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Old 4th March 2004, 12:19 AM   #1
DeonC is offline DeonC  South Africa
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Default Small trannie and big caps

Hi guys

I hope this is not a too stupid question, but here goes:

I have a Naim NAC42 pre that I got in a trade for duplicate LPs I had. It came without a PSU, so I want to build one for it. Just to start off I want to build it from parts I have in my parts bin (some I go from friends, some I got from stripping old equipment). I have a small 18V-0-18V trannie (about 50W - 80W) as well as a pair of huge caps (65000uF, 35V) as well as a pair of 21000uF caps. I got both pairs from a friend of mine(he got it from a mainframe he stripped), and I would like to use them to build a split 24V-0-24V PSU for the Naim (seperate rails for the phono-stage and pre sections). I also have a 25A brigde rectifier from a failed amp project- I tried building a JLH 10 Watt class A amplifier a few years back, but I think the transistors I used were all blown (they came from another amp I got). I might try it again some time, but I am getting off my original point.

My question is this- will the trannie not be harmed by the huge current draw of the large caps? I will add other smaller caps to the equation as well (to add a bit of speed), so in total the capacitance of one rail can get as high as 90mF - 95mF! I hope this is not a too stupid question

Enjoy,
Deon
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Old 4th March 2004, 01:40 AM   #2
mwh-eng is offline mwh-eng  United States
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The capacitors will only draw a large current on initial power up. This short duty surge should not matter to the transformer. I see no problems.
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Old 4th March 2004, 01:50 AM   #3
DeonC is offline DeonC  South Africa
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Default Thanks

I thought it might not be an issue (I remembered the massive supply for Hiraga's Le Monstre), but I just wanted to be sure. I will probably build a better supply as funds allow- this is just for experimentation.

BTW, what do you think will sound the best:
A. A regulated PSU as per normal Naim amps (using LM317 regs), or
B. A C-L-C, or even a C-L-C-L-C, choke-rectified PSU?

I tend to lean toward the double-Pi filter (i.e. C-L-C-L-C), but I would like hear other's opinions/experiences

Enjoy,
Deon
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