Capacitor Resonance

.

80hinhiding said:

Why do capacitors have different resonant responses?

One example, I just changed a 0.1uF MKT1822 film cap with a 0.1uF K40Y-9 paper in oil and the difference isn't slight, it's quite noticeable.  One of the two emphasized an acoustic guitar in a mix that could be barely heard through the other.  Notes played on an electric organ through one capacitor resonant while the other just fall off quicker.  Not arguing for or against either, I just want to know why this happens.

Adam

Click to expand...

In order to answer your question, we would need to know where this cap is in the circuit, and what the circuit is.
It is quite rare to find a situation where changing the technology of a cap without changing the value makes a clear-cut difference. I would first check if they really are of the same value. For example, if one is 0.1+10% and the other one 0.1-10%, the difference of resonant frequency in a tuned LC circuit could be 10%, that's two semi-tones.
The other factor that may be audible would be a very different dissipation factor, which would result in quite different amplitude of the boost or cut in an EQ.

80hinhiding said:

It was on the input of the bare bones differential amp  PRR drew up in the thread about an ideal line input stage.  That diff amp output then went to a voltage follower I made with a JFET, which then feeds an output amp that is Class B in design.  Output transformer was used, sent unbalanced to a speaker.

One capacitor is rated for 250V, the other rated for 200V.  I believe they're both +-10%.  Both 0.1uF.

Adam

Click to expand...

I don't see how the cap's technology could make a significant difference in this application, unless there is a large effect due to stray capacitance. I can't comment without having some objective data, such as  a frequency response. BTW what was the source?

polyester caps are sometimes not considerd high end audio caps.
while paper in oil seems to have the strength of being non inductive. (could be wrong)

but all that means more or less depending on what circuit it is used in.

Not all things are created equal. Take a 1 Lb. of metal and mold it into a long bar. Now if we use Steel it will be very hard to bend. If we use Aluminum if will bend much easier.  If we use Copper is very soft we can bend by hand. They are all 1 Lb. of metal.

Capacitors are much the same. The dielectric material, temperature coefficient, dissipation factor, construction and other factors cause changes as current flows and voltage across the capacitor cause non linearity to show up. Everything is some type of comprise to performance.

The design engineer must know what he/she need to best meet the needs of the product.  They need to read the Data Sheet and select the best part for the application.

I hope this will help.
Duke

Audio1Man said:

The dielectric material, temperature coefficient, dissipation factor, construction and other factors cause changes as current flows and voltage across the capacitor cause non linearity to show up.

Click to expand...

In the actual configuration (in series with a 100k resistor) I very much doubt the effects of dielectric absorption or dissipation are detectable compared to the distortion level in a single transistor with current NFB, unless one of the caps is seriously defective.

Context and measurements are always needed to answer these types of questions.

The capacitors might be rated the same, but what do they actually measure?  A cheap LCR meter will work wonders here. You can pick them up for under 20$

If one capacitor makes an acoustic guitar sound clearer in a mix, then you should be seeing a difference in frequency response. Take some frequency response measurements and then we can go from there.

Without context, you are going ro get many views and opinions that may and/or may not apply to the circuit in question. That's the danger of asking a question this open ended.  8)  ;D