Ceramic Capacitor Negative Bias?

[user 37518]

According to Cyril Bateman's series of articles on capacitor sound,  one of the best capacitors for audio are ceramic NP0/C0G, yet I have seen very little of them used in pro audio equipment applications, they are usually very small to be used as coupling caps, but for other stuff such as integrators and filters, mostly polypropilene is used. It almost seems like manufacturers don't want to gamble using ceramics due to their bad rep. Thoughts?

 

[john12ax7]

It can take a while for perception to change.  For many people,  myself included,  their first exposure to ceramics was other inferior types unsuitable for high quality audio.  But these days I'm using  C0G/ NPO for some through hole designs and it's almost a must for SMT.

The other issue is one of marketing. The public accepts Wima film as high quality,  it's a harder sell with ceramic.

 

[Bo Deadly]

C0G refers to the dielectric which is a sort of class of quality with C0G being the best. C0G are basically ideal capacitors. Unlike the other dielectrics (like X7R which is the next step down), C0G has very low dependence on temperature, they're not microphonic, they don't loose capacitance with DC across them, etc. But over ~10nF, they start to get expensive and scarce enough that film becomes favorable. But once you get to ~1uF, film gets scarce and expensive enough that electrolytics are favored. But unlike C0G ceramics and film, electrolytics do have some imperfections that might dictate how they're used. In particular, they can distort if used in a low impedance circuit with a large voltage across them and they're leaky. But with the low ESR (aka "audio grade") this is almost never an issue and it is very unusual to run into a circuit where a few nA of leakage would matter.

 

[user 37518]

C0G refers to the dielectric which is a sort of class of quality with C0G being the best. C0G are basically ideal capacitors. Unlike the other dielectrics (like X7R which is the next step down), C0G has very low dependence on temperature, they're not microphonic, they don't loose capacitance with DC across them, etc. But over ~10nF, they start to get expensive and scarce enough that film becomes favorable. But once you get to ~1uF, film gets scarce and expensive enough that electrolytics are favored. But unlike C0G ceramics and film, electrolytics do have some imperfections that might dictate how they're used. In particular, they can distort if used in a low impedance circuit with a large voltage across them and they're leaky. But with the low ESR (aka "audio grade") this is almost never an issue and it is very unusual to run into a circuit where a few nA of leakage would matter.

Yeah, thats not what I was asking, I already know that, my question is why manufacturers do not commonly use C0G types in stuff like say EQs or filters favoring film capacitors, a search in Mouser revealed C0G capacitors up to 0.47uF, more than enough for most filtering applications.

 

[Bo Deadly]

I did answer your question. Cost and supply. 470n for a C0G ceramic is huge. You can't design something around one part on mouser that costs 10x that of the equivalent film cap.

 

[user 37518]

I did answer your question. Cost and supply. 470n for a C0G ceramic is huge. You can't design something around one part on mouser that costs 10x that of the equivalent film cap.

Didnt look at the prices!, for lower capacitances say 100nF they both seem to cost around the same C0G and PP.

 

[JohnRoberts]

According to Cyril Bateman's series of articles on capacitor sound,  one of the best capacitors for audio are ceramic NP0/C0G, yet I have seen very little of them used in pro audio equipment applications, they are usually very small to be used as coupling caps, but for other stuff such as integrators and filters, mostly polypropilene is used. It almost seems like manufacturers don't want to gamble using ceramics due to their bad rep. Thoughts?

NPO/COG are very linear so good for filters and EQ, might get expensive for larger DC blocking applications, but I haven't looked at prices lately.

Availability of a decent selection of NPO/COG smd caps is a relatively recent development. I had one project early this century, now almost 2 decades ago, where I tried to use decent film dielectric capacitors for audio filters in a DSP project I was working on. The contract manufacturer we used melted the film caps (literally, changed values and distorted the components), despite them being rated for SMD reflow temperatures.  If COG/NPO were available to me back then I would have gladly specified them in.

I vaguely recall these (cog/npo) caps being used back in the day for stabilizing crystal time bases because of their good linearity and temperature stability but were IIRC only available in small values for that one application. Thankfully the demand for good audio capacitors that can handle SMD processes has increased availability of these into a wider range of useful values. At least for SMD. This recent popularity may have come too late for development as through hole components (a fading technology).

FWIW my favorite dielectric (polystyrene) could barely survive wave soldering, let alone reflow.  :


JR

 

[user 37518]

FWIW my favorite dielectric (polystyrene) could barely survive wave soldering, let alone reflow.  :


JR

PS caps are a dying breed, there are only few manufacturers that still make them and you cant find many different values, still they are some of the best caps, as long as you dont heat them up too much.