Are Mica capacitors legit for pedal building?

[Caldo71]

I just notice that they tend to be available with far tighter tolerances than their ceramic disc counterparts.

Never used em in a build before, so I didn’t know if there was anything about their function or how they affect signal/tone that makes them verboten for pedal building?

they are pricey AF but that doesn’t bother me so much...

 

[Gordo]

To my knowledge they're perfectly fine but tend to get more use in amps, where size isn't an issue. They tend to be $$, as you noted, and they're also considerably bigger than MLCC, ceramic, or film equivalents.

 

[Feral Feline]

Mica are worth it in some cases for "in the signal path" sorts of things, like the feedback loop of an op-amp. If it's something power related, or going to ground or non-signal related like an LFO — you're just flushing money away.

I only use them if the build specs them.

 

[varlogtim]

I believe that MLCC capacitor values change over time (decrease in value). So, as @Feral Feline mentioned, if the capacitor is used to control the frequency response of a gain stage and you don't want that to change overtime, they might be a good option. Actually, I try to use MLCCs as little as possible because I think their reactance changes when DC bias is present. Since most pedal circuits (without a charge pump) need to DC bias the audio signal, it is a good idea to use metal film when possible.

I just put a couple in a Rat clone. One for the slew rate and one for the low pass filter in the op amp feedback loop. They are bigAF ... but usually you can leave the leads long, bend and squeeze.

 

[Chuck D. Bones]

Silver Mica is as close to an ideal cap as you can get, much better than ceramic. They are bulky & more expensive. I use 'em because I have 'em.

 

[Caldo71]

Thank you all for the great insights!

 

[Chuck D. Bones]

I believe that MLCC capacitor values change over time (decrease in value). So, as @Feral Feline mentioned, if the capacitor is used to control the frequency response of a gain stage and you don't want that to change overtime, they might be a good option. Actually, I try to use MLCCs as little as possible because I think their reactance changes when DC bias is present. Since most pedal circuits (without a charge pump) need to DC bias the audio signal, it is a good idea to use metal film when possible.

I tried, but I couldn't let this one go.

Aging affects all electronic parts to some extent. The aging rate is an exponential function of temperature, so as long as you keep you parts near room temp (like under 50C) it will take decades for aging to produce a noticeable effect in a pedal.

DC bias will affect ceramic caps, but we're talking about high voltage. A 100V cap exposed to 9V won't undergo a noticeable change. I try to avoid MLCCs that are rated for less than 100V because the dielectric layers are very thin on the lower voltage parts and that can impact reliability.

To me, the worst properties of ceramic caps are microphonics and dielectric absorption. Dielectric absorption is a kind of short-term memory that muddies the signal. Not a problem when used as a power supply bypass cap, but bad news in the signal path.

 

[varlogtim]

I tried, but I couldn't let this one go.

Aging affects all electronic parts to some extent. The aging rate is an exponential function of temperature, so as long as you keep you parts near room temp (like under 50C) it will take decades for aging to produce a noticeable effect in a pedal.

DC bias will affect ceramic caps, but we're talking about high voltage. A 100V cap exposed to 9V won't undergo a noticeable change. I try to avoid MLCCs that are rated for less than 100V because the dielectric layers are very thin on the lower voltage parts and that can impact reliability.

To me, the worst properties of ceramic caps are microphonics and dielectric absorption. Dielectric absorption is a kind of short-term memory that muddies the signal. Not a problem when used as a power supply bypass cap, but bad news in the signal path.

Very cool info. I had read about MLCCs being affected by DC bias but wasn't able to find a formula for it to calculate the potential impact. I know that it is considered in certain applications, like medical equipment, but might not have a reasonable impact on pedal electronics.

From your comment, I am gathering that the change in reactance is a function of the voltage rating of the cap and DC bias?

 

[Chuck D. Bones]

Yes, but it's also dependent on the specific dielectric material. Here's a good discussion on MLCC dielectric properties from the DigiKey website.

 

[jcrhee]

Is using box film cap(s) instead of ceramic/mlcc an option similar to Mica?

 

[Chuck D. Bones]

Yes, as long as you can find the right value & physical size.