Anyone built the Simple Phaser or know if this thing works?

[chumbox]

[timd]

Total noob question, but what defines a "phaser stage?" Is this a stage that is standardized and repeats with no variation?

[deadastronaut]

no idea, but interested to read about this..

we need rick!!!..

[daverdave]

A 'phaser stage' typically refers to an all-pass filter section, the filter pases all frequencies but causes a 90 degree phase shift at the centre frequency set by the timing components (usually the capacitor and resistor making a voltage divider pasive filter at the non-inverting input in the case of a typical first order all-pass used in the majority of phasers).

Ganging multiple identical first order filters together in series causes the input signal frequency content to be shifted at certain frequencies, 180 degrees at the centre frequency and upto 360 degrees at the 'stopband' frequency range (frequency range higher or lower than the cutoff depending on the setup of the timing components) when using two all-pass filters. Usually the cutoff of the allpass filters are varied by varying the resistors in the timing network of each all-pass simultaniously.

I can't see the circuit diagram because I'm at work, but I'll hazard a guess that it's using typical op-amp allpass filter section. If you look for the all-pass on google then you'll find far more info.

[Thomeeque]

 Just in case you did not notice:  to get classic phaser fx there must be yet LFO added (source of "0-12V control DC") and circuit as-is requires bipolar power supply. For guitar signal input buffer will be probably neccessary too.

EDIT: if the question was about 1N4148/1N4148 used for the phase control I'd be interested too

[slacker]

To add to what Dave said a stage in this case is from the input to the output of the 220n cap, so if you want a four stage phaser you copy and paste that twice in series.

This is more of a theoretical circuit than something you can just build, the idea of using diodes as voltage controlled resistors, instead of the typical Fets or LDRs, is sound, but it would probably take a lot of work to get a working phaser. There are designs that use this method, like the infamous EMS Synthi Hi-Fli, but thats a hell of a lot more complicated.

[artifus]

tim's wobbletron is a nice and simple start down this path:



a few folk have reported problems getting the fet to work and instead use an ldr with the led, as did i.

[R.G.]

In reply to the first post and schematic:

Yes,  you need an LFO to drive it, going into that '0-12dc' input. I don't see anything about it that says it would specifically not work. But there are some unstated things about it that you'll be interested in.

The input impedance is 5K. As a practical matter, it needs a buffer before the input to avoid loading whatever drives it. Even some effects, let alone a guitar pickup, would have trouble with the low input impedance.

An LFO signal from 0-12Vdc is BIG compared to most LFOs. And the LFO circuit needs at least 12V, probably 15-18V to do this well. Special power provisions for the LFO will be needed in one form or another.

The variable resistors doing the phasing are the small-signal resistances of the two diodes. Diodes make great variable resistors as long as you don't expect them to work well with signals of over 10-25 millivolts. Above that, they do rapidly increasing distortion as well as variable resistance.  A nominal value for a modern single-coil guitar pickup might be 100mV, so you'd likely have to attenuate the signal before this phaser, then amplify it back up. Driving it with the output of many effects will be a problem, because many modern effects have signals of one to several volts.

It's a handy phase stage, OK, but there are some gotchas.

[earthtonesaudio]

Also not stated is the power supply for the op-amps, which must be bipolar and centered around zero.

[pinkjimiphoton]

i don't know if ANYONE ever got the wobbletron working...if you do a search on magnavibe tho, you can find something based on it that does indeed work.

[artifus]

i don't know if ANYONE ever got the wobbletron working...if you do a search on magnavibe tho, you can find something based on it that does indeed work.

mine works. they are one in the same thing as far as i can see.

*edit* http://www.diystompboxes.com/smfforum/index.php?topic=90962.0   http://i605.photobucket.com/albums/tt137/pinkjimiphoton/MagnavibeSchem.png

just trying to join up some dots. (in my own head, that is)

[PRR]

> what defines a "phaser stage?" Is this a stage that is standardized and repeats with no variation?