Polarity changer Switch

Posted on Mar 24, 2013

This project is useful if you wish to experiment with absolute phase, or are just interested in the possibilities of a polarity reversal circuit. In the case of absolute phase, many studies have shown that there can be an audible difference between polarities, but be aware that there is no way to really know for certain what the original phase was. Typical microphone methods mean that in some cases the polarity may be reversed compared to the way you may hear the same sound live. As a result, there is not necessarily a 'correct' polarity, since there are so many different ways that a signal may be processed before you hear it.

Polarity changer Switch
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The more conventional method is shown in Figure 1, and is simply an inverting buffer with a switch. Simple, and does exactly what is needed, but as noted above requires a double pole switch and 3 wires for each channel. While there is no requirement to have an especially low source impedance, it is highly recommended that it be as close as possible to that used for the inverter (typically 100 Ohms). By selecting the normal output or that from the inverter, the output polarity is inverted (or shifted by 180° if you prefer). The additional loading on the normal output is negligible, but it must be low impedance to prevent the normal and inverted signals from having different output impedance, and therefore possibly different levels. This circuit has similar constraints to the previous version - source impedance should be low, and in this circuit the impedance changes when the switch is opened or closed. With the values shown, Zin will be very high (typically >1M?) with the switch open, and 11k with it closed. This can be increased if desired by increasing the value of all resistors. A maximum of 100k is suggested to keep noise to the minimum, and to ensure that stray capacitance does not cause a problem (see construction notes below for more detail). Source impedance should be no more than around 220? if you use 22k resistors, or about 1k if you use 100k resistors. This gives an error of a little under 0.15dB. For...

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