un chained can become un hinged

[djmiyta]

Building Unchained. Needing 25pf caps. Have none.
Have 22pf and 27pf figured one will be high or low and get close to the 25pf
HELL NO. MY BATCH OF 22 AND 27PF measure between .078nf and .092nf = 78-92pf seems real high
I pull out 15pf to measure and get 0.076nf. I couldnt tell you which ones but I know in some circuits no big deal up to now I took it for granted that the caps I get from Tayda are at least close to stated value and really have had no issues that I know of using them at face value. Measuring them and seeing how far off they are just got me curious about this large value difference(side note I havent completely ruled out my multimeter with built in cap reader not being accurate but its been good on everything else so.........can anybody school me about this? A big deal /no big deal ? thanks anybody and everybody
Cause I'm leaning toward going for it with 27pf only 2pf's off or higher than called for but then I do it and cause of that the sound sux wicked dirty nads and I mess the board up trying to fix it
Having little to none in patience I hope to get a quick reply and yes I did try and research a bit down the rabbit hole of capacitors. Rabbit hole.

 

[swyse]

Some meters have a lot of trouble figuring out low capacitance values. 27pf plenty close enough since its going to be well within the tolerance rating for a 25pf cap. I'd try it and see how you like it and worry about it later if you lose too much treble.

 

[Diynot]

If you wanted to be really anal ab it, you could run 2 smaller values in parallel to get where you need. My little transistor meter also does caps and it won’t read below like 20pf where as my DMM will. Some meters just don’t have the range. Pretty sure you would be fine with the 27pf though

 

[Alan W]

20 pf is very sensitive. Chances are your probe cables have more capacitance than that. The cap. meters in multimeters are great in terms of getting you close, but you’ll need a more specific meter to try and get accurate measurements, especially that low. A good LCR meter will have a way to null the test leads, for example.

 

[HamishR]

Another way to look at it is from a designer's POV. Why did they use 25pF? Probably because that's what they had available at the time. 27pF is most likely fine because that's what you have available. I doubt you would hear a difference.

 

[DAJE]

Anything much below 100pF won't read properly in tests.

To measure anything below 100pF, I get a 100pF cap and measure it (so I know what the actual capacitance is) and then measure the smaller one in parallel with the 100pf.

So if I have a cap that reads 90pF and the two of them add up to 113pF, I know that the smaller one is 23pF.

 

[jimilee]

If you wanted to be really anal ab it, you could run 2 smaller values in parallel to get where you need. My little transistor meter also does caps and it won’t read below like 20pf where as my DMM will. Some meters just don’t have the range. Pretty sure you would be fine with the 27pf though

Parallel will add the two together, series will roughly divide them in half, where as resistors are just the opposite.

 

[djmiyta]

Thanks to all those who take time to read my question and go further to give a response. We're all still learning to some degree I believe
So I just used the 27pf I honestly don't and didn't think it'd have an impact on the circuit. What really caught me off guard was the (IMO) was the very large difference in the stated value and what my meter says it is ( and the big difference also why I thought my meter could be the problem) I haven't finished the build yet and if it sounds good to my ears thats at the end of the day all I really care about.

 

[djmiyta]

update
built it socketed the leds sounds like crap probably using 2 clear red leds and one diffused red? when cranking the gain it sounds like its saturating soo much it cant take anymore and sounds nothing like the demos which I thought sound good these sound like fets when over biased tmaxxed out starts it squealing

 

[Feral Feline]

Sorry to hear it's sounding like arse.

Prolly down to diodes?



As for testing pF caps, I've tested the same cap five times and only two readings were similar but not the same. I did that with a bunch of different pF values for a build, testing between 10–20 caps for the desired value and setting aside the ones that came closest, then retest the contenders only to get different values for each... Tests were done with my Fig TC-1, which is waayyyy better than my DMM for cap crunching.

 

[MichaelW]

I think anything under 100pf is a crapshoot when it comes to testers. Doesn’t mean your DMM or tester is off or that the cap is off. Just hard to get accurate readings down there. I usually don’t sweat those smaller values and roll with whatever the bag says it is.

 

[fig]

All great answers, from great folks.

FF is right about the TC-1*. It measures where many DMMs dare to tread, and is cheap too!
I have an LCR45 but usually grab the TC-1, unless I'm measuring Ge diodes or transistors.

*There is an updated version I believe.

I think I'll do another giveaway with a few of these.