Idea for a half sweep phaser

[patrick398]

Next project is going to be a phaser. I think i'll just get a phase 90 on the breadboard so i can try and get a basic understanding of what's going on but what i'd really like is what i can only describe as a half sweep phaser. That's probably an inaccurate and misleading thing to call it. I'd like to have the phaser sweep the frequency up but then instead of sweeping back down it would just reset at the starting position. While i'm waiting on some parts i thought i'd just put the feelers out and see if anyone had any ideas how to accomplish this. Since the frequency notch is controlled by an LFO could i use something similar to the 'spacing' pot on the tremulus lune? That uses LED/LDR so might not be idea but by slowly lighting the LED then having it turn off and slowly light again maybe i'd get somewhere close?
Am i in over my head here?
Thanks

[Plexi]

Something like the Bad Stone (ehx)?

[Plexi]

Or some kind of phaser with "range" of sweep?

[patrick398]

Not quite, thought i do like the idea of being able to disengage the lfo and manually select the frequency...very cool.
What i want is like a phase that only goes in one direction. So sweeps up but not down (or vise versa). When it's finished the range of the sweep 'up' rather than coming back down through the frequencies it just resets at it's 'bottom' starting position.
Actually would be cool if the sweep didn't begin right away but hung on the lower frequency for a while then began to sweep, then hung on the lower frequency then sweep etc.
Apologies if i'm not explaining this very well 

[Mark Hammer]

The Causality phasers (search for Causality Mk II on the forum) provide a means to do just that.  I can't say that I have been entirely pleased with how it sounds, but that may be because of the limitations of the type of LFO used.  A more appropriate LFO would be the classic 2-opamp form, that is often adapted to provide triangle, ascending ramp, descending sawtooth, and square-wave options.

Here's one example.  With S1 not connected to either diode (it's a center-off 3-position toggle), it produces a triangle and square output.  When the toggle connects R1 to D1, it produces an ascending ramp, like you seek.  When the toggle connects R1 to D2, it produces a descending sawtooth.

[patrick398]

Amazing, thank you Mark that looks perfect! I'm not entirely convinced by the sound of that causality phaser either. Sounds nice but not quite what i'm after but i think that LFO with the ramp and inverted sawtooth could work nicely.
I'll be spending the next two weeks hunched by my letter box waiting for the parts but in the mean time i'll get one of these LFO's up and running.

[patrick398]

Maybe a silly question as it's written on the schem, but do i need -12v and +12v supply. There's no chance i could run it off 0 and 9v is there?
I'll sit here quietly now, i might be able to hear the sound of thousands of palms meeting foreheads...

[key-bored]

So patrick398, I happen to like your thinking.

I'm a total fool for phasers.  I love phasers and have a dozen, anyway.  Being into keyboards, I'm not in love with, say, overdrive distortion the way I am phase shifters (and the occasional flanger/chorus).

Range switch:  good.
Enhancement (a la EH Small stone): very good.

One thing I think would be very cool is modulation waveform tailoring.  Probably along the lines of what you're thinking.  Sure, have a simple sine up/down, but what I'd like to see is a knob for time control of "Rise" and a control for "Fall". Almost like an envelope generator.

Came across someone's phase that had that instant changing thing you mentioned.  Didn't much care for it.  IMO, phase shifting needs to be continuous, even if quick.  There's something called a 'barber pole' or is it (?) Sherman function.  I remember hearing that and really liking it.  A four stage in barber pole, i think it was.

Also, multi-stage phasing works real nice, like hooking up a Phase 90 and an Ibanez in series.  Then play with rate settings getting all the cross modulation.  This is sorta what put the (obscenely overpriced) MuTron Bi-Phase on the map.

Oh, well.  Wish i had the eyesight to do this stuff, anymore.  Best of luck to you.

KB

[patrick398]

Yeah independent rise and fall knobs is a great idea! Would be able to get some fantastic rhythmic phasing going on with different speeds for the up and down sweeps. This may be a little above my pay grade but i'll see what i can do when i get it breadboarded

[Mark Hammer]

So patrick398, I happen to like your thinking.

I'm a total fool for phasers.  I love phasers and have a dozen, anyway.  Being into keyboards, I'm not in love with, say, overdrive distortion the way I am phase shifters (and the occasional flanger/chorus).

Range switch:  good.
Enhancement (a la EH Small stone): very good.

One thing I think would be very cool is modulation waveform tailoring.  Probably along the lines of what you're thinking.  Sure, have a simple sine up/down, but what I'd like to see is a knob for time control of "Rise" and a control for "Fall". Almost like an envelope generator.

Came across someone's phase that had that instant changing thing you mentioned.  Didn't much care for it.  IMO, phase shifting needs to be continuous, even if quick.  There's something called a 'barber pole' or is it (?) Sherman function.  I remember hearing that and really liking it.  A four stage in barber pole, i think it was.

Also, multi-stage phasing works real nice, like hooking up a Phase 90 and an Ibanez in series.  Then play with rate settings getting all the cross modulation.  This is sorta what put the (obscenely overpriced) MuTron Bi-Phase on the map.

Oh, well.  Wish i had the eyesight to do this stuff, anymore.  Best of luck to you.

KB

It's Shepherd function.

