XLR Question

Hi Marty,

Just a guess, but perhaps the XLR inputs of the Onkyo are actually unbalanced, with XLR pin 3 (that would usually carry the inverted signal in a balanced signal pair) being grounded (i.e., connected to XLR pin 1 in the Onkyo). And perhaps the AudioBox device generates the non-inverted signal that ends up being provided via your adapter cable to XLR pin 2 of the Onkyo by putting its inverted output signal (that ends up being applied to XLR pin 3 on the Onkyo) through an inverter stage (such as an op amp configured as an inverter).

In that scenario the result would be exactly what you’ve found.

Also, if my speculation is correct, and given also the low 51 ohm output impedance of some or all of the AudioBox models, shorting the signal it provides on XLR pin 3 to ground might not be healthy for it if done on a prolonged basis.

Best regards,
-- Al

Also, Marty, an inexpensive potential solution you may want to consider would be an ART DTI Transformer/Isolator ($60 plus appropriate cabling). Manufacturer’s description here.

I’ve used one for non-critical voice recording applications, and for those purposes, at least, it seems to work well.

Best regards,
-- Al

Many thanks to all

Ralph,

good diagnostic idea.  I'll have to dig up a balanced source and some xlr to xlr cables, but I'll try that first

Al,

if that fails, I'll try the transformer

Page 17 has the pin outs of the Onkyo XLR input:

http://filedepot.onkyousa.com/Files/own_manuals/PR-SC5508_En_web.pdf

Thanks, Mofi.  I had looked at that before posting, though, and it doesn't make clear how the input circuit treats what it describes as the "cold" input on XLR pin 3.

Best regards,
-- Al