I understand. There are two criteria that do not meet easily. The circuit ground should not touch mains earth, while it should connect to the potentiometers' shafts. The first soundcard was put in a chassis with the power supply built in so it had to be connected to mains PE. The potentiometers were then connected to circuit ground and insulated from the chassis with nylon washers. This soundcard is designed to use external psu so it doesn't need mains PE. That makes it very handy to connect the front panel - and the whole chassis- to circuit ground and be done with it. In this case pin #1 is both chassis and circuit ground. If you are going for a custom chassis you should improvise so that these requirements are fulfilled. The question is where commercial XLR to RCA or TS adapters -if they exist- connect ground coming from the SE end, to pin #1 or #3?
For a test/measurement system as this, I'd suggest to the SE output to the soundcard as follows:
output RCA tip --> balanced input "hot"
output RCA ring --> balanced input "cold"
At least that's how I do it with my RTX6001, which has the XLR pin 1 attached to the chassis, which in turn is on PE/mains-earth.
So, switch returns as bal/unbal and connects pin #3/ring either to cold or ground. Pin #1/sleeve currently stays not connected to anything. I see the standard XLR to RCA/TS adapters to short circuit pin #3 and #1. And then, there is the neutric ring pin "G" also not connected. Depended on chassis/front panel configuration as explained in post #181, you could bridge pin #1 and G with a short wire marked on the bottom side. What do you think?
I think you should not worry about an SE input. Just stick to the diff input.
I also think that since you are designing a piece of test equipment, it should not be "blessed" with the pin-1 problem. Just connect pin-1 as it should be and then leave it alone.
Edit: this is a nice and short description of how pin-1 must be used and connected.
I also think that since you are designing a piece of test equipment, it should not be "blessed" with the pin-1 problem. Just connect pin-1 as it should be and then leave it alone.
Edit: this is a nice and short description of how pin-1 must be used and connected.
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That assumes pin-1 and the housing of the XLR socket is always connected inside the plug or the cable. Is it?
I'd simply follow the standard procedure of connecting pin-1 to the chassis.
The output driver addresses a lot of connecton issues. I believe it is decended from the output driver of the HP 8903 with a self balancing circuit that adapts to a balanced drive, or short the - to ground and the output voltage adjusts to stay constant. It can also deal with ground loops if the low side is not grounded. The circuit actively senses the voltage differential at the load.
On almost every XLR cable I have seen (lots) pin 1 ties to the shield and the connector shell. Similar with TRS cables. A TS (mono) cable with short the low side to ground through the sleeve.
On almost every XLR cable I have seen (lots) pin 1 ties to the shield and the connector shell. Similar with TRS cables. A TS (mono) cable with short the low side to ground through the sleeve.