I tried a quick and easy experiment with a Ropez/Ross phaser last night and was pleased with the outcome. The boards that Francisco Pena laid out and sells for that phaser make it easy to implement, but it can be applied to practically any phaser you can think of.
When it comes to phasing, the result is a product of the sum total of all phase-shift applied. So, 4 stages of phase shift provide up to a maximum of 90-degrees of phase shift per stage at any given frequency, which totals a maximum of 360 degrees of phase shift. Essentially, you get one notch produced per 180 degrees of total phase shift, so 360 gets you two swept notches.
Since the sum total phase shift is what matters, not all the stages have to sweep. certainly most of them need to, or else you wouldn't hear any swirl, but they don't ALL need to. A great many commercial phasers make use of this principle, and include some fixed stages on top of the swept stages. Probably the most commonly encountered example is the venerable MXR Phase 100, which uses 6 LDR-based swept phase-shift stages, but adds 4 more fixed stages on top of that for a total of 10 stages, producing up to 5 notches ("up to" because not all notches are audible or within the passband at all points in the sweep). Boss also uses the addition of some fixed stages to spruce up some of their phasers.
So, last night I decided to throw in 2 stages of fixed allpass/phase-shift to this Ropez, via a small daughter board that could be easily assembled in a postage-stamp, sized piece of perfboard, and hot-glued to the side of the chassis. I used what has become almost standard fare for such things: a 4558, 10k feedback resistors in each stage, 10k to the inverting input, .01uf to the noninverting input, and 10k to Vb. That's a total of one 8-pin DIP, 6 resistors, and 2 capacitors. You've seen this a million times.
The Ropez (at least the last iteration of it) has a number of pads aimed at integrating another quartet of swept allpass stages to make an über-phaser with 8 swept stages. On the diagram, two of these pads are labelled X and Y and are for inserting the additional 4 stages that Francisco made a daughterboard layout for. Cut the path between these two pads, run X to the input of one of the fixed stages, run the output of the second back to Y, connect your V+, gnd, and Vb, and away you go. You now have 6 stages, 4 swept, and 2 fixed. The same logic can be applied to a Small Stone, Phase 90, or whatever. The regeneration works exactly as before.
How does it sound? A little richer, and to my ears a little more pleasing at the top of the sweep. Not surprising since the added phase-shift really only starts to kick in above 1500hz or thereabouts. I tried it out with the piezo bridge pickup on my Parker this morning, and it sounds great for that. I like the vibrato produced when the dry is cancelled a little better too. On this particular phaser, I have a switch for going from phaser to phasefilter (two stages are converted from allpass to lowpass), and am pleased to report that the mod does not interfere with the pleasing sound of a phasefilter.
While it might be a little tricky doing this to a P90 installed in a 1590B chassis, it may well be possible to build it onto a small, low-profile board it you are handy with surface-mount op-amps and 1/8w resistors. It's one of those things that you can build on a small daughter-board and try out on whatever phaser you have handy. If you like it, keep it, and if you don't, it's no big deal to put things back the way they were.
But on the whole, definitely worth trying.
I don't want to detract from such a detailed and focused thread, but I looked around quickly for "phasefilter" as it seems really interesting.
Is it possible that this is how the EHX Worm gets all its multi-effects? At first glance, it looks like a multi-stage phase shifter, but by redirecting the feedback and a few outputs (?) you can get Tremolo, "Wah" and Vibrato all from the same LFO and "shifting network".
Are there any concrete or schematic examples of how to wire phasefilter from an existing phaser?
Thanks for all the info Mark. I'll surely try this and your new suggestions for additional fixed allpass/phase shift stages in the future.
Ton Barmentloo is a generous and well-respected member of this forum. I make a point of not inquiring about any of his designs in too much detail because I know that IP is his livelihood. The Worm is one of his. That being said, the Worm is optical, and the phase-filter option is something that essentially relies on using OTAs (3080, 13600, 3094, etc) for the allpass stages.
You can learn more by looking up the SSM2040 datasheet ( http://www.synthdiy.com/show/?id=85 ) and by looking at the design of the AMS-100 phase-shifter projects in DEVICE ( http://hammer.ampage.org/files/Device1-6.PDF ).
