Phase inverting / not inverting preamplifier

[andreaemme]

Hello! I need the simplest possible circuitry for a line stage preamplifier/separator able to produce a 0° phase output and a 180° phase output. This is necessary because I need to drive a single-coil subwoofer with a classic stereo amplifier.
Thank you very much.

 

[AndrewT]

Use an opamp to invert the phase.
This same circuit can be switched so that the opamp operates as a non-inverting and as an inverting stage.
This way the single opamp amp acts as a buffer and as an optional signal inverter.

The circuit is shown in Parr's "How to use opamps" fig 2.27 and is likely to be somewhere in this Forum.
Electronic switching of phase is shown in fig 2.28

 

[Chris Hornbeck]

If you can use a gain of +1 and -1 you might look into a split-load inverter, familiar to tube guys as a "paraphase" or "concertina" stage. To implement one with DC coupling maybe think along the lines of a complementary folded cascode with equal loading in the source-to-ground and drain-to-ground.

Good fortune,
Chris

 

[andreaemme]

Thank you for these indications, but can you give me a scheme? Better if using fet or jfet..

 

[chrisi]

You can use TI's drv134/drv135. Those don't need external parts and are cheap.
http://focus.ti.com/lit/ds/symlink/drv135.pdf

 

[Chris Hornbeck]

Here's an example of a paraphase "split-load" inverter made with a triode, Fig. 2, and with JFET folded cascode, Fig. 1. Trims are for DC offset. Equal R's give equal output magnitudes.



For most uses the current sources can be resistors.
All good fortune, Chris

 

[cbdb]

If you dont need any power gain the simplest thing would be to use an audio transformer with a secondery center tap. One leg to centre will be +ve the other -ve.