seek wah ?

[marrstians]

i hope this question isn't taboo or offensive... i'm not asking for the schem or anything but was curious of the ideas of how it works... does it shoot a signal to different chains in the series kindof like someone manually pluging the signal to different outputs? is that idea used in other pedals on the market? i was just wondering if that is how it works maybe the idea could be used for other pedal systems to have variable tremolos or switching from fuzz to distortion or whatever... just thinking....

[Paul Perry (Frostwave)]

http://www.geofex.com/Article_Folders/udrand.htm
and
http://www.geofex.com/Article_Folders/sing-wah/sing-wah.htm
from the mighty pen of R.G. will give you some ideas!

[zachary vex]

each pot carries only a control current for its led which is directed to the vactrol.  the resistive output of the vactrol controls the wah setting.  each of the pots is fired up in sequence using a cmos chip and a clock circuit.  the audio wah circuit is isolated by the vactrol and has its own filtered supply voltage.

the ooh-wah has an additional control board which has a constantly-varying number of rf pulses which are clocked and gated to create a pseudo-random selection of the output control channels.  three oscillators are employed to accomplish this... one operates sub-Hz to continuously vary a second RF oscillator's center frequency, and the third one is a 2 ms gating pulse that controls the other two, causing the channels to momentarily "spin" like a roulette wheel.

zachary vex

[Mark Hammer]

Zachary,

Excellent posting, for the following reasons:

a) generous with information
b) lucid
c) conceptual
d) shows that you can learn the most important features of a design without having to resort to schematics
e) does all of the above in a way that can spur someone onto producing another innovation

One more reason why you deserve respect.

Thanks,
Mark

[Ansil]

hey z is the man.   i think we all know that.

[EdJ]

Hear hear
Ed

[Ansil]

hey z did you ever get that family of 6  fit into the hammond 1590 yet..  last i heard it was a work in processs.  how many bedrooms did you get in there.??

[BillyJ]

This maybe too much info but here is a relative post from Mark Hammer.

"
EVERY lfo is intended to work akin to keeping your hand on some knob and tweaking them in a cyclical manner. Different sorts of sounds and feels can be created depending on how that tweaking occurs. In more technospeak, this is partly a product of the LFO waveform. So, for instance, many tremoloes these days have a triangle/square switch which selects between two waveforms the lfo is capable of producing (and just about any and every 2 op-amp LFO will do this). A triangle waveform creates the sense of the parameter being steadily increased then decreased, while a square wave makes it seem like it is turned on then off repetitively.

Othe waveforms can be created though, some that don't immediately strike you as a waveform or else are produced in ways you don't think of. For example, you can make an LFO waveform with a counter/sequencer. This is used in the Z-Vex Seek-wah, Ooh-Wah, and there is a circuit for something like this at geofex. Here, a counter that is capable of providing some maximum voltage steps through a sequence and provides that voltage at each of some number of separate outputs. Stick a trimpot at each output, and mix the trimpot outputs together and you can produce a cyclical change that varies according to the trimpot settings. So, set 4 trimpots in an 8-event counter/sequencer to max, set the next 4 to min, and as the sequencer keeps repeating its cycle you produce a square wave. Adjust all those trimpots so that #1 is maxed and each successive trimpot is set a bit lower, and the sequencer produces a descending "ramp" or sawtooth waveform. As you can imagine, all sorts of other possibilities are available (just one of the things that makes pedals like the Seekwah and Oohwah so nifty).

Changing the shape of waveforms is not only achievable by "building" waveforms as in the manner described above. Any of the techniques that synthesists have used to shape waveforms for oscillators to change the timbre can also be used to shape low frequency waves as well. Think of a sweep up/down as an "event" whose onset and offset can be used productively and altered and you'll get the idea.

Tim Escobedo has a "simple square-wave shaper" at his circuitsnippets site which he borrowed from an old Polyphony article. That article, in turn, simply piked it from a standard synth circuit floating around. An attack/decay envelope generator in a synth simply provides a voltage that ascends at some rate, and then descends at some rate. Essentially, that envelope starts out as a square-type wave, but one control limits how fast it rises, whie another limits how fast it decays. Tinker with those and the output can be all sorts of waveforms. Tim, and his source material, adapted that principle to take an *audio* square-wave and re-shape it so that it can be tweaked to rise or fall (or both) not quite as sharply as it started out. In between a simple event generator and an audio waveshaper, we have LFO circuits that also incorporate this variable rise/fall time control to produce other waveforms besides a triangle or square.

Some sorts of waveshapers play not so much with the ascending and descending "straightaways" but wiuth the "turns". One LFO waveform which is felt to be desirable for sweeping some types of effects at some speeds is referred to as a "hypertriangular" waveform, which is a typical triangle at one end and more like a sine-wave at the other.

