Differential Line Driver - Impedance Questions

[AndrewT]

Now I understand.

Jung also uses the bridge analogy and probably predates Whitlock.

 

[rcw666]

I would have thought connecting a 5532 or 833 like this is about as good as anything.
rcw

 

[dmills]

It needs line buildout resistors in series with the outputs, and they need to be fairly precisely matched. Somewhere in the 50 to 100 ohm region is usually ok.

This however is in most ways overkill, you can leave the lower section out and just connect output - to circuit 0V reference via a build out resistor and get almost all the benefit.
If is also usually better to make opamp buffers inverting as this usually gives lower distortion then the non inverting configuration due to the lack of common mode voltage swing at the opamp inputs.

Also it needs protection from P48 and some RFI protection (Common mode choke or something).

Regards, Dan.

 

[Chris Hornbeck]

There is one difference between both polarities driven and one polarity undriven ("impedance balanced") outputs - with both polarities driven, signal coupled _out_ of the stage to another nearby is minimized.

This is rarely important for home audio, but matters for snakes or other multi-channel constructions.

Thanks,
Chris

 

[dmills]

Depends, the coupling in that case is capacitive (The current in the two legs is substantially equal and opposite if the input stage is competent, the input common mode impedance to ground being large in any well designed stage), and audio frequency capacitive coupling is about the worlds easiest thing to screen.

Now I will grant that the two opamp driver returns the current on the other leg to a supply rail rather then the circuit reference plane, but with competent design that is pretty much an implementation detail.

Regards, Dan.