Electronic – What type of capacitor to buy
capacitor
Related Solutions
Without specific examples (i.e. links to the circuits you found) it's hard to give an authoritative answer.
In general:
Capacitors specified with no polarity (no + and -) and no voltage rating are usually ceramic types, and common voltage ratings (25V, 50V) should be fine.
Capacitors that show polarity are polarized types - usually electrolytic, sometimes tantanlum. Substitution with ceramic or other types usually isn't possible as the capacitance needed may require many in parallel. Polarized capacitors in the tens of microfarads or higher are generally electrolytic. Lower values could be electrolytic or tanatalum.
A voltage rating is a helpful hint. Never place a cap with a lower voltage rating where a higher voltage rating is indicated. A good guideline is to choose the capacitor with voltage rating, which is twice the nominal voltage across the capacitor in the circuit. High voltage, small values (picofarads to a few nanofarads) are generally ceramic; high voltage with higher values (tens of nanofarads and up) are often metal film or polypropylene capacitors.
Capacitors that say X, Y, X# (i.e. X2) or Y# (i.e. Y1) are safety-critical and must be special ceramic or film capacitors that bear safety markings (UL, TUV, etc.)
Since you said this is for audio, the answer is actually more tricky than you probably imagined. Electrically, you want a non-polarized capacitor, which means not electrolytic or tantalum in practise.
However, various types of capacitors have other tradeoffs that matter in audio applications. Multi-layer ceramics are nice in that they have good capacitance for the size and are not polarized. However, depending on the dielectric material, they can be quite non-linear and have another effect often called microphonics.
Microphonics is because the material exhibits a bit of the piezo effect. Vibrations will cause small voltage changes, which means the capacitor will act as a microphone. The effect is more subtle than piezo microphones deliberately designed for that purpose, but it can still be significant given the high signal to noise ratio of good audio.
The non-linearity is also a function of the dielectric material. A perfect capacitor will increase its voltage the same amount when a fixed charge is added no matter what the other conditions are. These non-linear dielectrics will have a different change in voltage for the same change of charge depending on the voltage. This is usually quantified as capacitance varying as a function of voltage. For example, a "10 µF 10 V" capacitor may act like 10 µF in the ±2 V region, but act more like a 5 µF capacitor to incremental change in the 8-10 V region. This non-linear response in audio circuits can cause harmonics that were not present in the original signal, which means distortion is added.
Ceramic dielectric types that start with "X" or "Y" in their name exhibit both these effects more than ceramic like "NP0". In a lot of applications, either effect doesn't matter, and the X and Y ceramics are useful because they give you more capacitance per volume. For audio applications it does matter, so you stick to the other types and realize that you won't be able to use the capacitors with the seemingly great capacitance and voltage combinations in the signal path. Heavily derating the voltage range also helps against dielectric non-linearity. For example, you might get a 20 V cap when the circuit guarantees the voltage accross it will always be within ±3 V.
Other dielectrics like mylar, polystyrene, and the like have less undesirable effect in the audio signal path, but also will have much lower capacitcances available and will be physically more bulky and probably more expensive.
Everything is a tradeoff.
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Best Answer
This is a very common Motor-Run cap worth about $10~$15 or more for higher voltage ratings.
Search 22.5uF metallized polypropylene radial capacitor 250Vac (min) 5%
e.g. M72A2822N22 AEROVOX 280Vac 5%
or another https://www.mouser.com/ProductDetail/Panasonic/EZP-Q38226MTA/?qs=TiOZkKH1s2QJT3hK7a6J8Q%3D%3D
You can solder to wire leads and silicone or PU adhesive to secure.