COG/NPO vs new small package SMD PPS and PET for high frequency decoupling and filter - diyAudio
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Old 18th April 2010, 02:44 PM   #1
qusp is offline qusp  Australia
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Default COG/NPO vs new small package SMD PPS and PET for high frequency decoupling and filter

Hi there, in putting together a few orders lately and in research for possible tweaks for some SMD builds i'm doing currently and possible small first time design projects. I started to notice the prevalence of new smaller package (0603 and 0805) PPS and PET smd film caps. I have experience and knowledge of their superiority in the realms of analogue filters, but started to think about the possibility of using pps for digital supply decoupling and compensation applications.

I got to thinking about how devices (opamps and transistors are what I had in mind) rely on the characteristics (MLCC) of ceramics and in particular NPO/COG particularly in very high frequency and/or heat. but I have started to see these lines becoming blurred somewhat mainly in HF filtering, but more and more in digital HF supply decoupling and wondered how an amp i'm building (a dual mono version of perander's QRV08 as the pre/buffer/headout of my dac) might react if I replaced the npo for opamp compensation with a panasonic 0805 pps. I googled it and noticed there are a few papers getting around making these type of comparisons, but nothing specific to this purpose.

anyone else here doing anything like that and can share knowledge and/or experience? i'm loving the wima and evox/rifa PPS and PET smd lately, but they mainly come in larger packages. I ask the question in a general sense too as well, who here is starting to find themselves replacing the higher quality ceramics with films now that the packages are getting smaller and for what purpose

thanks for reading

Last edited by qusp; 18th April 2010 at 03:05 PM.
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Old 18th April 2010, 05:45 PM   #2
jcx is online now jcx  United States
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is a good read - has smt C0G, pet, pen, pps comparison measurements

audiophiles claim low DA is a major quality spec - not that they offer reasonable physical/psychoacoustic basis for the claim

I haven't looked for pps distortion yet, C0G can be low, I've seen ~ -110 dB which went away when I replaced with polystyrene in through-hole - which won't survive smt soldering

Last edited by jcx; 18th April 2010 at 05:48 PM.
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Old 19th April 2010, 01:22 AM   #3
qusp is offline qusp  Australia
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hey jcx, thanks mate, seriously, I had read that document a little while ago as I have been using the evox/rifa (now kemet) smd pps and hadnt been able to find that again a couple of nights ago when I was looking for the direct comparison. there is a dodgy pdf file that google would keep on throwing at me with a very appropriate link title, that crash safari every time I went to open it , very informative it was :| so it does seem that apart from very slightly higher noise that smd films have caught back up and overtaken COG, a bit pricier and until recently only available in the sizes =>1210. so seems it could be worth trying the pana PPS in this and other buids. since that paper things have continued to march onward as well, with 0603 and 0805 becoming more widely available.

Last edited by qusp; 19th April 2010 at 01:25 AM.
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