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So complicated. Like the volume mute function.

I checked the forum members if they reacted to death of Norm Macdonald. Dunno why but somehow I knew he was beloved by forum members. Only famous person I've cried over his/her death. Read his book when i was "away". Imagine doing standup and made jokes about cancer and death for 20 mins (Me Doing Standup) while you're battling. Well at least he didnt lose his battle, it was a draw.

I think you are not measuring CMRR, but rather the common mode to differential mode conversion ratio. With the ‘conventional’ dual pot connection, the common mode signal at the input is attenuated at the same ratio as the differential signal; while with the shunt connection (without the help of a line isolation transformer), the common mode signal is not attenuated at all. Apx has common mode drive, why not use it to evaluate CMRR?

It looks neat, I like it.  Still gotta build the Iron Pre kit from diyaudio but what's another preamp.  I think I have the transistors too

I may be a hack, but I switched from using 4-gang pots to shunting stereo pots because I think they work better. A big part of the reason why I would build a balanced circuit is to benefit from its CMRR (and even order distortion cancellation by proxy). I measured the matching between gangs on a 20k RK27; it's better than the specified 20% tolerange, but it's not great. Here are some measurements at arbitrary rotations. Gang A Gang B Matching 51.4 51.6 0.4% 255.7 252.8 -1.1% 623 624 0.2% 1299 1300 0.1% 3042 3089 1.5% 4230 4368 3.2% 8470 9080 6.7% 14680 15420 4.8% 19100 19930 4.2% 19900 20380 2.4% The matching is directly proprotional to the CMRR. So I took a measurement of CMRR using the following circuit. The idea is that this simulates the balanced input of an amplifier and will tell us how balanced things actually are. Not very, it seems. Each trace is a different rotation angle on the pot, with the -115dB one being with the signal fully shunted. (There is some resitual resistance with the pot at 0.) -35dB of CMRR will significantly degrade an amp's performance. I repeated the measurements with a shunting pot configuration, using Yageo 1% 2k resistors and the same 20k pot.  Although the AP input capacitance degrades CMRR at high frequencies, even the worst 1kHz measurement is about 12dB better than the best measurement with the series pot. The low frequency degradation is most likely caused by the AP's 1/f noise-- we're measuring microvolts at this point. If I wanted to further improve performance, I'd use resistors with better matching. The Vishay ORN arrays are available in 0.01% and would probably be my pick. LT5400 isn't bad either.  https://www.mouser.ca/ProductDetail/71-ORNTA1001ZUF I don't know that this is necessarily relevant to the design in the first post-- looks like it doesn't use a pot at all-- but the circuit has its place.