One of the areas that doesn't get enough attention is quadrature oscillators.  These are able to provide an LFO with multile outputs, staggered by 90 degrees from each other.    The application would be that one has multiple phase shifters, either in series or in parallel, or stereo, with one starting its sweep after the other one does.  Here's one from Thomas Henry: http://www.birthofasynth.com/Thomas_Henry/Pages/QFG.html  Here'scan of two old POLYPHONY articles, detailing a Shepherd function generator, and a quadrature oscillator. http://hammer.ampage.org/files/quad-shep.pdf

[patrick398]

Will get my teeth into tomorrow, or try to at least
Thanks!

[sergiomr706]

I hope it s nota problem to link to madbeans Projects, ir ir os, delete pies de, but this is something that might interest you, phaser
related, http://www.madbeanpedals.com/forum/index.php?topic=20979.msg207280#msg207280

[patrick398]

Thanks for the link Not sure if it's a problem but it was a useful read none the less. I've spent a few hours trying to get a cycle i like out of this sawtooth generator. (I haven't yet got the parts for the one you suggested Mark)



Tweaked a few things to get the speed i was after so C1 is now 47u, R2 is a 1M pot, and R1 is gone all together. I hooked an LED up to the output so i could see what it was doing. I was swapping values in and out just to see what happened initially so let me know if i've done something weird.

It seems to be working well though, got a nice slow rise time like i was after and then cuts off instantly as expected.
I've just spent the last hour trying to figure out how to make the cycles irregular though. I've got the slow rise time i want but now the LED is off for too long. How would i go about keeping the same rise time but reducing the length of time it's in the 'off' position?

Did a lot of searching on the internet but all i got was a lot of results for 'irregular periods' and 'steroid cycles'...

[patrick398]

Just a cheeky little bump, i'm in the house all day today and would like to make some progress on this but i think i've hit the limit of my understanding

[Kipper4]

Basically you cant.
Other integrator, schmitt trigger lfo on the net. Try the tremulus lune lfo.
with the ramp diode mod. You will be able to shape the wave form more with a shape pot.
or you could go pwm to alter the timing of the on and off. But your probably going to need a another schmitt trigger after it too.

[patrick398]

Damn that's annoying. Oh well i'll keep looking, i'll get the trem lune lfo on the board this afternoon. Wish my bloody oscilloscope was working. Never really used one before, it powers up and i get a trace but does nothing when i hook it up to a circuit...i think this is probably another thread all together haha
Thanks!

[Scruffie]

You could try adjusting the voltage divider resistor values to pin 6 of the opamp while keeping pin 3 at half Vcc+. At a certain point the LFO will just latch up but you might be able to shift the rise and fall a little.

[GibsonGM]

Damn that's annoying. Oh well i'll keep looking, i'll get the trem lune lfo on the board this afternoon. Wish my bloody oscilloscope was working. Never really used one before, it powers up and i get a trace but does nothing when i hook it up to a circuit...i think this is probably another thread all together haha
Thanks!

Have you tried finding the manual for your scope online, Patrick?   I suspect you don't have the input sensitivity set properly for the voltage you're trying to measure...so when you connect it, the trace tries to "fly way up in the air' above the display.    If the input is high enough, you can 'break something' in your scope...this is how mine arrived, one channel working and one not - it was a diode that had popped on the other channel's input from over-voltage.    Not sure how digital scopes approach this issue and if they too can be damaged that way, but I would assume so. 

So you need to either know roughly what voltage you'll be measuring and set the volts/div accordingly, or start high and bring it down til you get something useful.  But try not to let it jump off the screen...this also happens if you are thinking about an AC signal that has a DC bias you didn't take into account, and instead of being centered, the trace flies up and away...setting input to AC blocks the DC bias voltage...

Just a thought...

[patrick398]

You could try adjusting the voltage divider resistor values to pin 6 of the opamp while keeping pin 3 at half Vcc+. At a certain point the LFO will just latch up but you might be able to shift the rise and fall a little.

So instead of pin 6 going to ground i could hook up a pot wired as variable resistor? Leaving pin 3 at ground?

Have you tried finding the manual for your scope online, Patrick?   I suspect you don't have the input sensitivity set properly for the voltage you're trying to measure...so when you connect it, the trace tries to "fly way up in the air' above the display.    If the input is high enough, you can 'break something' in your scope...this is how mine arrived, one channel working and one not - it was a diode that had popped on the other channel's input from over-voltage.    Not sure how digital scopes approach this issue and if they too can be damaged that way, but I would assume so. 

So you need to either know roughly what voltage you'll be measuring and set the volts/div accordingly, or start high and bring it down til you get something useful.  But try not to let it jump off the screen...this also happens if you are thinking about an AC signal that has a DC bias you didn't take into account, and instead of being centered, the trace flies up and away...setting input to AC blocks the DC bias voltage...

Just a thought...

I have a copy of the manual but it's only really the first page that says how to set up the scope. I'm pretty sure it's all set up correctly. If i hook the probe up to a point in the circuit and ground, on channel A with DC button selected it doesn't matter what i do to the time or voltage knobs, i just get a single trace line. I bought it pretty cheap online so wouldn't be totally surprised if it was knackered but then again i could be doing something wrong.

[Scruffie]

You could try adjusting the voltage divider resistor values to pin 6 of the opamp while keeping pin 3 at half Vcc+. At a certain point the LFO will just latch up but you might be able to shift the rise and fall a little.

So instead of pin 6 going to ground i could hook up a pot wired as variable resistor? Leaving pin 3 at ground?

Ah, I assumed you were using 9V rather than a bipolar supply so yes, wire a pot with pin 1 to +Vcc, pin 2 to pin 6 and pin 3 to -Vcc and yes leave pin 3 at ground.