Phone line isolation transformers indentifcation help

Humner · Jan 15, 2016

I picked up a 3u rack enclosure which came with what was described as phone isolation transformers cards. Looks to have come out of a broadcast studio. I didn't pay much and bought it for the 3u rack to use for another project, I was hoping someone might be able to identify what the transformers may have been used for exactly and if I could use them as output transformers for mic pres or other projects. Or maybe these were used for power supply isolation and have no use for audio?

My understanding is if they were/are used for phone duties they could be 600:600. They don't have any markings to identify their value or specs. I have contacted the manufacturer and they haven't got back to me regarding there specs etc.

I have attached a photo. They are quite large. They have a single primary and secondary winding.

Any thoughts or advice welcome, thank you.

PRR · Jan 16, 2016

http://www.dyne.com.au/ -ask them.

What is the DC resistance each side?

It may be interesting to know if the core is laced or gapped. You might have to bust-off a bracket to see.

Humner · Jan 16, 2016

I contacted dyne, but never heard from them.

40.5ohms
41.9ohms

I'm not sure what to look for to see if the core is laced or gaped. I tried to remove a bracket but found they are epoxy'ed on.

I can test frequency response, but that's about it, if it passes a flat signal then the only other part i would be worried about is how much signal it could handle, and I guess due to the size and weight of the transformer I could assume it will take quite a high level before it saturates. Would that be a fair assumption?

emrr · Jan 16, 2016

typical 600:600 resistance. Look up broadcast level standards. That's a clue.

PRR · Jan 16, 2016

They ARE frikkin large. I'd assume +8dBm on the average-meter with 16dB headroom for peaks down to 50Hz. Pretty much higher than any level you need to get fine audio around the building. (Such iron was used to send fine audio down miles of hostile telephone line to a transmitter or a radio network.)

Humner · Jan 17, 2016

thanks for the help guys. DYNE got back to me this morning.

"capable of up to 20 dBm at broadcast quality."

Looks like a nice set of transformers. I have 2 cards, so 8 of them, I'll have to save these for some worthy projects.