audio transformer

[dbyrd26]

Can anyone tell me how to use an audio transformer. I got one from radioshack for a couple bucks and am unsure how to wire it. I will post a picture later if needed.

 

[(*steve*)]

That's kind of a backward question unless you got it really cheap (i.e. you can't resist a bargain) and now you want to use it.

You would probably have to describe the transformer to us -- they have many characteristics (including power handling capacity) which are needed information if we are to suggest a use for it.

 

[dbyrd26]

That's kind of a backward question unless you got it really cheap (i.e. you can't resist a bargain) and now you want to use it.

You would probably have to describe the transformer to us -- they have many characteristics (including power handling capacity) which are needed information if we are to suggest a use for it.

Ok, so it looks like a step down transformer. Very small one. There's on one side 3 wires, blue, black, and green. And on the other 2 wires, a white and a red. Heres the specs:

Impedance 1khz, 1v, 0mADC
Input 1 kohms +10%
DC resistance (input) 70 ohms +20%
Dc resistance (output) .62 ohm +20%
Frequency response 300-10,000Hz +3db
Insulation resistance > 100 Mohm @ 100vdc

 

[(*steve*)]

Weird looking specs.

I'd say it's an audio coupling transformer, perhaps similar to one of these.

It's used (or was used -- modern designs don't use them) to couple a high impedance stage to a low impedance stage, possibly even to couple a signal to a low powered speaker.

 

[flippineck]

When I was a kid I used to make audio oscillators with small transformers like this. I had a Radio Shack (Tandy) 10-in-1 project kit, and with a small speaker, a resistor and a ceramic capacitor, and a 2SB56 transistor, it made a little beeper

I wish I could remember the circuit diagram. I learnt how to etch PCBs from that circuit

The resistor and capacitor were in parallel with one side of the pair connected to the transistor's base. one end of the transformer primary went to +9v. You took the output straight from the secondary to the speaker. that's all I can remember :-( The middle tap of the transformer went to... the other side of the RC pair? Maybe the emitter of the transistor went to the other side of the transformer primary, and the collector to 0v. Wild guesses, memory not so good

Juggling with the values of R & C, you could make the frequency go up & down.

This kit had the same circuit.. http://www.ebay.com/itm/1972-Radio-...ir-Electronic-Project-Kit-Hobby-/300997638574

"code practise oscillator"

 

[Externet]

Something to do with that transformer...
Connect the 0.62 ohm winding in series to only one telephone wire.
At the other 70 ohm winding, you can inject audio, background music, or record a conversation from the line.

 

[KrisBlueNZ]

When I was a kid I used to make audio oscillators with small transformers like this. I had a Radio Shack (Tandy) 10-in-1 project kit, and with a small speaker, a resistor and a ceramic capacitor, and a 2SB56 transistor, it made a little beeper I wish I could remember the circuit diagram. I learnt how to etch PCBs from that circuit

Yeah that brings back memories!

If it's the one I'm thinking of, it was a Hartley oscillator. The centre tap connected to the supply rail (negative, if you're using a 2SB56, which is - was - a germanium PNP). The collector connected to one end of the primary, and the base was driven from the other end via a capacitor, with a bias resistor to the supply rail. And there was a capacitor across the whole primary to tune the oscillator.

You could add an electrolytic with a resistor in series between the base and emitter to make it chirp like a bird! I never understood how that worked.

I remember doing the ferric chloride thing too, around that time. I made a few designs, which bordered on working as intended. I wish there had been someone who could have taught me stuff back then.

 

[(*steve*)]

I wish there had been someone who could have taught me stuff back then.

I wish I had paid more attention to why they worked rather than just that they did.

Wasted years of less education than I may have otherwise had

Damn Al Gore for not inventing the internet earlier!