[Flexradio] Delta 44 Breakout Box and Balanced audio

[Don Newberry]

Hello all,  I was considering using a DB 15 connector, appropriate plugs and shielded cable to interface between the SDR and the Delta 44, bypassing the breakout box altogether.  I thought this would make a little cleaner setup here (not that this has mattered much before, hi).  I traced out the wiring inside the box to find out the pinouts for the various ins and outs, and will list them below.    One interesting thing that I found was how M-Audio implements Balanced or Unbalanced configurations.  As you may know, they allow balanced audio ins and outs by using both the Tip and Ring, with the shield tied to the sleeve, But it appears that they are not using a true Balanced input at the sound card.  The Ring connection simply terms. into a 10k resistor in series with a 22u cap to common, while the Tip continues on to the sound card input.  The outputs are sim., the Ring is tied to common through a 130 ohm R and series 22u cap, while the Tip carries the actual output.  I suppose these components match the Z values on tip and ring as they appear to external equipment, but there is no signal present or used by the Ring half of the line.   In the past, there was some talk of using balanced I/Q signal paths between the SDR and Sound card, to gain noise cancelation and s/n improvment at the sound card.  This is a step up from our current unbalanced method.  Seems like M-Audio is defeating any advantage of using balanced lines, even if a new SDR incorporated them.  I wonder if the Delta 44 is typical of other higher end  "Pro" sound cards?  Just something you might want to keep in the back of your mind for future use.   Anyway, here are the breakout box pinouts:   TRS Jack          DB15 pin In 1 tip..............13 In 1 ring.............term'd  (Input ring terminations are 10k in series with 22uF to sleeve) In 1 Sleeve........14   In 2 tip..............6 In 2 ring............term'd In 2 sleeve........14 (Input 1 and 2 sleeves are tied together)   In 3 tip..............15 In 3 ring............term'd In 3 sleeve........7    In 4 tip..............8 In 4 ring............term'd In 4 sleeve........7  (Input 3 and 4 sleeves are tied together)   Out 1 tip..........1 Out 1 ring.........term'd  (Output ring terminations are 130ohms in series with 22uF to sleeve) Out 1 sleeve.....9   Out 2 tip..........2 Out 2 ring.........term'd Out 2 sleeve.....9  (Outs 1 and 2 sleeves are tied together)   Out 3 tip..........3 Out 3 ring........term'd Out 3 sleeve....11   Out 4 tip..........4 Out 4 ring........term'd Out 4 sleeve....11  (Outs 3 and 4 sleeves are tied together)   Pins 5, 10 and 12 are not used.  Pins 14, 7, 9, and 11 (sleeves) are grounded at the sound card's ground plane     73 and gn Don, wd4egf