Any reason not to use a switch to select output impedance?

[SoaDMTGguy]

That was the Audio Research version.

Yes, I know, but the ST-70 doesn't have anything to do with the D70.

yes, but you would have to lift the 96-97 link for XLR operation and link it when you want to use the RCA jacks like they did long ago.
You can run an RCA in the XLR But you have to change the RCA jack and isolate it from the chassis. But at the price of half the volume.
Another way would be to use little matching transformers and convert the RCA into XLR.

I have the little transformers. My original plan was to make converter boxes and feed XLR through the box to RCA into the amp. But, I thought if the amp could be made to natively accept a balanced signal, that would be even better.

Sounds like if I wanted to do that, I would have to lift 96-97 with a switch, and connect the extra XLR pin to 97 through a resistor. Right?

 

[thisusername]

Sounds like if I wanted to do that, I would have to lift 96-97 with a switch, and connect the extra XLR pin to 97 through a resistor. Right?

Correct if you wanted to keep how the RCA jacks are wired.

 

[SoaDMTGguy]

Except so far, we only see 96-97 on one channel. Which means we need to work out where the other channel's XLR jack connects. Right?

 

[thisusername]

Except so far, we only see 96-97 on one channel. Which means we need to work out where the other channel's XLR jack connects. Right?

Yes, it would be lifting R16 connection from the same place and adding a 39.2K input resistor to match the signal + signal path.