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1 hour ago
Hi Guys
Capacitors are everywhere in audio circuits and their power supplies.
A capacitor is formed when two conductors are separated by an insulator. That insulation is called the dielectric, and can be air (not very useful, but the cause of 'parasitic' capacitance), paper, oil, plastic, ceramic, mica, electrolytic materials, polymers, or organics. The conductors are called 'plates' and are effectively large flat metal surfaces with leads attached. The entire assembly is covered in a suitable coating to keep the environment out.
Capacitance value is in Farads, which is a huge value for an audio circuit, or even for a power supply, although small "super caps" of a few Farads were used in lieu of a battery as backup power in VCRs and similar to support memory circuits. In audio, we see values from picoFarads (pF) up to milliFarads (mF). Note that microfarads should be denoted as uF. Ancient schematics will show uuF instead of pF.
Man-made capacitors are imperfect with the following flaws in various extents:
DA - dielectric absorption is the inability of the dielectric to release built up charge
DF - dissipation factor is the inability of the dielectric to follow fast changing charge/discharge cycling
ESR - equivalent-series-resistance is a fixed internal resistance not the impedance based on frequency
Remember: the power supply is the other half of the signal path so the caps used here make a difference that is audible.
Ceramic caps
These are made from various rare earths and historically were single layer, where the dielectric is between two parallel plates, as the iconic capacitor model represents. Discs with radial leads are typical, and the value accuracy and stability depend on the specific materials used. The best ceramics for audio are C0G or NP0 rated, and are good up to values of 100pF.
Distortion is otherwise quite high with higher values and adds "grit" to the sound. In a guitar amp, this may be welcome, but in hifi it adds distortion that smears the sound.
MLCC Caps
Multi-layer ceramic capacitors are used in switching power supplies and have some quite terrible characteristics. Their capacitance varies with the voltage across the cap. The capacitance varies with frequency of the current through the cap.Their voltage rating is typically unusable, with half the rating being a common safe maximum. Even though they are designed to nominally handle high switching currents, this rating is often overstated. Unsuitable for audio.
Mica Caps
Mica is a natural material that can be shaved extremely thin. It has high voltage withstand and can be cut precisely for reasonable capacitance accuracy. Distortion is much lower than with ceramic and higher values can be used, although anything above a few nF may be expensive and impractical.
Plastic Caps
There are a few common plastics used as dielectrics in capacitors.
Polyester has a few trade names, such as Mylar, and is the most common plastic cap type. It has an unfortunate attribute of adding odd-order distortion to series audio signals. The higher the signal voltage is across the cap, the higher the THD. Compared to ceramic, a polyester cap will sound cleaner in a guitar amp, but it is best to use other polys for critical applications. placing caps in series can reduce the individual capacitor distortion but the composite effect may be not enough to justify the use of multiple capacitors.
Polyethylene is about equal to polyester.
Polycarbonate was favored for a while, but has its own distortion mechanism. Lower THD than polyester. Not as low as others.
Polypropylene is distortion-free! The best poly cap and its reach and breadth of available sizes, voltages and values expands every day. Although safety caps of the X and Y types use PP for its self-healing characteristic, the caps use impure PP and are unsuitable for audio.
Polystyrene is also distortion free but only available in very low values and at voltages <100V or so.
Paper Caps
paper dielectric is ancient obsolete technology that is entirely unsuitable for audio use. Yes, vintage equipment contains these caps, which decades ago were already dried out and behaving more like inductors than capacitors. Replace them with any type of poly cap and the amp will be loud and clear again.
Oil-filled Caps
There are usually meant for motor-start applications and are typically in a metal can with faston-style connections. Not suitable for audio.
Electrolytic Caps
Electrolytic capacitors have a dielectric that is formed using voltage and they require regular application of voltage to remain healthy. If you install a high-voltage cap in a low-voltage circuit, the cap will eventually reform to the lower voltage and not be able to meet its rating unless you slowly reform it by carefully applying higher voltages to it. In general, electrolytic caps have just about the worst combination of DF, DA and ESR possible, but this depends very much on manufacturing quality.
The rated voltage of an electrolytic capacitor is also its WORKING voltage, which means that you can use the cap at the rated voltage without concern.
Life expectancy is listed in 1,000s of hours at the rated maximum temperature and voltage. Realistic life doubles with each 10-degree drop in temperature, so that a 3,000-hr cap rated for 85C should be within spec for 64,000-hrs at 25C. If this were a 105C rated cap, its life would stretch out four times longer. For high-fidelity audio, capacitor life is considered over at 14 years, or when DF begins to go crazy (scientific, ya?)
High-values of capacitance are achievable and electrolytics are the mainstay in power supplies of all (conventional) types. Because of their poor audio qualities and wide value tolerance, electrolytic caps should never be used to define frequency roll-offs, such as in the feedback loop of a solid-state power amp.
Polymer Caps
This is a newer dielectric that is a sort of "enhanced electrolytic". Current surges are handled better and reverse voltages withstood better. They work well in stacked power supply situations, for example, full-wave voltage multipliers.
Tantalum Caps
tantalum capacitors have good value stability and can be made to tighter tolerances than electrolytics.king them an upgrade in old-style security systems that relied on fixed-frequency oscillators. On every other count, they are unsuitable for use in audio circuits.