The original phase-filter idea, from John Blacet, assumed the user would be combining clean plus processed signal. In playing around with it, I found that some excellent and truly distinctive sounds could be obtained by using only the wet signal. As a result, if I'm going to implement aphase-filter setting/function, I always include a vibrato (dry-cancel) switch as well.
The "WORM" is just a 3-stager... :icon_wink:
Mark: your understanding my positions is well appreciated!
Philtering, Worming, Wahbrating, and Vibwahting can be done with all those more or less known circuitries/technologies/topologies...
the "Worm" bore out of the fact, that the textbook "...pass-transformations" and the Fourier and Hilbert thesis`
didn`t tell me all I wanted to know...
for me, the all-pass was missing in there...
Now when you look at the simplest allpass building block: the phasesplitter with an R and a C
between the inverting and the non-inverting output of a triode or BJT,
1.: you`ll see that from one of the outputs
the R-C series-hookup
looks like a Lo-Pass,
while from the opposite phased output,
it looks like a Hi-Pass...
Combining (adding/summing) these, we get an All-Pass, as is well known...
now: Serially combining Hi- And Lo-pass gives a Bandpass...
Subtracting a Hi-pass from the dry turns into a Lopass,
Subtracting a Lo-pass from the dry turns into a Hipass;
... sorry- I got distracted while typing ...
now: if one combines the lowpass or highpass during the right phase-relationship
with the original ( = dry ) signal or with the 1st All-pass (@ the proper amplitude.relationship)...
[will be continued, one day...]
i didn't mean to sidetrack the thread, but at the same time, thanks for those comments!
On my Tonepad Small Stone PCB, it looks like an insertion point for the extra stages could be made by cutting the trace between R33 and R41 ?
The two added stages would consist of what is between Q6 emitter and Q10 emitter?
Yep. From the looks of it, that's a viable insertion point. And what you're going to insert there is essentially a replica of what you see built around IC6 in the RPH-10 diagram shown here. The diagram shows 5k6 resistors to Vb. I used 10k, but you can use whatever you want, keeping in mind that the corner frequency where they start contributing 90 degrees of shift is given by the ever-popular F = 1 / (2 * pi * C * R).
(http://img.photobucket.com/albums/v474/mhammer/rph10-b.gif?t=1257632668)
Playing around with the pedal last night, I became convinced that I need to figure out how to envelope-control it. The sound of a gradual upward swell with two notches and lowpass, and some resonance, using only the wet signal, is lush, lush, lush. Like a dreamy synth pad when applied to chords. Tack a bit of chorus and decent reverb on top, and you have no need for guitar synths.
The trick is not just getting envelope control, though. One needs to keep in mind that the sort of sound produced when the on-board LFO is set for slower speeds is NOT equivalent to a straightforward amplitude envelope. The LFO sweep moves upward exponentially, so there would need to be some sort of envelope follower that would:
a) provide sufficient lag and control over attack/rise time,
b) translate that attack into an exponential sweep,
c) convert that exponential sweep into suitable current to feed the OTAs.
But believe me, the resulting sound is worth it. I gotta make some clips of this.
You've definitely got my attention! I wonder if I could fit this (with the envelope) in a Phase 90 where the battery would reside?
With an envelope follower, it would need your battery slot to be able to fit in a 1590B, although without an envelope follower, the pair of additional stages actually take up fairly little room, and would even allow you to keep the battery in. The dual op-amp itself is the biggest part. 1/8W resistors take hardly any space, and you can certainly use small monolithic ceramic caps for the phase shift stages without any space or audio quality concerns.
Note, however, that the rising sweep I'm talking about is not attainable on a P90. It needs an OTA-based phaser like the Ross or Small Stone, or the DOD FX20.
What is the partial schem from ?
It's stages differ from the SS stages, no Q followers [ :icon_biggrin:], but it has a feedback path that...goes a different way than the SS's.
