Understanding the Pearl PH-03 phaser

[Mark Hammer]

Osamu Hoshuyama in Saitama, Japan sent me a note for posting here the other day, concerning the Pearl PH-03 phaser, which has a different architecture than what many of us are accustomed to seeing.  He writes:

"I found the discussions on Pearl Phaser at Aron's forum.

I wrote some explanation on the phaser at my blog, which might
be useful for you and the forum members.

  http://houshu.at.webry.info/

  Meaning of the blog name is
  "Reading Circuits of Analog Musical Instruments"

All the descriptions are in Japanese, but, most of the titles and
all the figure are in English.

On Pearl Phaser:

http://houshu.at.webry.info/200511/article_1.html
http://houshu.at.webry.info/200511/article_2.html
http://houshu.at.webry.info/200511/article_3.html
http://houshu.at.webry.info/200511/article_5.html

Some figures to explain Vibrato from the stompbox cookbook
may also be helpful."

Many thanks to Osamu (Sam).

[Dirk_Hendrik]

Google searches point to Japanese pages quite frequently. It always makes me think about the potential wealth of (historical) information which must be hidden there. Fortunately over the last few years some of this info seems to surface.

[stm]

A BIG THANKS!, Mark

These images are a revelation. What a good way to start the new year!

In the first place, I didn't even know the mystery IC was a CD4069, since the schem doesn't say so!
Now if it were possible to find a way to use all six stages for the task this would allow a very compact implementation of the six-stage Cookbook Phaser.

Regards.

[StephenGiles]

Thanks indeed Mark and a Happy New Year to you and all your family.
Stephen

[TELEFUNKON]

baddest stone from the sun?

[Bernardduur]

Maybe a bit OT, but from all the phasers I have ever played this one is the best I ever heard......

I love mine.........

[MartyMart]

I'm not sure if it's the "best" but I certainly wont let go of mine in a hurry !!
It has it's own "voice" so to speak ..
Thanks Mark, great info

MM

[Mark Hammer]

Don't bother thanking me.  Sam is the one who sent me the info.  I just passed it along.

While you're busy checking out his site, scroll way down and check out the 13600/13700-based  LFOs.  Useful info there.

It occurred to me when looking at them that a sort of dedicated phasefilter could be easily built with a pair of 13600s and a dual op-amp.  Two OTA sections do phase shift, one OTA does lowpass filtering, and the fourth forms the LFO.  The dual op-amp takes care of input and output.  That could actually be a nice little pedal.

[stm]

Do you mean like a sort of Leslie sim?

[Mark Hammer]

Do you mean like a sort of Leslie sim?

No.  There is a sound you can get by combining some allpass and lowpass filtering that sits somewhere between phasing, tremolo, vibrato and cyclical wah-ing. It's a very swampy watery sound, that doesn't sound like a Uni-Vibe, doesn't sound like a phaser, and doesn't sound exactly like a vibrato.

I stumbled onto it a couple of years ago when looking at some old docs for the SSM2040 chip.  The appnotes/datasheet shows how easy it is to convert the SSM2040 stages from allpass to highpass or lowpass.  John Blacet used this aspect in his late-1970's "Phasefilter", and Craig Anderton imported the idea into his AMS-100 series (shown in DEVICE at my site, starting around issue 4 or 5).  The light went on when I realized that the Small Stone and Ross phasers both used 4 OTA-based sections and had essentially the same component connections (if not the identical component values) as the SSM2040-based design used by Blacet and Anderton.  I tried grounding the caps of two of the allpass sections on a Small Stone to make them lowpass and sure enough it worked like a charm.  There are some samples over at Charlie "Moosapotamus" Barth's site, though I don't think they do justice to the sonic qualities (and neither does he...unless he's changed them).

By converting the latter two allpass sections to lowpass, you have a swept 2-pole lowpass filter with a notch just below the cutoff.  Combined with clean signal it sounds *sort of* phase-ey but not quite.  With dry-lift it sounds, as described earlier, very swampy and sexy, kinda like tremolo that has had a bit of madeira, starts nuzzling your neck and is undoing the top few buttons of its shirt  .  Turn up the resonance/feedback, and it starts to sound like an LFO driven wah as the resonance around the lowpass cutoff starts to make itself known.

Just exactly how many sections of lowpass there NEED to be, I could not say.  The standard 4-stage configuration of many phasers results in 2 poles of LPF being used because folks see 3 poles of allpass as not a whole lot better than 2 poles.  It might be that a single pole of lowpass is all you really need, over and above 2 allpass stages.  I don't know this to be true, I'm just wondering aloud.  Given that a perfectly lovely triangle LFO can be made from a single LM13600 section, a nicely economical and compact circuit could be achieved with a pair of LM13600s...if one found a single pole of LPF to be sufficient.

The 2-OTA LFO in the Small Stone and Ross produces a complex waveform (as the documents at Osamu's site show) which is triangular for one half-cycle and sinusoidal for the other.  This "hypertriangular" waveform is preferred for long slow sweeps, since it shows off certain parts of the sweep, but in my view shows no particular advantage once LFO rates starts to get faster than, say 1-1.5hz, because your attention is not permitted to linger on those dramatic parts of the sweep once it gets fast enough.  Should one decide to use a phasefilter circuit in the sorts of musical spaces one would normally insert a tremolo, that is pretty much the LFO range you'd be aiming for anyways, so foregoing the hypertriangular waveform for a "merely" triangular one is OK, I think, and not a significant sacrifice.

