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phase checker circuit


rets ain

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I'm assuming the OP means one of those gizmos that puts out a clicky type noise and a little box with a couple of LEDs on it says in phase or reversed.

 

Somewhere on the web is the waveform (I think with a .wav file) these blights used; I've seen it but despite much searching never found it again. But essentially its a wave that has the same area under the graph of the two half-cycles, but a different shape. Clever.

 

If someone with google-fu greater than mine can find this waveform I'd be most appreciative; play it back from a PC< and capture a mic to a 'scope (or even a PC 'scope application) and one can see by eye if the phase is right or wrong. Ok, it's not as sexy as a couple of little black boxes, but it would work with the kit I've got!

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If you have a scope to view an output waveform - the test signal is easy to produce. All you need is a series resistor (1K ohm will be OK) - followed by a parallel silicon diode (1N4148 will be fine).

 

Feed this simple network with a sine wave signal (+4dBu or so) - and the output is a sine wave with the top squared (or clipped) off.

 

So feed this into your mixer, amplifier or audio path - and view the outputs with your scope, checking that the clipped sine waves signals are all the same way up (or down!).

 

Unfortunately most people want to check speakers and microphones - then we are back to proprietary devices, such as the clicky type mentioned above......

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All valid stuff guys but to stick a spanner in the works here phase checkers really don't work well.

 

If you have any filters, digital electronics or in fact *anything* in the system that can change the phase or anything the time domain ( A-D / D-A converters ) these things give a false reading.

 

If you don't believe me, try one around a loudspeaker tuning port - the phase will be in/out depending where you put it! If you have a large system then these things are completely useless.

 

I understand of course the reasoning behind why you would want to know if the system is in phase, but this isn't the way to do it.

 

It makes far more sense to check each individual speaker in each individual cab *before* you connect anything to them. Make sure everything is connected from the rear connection plate inwards. Then at least you know that the cabs are ok. If you know that then each time you connect them up you at least know that any errors are *not* caused by the internal wiring of the cabs themselves.

 

Then check each of your cables to ensure that they are all correct - use a good quality cable checker!

 

We do one. Click here > Quest Cable Tester but there are plenty on the market to choose from ........then use your common sense.

 

It's only easy to get it wrong when you're unsure of the items of kit you're using. Take the time to familiarise yourself with the equipment and get to know "how it sounds" whan operated correctly.

 

Phase anomalies *can* be heard if you're using a good quality audio source to the system. Don't even think of using highly compressed heavy rock to detect problems - it just won't work. Measurements and test gear are fine but if it sounds bad, it sounds bad - even if the test gear says it doesn't. Trust your ears and your instincts!

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