I am using an audio transformer in a schematic, but I don't understand why. Can someone explain how a 1000 ohm to 8 ohm audio transformer works? (Radio Shack #273-1380)
give pinout audio transformer
I guess you know that if you use a transformer with two separate windings, they are electrically isolated. The audio transformer is used to match a 4 ohms load such as a speaker, to an amplifier which does well with say, a 100 ohms load. In that case, you use a step down transformer with ratio N 5. Note that N^2 is 25 and 100 ohms divided by 4 ohm is 25. The voltage is brought down by a factor of 5 while the current the transformer can deliver increases to five times that the amplifier can deliver. So it is used as an impedance matching device. Just as a 23VA transformer operate at 230V takes 100mA and delivers about 1 amp at 23V if it is a step down transformer of 10:1. the secondary voltage is 23V.
The transformer is for impedance matching, but in your circuit could be for some other purpose, e.g. I have one in a DC-DC voltage converter, putting out abt. 75V from a 9V battery. Another, I have as an isolation transformer from a computer soundcard to an external circuit. The impedance match function is usually matching a radio circuit impedance to a loudspeaker impedance (8 ohms). So far as pinouts, look in online catalogue. However, the primary connections are green and blue, with a black centre tap. The 8 ohm speaker secondary winding has red and white wires.
Audio transformers are rarely used today, as their function can be eliminated by direct coupled transistors. Transformers add distortion, and frequency problems, and should be eliminated where ever possible. I'd have to see the schematic, but I'd advise not using the transformer unless absolutely necessary. Radio shack provides zero in specifications for this, which also doesn't help. In so far as the pinout, from the photo, it appears the wires are labeled. .
Isolation Transformer Radio Shack
