Andrew L Weekes
Reverse Engineer
It's worth understanding why caps (and other components) may sound different.
So to start, capacitors are on the menu so look here: -
www.newson-consulting.com/emi-capacitors.htm
at figure 3 - this shows some of the non-ideal characteristics. As you can see our perfect cap now has inductance (ESL) and resistance (ESR).
In addition there's another resistor in parallel with the capacitor - this models leakage current, in addition to this add another RC compination in parallel with the C bit and you have now modelled dielectric absorption. In real capacitors the DA element is actually multiple sets of RC components, bringing non-linearities and circuit response effects that can totally ruin fast and slow dynamic performance.
Complicated isn't it!
Here's some options, with their respective characteristics: -
Polystyrene: -
Ultra low DA, good stability (circa 120ppm/deg C), high inductance (wound) - no longer available readily and high temp performance poor (85 deg C max operating)
Polyphenylsulphide (PPS): -
Almost as good in most parameters as above (Temp is better IIRC), but available in stacked plate form, so lower inductance. Wider temp range.
Polypropylene: -
Low DA, stable (200ppm), large, high inductance (wound)
Teflon: -
Low DA available, v. stable, good at high temp, inductive, expensive.
Polycarbonate: -
Stable, cheap, wide temp range, large, inductive, DA limits operation to 8 bit apps.
Polyester: -
Moderate stability, cheap, wide temp, low inductance (stacked film types), smaller than poly types above, but still large for value. Again limited to 8 bit app's
NP0 ceramic: -
Small, cheap, v.stable (30ppm), low inductance, DA generally low, but rarely specced, max value limited.
Aluminium electrolytic: -
Large values, high currents, high V and small size, High leakage, polarized, v. poor stability, inductive.
Tantalum: -
Small, large values (but low V) moderate inductance, high leakage, polarized, expensive, poor stability, don't take abuse readily
Then there's the time factor - many of the above (particularly electrolytic) change over time...
Have fun!
So to start, capacitors are on the menu so look here: -
www.newson-consulting.com/emi-capacitors.htm
at figure 3 - this shows some of the non-ideal characteristics. As you can see our perfect cap now has inductance (ESL) and resistance (ESR).
In addition there's another resistor in parallel with the capacitor - this models leakage current, in addition to this add another RC compination in parallel with the C bit and you have now modelled dielectric absorption. In real capacitors the DA element is actually multiple sets of RC components, bringing non-linearities and circuit response effects that can totally ruin fast and slow dynamic performance.
Complicated isn't it!
Here's some options, with their respective characteristics: -
Polystyrene: -
Ultra low DA, good stability (circa 120ppm/deg C), high inductance (wound) - no longer available readily and high temp performance poor (85 deg C max operating)
Polyphenylsulphide (PPS): -
Almost as good in most parameters as above (Temp is better IIRC), but available in stacked plate form, so lower inductance. Wider temp range.
Polypropylene: -
Low DA, stable (200ppm), large, high inductance (wound)
Teflon: -
Low DA available, v. stable, good at high temp, inductive, expensive.
Polycarbonate: -
Stable, cheap, wide temp range, large, inductive, DA limits operation to 8 bit apps.
Polyester: -
Moderate stability, cheap, wide temp, low inductance (stacked film types), smaller than poly types above, but still large for value. Again limited to 8 bit app's
NP0 ceramic: -
Small, cheap, v.stable (30ppm), low inductance, DA generally low, but rarely specced, max value limited.
Aluminium electrolytic: -
Large values, high currents, high V and small size, High leakage, polarized, v. poor stability, inductive.
Tantalum: -
Small, large values (but low V) moderate inductance, high leakage, polarized, expensive, poor stability, don't take abuse readily
Then there's the time factor - many of the above (particularly electrolytic) change over time...
Have fun!