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Old 4th February 2011, 01:27 PM   #1
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Default Cmoy Caps

hey guys
am building a cmoy based on opa2132pa op amp, the source would be Sansa Fuze (headphone out and line out)....i read a lot about caps and resistances, and i would like to know what caps i should go for. previously i had decided:

1000mf power caps (nichicon es, bipolar)
1mf wima in the signal paths

i would like to know if these would be fine for my setup.
my headphones are Sennheiser HD212pros, with 32ohms impedance.

also, can i use nichicons as the input caps too?
would be buying from Mouser India.provide links if you can.

Thanks in advance
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Old 4th February 2011, 01:47 PM   #2
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The power supply caps don't need to be bipolar, you can use almost any polar electrolytic cap. Aim for low ESR. Low voltage types like 16V or so are perfectly fine, but higher voltage ones (50V for example) work just as well.
Wima for signal path is fine, try to find MKS10. You can parallel caps if necessary. For availability also check ebay, but be aware that there are fake parts out there too...
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Old 4th February 2011, 01:55 PM   #3
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But what about the rating? 1000mf? or 470 mf would be enough?
what about the wima ratings? also, can i substitute the wima with some nichicons?
Thanks
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Old 6th February 2011, 08:22 PM   #4
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Can you post a schematic? How do you create the pos/neg voltage? Via resistors, or discrete pnp/npn, or rail splitter?
If I had to guess I'd say 1uF for the Wimas and 470uF for the PSU caps. I'd go with film and foil capacitors for the audio signal.
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Old 7th February 2011, 06:03 AM   #5
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yep yep, here's the schematic

i am using resistor dividers for virtual grounds
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Old 7th February 2011, 10:00 AM   #6
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With 0.1uF and 100k at the input, the cutoff frequency f=1/(2*pi*R*C) is at 16Hz. With C=0.47uF it goes down to about 3Hz, which is also okay but not necessary.
I'd stick with the values in the schematic. Use a film and foil capacitor for the input, stay away from electrolytics (polar or nonpolar) for coupling caps.

Just like Mooly stated in your other thread, the PSU resistors have to be tightly matched or you will have a significant DC offset at the output. I doubt that there will be an audible difference between 220uF, 470uF and 1000uF caps in the PSU.
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Old 8th February 2011, 08:21 AM   #7
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hey rodeodave
the input caps can be bipolar electrolytic, can they be?
i have a sansa fuze, and a line out cable diy (In Ear Matters: [REVIEW & MOD] FiiO L6 LOD for Sansa Fuze)
and the author used bipolar nichicon ES caps as well as bipolar Blackgates.
i was building this cmoy for using with a sansa fuze line out only, and this near to a tutorial shows nichicon caps used at input stages (my thoughts were, simply place these at the input in the amp, and i would be done).....worth it? or rather, would it be good to place these nichicon es caps in the input rather than on the dock connector?

thanx
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Old 11th February 2011, 06:28 AM   #8
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Exclamation TLE...2426?

Quote:
Originally Posted by noobman92 View Post
yep yep, here's the schematic

i am using resistor dividers for virtual grounds
you could get some samples from TI of the TLE2426 virtual rail splitter 'chip' and you won't need to worry about resistor matching. i'm not quite sure how that adds or subtracts from the sound but it works great in my CMoy
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Old 12th February 2011, 04:27 PM   #9
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You don't need perfectly matched voltage splitter resistors. It shouldn't affect the DC-offset.

Regarding caps, IMO you should use large "PSU" caps to get low crosstalk throughout the audio spectrum. Fancy caps might sound a little bit better but I'd recommend you save your money for future builds.

If this is a portable amp the TLE2426 is an attractive option since you won't be needing two large caps, just one medium size. Be sure to use small decoupling caps in close proximity to the OPA2134's power pins (0,1 uF or so from V+ and V- to ground, or just a small cap from V+ to V-) for stability.

If size doesn't matter you should go for a polypropylen cap not a polyester one as input cap. The cost will be about the same. I'd never use an electrolytic as input cap unless the size of a film cap makes it impossible to use. Even the best and most expensive like Black Gate Hi-Q sounds worse than cheap film caps.

I'm surprised to hear there's DC-offset from the line out of an audio player such as yours. I thought they all had internal caps. If it's so you have to use a cap and you can put it in the amp just as well, but be sure it's in front of the pot. By doing so you don't have to worry about size and use polypropylen, not electrolytic or polyester.
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