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Old 12th July 2004, 01:08 PM   #1
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Question Lynx Poweramps Cap Bank

Erm, i could use some advice... just a little bit!

I'm building 4 lynx poweramps, and need some general knowledge...

On the plans, it says that the amps need 15.000uf minimum bank for the psu, i'd be thinking they actually meant 15,000uf? would sound reasonable... and could i get away with 15 x 1000uf 100v caps (per rail, 30 in total?)... i know paralleling them adds up the capacitance but will i have problems with such small caps in such large numbers?

all help, as always is very appreciated!!
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Old 12th July 2004, 02:54 PM   #2
lucpes is offline lucpes  Europe
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Yep, it's really a pain to solder 30 caps )

Better go for 4(or more)x4700uf or 2x10.000 per rail/per side - you get the picture.

Guess I should put these in my signature:
http://www.tnt-audio.com/clinica/ssps1_e.html
http://sound.westhost.com/power-supplies.htm
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Old 12th July 2004, 11:42 PM   #3
mikeks is offline mikeks  United Kingdom
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Default capacitor slew rate???

This gentleman:

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

..makes an assertion that i could not resist.....

...capacitors do no have a slew rate.....

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Old 13th July 2004, 01:17 AM   #4
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Default Re: capacitor slew rate???

Quote:
Originally posted by mikeks
This gentleman:

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

..makes an assertion that i could not resist.....

...capacitors do no have a slew rate.....


Capacitance has no slew rate, but it affects the slew rate of active componants; like miller between PN junctions. This is why most OP AMPs have a poor slew rate when compared to descrete circuits do to the many many transistors (& miller capacitance) on the chip.

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Old 13th July 2004, 01:18 AM   #5
Eva is offline Eva  Spain
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Ooops

What a pity. So we have been fooled for ages into thinking that capacitor charging was predictable through this equation :

V(t) = V(t0) + 1/C * [(I*dt) integrated between t0 and t]

And that :

dV/dt (slew rate) = 1/C * I(t)

But no. These equations are wrong, capacitors have Slew Rate, you connect them to a toroidal transformer through a diode bridge and they slew... [When imagination takes over physics ]

PD: How much current is required to slew a 10.000uF capacitor at 100V/us ? [1.000A I think ]
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Old 13th July 2004, 03:17 AM   #6
mikeks is offline mikeks  United Kingdom
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Eva...you are correct.....perhaps i wasn't as clear as i should have been:

Capacitors of the same value but different manufactures cannot have different values of current required to charge them to the same voltage in the same time span....!

Which is what the good fellow here suggests...:

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

viz:

'By way of example, a typical commercial value capacitor, rated at 10,000uF/63V and costing some Euro 8-9, will have a speed of 30-40V/uS at best. An equivalent Elna for Audio series black, costing some Euro 15-25, will have a speed in the range of 80-90V/uS, i.e. at the very worst, double the speed of the best case in commercial cap land. A Siemens Sikorel cap, costing some Euro 20-30, will slew at over 100V/uS - but at a price.'

This is unadulterated excrement....

Oh....and how can the slew rate of resevoir caps. in the DC supply affect the slew rate of an amplifier?
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Old 13th July 2004, 08:12 AM   #7
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Well, its mainly due to price... i can get 120 1000uf caps @ 100v for 30 and i can get 4700uf caps for 6 each! so i cant really afford the bigger ones... the main point being will it blow up or morph into a smoke machine? or will it work, but would be better with the bigger ones... i wish my budget would allow for 50,000 per rail, but it's just not happening!
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Old 13th July 2004, 08:33 AM   #8
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I don't know where you buy your parts from, but I got a couple of 10,000uF 63V caps (Samwha) from CPC for about 3.50 each, and Profusion sell a similar range (Jamicon and Arcotronics) at similar good value prices.
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Old 13th July 2004, 10:32 AM   #9
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main problem is i'm building 4 amps, and i'd need *** EDIT at least *** 3 per rail (4700uf) that makes 8 rails x 3 caps = 24 caps, at 5 quid ish each is like over a hundred quid, however 1000uf x 15 per rail x 8 rails = 120 caps and i can get those for like 25p each, and as they are only for resevoir they should work right? around 63v rails with 100v caps? plus the inductance should be lower? helping stop oscilations?
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Old 13th July 2004, 10:49 AM   #10
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Yes, but if I am paying only 3.50 or so for a 10,000 cap, then a 4,700 cap may well be under 3... Or maybe you could use 2x 10,000 caps per rail at a cost of about 2*2*4*3.50=56 in total.

OK, not as cheap as your little caps, but a heck of a lot less wasted space and soldering.
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