I understand that most analog hardware phase shifting circuits seem to use OpAmps to get their job done. I am trying to build a tiny, non-powered in-line adapter for Mp3-players and such to quickly sum up multiple signals - which can easily be accomplished without external power using just resistor signal mixing. However, to make this adapter really nifty and interesting, a phase shifting switch would really make the icing on the cake. Now, this leads me to the question in the title of this thread: a passive audio phase shifter/inverter - can this be done?

Any input/idea/feedback/suggestion is greatly appreciated!


closed as unclear what you're asking by Leon Heller, PeterJ, Daniel Grillo, Matt Young, nidhin Jun 24 '15 at 5:31

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    \$\begingroup\$ Do you really want a phase shifter or do you actually want a signal inverter? \$\endgroup\$ – brhans Jun 18 '15 at 19:10
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    \$\begingroup\$ 180 degrees phase shift independent of frequency pretty much implies an inverter. Dead easy. 1:1 transformer and DPDT switch. (Or centre-tapped secondary and a single pole switch (per channel). \$\endgroup\$ – Brian Drummond Jun 18 '15 at 19:22
  • \$\begingroup\$ You really need to specify exactly what you need. \$\endgroup\$ – Andy aka Jun 18 '15 at 19:48

Although it's not so clear to me what you want I can point you to something that might help. Old telephones used a passive device, a transformer, to separate the incoming signal from the outgoing signal (so that your own voice is suppressed while you're speaking on your phone). This is a schematic of a T65 made by Ericsson. Almost everyone in the Netherlands had such a phone in the 1970's ;-)

T65 schematic

What is interesting is that the signal from the Microphone is fed into the transformer in-phase and in anti-phase. So you should not hear yourself on your own speaker. The same transformer also puts the signal on the phone line.

  • \$\begingroup\$ sorry, everyone, now I feel pretty dumb here; ich was thinking of how delays originating from latency and how this can cause phase shifting, but of course, you are absolutely right, what I am looking for is a phase inverter, not a phase shifter! apologies for that. let's reformulate the question as follows: if i sum up multiple audio sources using only resistors and some phase shifting occurs - will a simple polarity-swap solve the problem or would this affect the-output-volume significantly? \$\endgroup\$ – t0bias Jun 18 '15 at 20:26
  • \$\begingroup\$ Phase-shifting will not occur when you sum up multiple signals with resistors ! For phase-shifting of a signal you need a delay (at a certain frequency a phase shift corresponds to a certain time-delay). Only when you want 180 degrees phase shift for all frequencies it is the same as inversion = polarity swap = multiply by -1. The 2 are different things and not interchangeable ! So you can combine audio signals with resistors but don't worry/think about phase shifting etc. What you get out is simply an average of all combined signals. \$\endgroup\$ – Bimpelrekkie Jun 19 '15 at 7:57

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