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**Tim Farrant** · 3rd July 2009

Matt, because the output of the opamps is 180 degrees out of phase (assuming the inputs are) then the 100uF capacitors are not really in series. Imagine if the primary of the output TX had a grounded centre tap, this would be the same thing as the circuit stands. The caps should remain in the case an opamp fails and goes to +15V DC, which the TX would not like. If desired, one trick is to place a low value resistor across the output capacitors making the connection a little more DC coupled. I'd say 220ohms would still provide protection for the transformer.

I do not think the 100uF need to be any bigger. The calculated -3dB point into a 10k load would currently be 0.318Hz !!

Tim.

3rd July 2009	#143
Tim Farrant Moderator Joined: Jun 2002 Location: New Zealand Posts: 2,407 Thread Starter	Matt, because the output of the opamps is 180 degrees out of phase (assuming the inputs are) then the 100uF capacitors are not really in series. Imagine if the primary of the output TX had a grounded centre tap, this would be the same thing as the circuit stands. The caps should remain in the case an opamp fails and goes to +15V DC, which the TX would not like. If desired, one trick is to place a low value resistor across the output capacitors making the connection a little more DC coupled. I'd say 220ohms would still provide protection for the transformer. I do not think the 100uF need to be any bigger. The calculated -3dB point into a 10k load would currently be 0.318Hz !! Tim. __________________ "Come on, make my day" Dirty Harry (Clint Eastwood) Visit Buzz Audio