Small audio xfmrs used as inductors

[NewYorkDave]

As many of you know, small "transistor" type audio coupling transformers can sometimes be applied successfully as inductors in equalizer and filter circuits. Problem is, the inductances are almost never given, so you have to buy some samples and test them yourself to find the values you need.

I had a little free time last night, so I took inductance and resistance readings on several small audio transformers from Mouser. I figured this data could be useful to somebody. Please note that I did NOT measure distributed capacitance/self-resonance. Be sure to obtain and test samples of any type you intend to use before designing into a circuit. Fortunately, they're very cheap.

 

[CJ]

Cool Dave!
I have an idea on where to use those large inductances already!

Remember, you leave the secondary leads open if say, you are using the primary for your inductor, don't short them.

 

[Underthebigtree]

I'm sure others have already said this in other posts, but welcome back, NYD! So glad to learn from you, as always.

 

[clintrubber]

That's nice info ! Thanks (and indeed, good to see that Avatar again!)

That 42TM019 Mouser is featured in the PU-simul circuit from Jack 'AMZ' Orman:

http://www.muzique.com/lab/pickups.htm

Based on the circuit values & the freq-plot I figured around 2.45H each for the prim halves, about near your measured 3.5 H. Nice, can adjust the 330 pF cap (or take several switched values).

Don't know about spread of those inductance values between samples but since final adjustment should be by ear anyhow it'll be fine.

Bye,

Peter

 

[Steffen]

is ironcore based inductance more signal dependend than those made with ferrite cores? if yes the filterfrequency will be modulated by the signal?
maybe this sounds cool? dunno...just thinking loud...

 

[jhaible]

[quote author="Steffen"]is ironcore based inductance more signal dependend than those made with ferrite cores? if yes the filterfrequency will be modulated by the signal?
maybe this sounds cool? dunno...just thinking loud...[/quote]

Is there an overview somewhere that compares different core matrials?

Whan I read about "x percent Mumetal", "M6", "Amorphous core", "special audio core", I know it will make a difference, but not quite _what_ difference.

JH.

 

[CJ]

There are some cool articles at the Sowter website.

 

[Bigorno]

Hello,

First of all, thank you New York Dave for the good job!

Secundo, is it possible someone confirm the value measured for the 42TM019 please?
I want to use it in a kind of Pultec EQ for bass guitar.
But unfortunately I don't have a tester to measure it.

Or perhaps someone have a better idea?

Thank you very much for the help.

 

[rafafredd]

http://www.ebay.com/itm/1pc-A6243L-LCD-Capacitance-Inductance-Meter-Tester-Multimeter-2000pF-20H-/190580006507?pt=LH_DefaultDomain_0&hash=item2c5f741e6b

works great!

 

[ruffrecords]

If it's OK with you NYD I'll cut and paste your pic into my transformer inductance doc in its thread.

Cheers

Ian