Big Filter Caps

[richidoo]

A friend gave me these to try in my amp project. He has a collection of parts from 30 years of being a hifi tech. When I saw them I couldn't believe how big they were. He said they are from an old Levinson amp. I don't know whether they still work being kinda old, but they are impressive just to look at! They weigh about 2 pounds each. They are 50,000 uF each rated 125VDC, peak 150. My amp is ESP project 101, 150w/8ohms. I am running it at 56V with four transistors per channel to allow more current to my hungry legacy bass drivers (2ohm dips). Is 56V too low to make good use of these high voltage caps? Will they be too slow? I originally intended to use Jensen 4 pole caps until I priced them out at $450! for 8x10,000uF@80V. I have just finished the BOM and starting to layout the monoblock cabinets which I will build from wood. Any ideas, suggestions? Any solid state amp builders out there? That is a whole different kind of disorder, separate from audiophile. I'm just doing it to get cheap watts. Not sure it will be so cheap after all, but it will be fun. My 8yo son is gonna help me.
Thanks!
Rich

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[mgalusha]

Rich,

They would be fine for your amp project but I'd be leery of these if they have been sitting around for a long time. Electrolytic caps have a limited lifetime but can sometimes be re-formed if they are brought up to working voltage slowly. If you have a variac (a very good idea if building amps) hook up a transformer and diode bridge and slowly bring the voltage up. A Google search for capacitor forming should turn up more detailed information.

 As for the higher voltage, this is usually a good thing. It's good to maintain at least a 20% margin above your working voltage. Having a higher  voltage rating on the caps will usually provide lower ESR and a higher ripple current capability.

Also, keep in mind that having really large capacitors will cause very high peak current through the rectifier diodes. This is because the caps won't discharge very much between cycles and this will only allow the diodes to conduct for a small portion of each cycle meaning more current will be passed for a given load.

[richidoo]

mgalusha,
Thanks for the response. I have read about that reforming procedure. It sounds kinda intense. 125VDC is something I don't wanna be anywhere near. The guy who gave them to me has such a rectifier, I wil ask if he has ever done it. I was planning on using twin 35A bridge rectifiers per channel anyway, so that should be enough for anything.

I'll have to read up on that ripple current thing, I never could understand that.

Can you recommend a good brand of 2 pole filter caps, I really only need 20,000uF per rail, rated 80V. Have you any experience or knowledge of the 4 pole caps people are raving about? Jensen and DNM/BHC.
Thanks a lot
Rich

[mgalusha]

Rich,

The Jensen 4 pole caps work really well but as you mention, they are very expensive.

The Panasonic T-UP series are quite good and quite a bit less expensive. From Digi-Key the 80V/10,000uF caps run $10.08 each for the 4 pin. The 5 pin versions are rated for a 50% greater lifespan but cost a a little more. The 80V/22,000uF caps run $25.15 each but of course you need 1/2 as many, so they are not very much more expensive. Very low ESR and high ripple current. I have 4 of these I picked up for a project. I haven't used them yet, so I can't say how they sound but they should work very well. Other Panasonic caps perform nicely so I'm hopeful these will too.

One thing you can do if you want to use Jensen's but spend less $$ is to just put one Jensen 4 pole per rail after your main caps. This is suggested on the Jensen website and it's works well.

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Mike

[richidoo]

Yeah, the price is a lot better, and using the Jensen at the end for a clean up is a great idea. I'll read the datasheet on the Panasonics.  Thanks for the info. I might hit you again when I get going.
Thanks!!
Rich