A simple one-knob phaser with a looooong sweep?...

[PorkyPrimeCut]

Hi,

I'm new here & planning a build that's a little more adventurous than my other BYOC/PoodleParts builds.

I'm thinking of putting 3 effects in one unit, rather like the Vox Ultrasonic/Starstream guitar, but fancy changing things a bit.
Rather than a Repeater I'm thinking of adding a simple one-knob phaser. What I really want is something that rises & falls very slowly so a long range is essential.

Can anyone suggest a simple circuit for me to look at? This will be my first venture into the world of veroboard & I'm pretty excited about it.

So far I'm thinking Bass/Treble Boost > Fuzz/Distortion > Phaser

[deadastronaut]

Check out my youtube channel below, phase II.

ill post up pdf if you are interested in it...its pcb though.  Not vero. 

[PorkyPrimeCut]

Very cool!

I'm loving the simple etched graphics too. Something I'm tempted to try out myself actually.
The LED eye is a great touch. Almost a shame you couldn't have it fading/rising in time to the phase (but that's just me splitting hairs!)

I'd be interested to see the innards or any layout images you have, for sure.
At this stage I'm open to suggestions & am curious to hear how easy it would be to modify the Phase 45 circuit so the sweep is super long.

I'm very much a "painting by numbers" builder & rely on layout drawings. The actual magic is a mystery to me as I have zero electronics knowledge.
This time last year I couldn't tell my capacitors from my transistors!

[Ice-9]

Check out my youtube channel below, phase II.

ill post up pdf if you are interested in it...its pcb though.  Not vero. 

That phaser sounds great Rob, great work.

[deadastronaut]

Cheers mick...yeah its pretty cool.

heres the mods i did..

as you can see its a tonepad phase 45 pcb, just swapped a few values.




(for some reason i can't post pics today...

https://dl.dropboxusercontent.com/u/7464107/phaseII.jpg

[Ice-9]

Great idea to run an LED off the LFO for speed indication. I loved the sound about where you play a bit (I Think Rush).

[deadastronaut]

rush indeed... big fan.

yeah the led doesn't 'pulse' but its a cool add on indicator anyway..

edit: forgot to add the 1M pull down on this doc/build...but that will be remedied soon.

[DougH]

Sounds great!

I love the etching too. How did you do that? Link to a tutorial or something?

[deadastronaut]

Cheers Doug.

here's slades etching tutorial...i pretty much do this.

http://www.diystompboxes.com/smfforum/index.php?topic=80962.0

[PorkyPrimeCut]

Does anyone know if it'd be possible to modify a Phase 45 (or a Small Stone) circuit to increase the sweep length?

[B Tremblay]

Does anyone know if it'd be possible to modify a Phase 45 (or a Small Stone) circuit to increase the sweep length?

If you want to adjust the balance of the sweep, the voltage divider that provides Vref to the LFO can be modified to incorporate a pot.  The Tremulus Lune does this with a nearly identical LFO section.

In the Tonepad Phase 45 layout, you would replace the 150k resistor between +V and pin 3 of IC2 with a 100k resistor in series with a 100k-linear pot wired as a variable resistor (lug 3 to the 100k resistor and lugs 2 and 1 connected to pin 3 of IC2).

[Mark Hammer]

There are two elements being smushed together here: the rate of the sweep, and the width.  Most LFOs can be easily coaxed to achieve much slower sweeps by simply increasing the value of one capacitor.  Bear in mind that the speed of the LFO is a function of how long it takes to charge up that capacitor.  Charge-up time is a function of both the cap value (higher values take longer to charge up) and the resistance that limits the current flow charging it up.  In the case of the Phase 45/90, just double the value of the .01uf cap in the LFO to slow the LFO down by a factor of two.  A simple SPST toggle that adds another .01uf cap in parallel will do just fine.  There is a good chance you'll hear a pop when switching in the cap, so either turn down, or else flick the switch only when in bypass mode.

Now, having said all of that, there is a reciprocal relationship between sweep rate and width.  We generally want less width as the sweep rate goes up, and more as the sweep rate gets slow.

