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Old 3rd March 2008, 10:11 AM   #1
Shike is offline Shike  United States
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Join Date: Jun 2007
Default Power Supply Help

Hello everyone,

I know there's probably some threads on this, but I've searched and am not completely sure where to start.

I want to build a five channel gainclone, using the LM3875. How do I go about selecting a transformer, rectifier, etc. Basically, how do I make a PSU in general . . . ?

My friend and I are in college and trying to build one, but we're completely lost when it comes to AC to DC rectification and meeting the power requirements.

Any links to guides, explanations, etc, would be greatly appreciated.
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Old 3rd March 2008, 10:22 AM   #2
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Join Date: Jul 2007
Location: Cape Town
I can only tell you what i believe and did . others will do things differently and disagree with me.

Power Supply

500VA 25 - 0 - 25 toroidal ( use 8 ohm speakers)

4 x 10000uF per voltage rail.
Stick to the standard national circuit for each chipamp.
Use BIG cheap 35A rectifier diodes to avoid current problems.

I added 100uF and a 0.1uF decouplings caps on each voltage rail pins in each chipamp.

For powersupplies:

read this website: http://www.tnt-audio.com/clinica/ssps1_e.html

For chipamp schematic:

Read the lm3886.pdf file on nationals website.



After all of this Experiment , add decoupling caps everywhere , experiment with input noise filtering circtuits and so fourth.
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Old 3rd March 2008, 12:57 PM   #3
TheMG is offline TheMG  Canada
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Join Date: Jan 2008
Most importantly, remember that the unloaded voltage output from the ps will be the secondary voltage of the toroid multiplied by the square root of 2. Keep that in mind when selecting the transformer voltage.
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Old 3rd March 2008, 01:04 PM   #4
paulb is offline paulb  Canada
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Join Date: Jun 2001
Location: Calgary
Default Re: Power Supply Help

Originally posted by Shike
.... Basically, how do I make a PSU in general . . . ?
Any links to guides, explanations, etc, would be greatly appreciated.
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Old 3rd March 2008, 01:23 PM   #5
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Location: Wirral UK
This site has taught me a lot, but theres a lot to learn...

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Old 3rd March 2008, 10:57 PM   #6
gootee is offline gootee  United States
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Location: Indiana
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This has about everything you need for basic linear PSU design, in a nutshell:


But you should think about how the grounding will be done, to avoid hum. There are some recent threads discussing the differences between using one or two bridge rectifiers, one or two transformers, etc, for two channels, that should give you some insights about running five channels from one power supply. Check in the power supply forum, here, too, for those. Also do some searches, here, for 'star ground'.

Also, go to http://www.national.com , and do a search for AN-1192, and download AN-1192.PDF. It shows how to do the calculations to determine output power and safe operating area vs load & power supply voltages, etc.
The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg
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Old 3rd March 2008, 11:04 PM   #7
Shike is offline Shike  United States
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Hey, thanks everyone. I'll make sure to get reading then . . . it seems I have a lot of ground to cover.
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