Balanced output

[RSRecords]

Balanced output on a MCI jh24.

What’s the purpose of R28 (500ohm trim pot) in the feedback loop of ic200.  Just to match it to the Hi side?
What would that look like on a scope? Offset or some kind of asymmetric clipping?

Thanks!

 

[Khron]

Pretty sure that's for the ability to match the gains of the two opamps as closely as possible. Not 100% sure if and how much that affects CMRR, but i guess it's at least for "extra style points".

Further reading: https://sound-au.com/articles/balanced-2.htm

"For example "Each conductor is always equal in voltage but opposite in polarity to the other. The circuit that receives this signal in the mixer is called a differential amplifier and this opposing polarity of the conductors is essential for its operation." [ 3 ]. This, like many explanations in print (some in otherwise respectable books), describes signal symmetry - "equal in voltage but opposite in polarity" - but fails to even mention the single most important feature of a balanced interface.

SIGNAL SYMMETRY HAS ABSOLUTELY NOTHING TO DO WITH NOISE REJECTION - IMPEDANCE IS WHAT MATTERS!"

 

[RSRecords]

Awesome thanks. So is this something to calibrate via scope? If so how?

 

[JohnRoberts]

The gain for the positive side and negative side needs to be the same for a later differential stage to properly cancel CM noise.

JR

 

[Khron]

Does it, though?

The gain for the positive side and negative side needs to be the same for a later differential stage to properly cancel CM noise.

JR