Electronics > Projects, Designs, and Technical Stuff
Non microphonic, 1uF SMT cap in a high Z circuit?
Vovk_Z:
I would like to try C0G. It's can be almost as good as film with microfonic effect (and more temperature stable).
You dont need 0.1 uF parts, today we can buy 0.22 uF 1206 parts easily (even I have 20 pieces).
1 uF needs only 4-5 caps in parallel and they take very few space.
And yes, cheap (I mean usual) tantalum doesn't fit integrator circuits. I don't know about wet tantalum (haven't worked with) but it's price and parameters are not good enough too.
SeanB:
Wet tantalum is not at all bad with leakage, but will need a permanent bias to keep it that way. I did take 100 that had been in storage for around 2 decades, and measured them, half with no reformation, and half with them connected to 20V via a 1k resistor for a night. No difference really in capacitance, ESR or other parameters, just some were off the bat shown as near ideal capacitor, and others were shown with slight leakage of around 100k-1M. they were all 10uF 25v units. Do not use rubber seal ones, they only last 5 years like electrolytics, while the glass seal ones last till they corrode through from the outside. Rubber seal is cheaper, but not worth it if you are paying for tantalum. I was changing them by the hundreds.
But for low noise use polyputthekettleon, and use those in sealed housings, as the bare ones are a little sensitive to environmental parameters. Bare are cheap, and often available in SM forms, but temperature and humidity swings will cause havoc with leakage, plus PCB cleaning and solder flux residue as well.
Kleinstein:
100 nF C0G is available with soft termination.
If really needed one could consider a well placed slit to reduce the board stress.
With audio I see no absolute need for 1 µF: 100 nF should be plenty to get a cross over below 2 Hz and thus only marginal effect at 20 Hz.
If audio noise is critical one may want the extra attenuation behind the AZ OP alone for noise reasons. So one may not even need 100 nF.
With just a few 10 mV to compensate even 10 nF could be sufficient.
dmills:
Been doing some spice sims, and 1M/100n plus the usual non inverting passive pole at the integrator input from the same values as an RC network, an RC network on the output of the integrator a decade above the 1M/100n time constant to remove the chopper artefacts up at 800kHz and a 100:1 divider into the inverting node of whatever I am trying to correct looks good in ltspice.
And I can do that with all C0G! There is NOTHING wrong with ceramics in audio as long as you stick with type 1 dielectrics.
Just got to build the damn thing now and we will see how we go.
Thanks for the input guys.
Yansi:
Iam looking forward for your 1uF and 100nF in C0G.
Expensive nonsense, if you could find any.
1uF MKS will likely be cheaper.
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