Multi-winding transformers and loads

[OneRoomStudio]

I'm trying to wrap my head around how impedance is reflected in multi-winding scenarios.

Let's say I have a 1:1:1 transformer, and I drive one winding with a low impedance source (let's say 50 ohms), I then take an output from another winding into a low impedance input (let's say 600 ohm), and I use the third winding as an output into a high impedance input (let's say 10K).

-Does output see these two loads in parallel (reflecting ~ 565 ohms), or treat them 'separately' as two paths.
-Is the 10K input effected by the 600 ohm input (and vice-versa)?
-Is it a bad practice to drive unbalanced loads this way?

 

[JohnRoberts]

yes they appear coupled in parallel. 

Yes the output on the hi-z tap will reflect voltage drop from loading on the low-z tap.

The regulation (transfer losses ) of the transformer depends on the design.  Using it this way is ok if transformer was designed anticipating this application.

JR

 

[abbey road d enfer]

-Does output see these two loads in parallel (reflecting ~ 565 ohms)

Yes.

-Is the 10K input effected by the 600 ohm input (and vice-versa)?

A little. The loading is applied to the equivalent reflected impedance. Assuming zero DCR for the windings, the reflected impedance at each winding would be 50r in parallels with the load to the other secondary. This gets more complicated when introducing the windings DCR. The equations are not difficult: Ohm, Kirchoff and Thevenin are the usual suspects there, but solving lengthy 4-unknown equations is never funny. And afeter all not very worth it. Ballpark figures acn easily be found. If you want precision, use a simulator, such as LTspice.

-Is it a bad practice to drive unbalanced loads this way?

Not at all. I've done many distro amps using quad-filar xfmrs driving three separate outputs. These outputs would not be 100% independant, though. If one output is shorted, the level of all outputs will go down. that's why it is common to use separation resistors there. But any output can be grounded or floated without any issue.

 

[JohnRoberts]

note: in the installed sound (background music) industry, amplifiers routinely have multiple different voltage output transformer taps. You can pull power from multiple taps at the same time, but not more than the total rated amplifier output power.
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Some  tube audio  amps have different speaker impedance taps, similar rules apply

JR

 

[OneRoomStudio]

Thanks! That makes sense and confirms my suspicions. So, to confirm, it should be a workable solution to use a 1:1:1 transformer to provide both a low-z balanced (floating) output and an unbalanced "instrument" output by stringing a 10K pot across the other output. Does that make sense?

 

[JohnRoberts]

Thanks! That makes sense and confirms my suspicions. So, to confirm, it should be a workable solution to use a 1:1:1 transformer to provide both a low-z balanced (floating) output and an unbalanced "instrument" output by stringing a 10K pot across the other output. Does that make sense?

Yes as long as the combined load is reasonable.

JR