In the case of the Phase 45/90 and derivatives, the width of the sweep is partially set by the 3M3 resistor between the LFO and the gates of the JFETs.  You will find that component to be 3M9 on some issues/drawings.  A simple mod would be to use a DPDT toggle to both add the extra capacitor (for slower sweeps) and change the value of the 3M3 resistance, at the same time to have a wider sweep with slower LFO rates.  You could have a variable sweep control, but since you asked for a one-knob phaser, I assume you want something simple and compact, so we'll go with one knob and one toggle.

The sweep of the phaser will be wider to the extent that the LFO can send more current to the JFET gates.  You don't want to send too much or too little.  So, let's say we aim for around 3M as the resistor value for "wide" sweep, and 4M for "narrow" (those are suggested values, subject to individual taste, but I wouldn't go too much lower and not much higher).  You would use a 3M and 1M resistor in series, in the spot on the board where the 3M3/3M9 would normally go.    When one set of toggle contacts adds in the 2nd cap to slow things down, the other set of toggle contacts provides a "bridge" (shunt) across the 1M resistor.  That'll give you high-capacitance-plus-lower-resistance and lower-capacitance-plus-higher-resistance.

[PorkyPrimeCut]

OK, I'm a little out of my depth here! Heheheh!!

What I do know though (I think) is that a change to the existing circuit won't be too hard, to acheive what I'm after.
At least it seems that way from what you folks have just been explaining.

As I say, I'm aiming higher than normal with this build so bear with me if I come back for more questions.

I guess I should go ahead with using the Phase 45 layout that's available on this site.
It looks like the smallest & simplest of the lot, unless there's a Small Stone layout that's smaller?

[PorkyPrimeCut]

So, am I right in thinking that the Tonepad Phase 45 project just has pictures of the PCB?
Some links wouldn't load so I just looked at some Google images.

If so, I'm a little stuck as I can't really follow my way around a PCB that well. I'm worse with schematics!
I was planning on using a veroboard layout (my first attempt) as it's much easier to follow.

If I was to draw up the veroboard would any of you be able to point me in the right direction, with regard to which parts need swapping out etc...

I'm likely to be using this one.

[deadastronaut]

i'm sure someone here will help you out..

[Kipper4]

Quick question after a look at the tonepad schemo.
How come nobodys used a qaud op amp design in the phase 45?

[Mark Hammer]

It is always good practice to keep the LFO separate from the audio path as much as is possible.  The reason is that most LFOs will start with a square wave, and then reshape it into a triangle.  When the LFO suddenly jumps straight up to produce that square wave, it results in a sudden current draw, often resulting in a "spike" on the power supply lines.  We end up hearing that as a "tick".  I'm sure if you enter "ticking" into the search engine here, there will be no shortage of posts since the very beginning anxiously hopig for some salvation for a pedal that sounds great but has an annoying ticking sound that corresponds to the LFO speed.

If the op-amp used for the LFO is "decoupled" from the other chips connected to the same power supply, the ticking can be drastically reduced so that it does not pose a problem.  Of course, if a person uses a quad op-amp for the LFO and phase-shift stages, that becomes sort of hard to do.

The traditional solution is to use a low current op-amp, such as a TL022 or LM358, or TL062, or something similar, so that it doesn't "pull" as much current, and feed the V+ pin of that chip with a resistor/capacitor combination that provides it with its own teeny tiny little reservoir of "reserve power", to see it safely through the sudden surge.  Though not necessarily applicable to every single case, what you'll often see is something like a 100 ohm resistor between V+ and the V+ pin on the chip, and a 10uf cap to ground from that pin.

That, and the ease that dual op-amps sometimes provide over quad op-amps, when it comes to layout, are the principle reasons why you will rarely, if ever, see a Phase 45 using a single chip.

make sense?

[Kipper4]

Perfect sense Sir thats cleared that one up nicely.
Sorry about the thread jack but i just had to ask.
Appreciated
Rich

[Mark Hammer]

No problem.  Won't be long before you're providing the same info to someone else and helping them out of a jam.

[Kipper4]

Haha I wish Mark I'm a bit of a slow learner.
I love it though. Just getting into layouts and using software to create schematics lately.