swell device?

[Br4d13y]

http://images.google.com/imgres?imgurl=http://www.geocities.com/CollegePark/Library/1355/swell.gif&imgrefurl=http://www.geocities.com/CollegePark/Library/1355/beginners.htm&usg=__xBJJWEWp2x9CcWlcdOC8ghIcFMk=&h=412&w=626&sz=6&hl=en&start=1&tbnid=8fZqMU61fnKqAM:&tbnh=90&tbnw=136&prev=/images%3Fq%3Dswell%2Bdevice%26gbv%3D2%26hl%3Den



anybody know how this operates??  i found it on google images and if its a slow gear-like swell, i would like to take a shot at it

[Transmogrifox]

That circuit is not too far from brilliant.

It uses the second transistor as a variable resistor.  When signal swings negative at the base of the first, it forward-biases the second transistor  and charges the capacitor.  After a few cycles, the voltage on the capacitor gets too high to go into saturation and forward bias it, so no more current is bleeding off onto the capacitor. 

At least that's what I concluded must be the case without getting into very deep analysis of the circuit.  If that isn't the case, I can't see how the circuit would be anything but an interesting volume control.  If the transistors are always operating in linear operating regions, it's just a buffered negative feedback network.

[ppatchmods]

for the money, the behringer version of the slow gear is good.

[Mark Hammer]

Um, that's the add-on portion for the Prescription Electronics "Experience" pedal, which is essentially a hot-rodded Foxx Tone Machine. So, you're only looking at part of the overall circuit.

[anchovie]

From another section of the site (http://www.geocities.com/CollegePark/Library/1355/schematics.htm):

Swell Device - (Schematic has errors!) See RG Keen's site for explanation on these errors and info on what pedal (in addition to the foxx tone machine) Prescription Electronics copied to make up their Experience pedal.

[R.G.]

Actually, that is essentially ALL of Antony Leo's "Fuzz Adapter" from about 1969 in Popular Electronics.

The Prescription Electronics people found that the changing DC on the output causes a swell effect on the input of a tube amp by changing the bias of the input tube. It works maybe, kinda, sometimes with solid state amps. It's intended as a fuzz adapter in its own right, but when conditions are right, it does do a swell effect.

[MikeH]

when conditions are right, it does do a swell effect.

Funny, I'd say the same thing about a slow gear 

[DWBH]

If I were to make a swell pedal, I'd make a DOD FX15 clone. The pedal seems brilliant - easiest way of making swells (apart from volume pedals).

[R.G.]

Funny, I'd say the same thing about a slow gear 

So would I. It's actually technically demanding to get a swell pedal to work even notionally correctly. The disconnect is in what our minds expect versus what simple electronics can do.

- easiest way of making swells (apart from volume pedals).

Actually, a volume pedal comes far closer to doing what your mind expects once you've done the necessary foot/mind coordination training.

[DWBH]

Yes, indeed, but when I said making swells I didn't mean making 'good' sound swells.

[Mark Hammer]

Seems to me that, in the analog domain at least, EHX came closest to a decent swell pedal with the old Attack Delay.  

The difficult part with any attack/swell circuit is that you have to know when to begin the swell, and that means a reliable and valid "event detector".  So how do you know there is another new event that requires a reset of level and gradual swell?  In EHX's case, they bought themselves some time (13ms to be exact) to be able to detect the onset and apply the swell envelope where it should be, which is right at the very beginning and not a few msec after the onset.   One of the tricks it used was to insert a bit of time delay via an MN3007 such that the length of time needed to reliably detect onset and produce a rising envelope would be offset by staggering the audio output such that it lined up with the attack/decay envelope.

Rob Strand posted a nice redraw he did of the schematic.  I assume it is to be found somewhere.

[ninjadave7]

is there any pedal that will do a swell like the Line6 DL4?  i've heard the guyatone sv2, the lazy sprocket and even the echo park but i can't find anything that will swell chords nicely or that you can adjust to do a long swell.  will the dod fx15 do that? or any pedal besides the DL4?

[Mark Hammer]

The PAiA gator can adjust the rate of swe1l.  It is essentially a noise gate with a wide attack time range.  Like all gated devices, though, it's that damn problem of reliably detecting note onset across a wide range of playing styles.

[R.G.]

is there any pedal that will do a swell like the Line6 DL4?  i've heard the guyatone sv2, the lazy sprocket and even the echo park but i can't find anything that will swell chords nicely or that you can adjust to do a long swell.  will the dod fx15 do that? or any pedal besides the DL4?

The best way to do a swell is to have the pedal know ahead of time where you want the swells done. This is one reason that things like synths and violin players do good, musically valid swells. The synth triggers the note with a solid logic change, every time, so it's easy to do a swell on that. The violinist is directly connected to the bow, and hence the volume control on each note. Easy to do that one.

For guitarists, a good volume pedal is about as good as it gets. Inside your head, you know when you pick the note or chord and can do the swell in synchrony - well, some people can. We have one of the guys at the office that hooks up some distortion and reverb and a volume pedal then does "whale songs" with the rig pretty convincingly. You have to have a good volume pedal to do this, though. It has to be stable to stand on, with a long, even mechanical AND electrical throw, as well as noise free. It helps a lot if it's adjustable for rocker friction and stays where you put it when you take your foot off. There is a company that makes one of those, and for just these kind of reasons.

