Impedance

Practical Transformers 

In the rather loose world of electronic components, transformers are noted for being 

sloppy in their construction. If you are using a transformer only to adjust the power from 

P.G.&E. levels down to 24 volts, you aren't going to worry much about things like 

harmonic distortion. But if are using one to connect a $4000 microphone, worry. 

 

Power transformers 

Power transformers are found in power supplies. They typically have a primary rating of 

120 volts (In the US) and a secondary of 9, 12, 18, 24 or 48 volts. You often see multiple 

secondaries. If you need a + and – 15 volt supply, the transformer will have two 12 volt 

secondaries or a 24 volt secondary with a center tap. Power transformers have a current 

rating. Exceed that and they start to smoke. The primary and secondary wires are 

identified by color, and there's no handy standard, so keep the paperwork that comes with 

the thing. (Black for the primary is a good guess). 

 

Power transformers hum. Toroidal designs hum less than the standard kind. 

 

 

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Notes on Impedance 

Peter Elsea 10/21/11 

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