• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Measuring audio transformers

Status
Not open for further replies.

whiz115

Member
Hi guys!

some of you know me, that i like to play around and experiment and sometimes burn things! :D

So.. i want to measure some audio transformers, the problem is that the way i'm connecting them is totaly wrong!

Sound card speaker out > audio transformer output (~4ohm impedance) > audio transformer input (~3Kohm) > sound card line in.

Although with the above way i can use RMAA to take some measurements...i have the feeling that they are not acurate since it looks wrong, but no other way worked for me!

can somebody explain to me how this guy does it?

Lundahl 1545a Audio Transformer
 
Last edited:

kchriste

New Member
Forum Supporter
The transformers he is using are 1:1 and 1:2 turns ratio with maybe 600Ω impedance. The one you appear to have (3000Ω/4Ω impedance) is a 1:750 turns ratio which will give you different results.
 
Last edited:

whiz115

Member
i have several transformers 4k/8ohm, 3k/4ohm/8ohm... and i would like if possible to measure them all.

any help will be greatly appreciated!
 

Roff

Well-Known Member
The transformers he is using are 1:1 and 1:2 turns ratio with maybe 600Ω impedance. The one you appear to have (3000Ω/4Ω impedance) is a 1:750 turns ratio which will give you different results.
The impedance ratio is the square of the turns ratio.
3000:4 is a 27.4:1 turns ratio.
 

audioguru

Well-Known Member
Most Helpful Member
The transformer might overload the sound card's speaker output and its voltage will be much too high for a line-level input.

So you will smoke both ends of your sound card. Why use a transformer? Why use the wrong transformer?
 

audioguru

Well-Known Member
Most Helpful Member
You can use a power amplifier to drive the transformer at a fairly low level at first, then measure its output with an oscilloscope or audio voltmeter.
Of course you must load the transformer according to its spec's.
 

whiz115

Member
You can use a power amplifier to drive the transformer at a fairly low level at first, then measure its output with an oscilloscope or audio voltmeter.
Of course you must load the transformer according to its spec's.
Audioguru we live at 2009 we use software here! :D if i wanted to do it with DMMs, etc i could use this help! not yours! :D

http://www.radioelectronicschool.net/files/downloads/Testing audio transformers.doc

kidding... seriously now, i don't own an oscilloscope...i would like to try measure them with RMAA (i suggest you download it if you don't have it)

other than the amplifier you proposed what else should i do so i can connect it to the line in of a sound card?

thanx.
 

audioguru

Well-Known Member
Most Helpful Member
You can use a 5.1V zener diode back-to back to an ordinary diode to protect the input of your sound card from the very high voltages produced by your backwards transformers.
But I don't know why you are measuring lousy old transformers.
 

kchriste

New Member
Forum Supporter
whiz115,
Why don't you try to find a 600Ω line matching transformer instead? You can find them in scrapped modems or most things that interface with a phone line. It sounds like you want a high quality transformer which has a good frequency response in the audio band, so the one out of a modem probably won't be good enough but you could have fun testing it.

The impedance ratio is the square of the turns ratio.
3000:4 is a 27.4:1 turns ratio.
Ooops! :eek:
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading

 
Top