Getting an automated swell requires that the pedal guess when you want the swell to start. Best use of such an automated system requires you to learn what tips off the swell pedal to swell and then play in a manner that kicks the pedal off when you want it, if possible. It's quite demanding to do within the strictures of pedal electronics.

[jacobyjd]

Yeah, I don't really know why you'd want to do anything besides use a volume pedal...I use that trick all the time. It helps to have lots of sustain, so distortion or plenty of volume on tap, and I like to put a good digital delay after the volume pedal somewhere to keep notes ringing while you're backing off on the pedal for the next note/chord/phrase, etc.

[Lurco]

is there any pedal that will do a swell like the Line6 DL4?  i've heard the guyatone sv2, the lazy sprocket and even the echo park but i can't find anything that will swell chords nicely or that you can adjust to do a long swell.  will the dod fx15 do that? or any pedal besides the DL4?

The best way to do a swell is to have the pedal know ahead of time where you want the swells done. This is one reason that things like synths and violin players do good, musically valid swells. The synth triggers the note with a solid logic change, every time, so it's easy to do a swell on that. The violinist is directly connected to the bow, and hence the volume control on each note. Easy to do that one.

For guitarists, a good volume pedal is about as good as it gets. Inside your head, you know when you pick the note or chord and can do the swell in synchrony - well, some people can. We have one of the guys at the office that hooks up some distortion and reverb and a volume pedal then does "whale songs" with the rig pretty convincingly. You have to have a good volume pedal to do this, though. It has to be stable to stand on, with a long, even mechanical AND electrical throw, as well as noise free. It helps a lot if it's adjustable for rocker friction and stays where you put it when you take your foot off. There is a company that makes one of those, and for just these kind of reasons.

Getting an automated swell requires that the pedal guess when you want the swell to start. Best use of such an automated system requires you to learn what tips off the swell pedal to swell and then play in a manner that kicks the pedal off when you want it, if possible. It's quite demanding to do within the strictures of pedal electronics.

Will we see Tap Swell in the future? 

[R.G.]

Will we see Tap Swell in the future? 

Sure. How many would you like to pre-order?   

A tap swell is downright simplistic. I posted psuedocode for a tap tempo microcontroller here a couple of years ago. To do a tap swell, you take a voltage- or current-controlled amplifier (http://geofex.com/Article_Folders/VCA Applications.pdf), drive it from a resistor to a ramping capacitor as in LERA and others (http://geofex.com/FX_images/p90ramp.pdf, http://geofex.com/FX_images/ramp-lfo.pdf, http://geofex.com/Article_Folders/lera/lera.htm) and drive the filler for the ramping cap from the output of the uC which is doing the tap tempo. The uC's output is always high (signal ramping or on) except for a blurp to ground to reset the ramping cap through a diode at the next ramp time.

Actually, a slicker way to do this is to use a dual OTA and use one side for the CCA, use the other side for a current-controlled current source, feeding the output of a "ramp speed" pot into its Iabc to control the ramp speed, put the ramping cap on the OTA output and buffer the cap with the output darlington. The input is set so the uC changes the current direction from up to down by dinking with the input voltages and also turns on a reset transistor to ground at the ramping cap. I think that gets it down to the uC (could be a $1, 8-pin PIC), the 16 pin dual OTA, a dual opamp for housekeeping and the usual slew of Rs and Cs.

From here on it's just Ohm's law and poring through datasheets.

[RickL]

If you don't mind dealing with a metal pick attached to the pedal with a wire the Morley Pic Attack (or whatever it's called) is the best swell device for guitar I've ever used. It triggers perfectly every time since the pick touching the string resets the attack. The attack time is set by a pot so it will go from almost instant on, kind of blurring the attack to looong attacks. It works equally well on single notes and chords and a momentary footswitch could easily by wired in series or parallel with the pick so the swell only happened when the switch was either depressed or released.

See previous posts by me for my experiences with this circuit and the similar Pic -A - Wah.

[Mark Hammer]

Hi Rick.  Seen your "survey results" yet? (a very in government joke)

The Morley system is essentially an attempt to mimic what keyboards have always taken for granted: a 100% dependable indication of the onset of a musical event.  For keyboards, it is a simple matter of closing a switch when a key is pressed.  For guitars, with the possible exception of those guitorgan monstrosities, or the more contemporary Fretlight instruments, it has traditionally been a matter of interpreting the audio signal itself to determine if its a note or noise.  And that's not an easy thing to disentangle.  The metal pick arrangement operates pretty much the way a keyboard would: touching a string is like closing a switch.

Come to think of it, I wonder how easy it would be to modify a Fretlight to tell you what the note is and when it starts directly.

[R.G.]

For guitars, with the possible exception of those guitorgan monstrosities, or the more contemporary Fretlight instruments, it has traditionally been a matter of interpreting the audio signal itself to determine if its a note or noise.  And that's not an easy thing to disentangle

Hmmm...
Fiberoptics at the bridge, look for fluctuation in light level per string. Hex pickup where you don't much care how it sounds, just that it has signal above a threshold.