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XLR to Minijack Repair

I have two and 1/2 stereo adapters that take mic/line level inputs and match impedance (not sure on this one) to a 8/32" stereo phono jack for a video camera. We suspect that some of the x-formers are bad in the unit. Would this most likely be Low to high Z x-former or just

1:1 isolation transformers. The 1/2 side that works shows almost a short circuit on both sides of the x-former. However several of the ones that don't work show 5~600Ohms pure DC resistance. The 500Ohms sounds more normal for a small signal x-former than nearly zero. I plan on tracing the circuit with a scope and an injected sine wave to see where my signal disappears. However I am not able to find the x- former on the net. It has BEI MA392 R.2 RoHS stamped on the side. No other info.

Thanks, Chris Maness

Reply to
Chris
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One other possible source of confusion stems from the fact that there is no standard XLR wiring schema. So next to some units being faulty, you may be looking at wiring discrepancies. There is balanced vs unbalanced. And USA (2 cold, 3 hot) versus European (2 hot, 3 cold)

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met vriendelijke groet,
Gerard Bok
Reply to
Gerard Bok

The standard for XLR wiring is 1 ground, 2 hot, 3 cold. It wouldn't make much difference if 2 and 3 were reversed as long as pin 1 was always ground

Ron(UK)

Reply to
Ron

It certainly would if using two mics close together...;-)

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*Just give me chocolate and nobody gets hurt

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

Well yeah, on the other hand, two mikes close together may require the polarity of one to be reversed. But lets not complicate matters

Ron

Reply to
Ron

ke

Any idea on what the impedance of the x-formers would be?

Chris

Reply to
Chris

Usually something like 600 ohms to 50,000.

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*I wished the buck stopped here, as I could use a few*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW To e-mail, change noise into sound.

Reply to
Dave Plowman (News)

If nothing better comes up, you could probably get by with a resistor "H" pad attenuator for each channel of your audio. The four 1/4 Watt resistors can be fit into the XLR connector if you build it carefully.

This won't provide ground loop isolation like a transformer, but it will bring your (0 to +8 DB) 600-ohm line-level audio source down to the approximately -15 DB, 50k-ohm home-entertainment audio standard.

It won't help you with your XLR microphone-level audio, unfortunately. That starts out at about -50 to -60 DB at 600 ohms. You'd have to use a mic. to line level amplifier if you went with an attenuator, which is a bit inefficient and can bring up your noise floor. Not to say I haven't done it or that it didn't work pretty well.

Reply to
Mark Allread

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