Just dug out a cheap job lot of ceramic caps and on a whim tested them.
Question 1 : is it normal to discover all the 1nf caps range from 1.3-1.48?
Question 2 : is that, as I often say, near enough for jazz? Or are they useless if 1nf is called for.
Last question : can anyone supply a link to a cheap and reliable cap dealer?
tayda, or mouser (usa)
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Thanks. UK for preference. Scotland if I’m being pedantic 
The variance for cheap capacitors is around 20%, so your values seem a bit extreme. If they are still useful depends on the circuit. For something like a timing capacitor it should be pretty close to the indicated value, for decoupling of ICs you can use almost everything and for other things I have no idea 
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Was about to put together 2 as3340 vco and this 1nf is for the pin 11 to ground. Not sure if this will affect the buffer or the CM (CM anyone? I want to say something meter) . As Its an all in one chip I’ll just play safe and wait until I find a reasonable cap.
Plus every time I type vco my autocorrect changes it to Vicodin so I’m taking the hint and having a break. Many thanks
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Pin 11 is the timing capacitor for the as3340. Some people are using high precision (5%) mylar capacitors for this, but on Sam’s BOM it is a simple disc capacitor. I have also used a disc cap, because at the time I did not even know that mylar exists 
. It works, my tuning is a bit off when I go to higher octaves, but I don’t know if I can blame the capacitor here, it’s probably the octave switch and I need to re-tune using this guide by antoine.
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Pin 11 is the timing capacitor. Temperature stability is perhaps even more important than tolerance, so using a random ceramic capacitor isn’t ideal; there’s a ton of different dielectrics, some of which can change a lot over the supported temperature range (e.g. a Y5V is speced for +22/−82%), and you usually don’t know what type you have if they were cheap…
The CEM3340 datasheet suggests Mica but it was written in the late seventies so these days a good film capacitor is probably ok, or maybe a C0G class 1 ceramic (which unlike random ceramics is very stable).
Oh, it can get much worse than that; here’s the tolerance selector for 1 nF ceramics at Digikey 
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Figured it was timing. Time to buy shiny caps. Many thanks
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If the accuracy of your measuring equipment is 30 to 48 %, no then it is not …
This is of course an important thing. How accurate is your test equipment? At what temperature did you measure this? And with low values, how about the effect of the leads you are using? Things to keep in mind, is what I’m saying. I find it difficult or hit and miss to measure any capacitance below 1 nF. When checking a small capacitor’s value if it is not too far off from the specified capacitance I assume it is correct.
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when you test the ceramic caps hold them between your fingers for a bit [ to warm them up ] and you will see a noticeable difference .
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The NP0 type capacitors are temperature stable and more voltage stable. Y5V are pretty bad but work OK for power supply decoupling. X7R is better but not great. There are a lot of things that can change the value of ceramic caps. The value will change right after soldering and will return to the unsoldered value after a few days. They have voltage dependence so the value goes down as the voltage goes up. They have dielectric absorption so that after you have shorted it, if you remove the short, it can start to have a voltage after some period of time.
Just try and be aware that these effects exist and most of the time it is a wash and nothing to worry about but for timing circuits, you may want film (polystyrene and not polypropylene right?) or at least NPO ceramic. Try different ones and see how it changes.
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I don’t know if mica is excellent for stable values or not but I see a wealth of choices for capacitors if timing in a circuit is critical. I’ve wanted to use polystyrene as they are famed to be used in '80s audio equipment. There’s nothing bad about polystyrene but when I was educating myself how to build with polystyrene I learned that isopropyl alcohol is a solvent of polystyrene and that with too much heat from the soldering iron a polystyrene capacitor can melt. I could see it being used if the way of building neither of this concerns them. While I continued to look for some capacitors to use I viewed that polypropylene may be of great use. There’s some WIMA polypropylene capacitors (2.5% tolerance) that are 37 cents on Mouser so I’m hoping the builds with them go exceedingly well. There’s a field guide to capacitors by Harry Bissell online I’ve found useful.
-Fumu / Esopus
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Yeah, that is definitely true about polystyrene and heat. They are pretty well sealed against moisture and alcohol but it’s good to be careful .
Absolute tolerance may not be that critical to you because you can tune it to the right response. Repeatability and temperature drift may be more important. Can you get the value you need in mica or NP0 ceramic? Polypropylene is probably good too. The other ceramics (Y5V, Y5U, X7R) may give you some temperature drift issues. The three character are used to describe the temperature characteristics of the capacitor in standard terms. You can look that up.
If you choose ceramic, even NP0, give it a couple of days after soldering before expecting it to stay in tune.
Polystyrene and polypropylene are more often used in sample and hold amplifiers (SHA). Here is an article.
https://www.sciencedirect.com/topics/engineering/hold-capacitor
I used to have a chart that showed the different characteristics of caps. I think polystyrene is used in power converters because it is such low loss. Like inductive heating power converter circuits and such. Anything else just melts.
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Here is a table showing dielectric absorption for different capacitor materials. This more important if your sample and hold is not working right than for timing capacitors but it may be useful to some of you.
NP0 material is actually not that great for absorption. But it does have good temperature behavior.
For ceramics caps, use the highest voltage range you can accommodate on the board. Higher voltage parts will have less voltage coefficient effects than low voltage parts. Use 50V or 100V parts instead of 10V parts. They are also more robust.
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