Capacitor Values Explained

Capacitors appear throughout audio equipment, amplifiers and power supplies. Their value may be marked in picofarads (pF), nanofarads (nF) or microfarads (µF), and choosing a replacement requires more than matching capacitance alone.

For combinations and unit conversion, use our Capacitors in Series & Parallel Calculator.

Converting pF, nF and µF

1 nF = 1000 pF. 1 µF = 1000 nF = 1,000,000 pF.

For example, 0.022 µF is 22 nF, which is 22,000 pF. This is a common coupling-capacitor value in guitar amplifiers.

Capacitors in parallel

Parallel capacitances add directly. Two 22 µF capacitors in parallel produce 44 µF. Their working voltage does not simply add; each capacitor sees the applied voltage across the parallel network.

Capacitors in series

For series capacitors, the reciprocal values add. Two equal capacitors in series give half the capacitance of one. Two 100 µF capacitors in series therefore produce an ideal equivalent capacitance of 50 µF.

Voltage rating matters

A capacitor’s voltage rating is the maximum working voltage specified for that component under its stated conditions. A replacement should have a suitable voltage rating for the actual circuit. Using a lower-rated part can lead to leakage, breakdown or catastrophic failure.

Series electrolytics and balancing

Putting electrolytic capacitors in series can increase the total voltage capability in some designs, but real capacitors do not automatically share voltage perfectly. High-voltage power supplies often use balancing resistors across series electrolytics so the DC voltage divides more predictably.

Polarity

Many electrolytic capacitors are polarised and must be installed with the correct orientation. Reversing a polarised electrolytic can damage the capacitor and may cause it to vent or fail violently. Some audio circuits use non-polar or bipolar electrolytics where the voltage can reverse.

Capacitance is only one replacement parameter

Depending on the circuit, ESR, ripple-current rating, temperature rating, physical size, lead spacing and capacitor technology can all matter. In a switch-mode power supply, for example, a general-purpose electrolytic may be unsuitable even if the capacitance and voltage printed on the can look correct.

Why old filter capacitors cause faults

Electrolytic capacitors can dry out, increase in ESR or lose capacitance with age and heat. Symptoms may include hum, unstable supply rails, poor startup, excessive ripple or repeated protection faults. Diagnosis should be based on measurements and circuit conditions rather than age alone.

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