Applying T-net to Bridge

[TwoSpoons]

OK, its just theoretical (i.e. simulated), but I'd thought I'd post the idea for others to try / shoot down.

Interestingly the cross-coupled T network appears to reduce DC offset dramatically. Don't know why.
Excellent CMRR too.
Performance holds up well under Monte-Carlo runs using 1% resistors throughout. I even deliberately unbalanced the gains of the two halves of the bridge, and still the CMRR and DC offset were excellant.

How I wish National Semi would provide spice models for the 3886!

[Franz G]

Sorry, for me this circuit looks more like a inverting parallel amp, than bridged.

Do you know this application note:

AN1192

Regards
Franz

BTW: I think for bridged circuits, the t-network is an advantage for the inverting part: just configure it, to have the same Z like the traditional feedback path of the noninverting amp, this should enhance symmetry.

[TwoSpoons]

Yes, I know the app note, thanks.

Maybe the diff probe I left on the output is confusing - consider it as the speaker and you can see its not a parallel amp at all.
This circuit is more like two differential amps operating as a bridge. The idea is to drive from a balanced source (likeDRV134 etc) - this bit is meant to be just the power stage.

The point here is that the centre legs of the two T's in a bridge can be joined, and the 0V connection omitted alltogether.

[psychosteve]

im assuming that you used opa chips instead of lm3886 coz you didnt have the spice models??? coz the circuit looks good, nice and simple and with a ballanced drive chip, or just a twin opamp like lf353 there should be a good reduction in dc offset. im sure some one on here has the spice models for lm3886t. id be very interested to see the results, but there is no substitute for your ears. maybe ill try and build one. see you later, steve.. ..