[sdiy] Hand selecting capacitors

Mike Beauchamp list at mikebeauchamp.com
Sat Apr 10 19:03:01 CEST 2021


At some point depending on the quantity, it would make sense to invest 
the time in automating this process.

A pick and place machine could briefly land the capacitor into a text 
fixture before populating, which informs it what value trimmer capacitor 
to also populate.

I'm not saying it makes sense for how many Doc is making right now, and 
I'm certainly guilty of building a few "time savers" that took longer to 
make than the time saved :)



On 4/10/21 10:16 AM, Ben Stuyts wrote:
> Hi Doc,
> 
>> On 9 Apr 2021, at 08:45, David G Dixon via Synth-diy 
>> <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>>
>> Anyway, I ran low on capacitors to the point where I couldn't put 
>> together decent collections for the 18-stage filter (I need 4 102s, 4 
>> 103s, 4 104s, and 6 105s for it).  I bought 250 each of the smaller 
>> values and 200 of the 105s.  Tonight I measured all of the 105s, 
>> thinking that they would ideally form a Gaussian distribution around 
>> 1.000uF.  Well, they were nearly all clustered between about 1.030uF 
>> and 1.050uF, and in fact, about 20% of them were off spec (higher than 
>> 1.050uF, and these are 5% caps).  Not a single one of them was less 
>> than 1.020uF.  They are Kemet caps.  So now I've got to hope that the 
>> other values also tend on the high side of their tolerance ranges, or 
>> else I'm going to have to buy even more caps.
> 
> It is a pity they are all over the nominal value. Otherwise you could 
> perhaps add a small parallel cap. (Adding a series cap in this case 
> would not be practical…)
> 
> On the other hand, if you add a small cap to make them all 1.1 uF (e.g. 
> 1.03 uF + 68 nF) the tolerance on the smaller cap would be much less of 
> an issue. And then change the corresponding resistor values to match.
> 
> Ben
> 
> 
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