Manual phaser

[Unbeliever]

Any of you ever thought about a seekphase?

Done by 'somebody' 5+ years ago... 

[MarcoMike]

Well, I think it's pretty easy to make a "foot controlled phaser"... I had the morley PFA, just loved it, but then I sold it, as it was the only non-diy pedal left, the only 220V powered and it took the place of 4 normal pedals... ok, and also because I had an offer I couldn't refuse...

anyway... missing the pfa I made a ross phaser with of course the external foot controller: you can just tap the LFO input of the phaser with the wiper of your pot, wired as voltage divider between V+ and ground. this way moving the pedal you do exactly what the lfo did: give a different voltage to the lfo. you just need a pot and a switch, that's it! I'm still not sure which taper and which value are the best for mine, but it works fine and I'm ok with it...
the morley was better by the way, I really miss the "centre" and "phase travel" knobs...

[earthtonesaudio]

I just thought of a bit of info that might help you as you're working on this:

Most op-amp based triangle LFOs sweep between about 1/3 and 2/3 of the supply voltage.  Most foot rocker pedals don't sweep the entire range of the pot anyway, so this might work out nicely.  Just set the pedal's midpoint equal to the pot's midpoint and you might get pretty close to the sweep range of the LFO.

[DWBH]

So, it's as "simple" as this?

turns into this

?

[Zben3129]

I don't know if that will work,

Doesn't the phasing sound occur because of the changing sweep? If you stop the LFO at a certain voltage (or provide the voltage by a pot) I think it will just give a normal sound.


This is for the MXR style phasers, not farmiliar with step types.

Zach

[Mark Hammer]

anyway... missing the pfa I made a ross phaser with of course the external foot controller: you can just tap the LFO input of the phaser with the wiper of your pot, wired as voltage divider between V+ and ground. this way moving the pedal you do exactly what the lfo did: give a different voltage to the lfo. you just need a pot and a switch, that's it! I'm still not sure which taper and which value are the best for mine, but it works fine and I'm ok with it...
the morley was better by the way, I really miss the "centre" and "phase travel" knobs...

1) What pot value are you using?  It is my understanding that one doesn't want to feed more than a milliamp or two to the Iabc pins on the OTA or its fried OTA for supper.

2) If simply feeding a pot to the current limiting resistor going to the Iabc can move the notches around then wouldn't a second pot be able to set a default minimum frequency which the footswept pot would sum with?  Again, the issue is that the resulting current might tax the OTA chip.  The usual solution to the too-much-control-voltag/current problem in things like phasers and flangers is that there is a balance control (normally called a depth control) which trims the amount of voltage coming from the variable source as the manual offset is increased.  Take a look at the Boss BF-2 for an idea how it can be done.

[MarcoMike]

Right Mark, I was sloppy in my descriprion...
I'm using a 50K log pot (the one I had in my spare volume pedal).
1--9V
2------50K depth pot----5Klimiting resistor---OTA
3---47K resistor---ground

this is how I have it wired now... I used the 47K res because the sweep was too much on the "toe side". OTAs don't get fried even in the worst situation with the 5k res (pot all the way to 9V and depth to max: 0ohm) and the pedal really goes from 0 to 50k, it's a casio keyboard pedal...

[Franky]

Any of you ever thought about a seekphase?

Done by 'somebody' 5+ years ago... 

Who did that? RG? ZVex? Chuck Norris?

[earthtonesaudio]

Steven Seagal?

[RickL]

I built one of these this week in a hotel room to see if I could get it to work. I only got a chance to test it an hour or so ago. I used the first suggestion - to replace the FETs with a dual ganged pot. I used a 500k because I have several high quality units.

I got lucky with the build. Aside from inserting the FETs backward I didn't have to do anything except tweek the trimmer for the best phasing range. I used unmatched FETs to test it and I like the sound enough that I don't think I'll bother matching them. I should mention that I used a dpdt toggle to switch between the LFO controlled FETs and the pot.

The pot works, but only over a very limited range. I only got noticable changes in the sound from 0 ohms up to about 100k, maybe even 50k. In that small range though, it does work. It sounds best when the pot is being moved but even stopped there is a noticable tone change, kind of like the two-pickup sounds on a Strat.

My plan is to hook up another dual pot in parallel with the 500k I used and keep turning it down until I can use the whole range of the 500k. Then I'll remove it, measure the value and use two equal value resistors across the lugs of the pot. I'm guessing I'll end up with resistors somewhere in the range of 68k to 150k.

One other note - I added a switch to remove the dry signal to get vibrato like I do with all my phaser builds. The manual pot also works in vibrato mode but for obvious reasons you only hear the effect when the pot is being moved.