Tonepad Phase 45 Build Report

[Mark Hammer]

Son of a gun.  I'm not sure if this means that great minds think alike or that fools seldom differ, but JC's schematic that you linked to shows pretty much exactly what to do with respect to chassis-mounting the bias control.

The 150k output resistor can probably be replaced with a 100k linear pot and a 47k resistor between the ground lug and actual ground for volume adjustments.  On the other hand, this thing is designed for unity gain, so I don't know what value there is in adding a volume pot.   Maybe, if you upped the gain on the input stage, but then that would likely distort the FETs.

[Fret Wire]

Thanks Mark. I was just thinking that because sometimes, depending where in the effects chain the phaser is, the level gets boosted when the phaser's on. It would be nice to dial it back to unity.

[Michael Allen]

Mark, I understand the idea,,,, I was just wondering if you had a schematic for that RockTek Phaser?

[Mark Hammer]

Nope.  No schem.  On the basis of the components on board, I'd say it isn't too much different than a bunch of other phasers like the Vox or Ibanez PT90.  Essentially the identical structure (dual op-amps, 10k input and feedback resistor and 10nf input cap for each section, FET to ground, dual op-amp LFO, single FET-switching for effect bypass).  The only major difference between this and things like the P90 is that the effect switching is done with a 4027 or 4053 (I forget which, and I'm at work now) instead of the discrete-based flip-flop in "name" pedals, and there is a cap/resistor combination between gate and drain on each FET to reduce distortion (see the Korg and Ibanez phasers for examples of this).  And, of course, the FETs are K30's instead of 2N5952's.

Tracing it out is probably a nonstarter these days.

[RDV]

Would a Phase 45 benefit from a higher input impedence, like a unity gain buffer? Mine sounds a little funny with a distortion driving it.

Regards

RDV

[Fret Wire]

What I always noticed with the Phase 90 (basically the same) is if you put it after a distortion or overdrive, the phasing effect is way more pronounced. It also seems to boost past unity gain. With the speed all the way down it even starts to sound more like a flanger.

[bwanasonic]

Would a Phase 45 benefit from a higher input impedence, like a unity gain buffer? Mine sounds a little funny with a distortion driving it.

I always use mine before distortion. Sounds more univibey. Try it. Wah-Phase-Fuzz Face is the combo I really like.

Kerry M

[Fret Wire]

I always use mine before distortion. Sounds more univibey. Try it. Wah-Phase-Fuzz Face is the combo I really like.

Kerry M

Same here. Like I said above, if you use a phaser after the dist., it seems like double the effect. If I use it after a dist.+, fuzz, or DS-1, I have to leave the speed all the way down or it's useless. Maybe that's what you're hearing, RDV. It's even worse for someone using the reissue phase 90, with the added distortion in the unit. Used before the OD's/Dist.'s, the full speed range still comes through with the nuances. Flangers and Chorus's behave the same way. Sometimes, it's a cool effect for the phaser or flanger after the distortion pedals. Can give an EVH sound.

[RDV]

I haven't had a Phaser since I was a kid(Small Stone), & I sold that one. I really didn't know where in the signal chain they normally go. I just wondered if everybody else's sounded weird after distortion. Now I know.

I also didn't like the Univibe mod. With a Phase 45 it just seemed to take the swirl away, I bet I would like the mod on a Phase 90 as it is a four stage unit like a Univibe.

My particular Phase 45 may not have taken well to the mod though I think maybe cause I didn't electrically match the Fets, I just plugged them in till I found something I liked, which to me sounded kinda univibey already, so when I did the cap mod, it just seemed to make it sound so linear in the sweep, and actually undo the univibeyness(is that a word?).

Thanks

RDV

[Mark Hammer]

Okay, here's the deal.

1) Anything that provides a filtering action will have a more noticeable filtering action if it is provided with a harmonically richer signal, or any signal whose spectral content is pretty full from low to high.  So, your phaser/flanger/wah will have a very robust effect if it is inserted after a fuzz or processing white noise or a cymbal, and appear to not be working at all if you process the subwoofer output of your electronic crossover.

2) We too often forget that filters of every kind are inherently amplitude-altering devices.  That is, they reduce the amplitude of this part or that part of the frequency spectrum.  If a filter is swept around, what that means is that there will be a shifting impact on the amplitude of parts of the signal.  Some parts will stay unaffected, while others will get louder and softer, depending on what the filtering is doing at the moment.  Should there be any resonant peaks in the input signal being processed, filters can also momentarily *increase* the loudness of those peaks if there is any gain/emphasis built into the filter.

3) Distortions are largely threshold-based devices.  That is, signals below a certain threshold will have little harmonic content added to them, while signal at or above the threshold will have sharp increases in how much harmonic content is added.

When you put #1, #2 and #3 together, what you get is this.  
As the flanger/phaser/wah sweeps, there are peaks and dips introduced in the spectrum.  If the filtering action occurs after a source of rich harmonic content, it will have no effect on what harmonic content is generated but will have an effect on what part of that is heard.  

If the filtering action is inserted *before* the distortion, it will have a very different effect in that it will vary whether different parts of the input signal fall below, at, or above the threshold for clipping.  So, perhaps, that part of your signal in the 900-1200hz range is just right for producing harmonic content as it passes through your clipping stage (fuzzbox), but as the notches in the phaser pass through that zone, momentarily that range falls below clipping threshold, and then resumes "clipability" when the notches move elsewhere.

So, inverting the order of filtering pedal and distortion device alters what harmonics are being generated, as opposed to what existing harmonics/bands are being heard.  If it was the case that distortion devices only generated a single overtone (say, double the input frequency), then the harmonic content would seem to track the notches in an obvious manner.  However, distortion devices sprinkle the entire audible spectrum with harmonics of what you feed them, such that an input note of 300hz will generate harmonic content way up past 10khz (very often the upper limit of amp speakers).  As such, the shifting notches and peaks don't really eliminate harmonics as much as alter their relative distribution.  There may well be a dip at 2khz introduced by the flanger, but there is harmonic content in that band from lower notes as well.

Like Bwana, I too find that a phaser before a fuzz sounds more Univibey.  Bear in mind that the cap values in a Univibe result in broader distribution of phase, for want of a better descriptor, so that cumulative phase shift is not focussed or clearly different at some specific frequency.  This results in less peakiness/dippiness in Univibes.  I think the way that phase shifters will effective shift the balance of harmonic content (in the manner described above) when placed before a distortion device does the same sort of thing.  That is, it results in a more diffuse, rather than focussed effect on the signal, yielding a more animated sound.

The down side is that a consistently strong signal is essential to using any distortion as means to sustain a note.  Since the phaser will vary the amplitude of the signal through its filtering action, notes held via finger vibrato will behave very differently in the phaser-fuzz arrangement compared to the fuzz-phaser arrangement.

Having said all of that, you can see why a fuzz-phaser combination pedal with a sequence-flip switch would be a nice thing.  That would need some kinda switch, though, if you wanted to do order-flipping AND have a status LED.