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shdesigns
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join:2000-12-01
Stone Mountain, GA
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Low-noise ceramic caps

Designed a simple headset amp. Was basically a replacement for a thru-hole one done surface mount.

I used NPO ceramics. That is supposed to be the best for low noise and linearity.

The board make a great microphone .

I suspect the client substituted different caps.

At 0.1uf, I can't find inexpensive film caps in 1206 package. I find acrylic in the same package, but have never used them; I'm used to polimer caps for audio.

Any recommendations?
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder

lutful
... of ideas
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join:2005-06-16
Ottawa, ON
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1 edit
Maybe 1206 package is just too small for 0.1uF C0G/NP0?
»www.avx.com/docs/catalogs/ccog.pdf

*** OK, AVX is recommending the "CB Series Polyester" chip capacitors for car audio systems in »www.avx.com/docs/masterpubs/filmchip.pdf

said by shdesigns:

Designed a simple headset amp ... board make a great microphone .

OK, I am mainly a digital guy but your comment got me thinking about a recent mysterious analog phenomenon.

My son was yanking my computer headphone and maybe some wire inside the stereo jack got a bit loose. I started hearing a local radio station very faintly and I can make it a bit louder by pressing the cord against my arm. I can hear it, he can hear it ... but I can't explain it to him except referring to the germanium diode + long wire antenna AM radios we used to build when we were in school.


SparkChaser
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reply to shdesigns
Ceramics can be a real killer. We had a product that had poor performance on some units. It turned out that some motors but not all had noisy gears that were being picked up by the caps


shdesigns
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reply to lutful
said by lutful:

Maybe 1206 package is just too small for 0.1uF C0G/NP0?

That is what I used C3216C0G1E104J

Or, intended, no reply back from client if they dropped something else in. 0.1 is used in my digital designs but are cheap, +80/-20% Z5U ones.

May try the acrylic or tanalum.
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder

lutful
... of ideas
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join:2005-06-16
Ottawa, ON
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I noticed that TDK part is listed as "obsolete - to be discontinued" at Mouser although Digikey still has some stock. Maybe that could be the reason they substituted.

However, Mouser lists quite a few low cost C0G 0.1uF caps in 1206 size from Murata, Kemet, etc.


aurgathor

join:2002-12-01
Lynnwood, WA
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reply to shdesigns
What's the purpose of those 0.1uF caps? Are they in the signal path?


shdesigns
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Yes, isolation and high pass on the input side.


shdesigns
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Ah, got reply from client:

"Sorry, I used a part we already stock for use on Test boards. I didn't know
it was special."

I spec'ed some acrylic film caps for production.
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1
said by shdesigns:

I spec'ed some acrylic film caps for production.

Please share the part# ... I need to give myself a crash course on capacitor specs.


shdesigns
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Cornell Dubilier Electronics FCA1206C154M-H1

Here's the PDF: »www.cde.com/catalogs/FCA.pdf


aurgathor

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reply to shdesigns
said by shdesigns:

Designed a simple headset amp. Was basically a replacement for a thru-hole one done surface mount.

I used NPO ceramics. That is supposed to be the best for low noise and linearity.

The board make a great microphone .
Any recommendations?

If that headset also includes a mike, you can now take it out, and cost reduce the design.

If you actually have the board they made, I'd probably replace suspected caps one by one with know good ones to find out which one(s) is(are) responsible.

Personally, I don't like ceramics in signal path, although some are admittedly better than others.
--
Wacky Races 2012!

public

join:2002-01-19
Santa Clara, CA
reply to shdesigns
said by shdesigns:

At 0.1uf, I can't find inexpensive film caps in 1206 package. I find acrylic in the same package, but have never used them; I'm used to polimer caps for audio.

Acrylic is a low temp polymer not really compatible with lead free reflow.
Why not use 1210 or bigger for multiple sources of film?

lutful
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Ottawa, ON
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said by public:

Acrylic is a low temp polymer not really compatible with lead free reflow.

The FCA datasheet says the caps have lead-free solder tabs and is rated for 200s@235C ... compared to 40s-80s@220C required for lead free soldering.