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

[deadastronaut]

@mark: great explanation as always...

one day i'll actually breadboard the phaze 45 and try out all the various tweaks + tinkerings...cheers.

[DougH]

Cheers Doug.

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

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

Thanks, Rob. 

[PorkyPrimeCut]

I've drawn out the circuit layout...



Can someone point out which area of the circuit would need changing in order to get my desired extra-long sweep?

Many thanks.

[duck_arse]

for the long sweep mod mark suggests, you wanna hack at the 3M9 resistor directly below IC2. I think the speed cap is the 10n at "04" and "P4".

hey, porky, back in the days of vinyl lps, cutting engineers used to scribble messages in-between the run-off groove(s). one of the joys of trainspotting lp's in those long gone days, was squinting to see what the message was. and one of the most recurrent ones, which I couldn't find on any of the albums I thort it would be on, was "another porky prime cut". googoo has some scribble on the topic.

is you the same person?

[samhay]

I don't think the 10n cap will affect the speed very much - it mostly just rounds off the LFO waveform and keeps the op-amp happy. If you increase the 10u cap underneath the 3M9 resistor, you will slow the rate of the LFO, and vice versa.

If you play with the value of the 150k resistor between O3 and Q3 (vero x and y's), you may be able to get a bit more, or less, swing out of the LFO and affect its sweep - smaller values = more swing. This is untested, but worth a try on a breadboard.

[PorkyPrimeCut]

for the long sweep mod mark suggests, you wanna hack at the 3M9 resistor directly below IC2. I think the speed cap is the 10n at "04" and "P4".

hey, porky, back in the days of vinyl lps, cutting engineers used to scribble messages in-between the run-off groove(s). one of the joys of trainspotting lp's in those long gone days, was squinting to see what the message was. and one of the most recurrent ones, which I couldn't find on any of the albums I thort it would be on, was "another porky prime cut". googoo has some scribble on the topic.

is you the same person?

I'm not actually THE Porky, no (that was George Peckham, famed cutting engineer) but I, like you, used to check all the vinyl I bought for mysterious inscriptions.
A PORKY PRIME CUT was one of the most common finds & also seemed to appear on all my favourite records. I ended up convinced that his stamp meant the record was going to be good.
In reality, he probably paid little attention to the style of the music & just did his job well, get all the sound levels correct.

Thanks for the suggestions folks. Keep 'em coming!!

[duck_arse]

for the long sweep mod mark suggests, you wanna hack at the 3M9 resistor directly below IC2. I think the speed cap is the 10n at "04" and "P4".

hmmm, well, I know why I said 10nF, but I don't know why he said 10nF. it should, of course, be the 10uF at s/t 14 connected to the 3M9.

[Mark Hammer]

I don't think the 10n cap will affect the speed very much - it mostly just rounds off the LFO waveform and keeps the op-amp happy. If you increase the 10u cap underneath the 3M9 resistor, you will slow the rate of the LFO, and vice versa.

If you play with the value of the 150k resistor between O3 and Q3 (vero x and y's), you may be able to get a bit more, or less, swing out of the LFO and affect its sweep - smaller values = more swing. This is untested, but worth a try on a breadboard.

There is where I was always a little confused.  I had always thought that the 10nf set the charge-up time, and the 10uf (15uf if one adheres to the original) introduced enough lag to make a square wave into a triangle.

[duck_arse]

ahhh, see, I always avoid the single op-amp circuit. but if you multiply the 10uF by the 500k (as seen on a phillpot diagram), you end up with "5". the 10nF would be 100 times smaller, and a bit fast for the masses.

[PorkyPrimeCut]

So, could it be as simple as this?....



Could I go even lower & higher with the resistor/cap values?

I assume the existing pot would still be able to operate a full sweep, even if the sweep was longer.

[duck_arse]

the 30uF will extend the lowest sweep frequency lower, by 3X. I don't think the 150k is the one you want, they are feebacks, no?

[PorkyPrimeCut]

Ah, hold on. I'm getting my wires crossed (god, I bet you've heard that one before).

So, do I need to decrease the value of the 3M9? Maybe to 1M?

What do you suggest for the cap?

[samhay]

If you want the sweep to be ~ 2x slower, then try increasing the cap to 22u (which unlike 30u, is a conventional size).
The 150k resistor you circled does have some influence on the LFO swing and 75k is probably not an unreasonable value to try. How this will sound, I have no idea.
The 3M9 resistor is the one that Mark suggested, and I would try this before the 150k.

I strongly suggest you try this on a breadboard first.

