Glodark Audiophile Capacitor Page

You should measure the ESR of electrolytic capacitors to determine whether they need to be replaced. This can be carried out in-circuit provided that:

  • 1. You have an ESR meter (!)
  • 2. No capacitor is directly in parallel with any other.
  • 3. You make sure the voltages are fully discharged first.


  • 1. ESR meters available from Dick Smith electronics in Australia, SatCure in the UK and various US companies.
  • 2. If capacitors are connected in parallel, disconnect one end to measure.
  • 3. Leave amp unplugged for an hour then connect a 10R/2Watt resistor across each capacitor for a second to ensure it is discharged fully.

Capacitors have a temperature/time rating. For example 85'C/4000 means that a capacitor will withstand typically 85' Centigrade for 4000 hours before serious degradation sets in. Derate according to actual temperature. Don't be fooled by the temperature rating. A 105'C/2000 is no better than a 85'C/4000.

In equipment that runs warm in a centrally-heated room, you can expect a life of between 1 year and 6 years for electrolytic capacitors. (Work it out - how many years is 4000 hours?)

Most amps are over designed so they will tolerate quite severe degradation before the effects become audible. You could use an amp for a dozen years before you notice a problem.


Be *sure* to use the correct type of capacitor. There's no point in replacing an Ultra-low ESR capacitor in a power supply with a "high quality" one with "gold-plated wires" if it actually has a worse electrical or temperature/time specification!

However, for capacitors used in front-end circuits, low leakage is more important than low ESR so measure leakage current.

More about capacitors

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