Line transformers

JoleFIN · Jan 19, 2010

I've got two of these line transformers, dating back to somewhere mid 80'ies I believe (these were part of a video conference system with Shure ams8000 mic mixer and ams series mics) and I've kept them safe in case of needing them some day for their specific purpose. Which I don't know exactly. They've got small transformers inside, and I measured the impedance between the tip and the ring at the plug side, both were around 112-113 ohms when the switch was in "Low imp" but differed from each others at "High imp" by figures of 1272ohm and 1310ohm so I believe they're not good for any serious stereo apps. The XLR end gives me 112ohm on both, regardless of the position of the switch. Are these any good for instrument line input or alike? Any ideas where to use these?

-J

ihscoutlvr74 · Jan 19, 2010

They are mic to line transformers often used on cheap pa mixers (like old shure) that don't have mic inputs or not enough for an application.

Many companies still sell them like audiotechnica, etc for under $20 and I wouldn't use the trafos in anything for a studio application.

Hope that helps, Nathan

PRR · Jan 20, 2010

What Nathan said, with different slant...

They may be very suitable for not-LOUD voice-range use.

The audio impedances are much higher than the DC resistance. Perhaps 10X-20X. So perhaps like 1.5K:15K or thereabouts; maybe a bit higher (the secondary winding may not be as thin as would be optimum).

Therefore your 38 ohm "unbalance" is completely insignificant compared to ~~15K nominal or the usual 22K-500K "hi-Z" input. 0.01dB difference. The DCR may reflect a few extra turns and different ratios: this could be another 0.25dB difference. Your mikes and other gear are surely 1dB or more off-balance, and you always have some way of trimming balance in the mix.

They may not be flat past 10KHz. They may saturate on loud bass. They have a several dB noise figure even if you had an Ideal Amplifier. These things matter for some work, not for other work.

They are killer when you find yourself needing a "PA system" but only have XLR mikes and a guitar amp. It mates the connectors and gives the little boost a dynamic needs to get a guitar amp up near howl-gain. Party. Impromptu talkback. Folk-singer in a rowdy dive.

And yeah, you can get more for $17 each.

CJ · Jan 20, 2010

first band was bass and guitar into the vibro champ, (can you imagine the poor speaker?)

and lead guitar and vocals into the princeton reverb, and that prroblem solver thingys for the mic.

hey, we made the talent show, but the paul revere copy band won out, because they had uniforms and dance steps.

PRR · Jan 20, 2010

> uniforms and dance steps

Every once in a while, it is good to remember the IMPORTANT things in life. It's not the tenth-dB-at-13KHz or 2%THD-at-57Hz stuff.

CJ · Jan 21, 2010

i guess they were not ready yet for a grade school version of the Stones.

everything was still Fab at that point. Frankie Avalon had just left the building.