So, no, not a Leslie sim.  Incidentally, in the December 2005 issue of Practical Electronics, there is a "solid-state Hammond" project that uses a ripple counter and CMOS switch to distribute a sound source to multiple amp/speaker modules for greater sonic animation.  Had this been 5 years ago, I would have been interested in it, but now that I have a real Leslie and the Roto-Machine pedal, my own interests in faking spinning speakers with analog circuits has dwindled considerably.  For those who wish to experiment with sonic relocation, though, it looks like an interesting circuit.

[StephenGiles]

Mark, in our local newsagents it is possible to buy any of 30 PC mags and those with a picture on the front of ladies with huge frontages, mags on horseracing, shooting, fishing, guns, guitars.......but no Practical Electronics!!!!!
Stephen

[gez]

Incidentally, in the December 2005 issue of Practical Electronics, there is a "solid-state Hammond" project that uses a ripple counter and CMOS switch to distribute a sound source to multiple amp/speaker modules for greater sonic animation. 

I read through that article and to anyone thinking of getting a back issue I don't think you're going to get much of a Leslie sound out of it.  Bit of a perverse approach if you ask me.  If I recall it just uses a multiplexer to switch a sound source to umpteen speakers in sequence, which you'd arrange round the room to get 'spacial' interaction...think I'll pass on that one! 

[gez]

Mark, in our local newsagents it is possible to buy any of 30 PC mags and those with a picture on the front of ladies with huge frontages, mags on horseracing, shooting, fishing, guns, guitars.......but no Practical Electronics!!!!!
Stephen

I have to say you're not missing much Stephen.  I skim through it in WH Smith when it comes out and buy a hand full of issues a year when they have an article/schematic of interest.  Heavily PIC influenced, which isn't necessarily bad (especially as I'm having another go at coming to terms with these damn things), but I don't really want to build something that flashes on and off to tell me the fridge door isn't shut...I have a partner for that!

[Mark Hammer]

Mark, in our local newsagents it is possible to buy any of 30 PC mags and those with a picture on the front of ladies with huge frontages, mags on horseracing, shooting, fishing, guns, guitars.......but no Practical Electronics!!!!!
Stephen

I have to say you're not missing much Stephen.  I skim through it in WH Smith when it comes out and buy a hand full of issues a year when they have an article/schematic of interest.  Heavily PIC influenced, which isn't necessarily bad (especially as I'm having another go at coming to terms with these damn things), but I don't really want to build something that flashes on and off to tell me the fridge door isn't shut...I have a partner for that!

I've got two kids and a wife for that myself!

Our local Chapters (a large Canadian bookstore chain) carries an excellent selection of magazines (some with "large frontage, though I prefer to call them the "bad posture" magazines, since none of the women shown ever seem to stand up straight).  Many of the ones that interest me have cover CDs or DVDs.  Of course these days, you seem to have your choice of browseable mags whose cover CDs can fall off or be stolen, and mags that come in a sealed bag so you can be sure to receive the cover disc, but can't see what's on it until you buy the mag.   And yes, if I could figure out how to make good use of the 16F84 sitting in my parts bin, I suppose Practical Electronics and Nuts and Volts *would* be of more consistent interest to me.

[stm]

Do you mean like a sort of Leslie sim?

No.  There is a sound you can get by combining some allpass and lowpass filtering that sits somewhere between phasing, tremolo, vibrato and cyclical wah-ing. It's a very swampy watery sound, that doesn't sound like a Uni-Vibe, doesn't sound like a phaser, and doesn't sound exactly like a vibrato.

Interesting! Thanks for the explanation.

[Mark Hammer]

De nada.  I should clarify that it does not produce tremolo or amplitude modulation.  Rather there is a slight, but noticeable perceived volume fluctuation produced because of the lowpass filtering and notch.

[stm]

There is a sound you can get by combining some allpass and lowpass filtering that sits somewhere between phasing, tremolo, vibrato and cyclical wah-ing. It's a very swampy watery sound, that doesn't sound like a Uni-Vibe, doesn't sound like a phaser, and doesn't sound exactly like a vibrato.

Mark, be warned that I will cite your words when I build and advertise this effect! 
What a gracious and attractive way of describing a sound!

I maybe wrong, but this description evoked me part of the guitar sound in "Pigs (three different ones)" from Pink Floyd's "Animals" album, starting from 4:15 approx.  It's watery and vowel like. When I actually played the track I found no apparent change in volume or loss of brightness though, nevertheless doesn't sound to me like any stock phaser I've tried.

[Mark Hammer]

Well then you'll need to look at Craig Anderton's description in DEVICE.  He has a review of the Blacet module, and also describes the two voltage-controlled phasers he designed, one of which has switchable allpass/lowpass sections.

If I was going to go into the business of producing pedals, this is one of the things I'd make.  Notsomuch because it is a mindblowing effect, but because as far as I know it is a niche that has simply not being occupied in the world of guitar pedals, whether by dedicated pedals or by a toggle-equipped phaser. I haven't looked to closely at either the E-H Worm or Wiggler so I may be talking naively there.

If you start making and selling them, send me one, and we're even.

[A.S.P.]

WORM video clip
Modulated Wah @ 2:00 ...

Worm = (not so) classic optical solidstate... 

Wiggler = completely different Pure Tube animal...