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Old 23rd December 2005, 05:20 AM   #1
doggy is offline doggy  Canada
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Default build power supply for35vdc rails

Hello and hi,

I am in the process of getting ready for another amp, solid state this time and I want to build a good power supply giving 35-0-35 vdc. A few questions please: are electro caps rated for 50 volts good enough or do I have to use 63 volt. I wanted to use the panasonic fc but digikey only go to 2200uf 50 v or 1800 63v. When you make that jump in voltage the price goes up. I thought of using multiple smaller electros in parallel rather than let's say 4 10000uf 50-63v; one transformer'400va{eventually] may use a 160va for now I have on hand. dual secondaries. 2- 35a bridge rectifiers. I source parts from the USA or Canada. In the big electro's how are the panasonic ts? or are there any others I could consider here in north Amer.?

thanks and happy holidays,
doggy
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Old 23rd December 2005, 05:27 AM   #2
lineup is offline lineup  Sweden
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VDC = 1.3-1.4 x VAC
so you need a trafo with 2x 24-28 VAC to get 35 VDC
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Old 23rd December 2005, 05:42 AM   #3
doggy is offline doggy  Canada
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Thanks, that I have, 25vac.its basically info on the caps I would like

cheers
doggy.
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Old 23rd December 2005, 06:45 AM   #4
quasi is offline quasi  Australia
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All else being equal the use of parallel caps is better because you will achieve a lower ESR and lower inductance. This is of course if they will fit in the case.

I would go for the 50 volt caps and take the extra capacity. Rule of thumb for me is working voltage + 20% = capacitor voltage minimum, so 50 volt caps will be more than adequate.

Cheers
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Old 23rd December 2005, 07:25 AM   #5
doggy is offline doggy  Canada
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I was hoping to hear that. It helps to save some money. Also as I had hoped to use the panasonic fc. More smaller caps would also give the ability to add or subtract capacitance to experiment with the supply size

cheers
doggy
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Old 23rd December 2005, 07:35 AM   #6
quasi is offline quasi  Australia
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Cool.

Is that you in the canoe?
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Old 23rd December 2005, 11:05 AM   #7
doggy is offline doggy  Canada
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No, I have had all kinds of boats and have a folding portabote in the garage; I was very kean on getting one last year/I thought it would be good to do some quiet exploring; maybe this year.

cheers
doggy
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Old 28th December 2005, 01:35 AM   #8
doggy is offline doggy  Canada
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greetings all;still exploring cap choices

For something to do, I pulled the top off my lm3875 chip amp. I wasn't planning to keep it, so I stripped off all the extra ps caps I had put on earlier. using it, it didn't sound to bad with the original 1500uf pana. fc.; but a little harsh. So I was having some fun and removed the fc's and put in just 2- 100uf on each side. It works but not enough power. I found out I don't like the panasonic fc's-strange that; but stranger still is what I ended up using and liking. You know those 330 uf 200volt caps you find in most computer ps? the ones no one think they are any good for anything? thats what I put in and they sound excellent. I also tied the 2 caps together with a 200 volt 470 on each side. I also increased the gain by adding a carbon comp 285r to the bottom of the board. The chip seems to have woken up but also a little more diode noise which I have not been able to fully suppress. This is the briangt kit.

cheers
doggy
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Old 28th December 2005, 01:47 AM   #9
poobah is offline poobah  United States
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Guys...

The rule for "working voltage" in caps is to run them AT their working voltage. A slight increase, the 20% cited by Quasi, is fine but there is no motivation to go further unless you suspect that you may exceed the MAXIMUM or SURGE voltage.

Electrolytic's benefit by being run at or near their rated working voltage. This maintains the chemistry of the plates.
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Old 28th December 2005, 01:53 PM   #10
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Default Off Topic

Poobah,

The dog trick works very well.
My dog went nuts to get the third biscuit out of my pocket.
(then she stopped--knew there wasn't a fourth one)
My wife is convinced it has nothing to do with counting -- the dog just sniffs the biscuit on me-- but I still think it's a good party trick.


Andy
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