[Mark Hammer]

If you want the sweep to be ~ 2x slower, then try increasing the cap to 22u (which unlike 30u, is a conventional size).

Is there a reason why replacing the 500k pot with a 1M pot would NOT do the same thing....apart from the difficulty of getting a reverse-log 1M?

[samhay]

If you want the sweep to be ~ 2x slower, then try increasing the cap to 22u (which unlike 30u, is a conventional size).

Is there a reason why replacing the 500k pot with a 1M pot would NOT do the same thing....apart from the difficulty of getting a reverse-log 1M?

Not that I can think of right now.

[PorkyPrimeCut]

Thanks for the help guys, it's much clearer now.

Another question or two....

I originally wanted to make a Small Stone but couldn't find a veroboard layout (anyone?). It has a much more pronounced tone to it, regardless of the TONE switch.
The Phase 45 is a bit subtle & I'd love to be able to somehow make the sweep a bit similar to the Small Stone, characteristics wise (if that makes any sense).

I'm a bit new to this whole discussion of waves/sweep etc... but is there anything else I could do to the circuit (maybe tampering with the depth of the sweep) so the peaks are much more pronounced.

As for breadboards, I've never used one but now seems like a good time to check them out.

[PorkyPrimeCut]

Back again.

My plans have taken a small turn & I'm now thinking of modding my BYOC Phase Royal.
Hopefully it's as simple as what's been suggested already - switching out a capacitor & maybe a resistor or two.

Here's the schematic & a photo of the PCB....




Can anyone suggest which part of the circuit needs altering, and how?
Sorry if I didn't supply better images. These were the only ones I could find.

[duck_arse]

for a lower speed lfo, add more capacitance to the 10uF C14. as for sweep mods, I'm out.

[Mark Hammer]

The Phase Royale (or is that Phase Royale with cheese?  ) is a P90 with some bells and whistles, including two additional phase shift stages, variable sweep width (the "Depth" control), and variable wet/dry mix.

Attainment of slower speeds comes about exactly the same way as it does on the P45, since it is exactly the same LFO.  

Use of more than 2 stages means there is the possibility for feedback/resonance/emphasis, that increases the obviousness of the notches and peaks.  The PR incorporates a switch to select between 4 or 6 stages, but it taps the feedback signal from the 4th stage.  If SW2 were replaced with a DPDT toggle (it is currently an SPDT), you could take the end of C7, that normally connects to R14, and route it to the same sort of connection to R21.  IN other words, you switch both the number of stages, AND the number of stages in the feedback loop, at the same time.  That should provide a more intense sound.  Alternatively, you cankeep the #stages and feedback tap functions separate by using a 2nd SPDT to move C7 from here to there.

A word of caution, though.  Allpass/phase-shift sections, like those used here, are theoretically supposed to be unity gain.  After all, 10k input and 10k feedback, right?  But unless you are using 1% resistors throughout, there is the risk that one or more stages will have just the teensiest amount of gain.  And when yu add in gain to a feedback loop, you get.....wait for it.....oscillation.  Tapping the feedback point from stage 6 instead of stage 4 increases the risk of there being just enough gain to produce an irritating howl.  It IS manageable, though.  And it is managed by setting the Resonance control just a little lower, so as to avoid surprises.

Deepest notches will always come from flawless balance between wet and dry signals.  The Mix control permits achieving that.  Will the perfect 50/50 balance be achieved when the knob pointer looks like it is in "the middle"?  Maybe.  It will depend on your Mix pot, and if it's a 12mm Alps pot, chances are it won't be terribly precise or an absolutely perfect linear taper.  Close, but not perfect for the 50 cents it cost.

One way to facilitate precise matching is to replace it with a 5k pot and a pair of 2k7 resistors on each outside lug of the pot (the pot itself will likely be less than 5k so the whole mess should add up to 10k).  The net effect of that is to effectively expand the zone where balance is nailed down.  The downside is that you can't attenuate each signal (wet/dry) to the point of nothing, so it won't let you simply dial in vibrato.  BUt if you want vibrato, all you need to do is lift one end of either R25 or R26.

The frequency range where the notches are produced can be moved around by varying the value of R30.  A useful control might be to replace the 1M resistance with 560k and a 500k pot, or even 390k and a 1M pot.  Higher resistance values = lower frequency range (i.e., more gurgly).  Note that 6 stages makes 3 notches.  Will you hear 3 notches?  Not if you're sweeping the unit higher than the frequency content of your instrument, you won't; there has to be something to notch, after all.  

In sum, learn to adjust the sweep and resonance to suit the number of stages being employed, and you'll be happy.