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different value capacitors in Parallel.
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markie View Drop Down
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    Posted: 25 July 2021 at 3:19pm
I'm trying to produce a crossover (hi pass filter) for some Celestion KR2s. I have one to copy but intend to seriously upgrade the quality of the components.

In the original, C1 is 8uF and C2 is 4uF. I'm wondering if I can replace C1 with 3u3 and 4u7 in parallel.

For C2 I can either use a 4u7 or 2 x 2u2 in parallel. Close enough????

I have wound an inductor of the same value, but have used 1.2mm wire instead of the original 0.7mm.

All caps will be 250v polypropylene.

Anything I need to be careful of, or any comments?????


Edited by markie - 25 July 2021 at 3:21pm
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fatfreddiescat View Drop Down
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Points: 1083 		Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2021 at 4:23pm
Not a problem at all to use the caps in parallel, re the 4uf then you are approx 10% out, quite likley not audible. The inductor using larger guage wire will have a lower DCR, how that affects the system is very much dependant on it's location in the circuit, if in series with the LF then will change the apparent 'QTS' of the driver. To be honest, unless the caps are goosed or replacing an iron cored inductor with an air cored, then probably not a lot to gain in changing things.
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snowflake View Drop Down
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Originally posted by markie markie wrote:

I'm trying to produce a crossover (hi pass filter) for some Celestion KR2s. I have one to copy but intend to seriously upgrade the quality of the components.

In the original, C1 is 8uF and C2 is 4uF. I'm wondering if I can replace C1 with 3u3 and 4u7 in parallel.

For C2 I can either use a 4u7 or 2 x 2u2 in parallel. Close enough????

I have wound an inductor of the same value, but have used 1.2mm wire instead of the original 0.7mm.

All caps will be 250v polypropylene.

Anything I need to be careful of, or any comments?????

3.3+0.68 gets you closer to 4uF with standard values.

or get some made to spec:
https://www.ansarcap.com/

maybe get lots of 4uF and use two in parallel for 8uF.
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markie View Drop Down
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From my limited knowlege I believe the original is an 18dB hi pass filter so inductor is across the tweeter and caps are in the -HF line. I believe this would indicate the tweeters are out of phase?

Probably not worth getting caps made. I have 6 cabs and am only short of 1 crossover. But of course I would replace a pair, then see if the difference was worthwhile. If it is I would replace the remaining 4. 

I am also trying to make use of what I have (loads of caps and 1.2mm wire).

Thanks for the input, I'll give it a try.
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kedwardsleisure View Drop Down
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Points: 4947 		Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2021 at 7:48pm
this is how convair make their crossovers, multiple parallel capacitor options on the pcb.
Kevin

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snowflake View Drop Down
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Originally posted by markie markie wrote:

From my limited knowlege I believe the original is an 18dB hi pass filter so inductor is across the tweeter and caps are in the -HF line. I believe this would indicate the tweeters are out of phase?


not necessarily the caps could both be on either side
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markie View Drop Down
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Actually I got that slightly confused. The caps are on the +HF line from the input, but then go to - terminal on tweeter hence my assumption that HF is out of phase.
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Points: 10919 		Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2021 at 9:16pm
Originally posted by markie markie wrote:

Actually I got that slightly confused. The caps are on the +HF line from the input, but then go to - terminal on tweeter hence my assumption that HF is out of phase.


If they’re third order slopes then an inverted alignment produces a first order allpass response, which has less phase distortion.
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markie View Drop Down
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Points: 4570 		Post Options Post Options   Thanks (0) Thanks(0)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2021 at 10:05pm
Just found some 0.82uF which I guess in parallel with a 3u3 would be closer to the 4uF I need.
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