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Input DC blocking caps
Input DC blocking caps
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Old 2nd August 2016, 08:46 AM   #21
Bonsai is offline Bonsai  Europe
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Just go to Mouser and look for bipolar caps - good selection. Anything at 47 uF and above will do. Bypass with a 1 uF film as already mentioned above. I think you can pick the bipolar caps up for about 50c or thereabouts a pop.

I'm using bipolars decoupled with film on my preamp and have gotten very good results.

Don't agonize. Just get on with it.

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Old 2nd August 2016, 09:36 AM   #22
simon7000 is offline simon7000  United States
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http://www.mouser.com/Search/m_Produ...LS2qOegA%3d%3d

I would suggest ten of these in parallel. Five facing one way and five the other. Mounted vertically on a PC Card they will have the least induced microphonics and pretty much unmeasurable distortion even at high levels.

Electrolytic or oil filled capacitors do get damping from the liquid. The electrolytics age and the oil filled have more distortion. A feature to some!

Not cheap but better performance at a lower price than boutique capacitors.

The recommendation is based on measurements. No guarantee humans can hear a difference.
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Old 2nd August 2016, 11:07 AM   #23
erik777 is offline erik777  United States
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My balanced pre-amp has 10db gain, Input impedance: 100 kΩ 1 % ,Output impedance: 50 Ω 10 Ω

Will these pre-amp numbers change the 47uF or higher as suggested?

How does this look for example the + side: 2 x 150uF bipolar= 75uF bypass with 1uF film?

Quote:
Originally Posted by Bonsai View Post
Just go to Mouser and look for bipolar caps - good selection. Anything at 47 uF and above will do. Bypass with a 1 uF film as already mentioned above. I think you can pick the bipolar caps up for about 50c or thereabouts a pop.

I'm using bipolars decoupled with film on my preamp and have gotten very good results.

Don't agonize. Just get on with it.


Last edited by erik777; 2nd August 2016 at 11:09 AM.
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Old 2nd August 2016, 11:15 AM   #24
Bonsai is offline Bonsai  Europe
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Looks good Erik.

If you set your -3dB point at 10x lower or more than 20Hz, you will be good to go. So 75uF combined capacitance is fine.

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Old 2nd August 2016, 11:26 AM   #25
erik777 is offline erik777  United States
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Thanks Dude!

Quote:
Originally Posted by Bonsai View Post
Looks good Erik.

If you set your -3dB point at 10x lower or more than 20Hz, you will be good to go. So 75uF combined capacitance is fine.

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Old 14th September 2016, 11:39 PM   #26
Fast Eddie D is offline Fast Eddie D  United States
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Originally Posted by xrk971 View Post
No joke. Sure, they are big and industrial looking. But far from silly if you can get past the looks. They do sound very good. Basically foil coated plastic film in oil caps for cheap.

Here as used in a transient perfect XO:

Click the image to open in full size.

Click the image to open in full size.

Step and impulse response:
Click the image to open in full size.

But if you want a much more compact and decent sounding cap of about same value go with bipolar electrolytic for 47uF and bypass with a 1uF 400v MKT film cap. Compact low cost sounds great.
They're silly, and detrimental, in active electronic circuits. In passive crossovers, their microphonics and pickup of stray magnetic fields is not a factor.

I have some big old caps I pulled out of a ceiling fan (3.3 uF and 6.8 uF/ 400V) that I could use in a passive speaker crossover circuit. I probably won't, though.
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Old 16th September 2016, 12:46 AM   #27
restorer-john is offline restorer-john  Australia
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Bonsai is correct. Don't over complicate it.
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Old 17th September 2016, 12:03 AM   #28
Monte McGuire is offline Monte McGuire
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Input DC blocking caps
Is there any reason why the input impedance _must_ remain at 2K2Ω?

If you pushed it up to 10KΩ, you could use a 10F polypropylene, which is already sort of large, but not "motorcycle battery sized". Or, use a 22-47F electrolytic, which will be large enough to avoid distortion, and small enough not to have bad leakage problems.

Sure, you could also use a buffer, but maybe it's as simple as increasing the value of one resistor, and not adding an entire amplifier stage?
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