crossover needs 75 uF caps

11tsteve

i have some Infinity RSb's which i am recapping, and would like to use Clarity caps (SA or PX... not sure which would be better) if possible. I used Sonicap Gen 1's on my Polks, and want to try something different. i might even replace the high pass Sonicaps in mt 11T's with Claritys, as i have been reading they are just a tad smoother in the high frequencies.
so with the RSb's, each Xover requires 2 75 uF caps, which doesn't seem to exist in the better grade caps, so wondering how people go about such a situation.

here is the schematic for the Infinity's... http://www.infinity-classics.de/technik/manuals/RSb_technical_sheet.pdf

even with a +- of 5%, and 82uF is too much and 68uF is too low, correct?

NSklavos

You can use a 68uF and a 6.8uF in parallel with it to give you 74.8uF, which is close enough.

phocion

Yes, you should try to get close to the specified capacitance.

Fortunately, caps in parallel are added, so 3x 25 uF in parallel will give you a toal of 75 uF, as would a 50uF and a 25uF (The 68+6.8 clarity is also close enough to 75, if you want to go that route). Check your board space and see what combo of caps will fit, and go from there.

soundfreak1

Cant speak to the other caps however i ised the clairty SA caps in my 5jr+ rebuild and am very pleased.

11tsteve

ok folks. i wasn't sure the parallel thing would work... i am a bit of a newb at this, but was hoping that was the answer. the infinity board is actually quite large, and is not actually pcb, so i can pretty much arrange many differing configurations.
and thanks soundfreak1 for the specifics...

F1nut

When using caps in parallel you want to use values that are as close as possible to each other. The suggestion of using a 68uF and a 6.8uF is not good advice.

11tsteve

so 3 25uF would possibly be the best scenario? or in the Clarity, possibly a 33uF + a 39uF, which should be close enough for tolerances?
does there need to be some sort of barrier between them, such as a layer of hot glue between the caps, or are they fine stacked right next to each other?

Face

They should be split evenly, so 3 x 25uf would be best. No need for a barrier between them, but a layer of hot glue would prevent them from banging around.

phocion

I used double sided sticky foam tape between the caps, which gives them some cushion, and helped hold them in place for the hot glue.

For the cap values, I was under the impression that parallel caps with differing values could benefit from having significantly different uF (usually by a factor of 10), because the impedance is reduced across across a greater range of frequencies, even though capacitance is additive. I don't know how that would translate to differences in sound, so maybe it turns out to be bad? Face or F1, any additional insight here?

skrol

F1nut wrote: »

When using caps in parallel you want to use values that are as close as possible to each other. The suggestion of using a 68uF and a 6.8uF is not good advice.

True, mathematically the 68uF + 6.8uF works but in practice it does not sound right. I know because I tried it.

F1nut

phocion wrote: »

For the cap values, I was under the impression that parallel caps with differing values could benefit from having significantly different uF (usually by a factor of 10), because the impedance is reduced across across a greater range of frequencies, even though capacitance is additive. I don't know how that would translate to differences in sound, so maybe it turns out to be bad? Face or F1, any additional insight here?

What you're referring to is a bypass cap. In my experience, that should be avoided at all cost when using high quality film caps.

phocion

Hmm, I think I got it. Found a few pages on capacitor cascades and bypass caps, and the smaller value caps are used to bolster the higher frequencies, supporting a smoother wide frequency spectrum. I expected that from things I have seen with bypass caps on boards with chips and voltage.

Sounds great, but the x-over is designed to split off the highs to the most appropriate speaker, so pushing a small value cap like a 6.8uF in the mids may be counter productive, since the frequencies that it will be most efficient at conducting will be outside the desirable range of the mids.

Also, it seems that people (here and elsewhere) suggest that quality caps eliminate the need for bypassing entirely. So, the correction mentioned by F1, Face, and Skrol makes sense: get the 25uF caps, and good luck with your mods!

11tsteve

thanks again for the info folks... going to get my order in so i have a Thanksgiving weekend project to work on.

Face

phocion wrote: »

For the cap values, I was under the impression that parallel caps with differing values could benefit from having significantly different uF (usually by a factor of 10), because the impedance is reduced across across a greater range of frequencies,

I would only do this in power supplies.

zingo

Face wrote: »

I would only do this in power supplies.

I agree. I've done this in power supplies and it works great for filtering and can prevent surges caused by single, large caps.

I would prefer to go for one, correctly valued cap, and if they are not available online, many manufacturers will make them for you for little or now extra fee; I've done it a few times with a few different manufacturers.

zingo

Dayton Audio offers a 75uf poly cap which is a solid replacement choice; but not an upgrade like a Clarity Cap would be.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=027-445

11tsteve

i did see that zingo, but i really wanted a higher quality cap in the mids. i also saw that i believe clarity would make to order, but with a lengthy turn around. if it is better, i would do this, but i am not aware of what all of the pros and cons are of using multiple caps in parallel.

westmassguy

11tsteve wrote: »

i did see that zingo, but i really wanted a higher quality cap in the mids. i also saw that i believe clarity would make to order, but with a lengthy turn around. if it is better, i would do this, but i am not aware of what all of the pros and cons are of using multiple caps in parallel.

As long as all the caps are of equal value, there is no downside, other than cost. Widely different values on the other hand, can cause problems. That's not to say I haven't done it, but I would never do it on the high-pass or mid-band pass circuit.

11tsteve

it turns out Erse has a 250V and a 400V 75Uf cap.....

http://www.erseaudio.com/Products/PulseXAll?range=101%2C142%2C142

does anybody have and opinion/advice on the use of these for my Infinity crossovers?? and i would be thinking the 250V would be the one i want?

F1nut

Either will work, but there's no need to use the 400V version, which is also going to be much larger. Get the 250V version.

11tsteve

Thank you sir. Just checking if erse would be as good as the clarity caps quality-wise.

F1nut

No, Erse would not be as good as Clarity or Sonicap.

11tsteve

ok, i really appreciate the help and patience so far, and thanks for sticking with things. due to job, holidays, and funerals, this project is going slow, which is fine, but i have more questions.
i have finally had a chance to disassemble the speakers, pulled the drivers and crossovers, and started refinishing the veneer. this morning, i was going to start putting together orders for caps (i know, finally), and have found these have a completely different design than the spec sheet. as with any speaker life, these underwent design changes during production i am sure, but it seems such a difference, i was curious as the the large disparity in capacitance.
i actually have three crossovers, one being of the original spec, these two with the differing values, and the inductors are of differing values on the matching two.

tweet cap went from 3.5 uF to 7.5 uF
mids from 2 x 75 uF to a 12.5 uf + 16 uF
low pass from 100 uF to 125 uF.

tweet inductor from .3mH to .1 mH
mids from a 1.5mH + 2.0mH to .6mH + 2.0mH
low from a 2.5mH to a 2.0 mH.

just curious how especially the mids might have dropped so much in values? the drivers are the originals indicated on the spec sheet...

i guess the mid caps will at least be cheaper than ordering the 12 25uF i was going to need.:cheesygrin: unfortunately, the values are not typical... figures.

Face

It's possible there were driver changes as well. Changing from an 4 ohm to 8ohm mid would justify the large capacitance difference in the midrange circuit.

11tsteve

i see.
well, i really wanted to try the PX line of Clarity caps, but the values are difficult. Sonicap would work for some but not all. so far i have contacted Clarity directly to see if they can help me out.