Well, I made a 2-stage daughter-board last night, as small as I could, using 1/8W 10k resistors and small ceramic .01uf caps. The op-amp was a normal 8-pin DIP dual. Total footprint when done was 5 perf holes by 10 (plus the board area between the holes along the perimeter and where the next row of holes would be). The small caps and resistors assured that the IC (unsocketed) was effectively the "tallest" component on the board. So, this is pretty darn small, and the sort of thing one could easily fit somewhere in a 1590B, between a pot and the side of the chassis. In some respects, the wires connecting it to the main board occupy more space than the daughter-board itself.
pete,
The partial schem is the Boss RPH-10, which uses a pair of IR3109 chips for allpass stages, in addition to the op-amp stages shown. It is basically the Boss PH-2 phaser pedal, plus some extra bells and whistles. The IR3109 is four OTAs in a package, similar to the old SSM2040, but made specially for Roland/Boss. It allows for a fairly compact phaser when you want to have a lot of stages. Consider that it would replace four CA3094s or a pair of LM13600 chips.
Quote from: Mark Hammer on November 09, 2009, 07:15:40 PM
With an envelope follower, it would need your battery slot to be able to fit in a 1590B, although without an envelope follower, the pair of additional stages actually take up fairly little room, and would even allow you to keep the battery in. The dual op-amp itself is the biggest part. 1/8W resistors take hardly any space, and you can certainly use small monolithic ceramic caps for the phase shift stages without any space or audio quality concerns.
Note, however, that the rising sweep I'm talking about is not attainable on a P90. It needs an OTA-based phaser like the Ross or Small Stone, or the DOD FX20.
Thanks Mark. 5x10 perf is tiny!
If I really feel the need for a rising sweep, I'll take a look to see if my other phaser is OTA based. It's an old Tokai, which I haven't really analyzed circuit of.
I have the parts, hot iron, everything laid out...but just couldn't seem to try it without understanding better, or having a schematic for it.
The RPH-10 opamps [around IC6] are wired quite differently than the arrangement in the Small Stone.
Looking at the Tonepad Schematic, Cut the connection between R33 and R41.
Describing the RPH-10's IC6 ..Insert circuit:
10k/.01uf [10k to an OA Neg input, also the 10k feedback resistor], .01uf to "10k-Vbiased" +oa input.
Output through 10k to a duplicate wired circuit [the other side of Dual OA] 6k8 output from the second opamp back to the board splice point.
Also V+ and Gnd. to Dual opamp.
The reason I ask is because the circuit I wish I could draw up [layout creator giving fits for sometime trying], looks quite unrelated to the phase stages shown in the Small Stone, at the same time, I like that they look simpler.
Quote from: Mark Hammer on November 09, 2009, 07:15:40 PM
With an envelope follower, it would need your battery slot to be able to fit in a 1590B, although without an envelope follower, the pair of additional stages actually take up fairly little room, and would even allow you to keep the battery in. The dual op-amp itself is the biggest part. 1/8W resistors take hardly any space, and you can certainly use small monolithic ceramic caps for the phase shift stages without any space or audio quality concerns.
Note, however, that the rising sweep I'm talking about is not attainable on a P90. It needs an OTA-based phaser like the Ross or Small Stone, or the DOD FX20.
This is my adaptive peak following envelope generator
(http://img.photobucket.com/albums/v317/StephenGiles/SHenvgenerator.gif)
Could be useful in this application.
Watching this thread like a hawk!
So Mark, how would you contrast the addition of two static stages versus the addition of two modulated stages?
It's a slightly different sound. Remember that when all stages are modulated, the point where they add up to enough phase shift to produce notches keeps moving. The fixed stages I described add their maximum phase-shift above 1590hz (with amounts lower than 90 degrees below that point), but not before it. So in a way, the effect becomes a little stronger or more evident during the uppermost parts of the sweep. It's not huge, I have to say, given that it is after all only 2 stages. But it's almost like the unit evolves from 2 to 3 notches as you move past the halfway point in the upward sweep. All those companies that added fixed stages on top of the swept ones knew what they were doing.
I just received my Ropez PCB and the 4 extra stages board. Well I might as well wedge a few more (static) stages in there too! I was thinking of two quad opamps on a daughter board, both configured as 4 static stages, so with 4 static stages either side of the Ropez extra stages board. :icon_mrgreen:
Quote from: frequencycentral on November 14, 2009, 10:08:08 AM
I just received my Ropez PCB and the 4 extra stages board. Well I might as well wedge a few more (static) stages in there too! I was thinking of two quad opamps on a daughter board, both configured as 4 static stages, so with 4 static stages either side of the Ropez extra stages board. :icon_mrgreen:
Mmmm could be easier to just build an Eventide Instant Phaser!
