An electrolytic capacitor is a polarised type of capacitor that is inside many electronic circuits, including Rhodes preamps and Wurlitzer amplifiers. The reason they are used is because they can store a much higher charge, or capacitance, then regular film or ceramic capacitors. In audio circuits like a Wurlitzer or Rhodes amplifier this is done for several reasons:
- Decoupling – a technical term for filtering unwanted noise and stabilising the the power supply. Larger electrolytic capacitors can help in reducing ripple in the power supply, meaning less noise and improving sound quality.
- Storage of energy – like other capacitors, electrolytic capacitors can store energy, though potentially much more. With a wide dynamic range in a Wurlitzer amplifier for example, when the piano is played loudly, capacitor can help deliver extra energy to combat distortion of sound.
- Stabilising voltage – in an amplifier, the DC circuit that amplifies the signal can have a voltage that is irregular. Electrolytic capacitors help stabilise this to create a more even signal that translates into a better sound.
The main difference between this type of capacitor and other varieties is that these have positive and negative ends, also called polarity. The positive lead tends to be longer, and the negative end is usually marked. On older capacitors this can be less clear though.
The way capacitors are measured is in farads, usually microfarads (uF) or picofarads (pF). In Wurlitzer pianos they vary from 1uF to 2200uF in capacitance, with the latter capacitor being much larger in size.
Electrolytic capacitors deteriorate quicker than other types of capacitors, due to the electrolyte solution inside gradually evaporating. A common part of Wurlitzer amp repair is to replace all of these capacitors. Along with replacing ceramic resistors and transistors, this can hugely improve the tonal condition of the amp, notably hiss and noise.
When installing these is very important to insert them with the correct polarity, as incorrect installation can lead to a myriad of problem including the amp not working, blowing fuses, and the capacitors themselves burning out.
Larger electrolytic capacitors in amplifiers require discharging before being removed in order to avoid electric shocks and damage to other audio circuits. As always, take care when taking apart your Wurli or Rhodes amp.
