in some countries).

Alexis
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Old 23rd July 2007, 06:58 AM   #9
Netlist is offline Netlist  Belgium
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Electrolytes and Tantalum capacitors have a polarity that should always be respected.
In laymenís terms: Always connect + to + and Ė to -.
All other capacitors donít mind how you place them, electrically spoken.

/Hugo
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Old 23rd July 2007, 07:10 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
a 15Vac + 15Vac 50VA transformer will give about +-20Vdc and sufficient power for two channels with maximum power between 10W and 15W/channel.
Use +-10mF on each amplifier's supply rails.
Your smoothing caps could be right on the limit @ 25Vdc. I would use 40Vdc to allow for higher than normal mains voltages.
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