Here's a picture to illustrate just how small and compact you can make the daughterboard. The Ropez board is shown for reference. Again, note that the height of the add-on board is basically the height of the chip itself.
(http://i414.photobucket.com/albums/pp228/Mark_Hammer/add-onboard-1.jpg)
Quote from: Mark Hammer on November 06, 2009, 09:12:29 AM
So, 4 stages of phase shift provide up to a maximum of 90-degrees of phase shift per stage at any given frequency,
Shouldn't that be 180 degrees per stage? Well ok, not quite 180, more like 170 in practice. (This is my first foray into phasers!)
If you connected the non-inverting (+) pin directly to ground, and didn't have the JFET or the cap tied to the + input, yes, you would be right. It would be a 180-degree inversion of the signal. It is the differential nature of the signal applied to the inverting and non-inverting pins that limit the phase-shift of some content to 90 degrees max, per stage.
Although let me take a few steps back from that and ask for the experts to step in here. I know that, at one level, each stage IS essentially inverting. We can easily demonstrate that by the fact that resonant feedback needs to pass through an odd number of stages to have the appropriate phase relationship, regardless of how many stages there are altogether.
So, the phase-shift that is applied, is essentially phase shift within each stage, ( ??? ) though we think of it cumulatively across the stages.
The use of "maximum" implies that some frequencies enjoy less phase shift by being closer to the boundary of the passband. So, while there may be 90 degrees of phase-shift in stage X for anything 1khz and above, there may be only 45 degrees phase shift for content at 500hz, and less for 250hz, 125hz, etc.
Regen passing back to an even number of stages sounds really good. You should have a listen to my Sonic Death Ray soundclips.
Quote from: Mark Hammer on October 08, 2010, 04:30:43 PM
If you connected the non-inverting (+) pin directly to ground, and didn't have the JFET or the cap tied to the + input, yes, you would be right. It would be a 180-degree inversion of the signal.
But when the FET is driven hard on then the + input basically is shorted to ground?? I got this:
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5703.mp4
I'm not seeing things right, that is swinging from zero to 180 degrees?
Is that an emulator, or an actual functioning circuit?
Quote from: Mark Hammer on October 08, 2010, 06:26:39 PM
Is that an emulator, or an actual functioning circuit?
Real circuit, hooked straight up to the scope. A single opamp band-pass stage (no resistor in parallel with the transistor though, like you sometimes see). Signal 1kHz, 200mVp-p.
Quote from: merlinb on October 08, 2010, 06:28:14 PM
Quote from: Mark Hammer on October 08, 2010, 06:26:39 PM
Is that an emulator, or an actual functioning circuit?
Real circuit, hooked straight up to the scope. A single opamp band-pass stage (no resistor in parallel with the transistor though, like you sometimes see). Signal 1kHz, 200mVp-p.
I reckon it's your 1khz test signal that's the issue.
Take your signal's frequency down to 82.4Hz (this being the frequency for low open 'E' on a guitar) & rerun the test - for a one stage allpass, you should see an initial 180 degree inverted signal (ie vs the original - & provided you're at the right end of the 'sweep') which will lag as you 'sweep' ...for typical components used in a phaser stage, certainly at 82.4Hz, it won't shift a full 180 degrees (the max 'shift is likely to be nearer 30-60 degrees)
here's a video I've just made like yours, but at 82.4Hz, a real circuit (not a sim) using a 4.7K & 0.1uf (it was all I had to hand), blue trace is the circuit's input signal, pinkish trace is output from a one stage all pass...
http://www.youtube.com/watch?v=jbMc0uPN_pg
(http://dl.dropbox.com/u/967492/4%20x%20fixed%20PCB.gif)
(http://dl.dropbox.com/u/967492/4%20x%20fixed%20PnP.gif)
Verified:
(http://dl.dropbox.com/u/967492/Borg%20Implant.jpg)
I've got a Phase 90 PCB hooked up to my breadboard ATM, just testing a few ideas using the fixed stages board. First result that I REALLY REALLY like is to use 0.01uF for C1, C2 and C3; remove C4 and stick the PCB in the regen loop - really nice, almost 'vocal' sounding.
