How to Choose an Audio Transformer for Clearer Sound Quality

Let us think about the experience when installing a new sound system and starting playing your favorite song. You know that the speaker and amplifier are fine but still feel that there is something wrong with the sound. You hear the voice of the performer less clearly than usual and lose some of the details of the sound. You have tried all options but it did not help to change the situation.

The reasons for such problems can be various. There can be troubles with the amplifier or speaker. However, there can be another element which does not allow the sound to be good enough but remains unnoticed at first glance. One of the examples of such elements is an audio transformer.

It might seem that this element has nothing in common with the sound quality. However, it can be used to transfer the audio signals between circuits and perform impedance matching or electrical isolation. Selecting this element requires taking into account more factors than just its cost or size.

Start With the Equipment You Are Building

The first question is simple. Where will the transformer be used?

A microphone preamplifier has different requirements from a power amplifier or a professional sound system. An audio transformer used in microphone equipment may help balance the signal and isolate connected circuits. In other equipment it may transfer a signal between stages or help connect circuits with different impedance requirements.

First, determine what function the device will be performing, and then compare different transformer types. For instance, a sound reproduction facility would require accurate sound reproduction and low distortion. On the other hand, a public address system will need reliability in functioning for a prolonged time span. The amplifier for a musical instrument would have to cope with a certain signal level and frequency range.

This is important since some transformer types might work perfectly fine in one circuit but provide very poor performance in a completely different one. Once you know the role of your device you can make an appropriate choice.

Get the Impedance Right

Impedance may sound complex at first but it is quite easy to comprehend when you consider the function of impedance in relation to two circuits operating in tandem. These circuits have different electrical characteristics. The transformer has to match their connection.

Let's take the example of connecting a microphone to an audio circuit. Should there be any mismatching of the transformer ratio, the signal transfer may not occur in the manner desired. This would result in some changes in terms of the signal level and/or frequency.

The impedance ratio of the audio transformer is one thing that should be considered, aside from the input and output of the other equipment when selecting an audio transformer. Do not assume that two pieces of equipment will complement each other just because the connectors fit.

Remember also that impedance matching doesn't necessarily mean that you have to match two impedances perfectly, since the required ratio depends on the circuit design and desired results.

Make Sure It Handles the Frequencies You Need

Consider the difference in frequencies between a low bass tone and a sharp noise from a cymbal. Although both tones belong to the same musical composition, they occur at various frequencies within that composition. It is important that the transformer be able to cope with the frequencies of the equipment without affecting the signal to any great degree.

In case of a weak low frequency response, the tone of the sound will be distorted. Weakness in high frequencies makes music and speech less clear. Such deficiencies can be easily overlooked until you become accustomed to listening and comparing your equipment to other devices.

The response of an audio transformer is based on various aspects like core material, winding design, inductance, and the load that is attached to it. Even the signal level affects its performance.

One should consider checking the frequency range and conditions at which the test was done before coming up with a conclusion. Just because a datasheet shows a broad frequency range does not necessarily mean that the transformer will work well under all conditions.

Avoid Distortion When the Volume Goes Up

Have you ever tried turning up the volume and noticed the sound quality deteriorating? The first reaction would be to look at the speakers, but there could be another reason why this is happening.

Magnetic core saturation is one such reason. Magnetic core saturation is a situation where the magnetic core has been overloaded beyond its capacity. As a result, the transformer produces distortion. Low-frequency signals especially put high demands on the magnetic core.

This can be overcome by selecting the right transformer for the job based on its requirements and capabilities. The size of the core, as well as its material, have an effect on its performance. The design of the windings also matters.

Don't make your selection based on just one perfect figure of performance. Look at the distortion levels of the transformer under operating conditions. In case you need a transformer that has to work with low-frequency signals, take this into account too.

Keep Signal Loss Under Control

Another thing that needs to be investigated in regard to transformers is the insertion loss. Simply put, insertion loss measures how much signal the transformer loses under specified conditions.

There should always be some signal loss but there are cases when the loss is too great and as a result the next circuit receives a weak signal compared to expectations. This becomes especially important in devices where it is important to keep the original signal strength.

When investigating an audio transformer take a closer look at the insertion loss specifications and pay attention to the conditions in which they were obtained. Source impedance and load can influence the measurement so the results should make sense for your case.

But again, having good insertion loss values does not necessarily mean that the transformer will provide better performance. An audio transformer can have a low insertion loss but an improper impedance ratio and frequency response.

Look Beyond the Size of the Component

Transformers that appear to be very similar from the exterior can function in vastly different ways. This is often due to differences in their internal materials and construction.

Properties of the core materials will affect the transformer’s reaction to the changes in the magnetic field. It will affect its performance and losses within the required frequency range. The configuration of windings also plays an important role as it will affect the electrical properties of the transformer and possible interference.

Shielding can become necessary when the transformer functions close to power supplies and other sources of electromagnetic interference. Different constructions can be necessary depending on the equipment and environment it is expected to operate in.

It does not necessarily mean that small transformers are worse while large transformers are better. All that matters is whether it is suitable for the application. You should consider specifications and physical properties together.

Don't Ignore Hum and Unwanted Noise

The buzz of faint frequency can be very irritating. Lowering the sound level will do nothing since the noise will still persist. Switching one of the cables around will not remove the noise either. Sometimes the reason for the noise can lie not in the audio signal but in something else.

In order to isolate circuits electrically an audio transformer can be used. In case of proper installation it can help diminish the noise created by certain ground current lines. Also, it can be one of the components of a balanced audio connection, which can decrease the influence of external interference on the system.

But a transformer cannot solve all noise issues. Incorrect grounding, damaged cables and interference created by nearby equipment can create noise problems as well. If the transformer is not the source of the noise it will not resolve the issue even after its replacement.

When dealing with existing equipment it is necessary to check connections and establish the moment when the noise happens.

Test It Before Making a Final Decision

Specifications will be helpful in reducing choices; however, testing will let you know the behavior of the element within your own circuit.

Test the signal in the frequency range that you require and at different operating levels. Observe the audible differences while making measurements of the frequency response distortion and signal attenuation when the proper equipment is available. Aim to emulate the conditions that the transformer is expected to see during its operation.

This phase is especially important for manufacturers prior to mass production since it will help to find the potential problems of compatibility and avoid choosing the wrong component for your equipment.

The CET Technology provides OEM clients with both standard and customized magnetic components for various equipment. Whatever the project you have, the key point for you is to make sure that the chosen design meets the circuit requirements.

Choose for Performance Rather Than Appearance

It is not difficult to select the correct transformer provided you know what you are dealing with. In addition to learning about the type of equipment you are working on, consider the frequency response, impedance ratio, distortion, and insertion loss of the component.

These features all contribute to forming an overall idea of the performance of the transformer. Selecting an appropriate audio transformer will provide for accurate transfer of the signal and good sound quality of the equipment.

There is no such thing as the perfect model; the appropriate one is the one which works best for your design. Make sure that you take your time to analyze the specifications of the component.

Good sound can be achieved if everything is done right. Selecting the appropriate transformer is one of those little things that will definitely affect the performance of the equipment.