Large NON polarized

[Madmike2]

Hi one of the circuits i need to make calls for a 14839 uF cap. Thats huge, i have never seen NP bigger then 440. Is polarized acceptable for a zobel ?

[Madmike2]

Never mind disregard this n00b. I went to another calculater and got 8.38 uF which makes much more sense.

[PRR]

> i have never seen NP bigger then 440.

DigiKey has 6,800uFd 35V NP.

I have designed a mike-amp where that was a limiting factor. The gain-set resistor should be under 100 ohms, and must vary more than 100:1, which leads to a minimum value of about 1 ohm. It also should be DC-blocked, yes has no predictable DC, so it has to be NP. Is this design "impossible"? With the 6,800uFd NP it is just-reasonable. Bass limit is higher than 20Hz at the highest gain, but that actually works out well with typical sources and studios. The lowest-gain settings are above the 100 ohm goal, but that isn't a serious problem.

> calls for a 14839 uF cap.

Two of the 6,800uFd in parallel puts you in the ballpark for I think about $13.

> I went to another calculater and got 8.38 uF which makes much more sense.

Yes, be suspicious of incredible answers. Check your math. Look at the situation several different ways. 10,000uFd is about 1 ohm at the bottom of the audio band and much less than 1 ohm at higher frequencies: can you possibly be working at such insanely low impedances? Seems unlikely. If you are, can you really build it? In my super-low resistance gain-set scheme, fractional-ohm parasitics in the wiring and switch really screw-up the results.

I don't know if 8.38uFd is the right answer, but 14,000uFd is probably a wrong answer, or the right number for the wrong solution to the problem.

Remember if two approaches give two answers, at leat one is wrong, but maybe BOTH are wrong.

[Steve Eddy]

Originally posted by PRR
DigiKey has 6,800uFd 35V NP.

Got a part number for that? I was recently looking for an alternative to a Black Gate 4,700uF 35V non-polar and I wasn't able to find anything from anyone else above 2,200uF at that voltage in a non-polar let alone 6,800.

se

[quasi]

2 x 10,000uF polarised capacitors in series and back to back will give you 5,000uF non-polarised etc...

Back to back means either the negative terminal or postive terminals tied together.

Cheers

[PRR]

> Got a part number for that?

jeez, I knew someone would ask.

http://digikey.com

Put "6,800" in the Search-box, you don't get any cap.

Put "6800" in the Search-box, you get many things including "200 capacitors".

Click that, highlight "6800uF" and "Bi-Polar", Apply Filters.

Bingo. Digi-Key Part Number P1151-ND

I wuz wrong. It is only 6 volt, and only $2.44.

Indeed, at Bi-Polar 35V, DigiKey only has up to 470uFd, P1194-ND. They are only $1.08 each and cheaper for 10, so you could parallel-up a 4,700uFd 35V NP cap for $7.72. I found one listing for Black Gate 4,700uF 35V non-polar and it shows $120. So neglecting any special magic in a Black Gate, in effect you do 20 minutes soldering for a $112 savings, $336/hour, which is a fine labor-rate.

[Steve Eddy]

Originally posted by PRR
I wuz wrong. It is only 6 volt, and only $2.44.

I was pretty sure there had to be something wrong. I'd looked through the catalogs of about a dozen different electrolytic cap manufacturers.

Indeed, at Bi-Polar 35V, DigiKey only has up to 470uFd, P1194-ND. They are only $1.08 each and cheaper for 10, so you could parallel-up a 4,700uFd 35V NP cap for $7.72. I found one listing for Black Gate 4,700uF 35V non-polar and it shows $120. So neglecting any special magic in a Black Gate, in effect you do 20 minutes soldering for a $112 savings, $336/hour, which is a fine labor-rate.

Oh sure. But I rather liked the idea of a single case solution.

se

[Madmike2]

Originally posted by PRR
> i have never seen NP bigger then 440.



> I went to another calculater and got 8.38 uF which makes much more sense.

Yes, be suspicious of incredible answers. Check your math. Look at the situation several different ways. 10,000uFd is about 1 ohm at the bottom of the audio band and much less than 1 ohm at higher frequencies: can you possibly be working at such insanely low impedances? Seems unlikely. If you are, can you really build it? In my super-low resistance gain-set scheme, fractional-ohm parasitics in the wiring and switch really screw-up the results.

I don't know if 8.38uFd is the right answer, but 14,000uFd is probably a wrong answer, or the right number for the wrong solution to the problem.

Remember if two approaches give two answers, at leat one is wrong, but maybe BOTH are wrong.

It was to build a zobel for a passive x-over. One online calculator is on crack because the other two gave me nearly identical answers.

http://www.apicsllc.com/apics/Misc/filter2.html#TOP this one gave me the 14k cap zobel with a 8.3 ohm resistor.

http://www.mhsoft.nl/spk_calc.asp and this guy and a formula and a calculator gave me nearly identical 7.78 or 8.1 cap results with approx 8 ohm resistor.

So the top site has been removed from my bookmarks just in case

Go ahead and enter 6.5 RE and .61 Le and see what you get. Tell me that someone has a different formula and that the top link is for designing anti gravity units or something.

[Geoff]

Originally posted by Madmike2
Go ahead and enter 6.5 RE and .61 Le and see what you get. Tell me that someone has a different formula and that the top link is for designing anti gravity units or something.

The result is 8R1 and 14.4uF. It would seem that you did not enter Le in Henries!

[Madmike2]

BAHH ! ! How am i supposed to know that ? Everything should be in mH for the un initiated DAMN the british and their superior reading ability.

edit: corrected my spelling before Geoff could point it out. Leave my grammar alone. It never harmed anyone.