So............even lower values for C1, C2 and C3 are even better, such as 3n3 or 2n2. It works well with 3 stages but dissapears if I add any cap in the C4 position. I've added a switch to select between normal regen and Borg Implant regen. I've got a whole new range of regen timbres now at the flick of a switch. This phaser also has the width and bias pots. As a side note I had no 4.7v zeners, so I used a 3mm blue LED + 1n4148 / 1k resistor to get a 3.5v vref.
TBH, I started off by using the fixed stages in the phase path, the effect was quite subtle, much less than I expected. As Causality 4 has 2 fixed stages at it's heart I was surprised how little adding 4 fixed stages in the phase path added. However, 3 fixed stages in the regen path sounds great.
I'm trying to figure out what's actually happening. I guess I'm filtering the regen in some way. As well as adding 270o of shift in the regen path. Any good explanation would be great - Mark? Stephen?
I've got two of these Borg Implant boards to play with (thanks SC!), so I'll make up the other one and continue to experiment.........more results pending.
(http://dl.dropbox.com/u/967492/We%20are%20Borg.jpg)
Humour me here.
In the absence of a schematic (of how it 'slots' together)...what role does the above layout play.....4 fixed stagees? (I know what a stage is, I know how a phaser works, but wondering what role a 'fixed' stage has to play?!)
I thought Mark explained it in the first post. I'll have to go back a read it again but that's where I thought I got my understanding of how the fixed stages worked.
Indeed he did (I've a bad habit of just picking up the last few posts in a thread...!!!)
Hmmm...still not locking into this one....if you apply four stages of 'static' phase shift, with some frequencies, you could very well be wrapping them around to where you started out? (ie a full 360 = 0 degrees phase shift.....particularly wrt higher frequencies)...surely all it's gonna supply is a 'phase offset' from where the modulated stages start.....but like I, since these will wrap around & could be back near zero shift....not understanding fully the 'win' here?
^^^
Each stage introduces a small delay inherantly, so even if you did end up with 360o, the shifted signal will be delayed with respect to the dry signal. You can't ever go back, only forward.
Quote from: merlinb on October 08, 2010, 05:39:38 PM
But when the FET is driven hard on then the + input basically is shorted to ground?? I got this:
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5703.mp4
I'm not seeing things right, that is swinging from zero to 180 degrees?
That's what will happen if you drive the Fet from hard on to off, like you said when it's on the + input is shorted to ground so you've just got an inverter. When it's off, so it's some huge resistance, the corner frequency of the RC filter is so low that the you've just got a non inverting buffer. That's what the simulator says anyway :)
In a phaser the fet or whatever you use would sweep between some limited range of resistances to put the corner frequency somewhere in a useful range.
Quote from: frequencycentral on October 24, 2010, 05:32:46 AM
^^^
Each stage introduces a small delay inherantly, so even if you did end up with 360o, the shifted signal will be delayed with respect to the dry signal. You can't ever go back, only forward.
Once you get past 360 degrees wrt phase shift, you're starting again wrt the dry signal ...there's no such thing as 361 degrees. (361 degrees = 1 degree of phase shift or in other words you're right back where you started)....so you
definitely do go back. In other words, adding more stages is counter intuitive eg 365 degrees of phase shift is not more delay at all, it's just a mere 5 degrees phase delay wrt the dry signal.
Additionally, once you get past 180 degrees of phase shift, you are essentially 'leading' the dry signal not delaying at all. (therefore 358 degrees of phase lag shift...is nothing more than a 2 degree phase 'lead')
Quote from: slacker on October 24, 2010, 05:50:58 AM
In a phaser the fet or whatever you use would sweep between some limited range of resistances to put the corner frequency somewhere in a useful range.
No, the sweep isn't to put it in a useful range (that comes from the choice of capacitance & resistance in the all pass). Sweeping is done to move the phase shift & thereby make the overall effect interesting (because a static phase shift just sounds relatively dull by comparison)
360o of shift is one full cycle delayed with respect to the dry signal. It may look the same on a 'scope when analysing sine waves, but with a harmonically complex guitar signal.........
