An audio transformer is an electromagnetic system designed to separate an input circuit from an output circuit and produce a signal that passes through it with filtering. A varying electromotive force (voltage) in the secondary winding linked to the other circuit is caused by this changing flux.

Ⅰ Introduction of transformer

A transformer is an electrical system that enables an AC input signal (like audio) to generate an AC output signal connected to it without physically linking the input and output together. By having two (or more) coils of insulated wire wrapped around a heart of magnetic metal, this is done. Those coils of wire are called windings. As an AC signal passes via the input winding (the primary), through a mechanism called inductive coupling, a similar AC signal occurs on the output winding (the secondary). Transformers can be manufactured to have varying impedance ratios by adjusting the number of wire turns in each winding. A signal level gain or loss is given by the ratio between the input and output impedances as the signal passes through the transformer. In order for an input winding to become the output winding and output to become an input, transformers are bidirectional. It may have a gain in signal level when used in one direction or a loss when used in reverse, owing to the bidirectional nature of a transformer.

With different main or secondary windings, transformers may be fabricated. There may also be several connections or "taps" for a winding. Many taps, along with different gains/losses, give different impedances.

Ⅱ What is an audio transformer?

A Transformer receives and transforms a sinusoidal input signal to an output signal. There are no physical relations between the two during this phase of transfer. The two or three insulated copper wire coils (which are referred to as windings) wound around a magnetic iron core directly produce this conversion.

Audio Transformer

The Audio Transformer utilizes this separation property which produces isolation for the transformer's input side amplification mechanism with the output speakers or audio circuitry. In that case, the ratio of the main and secondary winding turns is set at 1:1. The transformer does not change the voltage or current level because of this. It just produces separation for the output speaker system between the input amplifiers.

There is also another audio transformer other than the isolation transformer, which, depending on the input AC signal, can change the output voltage frequency. To generate proper sound vibration, the loudspeaker is a big load and needs to have the necessary current and voltage through it. In order to move a load through it, an Audio Transformer with a Step-Up feature can raise the voltage or current level. The same goes with the Stepdown transformer as well. With the increased current output, it transforms the voltage from higher to lower.

Impedance matching parameters are also given by the audio transformer. When the output of one circuit or device is attached directly to another device's input, it is very important to compare the output impedance of the device and the input impedance of the device. This function is provided by an impedance matching transformer that transforms higher impedance output to lower impedance to drive a low impedance speaker or to feed another low impedance unit.

Ⅲ Functions and Types of audio transformers

1.Functions of audio transformers

1)Step up the signal voltage (increase) or step down (decrease);

2) Raise or decrease a circuit's impedance;

3) Convert from unbalanced to balanced circuits and vice versa;

4) Block DC current in a circuit when permitting the flow of AC current;

5) Separate one audio unit electrically from another. In other uses, although transformers are useful, this paper deals mainly with the use of audio.

2.Types of audio transformers

The Audio Transformer can be used in several implementations. But typically, for audio-related applications, three types of audio transformers are primarily used.

1) Impedance matching Transformer

2) Step up Audio Transformer

3) Step down Audio Transformer

Another special audio transformer is also available, which is useful for digital audio applications and operates at high frequencies in general.

Transformers may also have many main and secondary taps, providing the consumer with the flexibility to adjust the output instruments without modifying the expensive audio transformer. A transformer, for instance, may have multiple secondary taps to link multiple loads with an impedance of 4 ohms, 8 ohms or even 16 ohms, but when operating with it, only one tap must be attached to the load. In general, such transformers are pricey and can be used in retro music systems or amplifiers.

Based to where it may be used, the transformer will have distinct bodies. In order to accommodate the bulky weight, a chassis mount transformer requires a supporting chassis. Based on their characteristics and use, PCB-mounted audio transformers are also available in different shapes and sizes.

Ⅳ Working of audio transformers

While there is no actual link between the main and secondary coils of an audio transformer, the transformer provides bidirectional features between these two windings. The same primary side can also be used as secondary and secondary as primary. In such cases, signal loss in one direction and signal gain in the opposite direction or vice versa is given by the transformer.

The audio transformer operates at frequencies ranging from 20 Hz to 20 kHz. So, there's a much larger frequency spectrum for the application of an audio transformer.

The audio transformer uses the Impedance Matching method, as discussed above. It is very useful for balancing amplifiers and loads that use separate input or output impedances for full power transfer applications (Loudspeaker and others).

Speaker impedances vary from 4 to 16 ohms in modern days, while transistor or solid-state amplifiers use 200-300 ohms output impedance, usually 4 ohms, 8 ohms, or 16 ohms speakers are available. If the amplifier is a retro style, such as an old Valve or Tube amplifier then the output voltage often exceeds 300V with 3k impedance. We require an impedance matching converter that transforms high impedance to low impedance and converts the voltage and current to a degree that powers a loudspeaker directly.

A Transformer may have several windings on the main and secondary side. The ratio of main and secondary windings, the number of coils on the primary side (Np), and the number of coils on the secondary side (Ns) are called the ratio of turns. The main and secondary voltage ratios are also defined by this turn ratio since the voltage is directly proportional to the primary and secondary winding turns.

Ⅴ Limitations of audio transformers

Frequency reaction is the first constraint. Audio transformers, by default, transmit only audio signals. An audio transformer can either limit or obstruct signals that are below or beyond the 20 - 20,000 Hz audio spectrum. Depending on the case, this may be a disadvantage or a gain. A second restriction is that, without causing a skewed sound, audio transformers have a limited input level that can not be surpassed. The transformer is considered to be "saturated" when the full amount is surpassed, i.e. it does not carry any additional signal. A third restriction is that, when used in standard audio circuits, audio transformers do not move up a signal by more than around 25 dB. Because of this restriction, a microphone preamp will not usually be replaced by an audio transformer. An active pre-amplifier must be used instead of a transformer if more than 25 dB of gain is needed.