Audio Transformer Impedance

[Tenderfoot]

Impedance in series is simply added, or so I thought. So why do two 150 ohm primaries add up to 600 ohm according to this data sheet. Am I missing something here, or reading it wrong? Just for information I'm looking to convert a single-ended audio sig-gen output to balanced, for a general purpose test lead.

[nctnico]

Twice the windings gives 4 times the inductance. Lookup the formula to find inductance per number of windings.

[Roehrenonkel]

Hi Tenderfoot,
 
since the two windings are on the same core
and inductance goes by the square you get
2x2x = 4-times the impedance.

Have fun

[Tenderfoot]

I should have known that, I guess at one time I did. But who puts audio through transformers nowadays. Many thanks for your fast replies.

[themadhippy]

But who puts audio through transformers nowadays

plenty of people

[Analog Kid]

Yes, I'm always amazed to be reminded of all the high-end studio microphones that are routed through transformers, right at the source. You'd think that they would degrade the signal somehow, but apparently they don't.

[Marco]

4x the inductance ... but that's not the impedance.

The impedance is with a given recommended load. If you aren't using it in ancient circuits, that probably won't be the impedance.

[TimFox]

A good transformer (probably expensive) run well within its ratings, should not degrade the audio.
Check out the data sheet for this transformer:  note that the distortion rises at low frequencies and higher power.
(0 dBu = 0.775 V RMS, the voltage that gives 1 mW across a 600 ohm load.)
https://www.tubesandmore.com/sites/default/files/associated_files/p-t-lehle-mz-l.pdf
(That vendor has two transformers in that case size, with different impedance ratios, from that manufacturer.)

[trobbins]

Such a transformer 'matches' or 'reflects' the impedance on one side, to an impedance on the other side.  Impedance transfer is related to the turns ratio and is proportional to N squared.  If you don't have 150 on one side you won't present 600 on the other side, or vice-versa.

Your application of single-ended to push-pull (balanced) is very common.  There is still a substantial commercial market for valve related amps (that use output transformers to match impedances) and signal line related transformers.  Many vintage oscillators and distortion meters and signal measuring instruments use a high quality input transformer that allows a variety of matching configurations.