LFOs can be combined to produce more lively and richer modulations. An article I read in the Journal of the Audio Engineering Society about 20 years ago or more addressed the elusive "fat" sound from synths. In the early days of synthesis, before digital sampling of existing "fat" acoustic sounds became popular, people would complain that keyboard synths sounded wimpy and uninspiring. The authors of this paper tried to find out how much modulation you needed to make a sound from an standard poscillator sound animated, lively, rich, and attention grabbing. Peak interesting qualities seemed to emerge around 3-4 sources of modulation and after about 5-6 you were way past the point of diminishing returns. So, to illustrate, perhaps one LFO would vary the pitch a bit, another would vary the pulse-width or some other aspect of the waveform, while another would vary the amplitude. They weren't all at the same speed and were certainly not all modulating by the same amount, but this would have produced a "fatter" sound. The CV inputs that some effects pedals have (and this can include inputs for "expression pedals") permit the user to combine multiple LFOs and feed their mixed value into that input to provide more animation.

One term you will hear occasionally is "periodicity". When an effect is swept in a "periodic" manner, that means you know exactly when it is going to sweep up and down. Very predictable, very repetitive, very boring, and sometimes very intrusive. Indeed, it can be the very obvious repetitive nature of a modulated effect that *distracts* away from the notes and focusses too much attention on the up and down stuff. Here, there are several solutions. One solution commonly used is to avoid using an LFO and use a noise source as a way of generating random voltages and random modulation as a result. That has its moments and its pros and cons. Another way is to use multiple LFOs that are not synchronized and may even output different waveforms. Mix 'em together and you can get modulation that, if not strictly random, is noticeably less periodic, and so less intrusive or attention-rivetting. When you have a chance, stick a pair of phasers or pair of chorusses or flangers in series and set their sweep off from each other a bit. You still hear the effect but you don't get quite as seasick.

Many of the synth DIY sites have tons of schems for LFOs. I have a couple of older articles on these things at my site too. Check out the hypertriangular clock, and the SEWAR project (http://hammer.ampage.org or go directly to hammer.ampage.org/files) for some ideas. "

Don't know which thread I yanked this but it seemed like worthy information. hope it helps.

[The Tone God]

I have an article on a simlar topic in the works. Looks for it soon.

Andrew

[doug deeper]

z...did you get this idea for this from all those "sequencer" circuits from early 80s electronics books???
ive played with this idea in ring mod form before....CRAZY STUFF!!!
take care,
doug

[zachary vex]

i don't remember exactly how i came up with the ooh-wah circuit.  it was one of those ideas where i tried one thing, and it drew too much current, so i tweeked in until it didn't draw hardly any, and had multiple clocks going.  i realized pretty quickly that the multiple clocks in my "random" circuit were creating aliasing as they went naturally in and out of sync, so patterns would evolve, so i decided to go to the varying-rf route.  it was a matter of squeezing as many clocks and controllers onto a tiny 1" board as i could and making it fit into the box with the sequencer, and not introduce any clicking to the audio portion, which necessitated a ground plane board between the pc board and the jacks.  

in developing the circuit i manually moved the RF generator's center frequency with a pot and eventually controlled it with a crude transistor "pinch" across the R in the RC combination, driven by a tri-wave generator.

[Paul Perry (Frostwave)]

Ken Stones "psycho LFO" is a mixed LFO device.
If I was maig a seq-wahish device, I'd use a normal lfo & put it into a LED driver chip (that do the level indicaror led rows) and run separat pots from each led output, sum them (only one is on at a time) and drive a led/ldr from that, to control the wah or whatever.Minimum parts count!

[zachary vex]

i considered doing that, but bar-dot drivers draw a horrendous amount of current just idling.  i tried every which way to reduce it but it refused to budge...

[gez]

it was a matter of squeezing as many clocks and controllers onto a tiny 1" board as i could and making it fit into the box with the sequencer, and not introduce any clicking to the audio portion, which necessitated a ground plane board between the pc board and the jacks.

Excuse my ignorance, but could somebody explain to me what a ground plane board is?

[zachary vex]

you can fill all of the blank space on a circuit board with grounded copper, and just cut lines on either side of wiring going from place to place, which helps reduce noise on the board and keeps signals from leaking into places where they don't belong.  in my case i needed a board that was all copper with a single pad to solder a ground wire to, to use as a shield between the circuit board and the jacks/battery/switch so clicking noises from the digital parts of the control circuit didn't get into the analog audio circuitry.

[gez]

you can fill all of the blank space on a circuit board with grounded copper, and just cut lines on either side of wiring going from place to place, which helps reduce noise on the board and keeps signals from leaking into places where they don't belong.  in my case i needed a board that was all copper with a single pad to solder a ground wire to, to use as a shield between the circuit board and the jacks/battery/switch so clicking noises from the digital parts of the control circuit didn't get into the analog audio circuitry.

Thanks.  Is this method better than using shielded wire, or is it in addition to it because clicking was such a problem?

[zachary vex]

shielded wire works for different problems.  it's all about the location of the problem.  if you have to shield something close to a noise, you have to put a ground plane between the noise and the sensitive point.  you choose the method based on what direction the noise is headed and what you can do to stop it.