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coupling cap too big?

post #1 of 10
4/18/11 at 2:27pm
Thread Starter 

I'm considering upgrading input cap on cmoy. I have found some 10uF Vishay Roederstein MKP1839 polypropylenes ( http://www.vishay.com/docs/26022/26022.pdf ). At page 5 it seems 10uF 160Vdc is too much? From that datasheet I understand that smaller cap work better on higher frequencies. What would be nice value if I have plenty of space in amp enclosure? 1uF?

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post #2 of 10
4/18/11 at 2:41pm

1uF should be more than enough, but I wouldn't worry about such things with a CMOY.

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post #3 of 10
4/18/11 at 2:46pm

I like to use this one myself.

 

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post #4 of 10
4/18/11 at 5:03pm

The best input coupling cap would be NO input coupling cap - so long as you trust your source, there shouldn't be any DC coming out of it

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post #5 of 10
4/18/11 at 6:49pm

X2
 

Quote:
Originally Posted by El_Doug View Post

The best input coupling cap would be NO input coupling cap - so long as you trust your source, there shouldn't be any DC coming out of it



 

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post #6 of 10
4/18/11 at 7:51pm

IMHO - Too big (physically, unless you REALLY don't have any space limitations like you mentioned)  and too expensive (I'm assuming here, based on size and material) for a CMOY. Basically for a CMOY, extreme overkill - the 1uF's should suffice as mentioned by others.


Edited by IcantHearU - 4/18/11 at 7:54pm
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post #7 of 10
4/19/11 at 6:16am
Thread Starter 
Quote:
Originally Posted by IcantHearU View Post

IMHO - Too big (physically, unless you REALLY don't have any space limitations like you mentioned)  and too expensive (I'm assuming here, based on size and material) for a CMOY. Basically for a CMOY, extreme overkill - the 1uF's should suffice as mentioned by others.



It's not really that expensive compared to other caps. It's only 5$ each.

 

I calculated (http://tangentsoft.net/audio/input-cap.html chapter "Bass roll-off") that I have acceptable bass with my current ~0.4uF Wima MKP10. I'm more concerned about high frequency and phase distortion. As I understand more capacitance gives me less phase distortion in low frequencies but kills high frequencies.

 

Does 10uF really affect high frequencies so much?

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post #8 of 10
4/19/11 at 9:08am

 

Quote:
Originally Posted by tola555 View Post

Does 10uF really affect high frequencies so much?


Only because as caps get larger (more capacitance) they generally sound worse. If size constraints are placed the problems really stack up quickly.

 

If you have the physical room for a low to mid-quality 10uf cap, you have the physical room for a higher quality 1uf cap. 

 

When running the cap roll-off frequency calculators, it is advisable to calculate for a -3db point several octaves below the lowest frequency you want reproduced "cleanly." somewhere between 2 and 5hz is the general guideline. Maybe 10hz if you dont care about whats happening at 20-40hz. Tangent goes into some detail on this, but its worth restating. 


Edited by nikongod - 4/19/11 at 9:18am
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post #9 of 10
4/19/11 at 12:11pm
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post

X2
 



 


I removed cap from soundcard, it's left outputs -5.5mV and right 8.5mV DC. Cmoy output has 0.x mV DC offset.

 

My cmoy is 2xAD8610, and ground is TLE2426, AD8610, BUF634 as here: http://tangentsoft.net/elec/bitmaps/vgrounds/gnd-channel.png

 

I'm not sure removing cmoy cap works, amp has gain 5. Or then I could use pin 1 and 5 on AD8610 to trim offset? http://www.farnell.com/datasheets/59786.pdf says on page 14 that 50K trim pot could be used.to trim +-3.3mv. With gain of 5 worst offset at output would be 5*8.5=42.5mV. Not much help from -+3.3mV trim

 

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post #10 of 10
4/19/11 at 12:49pm

I would say "go with a coupling cap".

If the offset from the sound card were

lower and the gain of the amp less, you could

get away with it. The offset trim on the op amp

is not meant to compensate for global offset, only

offset local to the op amp.
 

Quote:
Originally Posted by tola555 View Post




I removed cap from soundcard, it's left outputs -5.5mV and right 8.5mV DC. Cmoy output has 0.x mV DC offset.

 

My cmoy is 2xAD8610, and ground is TLE2426, AD8610, BUF634 as here: http://tangentsoft.net/elec/bitmaps/vgrounds/gnd-channel.png

 

I'm not sure removing cmoy cap works, amp has gain 5. Or then I could use pin 1 and 5 on AD8610 to trim offset? http://www.farnell.com/datasheets/59786.pdf says on page 14 that 50K trim pot could be used.to trim +-3.3mv. With gain of 5 worst offset at output would be 5*8.5=42.5mV. Not much help from -+3.3mV trim

 



 

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