# Parallel Primary Coils of Two Different Transformers

Attached below please find a figure1 which is what I want to achieve (i.e. split a balanced audio line into two isolated outputs in a passive manner). The transformers that I currently have are 10 kΩ:10 kΩ with a 550 Ω primary and secondary resistances.

1. If the transformer is 10 kΩ:10 kΩ, this means that for maximum power output a 10 kΩ load must be used at the secondary and at the same time the primary should not be loaded? For example an output source with an output impedance of 10 kΩ will definitely load the primary of the transformer.

2. If I parallel the inputs of the two transformers as seen in the figure, will the effective impedance become 5 kΩ?

3. If the effective primary impedance becomes 5 kΩ, this means that the secondary output impedance of each transformer is now 5 kΩ?

4. If the effective primary impedance becomes 5 kΩ, is maximum power transfer still achieved?

Thank you!

• The transformers themselves don't really have an "impedance of 10k". What they do is REFLECT the impedance of your LOAD. Anyhow, to me these are clearly XLR jacks. You probably do not need to transfer "maximum power" for microphone level signals. Am I right with that guess??? Commented Jan 29, 2021 at 21:50
• @KyleB >What they do is REFLECT the impedance of your LOAD. If I put the primaries in parallel I will have a 5kΩ at the primary and so 5kΩ at the output? >Anyhow, to me these are clearly XLR jacks. You probably do not need to transfer "maximum power" for microphone level signals. Am I right with that guess??? Actually no since XLR jacks are used also between outboard audio gear not just microphones. Commented Jan 29, 2021 at 21:56
• Ok, so they're for audio signals. Still that's a "line level" signal of maybe 1 volt RMS. Not a power amp ;) (I'm very familiar with audio gear, I own a full PA and run sound for local bands & other groups for fun). Yes, if you have 5k LOAD, and these transformers are wound 1:1, you'll see 5k at the input. (Plus wire resistance) If you put these in parallel, each with a 5k load, your pad will see paralleled 5k, or 2.5k impedance. However, no modern audio equipment I've ever come across has an input impedance low as 5k. Usually they will be MUCH higher. Commented Jan 29, 2021 at 22:11
• One reason input impedances are so high is (very very often) the outputs of gear X will be capacitor coupled. If the impedance is too low, that turns the input into a high pass filter and you end up cutting your bass frequencies. "Generally" you should have maybe 20-30k input impedance. This value will definitely be specified in your manual. Keep in mind, you're not transferring "power", you're transferring a "voltage" signal. So ensuring you have a perfect match isn't really a super high requirement. What you REALLY want is to not introduce distortion. Commented Jan 29, 2021 at 22:16
• No, I will have a 10k load. I meant that if the primary of my transformers have a 10k impedance each and I put them in parallel, then at my input I'd have a 5k effective impedance. Having a 5k effective impedance at the primary will show as a 5k impedance at the output? Commented Jan 29, 2021 at 22:21