phase shifter

[the cracken]

i am trying to build a phase shifter for my guitar. (not like the normal effects pedals) all im looking to achieve is a variable phase shift from 0 to + or - 180 degrees and that it shifts all frequency's the same amount.
i have read about all pass filters but they are frequency dependent (i think?)
any suggestions on how i can do this???
any help would be appreciated thanks

 

[canadaelk]

Attached is an 1976 app note from National Semi. See if it helps. E

 

[the cracken]

Attached is an 1976 app note from National Semi. See if it helps. E

thanks for the great pdf i might have to build that! but this is an all pass filter. im not sure exactly how it works but the capacitor is used to shift the phase. this means that the phase shift is different for different frequency's. i need a phase shifter that changes the phase of all the frequency's to the same degree.

Just to give you an idea of what im trying to do. on my first guitar i built it with lots of switches to change the phase and whether the pickups where in series or parallel. now i know a bit more about electronics and i don't want a load of switches on my guitar i want to build a circuit with a variable resistor that can change the phase of all the pickups. in theory this would mean that i would have an infinite amount of positions and therefor sounds.

if anyone has a good idea of how i can achieve this i would be grateful. thanks

 

[crutschow]

I don't believe it's possible for any reasonably simple analog circuit to phase-shift all frequencies equally. Any usual phase-shift circuit will use reactive components to do the shifting, and that means the phase shift varies with frequency.

In theory it might be possible to do a series of Fourier analyzes of the signal, shift the phase of each component and then regenerate the signal, but I suspect that would take a large amount of processing power to do in real-time.

And what results do you expect from doing this phase shift?

 

[the cracken]

I don't believe it's possible for any reasonably simple analog circuit to phase-shift all frequencies equally. Any usual phase-shift circuit will use reactive components to do the shifting, and that means the phase shift varies with frequency.

In theory it might be possible to do a series of Fourier analyzes of the signal, shift the phase of each component and then regenerate the signal, but I suspect that would take a large amount of processing power to do in real-time.

And what results do you expect from doing this phase shift?

im trying to shift the phase of one coil so its out of phase with the other.
it changes the sound of the guitar quite a bit. i don't think its possible to describe the sound. all i can say is if you play guitar put a phase switch in and give it a go.

 

[bychon]

You have never had a phase shifter that changed the phase angle of all frequencies equally. How can I tell? Because you didn't have a computer between your pick-up coils.

 

[the cracken]

You have never had a phase shifter that changed the phase angle of all frequencies equally. How can I tell? Because you didn't have a computer between your pick-up coils.

of course i haven't had a computer between my pickups. i used a switch!
in phase +coil- +coil-
out of phase +coil- -coil+

 

[crutschow]

The best you can likely do to achieve your goal, is to use the circuit shown in the attachment posted by canadaelk. It has six all-pass phase shifters, each set for a different frequency. Thus, at least for groups of frequencies, the phase shift will be the same. From an audible perspective, this circuit may not sound much different as compared to the ideal. Certainly, you could add more phase-shifters and reduce the frequency difference between them to better approximate the ideal of shifting all frequencies the same. The trade-off is complexity versus closeness to the ideal.