....and how can opamps possibly perform the time travel back into the past that would be neccesary for a 360o shifted signal (and therefore delayed by one full cycle) to occupy the same time period as the dry signal?
Quote from: Gurner on October 24, 2010, 07:28:49 AM
No, the sweep isn't to put it in a useful range (that comes from the choice of capacitance & resistance in the all pass). Sweeping is done to make the overall effect interesting (because a static phase shift just sounds relatively dull by comparison)
That's not what I said :)
What I meant was that you need to sweep the resistance over the right range of resistances, and not from some huge resistance to a tiny one like I thought Merlinb was doing. If the corner frequency, and therefore the notches, spends most of it's time outside the frequencies generated by the guitar you aren't going to get much effect however much you sweep it.
Quote from: frequencycentral on October 24, 2010, 07:50:18 AM
360o of shift is one full cycle delayed with respect to the dry signal. It may look the same on a 'scope when analysing sine waves, but with a harmonically complex guitar signal.........
All a 'harmonically complex' signal is...is one made up of a lot of sine waves...so the theory stands. (besides most of the harmonics very quickly drop out....like within a few hundred milliseconds - and depending where you're playing on the fretboard, your often left with something akin to the fundamental ...which is in essence a sine wave)
Quote from: frequencycentral on October 24, 2010, 07:50:18 AM
....and how can opamps possibly perform the time travel back into the past that would be neccesary for a 360o shifted signal (and therefore delayed by one full cycle) to occupy the same time period as the dry signal?
Crazy I know.... I never said I had the explanation, just the concept down! Equally, Rod Elliot hasn't got the explanation, but it does happen (section 7.5)....
http://sound.westhost.com/articles/active-filters.htm#s75
Extract....
"Version "A" produces a lagging phase. That means that the output signal occurs after the input. For the values shown, the delay is about 155us with a 1.59kHz signal. Version "B" has a leading phase - the output signal occurs before the input. While this seems impossible, for a signal that lasts more than a few cycles it really does happen. In the second example, the output occurs 155us before the input"
In reality, this is just one of those polarity peculiarities that depends on how you view it (ie where you're referencing ...eg -5V will look like +5V if your 'reference' level is -10V!) . Is a signal with a 350 degree lag any different to a signal with a 10 degree lead wrt to the original signal ....no it's not, they're the same.
If you think a 361 degree phase shift is any different to a 1 degree phase shift, you need to do a bit more delving.
Quote from: Gurner on October 24, 2010, 09:04:04 AM
- the output signal occurs before the input.
No it doesn't, it just looks like it does.
Quote from: slacker on October 24, 2010, 09:37:28 AM
Quote from: Gurner on October 24, 2010, 09:04:04 AM
- the output signal occurs before the input.
No it doesn't, it just looks like it does.
ahem - That quote was Rod Elliot's quote not mine! (& Rod's one of the main men in my eyes)
but like I say, it's one of perspective - after one cycle, a 340° phase
lag essentially can be equally viewed/termed as a 20° phase
lead wrt to the ref (dry) signal ...but we're losing the main thread/point here...and that is, you can't get any more phase delay than 360°! (ie one complete cycle wrt any given frequency). And that once you're at 360°, you're back where you started.
What you do get by adding more & more (modulated) stages....is the ability to shift lower frequencies further in phase - & more phase
resolution for higher frequencies, eg 1°, 1.01°, 1.02° vs say 1°, 2°, 3° that you'd get with less stages (but with static phase shift stages, all you're getting is a phase 'offset').
I completely agree Rod's a top man.
This is how I see it though, which I think is relevant to what Rick is saying. If you look say at one of the troughs in the wave form, then the output looks like it's leading the corresponding input, but in reality the input that created that output trough isn't that bit of the wave that it appears to be leading. The input is the preceding peak, the phase shift turns this in a trough, so it then looks like it's leading the input, but it's not really, the output always lags behind the bit of the signal that actually created it. Which is what Rick was saying, if you phase shift it enough the bit of the waveform that creates the output won't be the preceding peak it will be the one before it, or even the one before that.
