Audio Transformer Impedance - Page 1
Forum section: electronics / projects

author: Tenderfoot
author_rank: Contributor
timestamp: October 22, 2024, 05:30:18 pm
content: 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.

author: nctnico
author_rank: Super Contributor
timestamp: October 22, 2024, 05:45:50 pm
content: Twice the windings gives 4 times the inductance. Lookup the formula to find inductance per number of windings.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: October 22, 2024, 05:46:20 pm
content: Hi Tenderfoot,since the two windings are on the same coreand inductance goes by the square you get2x2x = 4-times the impedance.Have fun

author: Tenderfoot
author_rank: Contributor
timestamp: October 22, 2024, 05:55:00 pm
content: 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.

author: themadhippy
author_rank: Super Contributor
timestamp: October 22, 2024, 06:46:48 pm
content: Quoteplenty of people

author: Analog Kid
author_rank: Super Contributor
timestamp: October 22, 2024, 07:10:56 pm
content: 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.

author: Marco
author_rank: Super Contributor
timestamp: October 22, 2024, 07:12:32 pm
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: October 22, 2024, 07:43:44 pm
content: 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.)

author: trobbins
author_rank: Frequent Contributor
timestamp: October 22, 2024, 10:48:53 pm
content: 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.