PDA

View Full Version : Electrolytic caps


webercw
03-08-2010, 09:15 PM
Why are the Bennic electrolytic caps so much cheaper than the polypropylene caps? I'm looking a 130mfd cap for a RLC Parallel notch filter. The price for the polypro really hurts my budget (first project). Is there a good reason not to use electrolytic and save money?

-Charlie
Andy_G
03-08-2010, 09:31 PM
Why are the Bennic electrolytic caps so much cheaper than the polypropylene caps? I'm looking a 130mfd cap for a RLC Parallel notch filter. The price for the polypro really hurts my budget (first project). Is there a good reason not to use electrolytic and save money?

-Charlie

There are possible differences in the sound of poly's and electros in high level systems, also possible long terms stability issues with some electros.... but for a first project, in an RLC notch, a reasonable quality non-polar electrolytic, such as I assume the Bennic is, should be more than adequate.
dcibel
03-08-2010, 09:39 PM
Electrolytic are much less expensive than polypropylene, period. For 130uF, I would surely buy the electrolytic cap as well. A Poly of that high value would be a very expensive purchase and a huge cap.
Wolf
03-08-2010, 11:40 PM
Electrolytic are much less expensive than polypropylene, period. For 130uF, I would surely buy the electrolytic cap as well. A Poly of that high value would be a very expensive purchase and a huge cap.

Just less than $50 for a Solen 200uF, and about 2" Dia x 4.5" long. So- it's ~$50, but not insanely expensive.
Later,
Wolf
dcibel
03-08-2010, 11:44 PM
As long as it's not more expensive than the driver it's connected to...;)
Wolf
03-09-2010, 12:03 AM
As long as it's not more expensive than the driver it's connected to...;)

Most of the time I agree with that sentiment.
Well said,
Wolf
webercw
03-09-2010, 01:24 AM
As long as it's not more expensive than the driver it's connected to...;)

Which would be the case with this design. I'd rather spend on the drivers possibly the inductors. There are other places the money would be better spent to improve my sound quality. Heck, with the savings over a poly cap I'd almost have enough to build myself a chip amp. :cool:
Chris Roemer
03-09-2010, 01:43 PM
Which would be the case with this design. I'd rather spend on the drivers possibly the inductors. There are other places the money would be better spent to improve my sound quality. Heck, with the savings over a poly cap I'd almost have enough to build myself a chip amp. :cool:

The only problem with npe's (IMO - besides their limited service life - like 20 to 30 years) is that PE's (and probably MOST) tend to run about 10% higher than their rated value. Depending on the notch, being off by 10% could be an issue, sliding the aim point off the target, and possibly worsening the situation. If you have a WT (or other LCR meter), and if the error is in the right direction, you could probably compensate by unwinding a coil to get back to the target freq.
Froste
03-09-2010, 02:24 PM
If you need 130uf, I would get a 100 ncp and a 25 poly and odds are together you will be deadon 130.
Andy_G
03-09-2010, 04:47 PM
If you need 130uf, I would get a 100 ncp and a 25 poly and odds are together you will be deadon 130.

Mad have some 10uF poly caps on sale for 60c each
Use 13 wired in parallel, you have 130uF of poly cap for less than $8 :D
tom_s
03-09-2010, 08:05 PM
Mad have some 10uF poly caps on sale for 60c each
Use 13 wired in parallel, you have 130uF of poly cap for less than $8

+1 on the Mad 10uF polys! My next project calls for a 125uF on the mids. Looks like I'll be ordering another bag of those yellow buggers!:D
Andy_G
03-09-2010, 08:27 PM
+1 on the Mad 10uF polys! My next project calls for a 125uF on the mids. Looks like I'll be ordering another bag of those yellow buggers!:D

Please show pics of the x-o when built ! :D
tom_s
03-09-2010, 09:26 PM
Please show pics of the x-o when built !

Will do. There's also a 150uF shunt in the woofer leg. That might end up being an NPE :D

We are planning a trip to Australia this summer. You want me to bring a couple dozen your way?
Face
03-09-2010, 10:13 PM
Will do. There's also a 150uF shunt in the woofer leg. That might end up being an NPE :D

We are planning a trip to Australia this summer. You want me to bring a couple dozen your way?
In today's climate, I wouldn't want to bring a bag of film caps on an airplane.
Andy_G
03-09-2010, 10:39 PM
In today's climate, I wouldn't want to bring a bag of film caps on an airplane.

why should global warming stop you taking caps on a plane ?? :rolleyes: ;) :D
Andy_G
03-09-2010, 10:42 PM
Will do. There's also a 150uF shunt in the woofer leg. That might end up being an NPE :D

We are planning a trip to Australia this summer. You want me to bring a couple dozen your way?

Nah, not to bother, I'll maybe buy some stuff from Mad at some stage if I see a 'special' I like, so if there's any left I might add a few of them to the order if still available.

Where abouts are you visiting ?
carlspeak
03-10-2010, 07:24 AM
Why are the Bennic electrolytic caps so much cheaper than the polypropylene caps? I'm looking a 130mfd cap for a RLC Parallel notch filter. The price for the polypro really hurts my budget (first project). Is there a good reason not to use electrolytic and save money?

-Charlie

I'm not sure any of the responses up to this one really answered your question.
I believe NPE's are much cheaper simply because of how and what they are made of. Film caps OTOH, require tight tolerances on film quality and winding specs.

I also think a bag of NPE's would look much more menacing than film types to a TSA inspector. Have you ever seen those old, high uF value Compulytics used in vintage AR LST's and 3a's?