Phase inverting / not inverting preamplifier

andreaemme · 21st July 2011, 02:20 PM

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 · 02:36 PM

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 · 30th July 2011, 12:37 AM

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 · 30th July 2011, 12:41 PM

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

chrisi · 1st August 2011, 09:52 AM

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 · 2nd August 2011, 09:17 PM

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.

Folded cascode paraphase.jpg

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

cbdb · 2nd August 2011, 09:23 PM

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.

21st July 2011, 02:20 PM	#1
andreaemme diyAudio Member Join Date: Nov 2008	Phase inverting / not inverting preamplifier 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.

21st July 2011, 02:29 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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 __________________ regards Andrew T. Last edited by AndrewT; 21st July 2011 at 02:36 PM.

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30th July 2011, 12:37 AM	#3
Chris Hornbeck diyAudio Member Join Date: May 2011 Location: Little Rock	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

30th July 2011, 12:41 PM	#4
andreaemme diyAudio Member Join Date: Nov 2008	Thank you for these indications, but can you give me a scheme? Better if using fet or jfet..

1st August 2011, 09:52 AM	#5
chrisi diyAudio Member Join Date: Jun 2011	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

2nd August 2011, 09:17 PM	#6
Chris Hornbeck diyAudio Member Join Date: May 2011 Location: Little Rock	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. Folded cascode paraphase.jpg For most uses the current sources can be resistors. All good fortune, Chris

2nd August 2011, 09:23 PM	#7
cbdb diyAudio Member Join Date: Oct 2008 Location: Vancouver	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.

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