If the signal is completely uniform then, like you said this is irrelevant, but I don't know enough to say whether this would necessarily be the case for a guitar signal.
Quote from: slacker on October 25, 2010, 03:34:47 PM
I completely agree Rod's a top man.
This is how I see it though, which I think is relevant to what Rick is saying. If you look say at one of the troughs in the wave form, then the output looks like it's leading the corresponding input, but in reality the input that created that output trough isn't that bit of the wave that it appears to be leading. The input is the preceding peak, the phase shift turns this in a trough, so it then looks like it's leading the input, but it's not really, the output always lags behind the bit of the signal that actually created it. Which is what Rick was saying, if you phase shift it enough the bit of the waveform that creates the output won't be the preceding peak it will be the one before it, or even the one before that.
If the signal is completely uniform then, like you said this is irrelevant, but I don't know enough to say whether this would necessarily be the case for a guitar signal.
I read that a couple of times but i didn't fully understand the point you're trying to get across (a topic like this is actually hard to phrase in language agreeable to all readers!).
Where I came into this was wondering what the point of a static phase shift stage was...a rx'ed a reply that the explanation was in the first post, & the suggestion there is that because phase stages are cumulative, that somehow by adding stages you get more 'delay' - for example 500 degrees of phase delay being more 'delay' than say 140 degrees - it's not ...they're the same for any given frequency (remember, we're not talking about delay as in the traditional 'time delay' sense, but phase delay through a filter ...& the max
time you can actually time delay a given frequency in this situation is one 'period').
And the most phase delay you can get for any frequency is 359.99999999 recurring ...once you get to 360, you're back at the zero point.
That's the bit I'm picking up on...not necessarily the resulting peaks/troughs (which are obviously a function of adding in/out of phase signals)
By peaks and troughs I meant looking at a sine wave fed into an allpass stage, and then looking at the output compared to the input. I didn't think about the double meaning in relation to a phaser, sorry for the confusion. Don't know if that makes my post make any more sense :)
Quote from: merlinb on October 08, 2010, 05:39:38 PM
But when the FET is driven hard on then the + input basically is shorted to ground?? I got this:
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5703.mp4
I'm not seeing things right, that is swinging from zero to 180 degrees?
Further to my earlier post I see my mistake. One stage can theoretically give you up to 180 degrees shift, but you can never
quite get that in practice. After cascading two stages I see that I'm get just slightly
less than 360 degrees shift, and hence not as many notches as I assumed.
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5808.mp4
http://www.youtube.com/watch?v=gYF2h5ry3kY&feature=related
Gurner, what you are talking about, 361 degrees shift being equivalent to 1 degree, is true only in the special case of an unchanging periodic wave, which is constant both in waveshape and pitch at all times.
This does not hold true for any real life instrument. Although it's true that any signal is made up of a bunch of sine waves, these sines are all changing amplitude and phase through time, so as long as a cycle is not identical to the preceding cycle, you will have a result quite different from 0 degrees shift.
It's quite possible to simulate phasers in real time with Falstad's analog filter app:
http://www.falstad.com/afilter/
I will put together something that looks like 0 degrees phase shift on the scope, but which offers obvious phase shift in a frequency plot, so we can see what's happening.
Edit: here goes. The first link shows a 6-stage phaser on the scope. Input and output look to be the same, in the same phase.
http://tinyurl.com/2bv9lud
Now, we look at that in the frequency analyzer. Go to http://www.falstad.com/afilter/ and paste in this code (unfortunately the filter app does not allow direct code linking).
