Simple Speaker Audio Output Transformer Circuit

Suppose you have a powerful voice, but you are whispering through a tiny straw to make the sound reach your friend far away.

That would not work well, in a stereo system where the audio output transformer acts like a megaphone for the electrical signal.

It takes the strong signal from the amplifier and adjusts it to perfectly match the speakers ensuring all the music comes out clear and powerful, just like you intended.

Circuit Working:

Parts List:

The above diagram shows the transformer is key for connecting the speaker to the circuit.

It is made by wrapping thin wires around a ferrite rod.

The number of turns on the wire not the rod size itself, determines how the transformer functions.

Here is how to wind it:

Secondary Winding: Start by wrapping 50 turns of the thicker 0.25mm wire around the rod.

Primary Winding: Now, carefully wind 300 turns of the thinner 0.1mm wire on top of the existing layer.

This winding ends with a loop the center tap.

Complete the transformer by adding another 300 turns of the thin wire.

Connections Do not Affect Performance:

The good news is that the order you connect the speakers wires top or bottom of the secondary does not affect the sound.

Similarly, for the primary winding, it does not matter which end connects to the transistors collector in the circuits used throughout this book.

Formulas:

From the above circuit diagram below is the formula for primary to secondary turns ratio of a transformer:

Turns Ratio (n) = N_p / N_s

where,

• n is the ratio of turns, not to be confused with units.
• Np is the central coils number of turns
• Ns is the quantity of turns within the secondary coil.

The voltage differential between the main and secondary windings is determined by this ratio.

This is how it operates:

It is a step up transformer if the turns ratio (n) is more than 1 (Np > Ns).

By a factor of the turns ratio, the voltage in the secondary winding (Vs) will be greater than the voltage in the primary winding (Vp).

V_s = V_p * n

A step down transformer is present when the turns ratio (n) is less than 1 (Np < Ns).

A factor of the turns ratio will determine how much lower the voltage in the secondary winding (Vs) is than the voltage in the primary winding (Vp).

V_s = V_p / n

Crucial Information:

The product of the voltage and current across the windings of a perfect transformer stays constant, this implies:

V_p * I_p = V_s * I_s

• Vp is the primary voltage
• Ip is the primary current
• Vs is the secondary voltage
• Is is the secondary current

Real transformers lose some energy as a result of core losses and winding resistance.

Usually, the efficiency ranges from 90% to 99%.

Uses for the Turns Ratio:

Transformers can be used to step up or step down AC voltages for a variety of purposes, such as powering electronic devices with varying voltage needs, by modifying the turns ratio.

Conclusion:

Audio output transformers were key elements in older amplifier designs ensuring a good match between the amplifier and speaker for optimal sound quality.

They addressed impedance differences and blocked harmful DC current.

While less common today due to advancements in amplifier design these transformers remain fascinating components in the history of audio technology.

References:

Can an ordinary transformer be used for coupling the speaker with a transistor amplifier