A big Magnavibe question

[Crontox102098]

Hey guys! A few days ago this idea comes drilling my fu***ng head and as my only guitar broke a few months ago  (neck broke by moisture when one day my house was flooded and my friend Jimi Photon is helping me in a campaign to repair it) I wanted to ask what would happen if the Magnavibe, instead of the LDR a variable resistor is placed to use the "wobble" like a Wah?

Could this work? 

Postscript: All good heart who want to help me to recovery my dad memory, can donate here: http://www.gofundme.com/RepairMyRemember

[knutolai]

The point of the Magnavibe is that the LDR is controlled by a oscillator. If you were to change it for a pot and vary the value yourself (very unpractical imho) you would get much of the same result. On the other hand setting it to one static position (as you soon get tired of varying it by yourself) would give you nothing more than a boring low pass filter.

Here's a great link which pretty much covers this: http://www.geofex.com/article_folders/phasers/phase.html

[Lurco]

The point of the Magnavibe is that the LDR is controlled by a oscillator. If you were to change it for a pot and vary the value yourself (very unpractical imho) you would get much of the same result. On the other hand setting it to one static position (as you soon get tired of varying it by yourself) would give you nothing more than a boring low pass filter.

Here's a great link which pretty much covers this: http://www.geofex.com/article_folders/phasers/phase.html

Make that: boring all pass filter (aka: phase shift).

[PRR]

I think C2= 0.1uFd is much too big for any practical part of a 500K potentiometer.

Or LDRs unless you can smack them with LIGHT.

C2 will probably be smaller before you are shifting the musical band. More like 10nFd.

> instead of the LDR a variable resistor is placed to use the "wobble" like a Wah?

As the others say, you do not hear a phase-shift if it does not move. Really has to move "rapidly". So rapid, you might not hear a single sweep. You gotta move it back-and-forth fairly fast for significant time for the ear to hear. I suspect it is "possible" with a really good Wah-mechanism and a very young ankle.

Also: a single stage has a very mild effect. Maggie rarely used less than two stages even when they were expensive. Ganging multiple stages to track together means a Wah-pot that is not only a good wah-pot (most action near the middle) but also a multi-gang pot (never seen both in one?).

If you have a 250 degree ankle-twist, you -can- find 4-gang and 5-gang pots from old surround-sound amps.

The beauty of Varistors (or LDRs or FETs or OTAs) is that one control-voltage can modulate multiple shift-stages, without elaborate mechanicals. (And surround-sound amps stopped using many-gang volume-pots as soon as acceptable VCAs were non-expensive.)

[Crontox102098]

I think C2= 0.1uFd is much too big for any practical part of a 500K potentiometer.

Or LDRs unless you can smack them with LIGHT.

C2 will probably be smaller before you are shifting the musical band. More like 10nFd.

> instead of the LDR a variable resistor is placed to use the "wobble" like a Wah?

As the others say, you do not hear a phase-shift if it does not move. Really has to move "rapidly". So rapid, you might not hear a single sweep. You gotta move it back-and-forth fairly fast for significant time for the ear to hear. I suspect it is "possible" with a really good Wah-mechanism and a very young ankle.

Also: a single stage has a very mild effect. Maggie rarely used less than two stages even when they were expensive. Ganging multiple stages to track together means a Wah-pot that is not only a good wah-pot (most action near the middle) but also a multi-gang pot (never seen both in one?).

If you have a 250 degree ankle-twist, you -can- find 4-gang and 5-gang pots from old surround-sound amps.

The beauty of Varistors (or LDRs or FETs or OTAs) is that one control-voltage can modulate multiple shift-stages, without elaborate mechanicals. (And surround-sound amps stopped using many-gang volume-pots as soon as acceptable VCAs were non-expensive.)

So, what i get if i put a small preamp in the end of the circuit and two more stages varying the value of C2 in each? (that of cannot test this myself, is a piece of s**t  )

[pinkjimiphoton]

carlos,
fwiw, i think what the guys are telling ya is you're better off not using a wah treadle for the sweep... if i were you, i'd use it to control the speed of the throb, and i would add 2-8 more stages so it would be more noticeable. the magnavibe is very sweet, but very subtle effect.

maybe try the values paul suggests, too, cuz to really get this thing to work well will probably take a lot of redesign.

the wobbletron it's based on is for all intents worthless.... never got it to do anything more than blink at me.