Audio Transformer

[walid1]

i have many Audio Transformer from my scrap, there is no part no., no spcification or anything to identify it.
i want to use them in audio circuits, but i want to made some experiments to make an initial idea about them, i kow they are consista of a primary and secondary coils, the primary has three terminals and the secondary has two.
in sammery i want to know its impedance ratio.
thanks.
note dont tell me that put connect it with say 1v rms (50Hz) and measure the output, i know this i want some thing new.
you all very good.
walid.

 

[ante1]

Hi walid,

Do you have an audio generator and an oscilloscope? You could then compare the characteristics with know transformers from a manufacturers list. The physical size reveal to some degree the power rating.

 

[audioguru2]

Hi Guys,
The physical size of a transformer reveals the lowest frequency it can pass power without saturation. When the core saturates at a low frequency, the primary is just a low resistance piece of wire. ;D

 

[ante1]

Hi Audioguru,

So in your opinion there is no relationship between size and power rating?

 

[Alun]

In general the lower the frequency the bigger the transformer you'll need for a particular power level but of course higher power ratings require larger transformers.

 

[ante1]

OK, given the fact that we are dealing with an audio transformer we can also assume that the frequency range is in the audio spectrum?  Would it then be false/true to state that “The physical size reveal to some degree the power rating.” ?

 

[audioguru2]

Hi Ante,
I've seen some fairly small high power audio transformers that overload an amp below 100Hz. For the same power at 20Hz the transformer is huge. ;D

 

[Alun]

Yeah, a 50W 50Hz mains transformer is pretty big, a 20Hz 50W transformer will need to be over twice as big, but there again if a 100W transformer has a mimimum frequency of 100Hz couldn't you just use it at 20W with 20Hz?

Hang on it might not be that simple, to avoid saturation you'd have to reduce the input voltage by a factor of 5 so the power level would be a lot lower than 20W unless you reduce the output load impedance by the same factor.