[sdiy] Where to buy ceramic caps

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Dec 30 09:38:34 CET 2017

On Dec 29, 2017, at 11:47 PM, Andre Majorel <aym-htnys at teaser.fr> wrote:
> On 2017-12-29 22:51 -0800, rsdio at audiobanshee.com wrote:
>> On Dec 29, 2017, at 6:19 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
>>> I've just laid out a quad opamp relaxation oscillator with
>>> four different resistor values (10k, 100k, 1M, 10M) for
>>> testing all 12 values of my capacitors to give frequencies
>>> in the hundreds of Hz.  The frequency is 1/[2 ln(3) RC], so
>>> with this I can quickly and accurately measure the true
>>> capacitance (since I don't trust my DVM) and sort into
>>> "within 1%" and "not within 1%" piles.  Then I can build my
>>> stupid 90 deg PDNs with confidence, and without trimmers.
>> Except that after you???ve gone to all of this trouble to sort
>> capacitors into ???within 1%??? and ???not within 1%??? piles,
>> you???ll find that the manufacturer has already sorted them
>> the same way and sold all of the ???within 1%??? caps to
>> someone willing to pay more. There will be a gap in your
>> measured values, such that the 5% caps will all be >+1% or
>> <-1% but none between -1% and +1%. If the capacitor technology
>> includes 1%, 5%, and 10% or 1%, 2%, and 5%, then you???ll find
>> similar missing gaps in the ranges of measured values.
> Even if that's the case, couldn't he use caps that all fall
> between, say, -1% and -2% of their nominal value ? Or +3% and
> +4%. Or whatever is right for the next E96 value, if the R/C
> ratio matters.

That’s a great idea!

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