All About Capacitors

In the realm of passive components, capacitors are second only to resistors in prevalence. They are everywhere, in almost every electronic device you can find.

We’re going to take a look at the importance of capacitors in music, with a specific focus on how they help get the most out of audio and communication equipment.

So what makes capacitors so important (and cool)? Well, they can be used to perform some very important functions:

• DC Blocking – Capacitors pass alternating current (AC), but block direct current (DC)
• Coupling – Capacitors are used in between various stages in audio circuits
• Filtering – Capacitors are key elements of filters, such as tone control
• Smoothing – Capacitors are used to smooth out ripples and noise in power supplies
• Timing – Capacitors are used to set the timing of circuits, such as low frequency oscillators
• Storing – Large value capacitors are used to store up energy. For example, the flash of a camera typically uses a capacitor to store and quickly discharge power

Units of measure

As with all passive components, you need to have a basic understanding of units of measure when working with capacitors. Luckily, it’s very simple. Capacitance is measured in Farads, named after English physicist Michael Faraday (very inventive!).

Capacitor Types

Although capacitors come in a wide range of types and sizes, there’s no need to get stressed about remembering all of the individual specifications. The majority of capacitors in audio & communication equipment designs fall into three types:

• Electrolytic: Usually for large capacitance values. These are usually polarized, meaning there are positive and negative leads.
• Film: The most commonly used types. These are non-polarized and can go in either way.
• Ceramic: Used for smaller values. As with Film capacitors, these are non-polarized.

With these basic types in minds, let’s learn a bit more about each.

Electrolytic Capacitors

Electrolytic capacitors are generally visually distinguished by their “can” appearance. They are commonly used in power supply filtering and decoupling applications. They are usually polarized which means that they have a positive side and a negative side.

Electrolytic capacitors come in several configurations, but are mainly found as:

• Axial: There are leads coming out either end of the cap. Typically mounted parallel to the board.
• Radial: Both leads come out of one end. Typically mounted vertical to the board.
• SMD: Surface mounted device, which are designed to be assembled/soldered by automated devices.

The polarity of the electrolytic capacitor is almost always indicated on the device. If you can’t see anything then it’s handy to keep in mind that the positive lead is usually longer.

When working with electrolytic capacitors, here are a few things to keep in mind:

• Polarity: Most electrolytic capacitors are polarized. If you hook them up the wrong way, you’ll block the signal passing through – if you’re lucky. If you’re not lucky, they’ll explode (for higher voltage applications), so users need to be very careful when dealing with capacitors.

• Safety Precautions: This is not usually a concern for low-voltage applications, but for high-voltage circuits, especially tube amplifiers, charge can be held for quite a while. Before you open up anything that plugs into the wall, research ‘capacitor discharging’ and approach with caution.

• Radial vs. Axial: To maximize the real estate on a PCB, you’ll almost always want to use radial leads. If you’re planning on ordering capacitors, get the radial ones. If you order Axial by mistake, it isn’t hard to bend the leads so as to mount them in a radial, upright configuration, so you have more room.

• Non-Polarized Electrolytics: To make things even more complicated, electrolytics are made in non-polarized versions. However, these are rarely used.

Film Capacitors

Film capacitors are typically available in ranges from picofarads up to 1mfd. They are used in decoupling stages, tone controls and sometimes in power supply filtering. Film capacitors also come in a very wide range of compositions, but you’ll probably find polyester film, metallized polyester film, and propylene to be the most commonly available. Film capacitors are non-polarized, and as such,lack orientation markings. Here are the configurations you’ll find:

• Axial: There are leads coming out either end of the cap. Typically mounted parallel to the board.
• Radial: Both leads come out of one end. Typically mounted vertical to the board.
• Box: Compact and easy to work with. Box-configuration capacitors are slightly more versatile than non-box capacitors.
• SMD (AKA Surface Mounted Device):Designed to be soldered on the surface of boards. This is useful in high volume applications where pick and place is used.

Ceramic Capacitors

Ceramic capacitors are typically used for lower capacitance jobs. Values are usually in the picofarad to low nanofarad range.

Most people won’t notice an audible difference between the two types in common use, so you’ll have to test it out for yourself to see what you prefer. A good rule of thumb is to remember that from an electrical engineering standpoint, film capacitors are generally preferred over ceramics in audio path applications. Ceramics are non-polarized and usually supplied in the radial lead configuration.

Which Type Should I Choose?

As with all component types, there are pros and cons for each type. In general, the choice of capacitor type will be made for you, either by the author of the schematic you are using, or by the simple factor of capacitance value. In other words, the schematic will specify electrolytic or film by the symbol used. That makes the choice easy.

But what about when a specific type is not specified, only the value is shown? In general, you look at the value specified, and choose the type appropriate for that value. Other factors may influence your choice of capacitor type, especially in audio circuits. So we’ve made sure to include benefits and drawbacks of each type in this article, so you can draw your own conclusions!