Capacitors are everywhere in audio circuits and their power supplies.
A capacitor is formed when two conductors are separated by an insulator. That insulation is called the dielectric, and can be air (not very useful, but the cause of 'parasitic' capacitance), paper, oil, plastic, ceramic, mica, electrolytic materials, polymers, or organics. The conductors are called 'plates' and are effectively large flat metal surfaces with leads attached. The entire assembly is covered in a suitable coating to keep the environment out.
Capacitance value is in Farads, which is a huge value for an audio circuit, or even for a power supply, although small "super caps" of a few Farads were used in lieu of a battery as backup power in VCRs and similar to support memory circuits. In audio, we see values from picoFarads (pF) up to milliFarads (mF). Note that microfarads should be denoted as uF. Ancient schematics will show uuF instead of pF.
Man-made capacitors are imperfect with the following flaws in various extents:
DA - dielectric absorption is the inability of the dielectric to release built up charge
DF - dissipation factor is the inability of the dielectric to follow fast changing charge/discharge cycling
ESR - equivalent-series-resistance is a fixed internal resistance not the impedance based on frequency
Remember: the power supply is the other half of the signal path so the caps used here make a difference that is audible.
Ceramic caps
These are made from various rare earths and historically were single layer, where the dielectric is between two parallel plates, as the iconic capacitor model represents. Discs with radial leads are typical, and the value accuracy and stability depend on the specific materials used. The best ceramics for audio are C0G or NP0 rated, and are good up to values of 100pF.
Distortion is otherwise quite high with higher values and adds "grit" to the sound. In a guitar amp, this may be welcome, but in hifi it adds distortion that smears the sound.
MLCC Caps
Multi-layer ceramic capacitors are used in switching power supplies and have some quite terrible characteristics. Their capacitance varies with the voltage across the cap. The capacitance varies with frequency of the current through the cap.Their voltage rating is typically unusable, with half the rating being a common safe maximum. Even though they are designed to nominally handle high switching currents, this rating is often overstated. Unsuitable for audio.
Mica Caps
Mica is a natural material that can be shaved extremely thin. It has high voltage withstand and can be cut precisely for reasonable capacitance accuracy. Distortion is much lower than with ceramic and higher values can be used, although anything above a few nF may be expensive and impractical.
Plastic Caps
There are a few common plastics used as dielectrics in capacitors.
Polyester has a few trade names, such as Mylar, and is the most common plastic cap type. It has an unfortunate attribute of adding odd-order distortion to series audio signals. The higher the signal voltage is across the cap, the higher the THD. Compared to ceramic, a polyester cap will sound cleaner in a guitar amp, but it is best to use other polys for critical applications. placing caps in series can reduce the individual capacitor distortion but the composite effect may be not enough to justify the use of multiple capacitors.
Polyethylene is about equal to polyester.
Polycarbonate was favored for a while, but has its own distortion mechanism. Lower THD than polyester. Not as low as others.
Polypropylene is distortion-free! The best poly cap and its reach and breadth of available sizes, voltages and values expands every day. Although safety caps of the X and Y types use PP for its self-healing characteristic, the caps use impure PP and are unsuitable for audio.
Polystyrene is also distortion free but only available in very low values and at voltages <100V or so.
Paper Caps
paper dielectric is ancient obsolete technology that is entirely unsuitable for audio use. Yes, vintage equipment contains these caps, which decades ago were already dried out and behaving more like inductors than capacitors. Replace them with any type of poly cap and the amp will be loud and clear again.
Oil-filled Caps
There are usually meant for motor-start applications and are typically in a metal can with faston-style connections. Not suitable for audio.
Electrolytic Caps
Electrolytic capacitors have a dielectric that is formed using voltage and they require regular application of voltage to remain healthy. If you install a high-voltage cap in a low-voltage circuit, the cap will eventually reform to the lower voltage and not be able to meet its rating unless you slowly reform it by carefully applying higher voltages to it. In general, electrolytic caps have just about the worst combination of DF, DA and ESR possible, but this depends very much on manufacturing quality.
The rated voltage of an electrolytic capacitor is also its WORKING voltage, which means that you can use the cap at the rated voltage without concern.
Life expectancy is listed in 1,000s of hours at the rated maximum temperature and voltage. Realistic life doubles with each 10-degree drop in temperature, so that a 3,000-hr cap rated for 85C should be within spec for 64,000-hrs at 25C. If this were a 105C rated cap, its life would stretch out four times longer. For high-fidelity audio, capacitor life is considered over at 14 years, or when DF begins to go crazy (scientific, ya?)
High-values of capacitance are achievable and electrolytics are the mainstay in power supplies of all (conventional) types. Because of their poor audio qualities and wide value tolerance, electrolytic caps should never be used to define frequency roll-offs, such as in the feedback loop of a solid-state power amp.
Polymer Caps
This is a newer dielectric that is a sort of "enhanced electrolytic". Current surges are handled better and reverse voltages withstood better. They work well in stacked power supply situations, for example, full-wave voltage multipliers.
Tantalum Caps
tantalum capacitors have good value stability and can be made to tighter tolerances than electrolytics.king them an upgrade in old-style security systems that relied on fixed-frequency oscillators. On every other count, they are unsuitable for use in audio circuits.