$ 1 5.0E-6 5 1 5.0 50
% 0 28853.998118144256
O 848 352 960 352 0
a 128 128 208 128 0 15.0 -15.0 1000000.0
r 208 64 128 64 0 10000.0
r 128 64 48 64 0 10000.0
w 208 64 208 128 0
w 128 112 128 64 0
c 128 144 48 144 0 5.0E-8 1.7514964460852651
w 48 64 48 144 0
r 128 144 128 224 0 50000.0
g 128 224 128 240 0
w 208 64 240 64 0
w 400 64 432 64 0
g 320 224 320 240 0
r 320 144 320 224 0 50000.0
c 320 144 240 144 0 5.0E-8 -4.232526694508851
w 320 112 320 64 0
w 400 64 400 128 0
r 320 64 240 64 0 10000.0
r 400 64 320 64 0 10000.0
a 320 128 400 128 0 15.0 -15.0 1000000.0
w 240 64 240 144 0
w 624 64 624 144 0
a 704 128 784 128 0 15.0 -15.0 1000000.0
r 784 64 704 64 0 10000.0
r 704 64 624 64 0 10000.0
w 784 64 784 128 0
w 704 112 704 64 0
c 704 144 624 144 0 5.0E-8 2.5647735075791105
r 704 144 704 224 0 50000.0
g 704 224 704 240 0
w 784 64 816 64 0
w 592 64 624 64 0
g 512 224 512 240 0
r 512 144 512 224 0 50000.0
c 512 144 432 144 0 5.0E-8 1.9216010425797787
w 512 112 512 64 0
w 592 64 592 128 0
r 512 64 432 64 0 10000.0
r 592 64 512 64 0 10000.0
a 512 128 592 128 0 15.0 -15.0 1000000.0
w 432 64 432 144 0
w 432 384 432 464 0
a 512 448 592 448 0 15.0 -15.0 1000000.0
r 592 384 512 384 0 10000.0
r 512 384 432 384 0 10000.0
w 592 384 592 448 0
w 512 432 512 384 0
c 512 464 432 464 0 5.0E-8 2.1448116575278924
r 512 464 512 544 0 27800.0
g 512 544 512 560 0
w 592 384 624 384 0
w 240 384 240 464 0
a 320 448 400 448 0 15.0 -15.0 1000000.0
r 400 384 320 384 0 10000.0
r 320 384 240 384 0 10000.0
w 400 384 400 448 0
w 320 432 320 384 0
c 320 464 240 464 0 5.0E-8 -4.147259331992092
r 320 464 320 544 0 50000.0
g 320 544 320 560 0
w 400 384 432 384 0
w 208 384 240 384 0
w 816 64 816 288 0
w 816 288 208 288 0
w 208 288 208 384 0
170 48 144 32 192 2 20.0 4000.0 5.0 0.1
r 624 384 848 352 0 992.0
w 48 144 48 624 0
w 48 624 848 624 0
r 848 624 848 352 0 992.0
o 0 16 0 34 10.0 9.765625E-5 0 -1
o 41 16 0 35 5.0 0.003125 0 -1
It's quite clear that we have 3 notches.
There must be something wrong with my browser, because I can't view those links.
But when I see you talking of notches, - it's only when you start adding/subtracting the phase delayed signal back with the original dry signal do your get notching - that wasn't my point.
To be clear, I was picking up on an earlier statement about allpass stages being cumulative & therefore by adding more in, that you get in excess of 360 degrees phase shift - you don't (& can't!).
What you do get when adding in more stages is greater resolution - & more phase shift for lower frequencies
High time to re-read your good ole Dome, Bode, & Nyquist... :icon_wink:
Not entirely sure we're all talking about the same thing! ???
And re the video linked top above... (http://www.youtube.com/watch?v=gYF2h5ry3kY&feature=related ) ....at 6m46s he actually says the same thing I've being saying all along - ie that once you get past 360 degrees, you're starting at zero again :icon_wink:. And referring to something as having a 720 degrees phase shift, well, it's just a convenient way of saying a particular frequency has completed a full cycle of phase shift twice.
Quote from: merlinb on November 07, 2010, 12:17:44 PM
Quote from: merlinb on October 08, 2010, 05:39:38 PM
But when the FET is driven hard on then the + input basically is shorted to ground?? I got this:
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5703.mp4
I'm not seeing things right, that is swinging from zero to 180 degrees?
Further to my earlier post I see my mistake. One stage can theoretically give you up to 180 degrees shift, but you can never quite get that in practice. After cascading two stages I see that I'm get just slightly less than 360 degrees shift, and hence not as many notches as I assumed.
http://s81.photobucket.com/albums/j207/merlinblencowe/?action=view¤t=CIMG5808.mp4
Once I find the time, I`ll link to a tube- (valve-) circuit that goes beyond 180° in one stage... :icon_wink: