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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!

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

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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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
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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.

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  • \$\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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