thunderaxe
Active member
over spec by how much? and how stable would that make them?
Getting Started with PCBA at JLCPCB
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z2amiller
Active member
I think it matters less for AC (signal), but for DC there's a pretty strong de-rating curve - the capacitance gets less as the voltage gets higher.
The package size is actually relevant here as well, with physically larger capacitors losing less capacitance with a DC offset.
I use X7R 1206 50V 1uF's (basic: C1848) when I do use 1uF ceramics in the audio path.
Murata has an online tool called 'SimSurfing' where you can look up the exact capacitance derating curve for any of their caps.
For example, that 1uF 50V 1206 capacitor is only 500nF when it's at ~40V DC bias. I imagine that the derating curve is probably
at least similar for other manufacturers with the same dielectric/size/voltage rating.
Since the caps in the audio path would usually be biased at 1/2VCC (4.5V or 9V if you're running 18V) I don't think it matters
much for this cap though -- it is stable at ~1uf until ~11V.
But if you were to try to use an 0603 1uF 25V capacitor there, it would be ~750nF at 4.5V and ~500nF at 9V!
(Sorry I'm on my work computer at the moment so I can't upload the screenshots but #trust)
X7R's are also pretty stable temperature-wise, ±15% over their whole temperature range, which is like -55C -> 85 or 125C.
I imagine at the human-tolerable temperatures in that range the difference will be pretty negligible though maybe
if your pedal consumes a ton of power and heats up to 45C or something it could drift by a measurable percent.
(but audio-perceptible? eh)
The package size is actually relevant here as well, with physically larger capacitors losing less capacitance with a DC offset.
I use X7R 1206 50V 1uF's (basic: C1848) when I do use 1uF ceramics in the audio path.
Murata has an online tool called 'SimSurfing' where you can look up the exact capacitance derating curve for any of their caps.
For example, that 1uF 50V 1206 capacitor is only 500nF when it's at ~40V DC bias. I imagine that the derating curve is probably
at least similar for other manufacturers with the same dielectric/size/voltage rating.
Since the caps in the audio path would usually be biased at 1/2VCC (4.5V or 9V if you're running 18V) I don't think it matters
much for this cap though -- it is stable at ~1uf until ~11V.
But if you were to try to use an 0603 1uF 25V capacitor there, it would be ~750nF at 4.5V and ~500nF at 9V!
(Sorry I'm on my work computer at the moment so I can't upload the screenshots but #trust)
X7R's are also pretty stable temperature-wise, ±15% over their whole temperature range, which is like -55C -> 85 or 125C.
I imagine at the human-tolerable temperatures in that range the difference will be pretty negligible though maybe
if your pedal consumes a ton of power and heats up to 45C or something it could drift by a measurable percent.
(but audio-perceptible? eh)
Rpschultz13
Well-known member
I asked this over on AllAboutCircuits. Great thread, especially the Cyril Bateman articles. Also the TI article in post #2 is fantastic.