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finished build, and a question about xlr pin 2

alpha24 (preamp/buffer, voltage DAC analog output stage, balanced ↔ unbalanced converter)

finished build, and a question about xlr pin 2

Postby tofurky » November 9th, 2019, 6:08 pm

hi,
after sadly sitting in a shoebox for about 4 years, i finally put everything together in the past couple months :-)

the intention of the build, especially when picking components originally (i.e. 1/4" input and xlr output) was to have 2 independent "DI" type boxes for use as instrument preamps in a dual mono unbalanced -> balanced setup. i built to that spec, but i'm wondering if it would be possible/advisable to use an xlr -> rca adapter to convert the balanced output back to unbalanced.

given only XLR output connectors, this would be more convenient in terms of connecting to different types of gear without opening up the chassis and rewiring the xlr jacks to use the balanced / unbalanced output as needed.

first off, would shorting the negative side of the balanced output to ground fry the thing? and if not, would it be inadvisable for other reasons? i've read that the signal level would be cut in half.

below are a couple pics of the build. as shown in the picture, i have the xlr jacks connected to the unbalanced terminal block outputs. this seems to work fine with the clunky xlr -> rca connectors i picked up from amazon, which ground pin 2.

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Re: finished build, and a question about xlr pin 2

Postby amb » November 9th, 2019, 6:17 pm

Yeah, such adapters would most likely short circuit the negative output to ground (dependent on the adapter).

The σ24 has an unbalanced output that you could connect to an RCA jack. That would be the preferred way to get unbalanced output. If you must use an adapter, change the 33.2Ω output resistors to at least 150Ω, so that it won’t overtax the OPA1632.
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Re: finished build, and a question about xlr pin 2

Postby tofurky » November 9th, 2019, 7:22 pm

thanks for the quick response.

separate rca would be ideal, but i kind of ran out of room on the smallish front panel. i suppose i could snake some wires to the rear panel, to the opposite side of the mains input, but that seems a little close to mains for my tastes.

i might be able to cram an 1/8" trs panel mount jack in between the 1/4" input jacks. not as good as rca, but wouldn't require changing output resistors or doing some questionable cable routing by the transformer.

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