DOD D.I. Transformer

[dpresley58]

Got an older DOD passive DI that simply has 2 1/4" jacks running through a small transformer out to a XLR jack.

How would I test that, and what would a good replacement be if it is found to be defective? Been trying to find general information on audio transformers and haven't come up with much in terms of principles of operation, specs, etc.

Thanks in advance.

[Enzo]

Test? Does it work? That's the test. it is a transformer, so it is not likely to change in value or anything. The windings coulb get burnt open if something got to it, ir the wiring could short out, but really, it pretty much either won;t work, or it will be right.

If I had to replace a part in a DI box, I;d have to consider what I could get a replacement DI box for first.

[dpresley58]

I understand the economics involved, but all this is more for my own education rather than the cost. It just puzzled me how something so simple is causing problems.

Metered the transformer and didn't get shorts across any of the leads. Don't have the notes in front of me, but the primary was somewhere around 1.8k if I recall correctly. The secondary is CT and was evenly divided across them, about 70 ohms or so across the outside and 35 +/- from the CT, so the transformer is doing its job. The jacks are functioning as intended.

I suppose the real question was regarding information about audio transformers in general.

[Enzo]

OK, well, a transformer is really just two coils of wire around the same form. SO once we establish that it is not open, and not shorted to its frame, we can then try to determine if it has shorted turns. Over at RG's Geofex page there is a tip on transformer testing. But really a shorted turn will seriously damp out the transformer. Like drivign your car with the parking brake on, you should notice the difference.

Your ohm meter measures the resistance of the wires in the winding, it does not measure impedance. A transformer doesn't really have an impedance. it only has ratios. For example a 10k ohm to 600 ohm transformer ONLY has a primary impedance of 10k when a 600 ohm load is across its secondary. I think of transformers as a set of gears. Gears have no speed of their own, only a ratio of speeds.