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Where can I get this transformer?

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In the project http://www.electro-tech-online.com/threads/simple-lie-detector.40/ I wanted to know where I might find the transformer? I have all the other parts put together and just need the transformer. I dont know a lot about transformers and did not know what that 200K to 1K was? I asked a guy at radioshack and I think he did not know what I was talking about. He said they have transformers but I did not what to get. If you know of a electronic device that has this transformer in it please tell me I might have it and can take it apart.


Thanks,
Kyle
 

daviddoria

New Member
what you need is called a mini-audio transformer. It comes in a package no bigger than .5"x.5"x.5" and has 4 leads coming out.

i can't remember where i got mine, however i remember it was rather hard to find.

But yea, ask for a mini-audio and they should start knowing what you are talking about more.

good luck
david
 

stevez

Active Member
The transformer described is a 1,000 ohm center tapped - using one half or 500 ohms. The other side is 200,000 ohms so the ratio is 1 to 400.

From what I know of transformers the turns ratio is what really matters however the impedance also matters in some situations. I don't know if this is one of those situations. Now for the confusing part - I don't think the 1k side actually measures 1k and the 200k side 200k but there are some rules of thumb on what the actual impedance should be. I recall something like 4x the actual impedance but someone else will have to confirm that. It's the turns ratio that will match a 1k circuit to a 200k circuit.

While I do believe that the circuit works I'd have trouble expecting an audio transformer to have a construction that would tolerate high voltages for any amount of time.

So in your search, look for small audio transformers with a ratio of 1 to 400 or 400 to 1 and you might get closer to what you need. Newark Electronics, MCM and others like Jameco might have them. I actually have one very similar - 600 ohms on one side and very high on the other side - made for some kind of telephone or transmittter interface.

Hope this helps.
 
After searching I found this transformer and wanted to know if this would work? Sense I dont really understand transformers yet.

http://www.jameco.com/cgi-bin/ncomm...nbr=91&prrfnbr=355000&cgrfnbr=501&ctgys=[url]

Thanks,
Kyle[/url]
 

Roff

Well-Known Member
stevez said:
The transformer described is a 1,000 ohm center tapped - using one half or 500 ohms. The other side is 200,000 ohms so the ratio is 1 to 400.

From what I know of transformers the turns ratio is what really matters however the impedance also matters in some situations. I don't know if this is one of those situations. Now for the confusing part - I don't think the 1k side actually measures 1k and the 200k side 200k but there are some rules of thumb on what the actual impedance should be. I recall something like 4x the actual impedance but someone else will have to confirm that. It's the turns ratio that will match a 1k circuit to a 200k circuit.

While I do believe that the circuit works I'd have trouble expecting an audio transformer to have a construction that would tolerate high voltages for any amount of time.

So in your search, look for small audio transformers with a ratio of 1 to 400 or 400 to 1 and you might get closer to what you need. Newark Electronics, MCM and others like Jameco might have them. I actually have one very similar - 600 ohms on one side and very high on the other side - made for some kind of telephone or transmittter interface.

Hope this helps.
The impedance ratio is the square of the turns ratio, so a 1:200 impedance ratio is only a 1:14 turns ratio. Using half the primary winding, the turns ratio will be 1:28. I don't think this is a direct indication of the output voltage, because the current is interrupted, which makes it a flyback pulse generator, and the voltage becomes a function of stray capacitance, load resistance (the victim's skin), etc.
 

Roff

Well-Known Member
Be careful you don't blow 20 bucks. This part ain't the one you're looking for. The one you want is 1K:200k. This part is 1k:20k.
Digikey has a Mil spec part for $21 that meets your requirements. The Digikey p/n is 237-1137-ND.
I think I would shop some more.
 

Gene

New Member
Woops. Miscounted the zeros. Anyway, $20 is wat too much for these things. I would expect to find one (actually, in my junk box) at a parts store (certainly not Radio Shack) for $3 - $5 - tops.
 
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