subtle switching?

[sfr]

playing with panning pedal and mixer in my effects chain, I'm enjoying the effect I'm achieving . . .

Sometimes switching an effect, especially heavy modulation or distortion from "on" to "off" immediatly can be a little jarring.  Of course, sometimes you want this sudden change as a dramatic effect, but not always.  

So using the panning pedal or mixer, I've found it nice to create a subtle sweep from "effect on" to "effect off", sliding from the wet to dry signals.  It particularly helps with phasers that also effect the feel of the tone alot, and it's also nice to dial in a little more or less distortion with one pedal.

A variation of this works well with my cheap delay too - you can keep the delay on and in the signal path with a reverse splitter type of thing after the delay and the panning pedal before - simply stop feeding the delay signal by rocking the pedal back, and that way the last echoes of the line you just played will continue to fade out as you go to a non-delay-effected part of the song, rather than the abrupt "stop" of all the echo when you want to start playing dry.  (did any of that make sense?)

Sometimes I don't want to have to worry about rocker pedals though, and I've been thinking about ideas to implement a standard foot switch control, that when hit, would turn the effect on or off with a bit of slide into or out of the effect.  Being able to control the length of the "slide" would be nice, and it needn't be a very long one.  I just can't really think of how to tackle this at all - does anyone have any ideas?

[Ansil]

http://www.toneczareffects.com/lg-pedals-vfm.htm


if you want to buy something in the same vein.


if yo uwatn to build something in the same vein. you could mod this


http://geocities.com/austenfantanio/collegecircuits

[sfr]

thanks ansil!  i always love how quick people answer things here!

I guess I wasn't clear though.  (oops! seems i never am.)  I've already got that setup going with a panning pedal I built.  Originally I was using the mixer and then built the panning pedal after I found I liked the effect.  (I realize my original post makes it sound like I was always using the mixer or noI don't know - it wasn't clear)  

What I'm hunting for now is sort of an "automatic panning pedal" - where hitting a regular stomp switch sort of activates an automatic, short sweep from clean to effected signal or vice versa, so when I'm busy playing I don't need to think about rocker pedals, just hit a switch.

[Robin]

Man, what a great idea!

I saw a design for a simple discrete attack/decay circuit that used cap charge and discharge to ramp the signal slowly up and down. I'll try to look it up and see what's possible for this use.

Any other ideas out there?

Rob

[sfr]

What about basically building the circuit from a panning pedal (like R.G.'s over at http://geofex.com/Article_Folders/panner.pdf ) and replacing the variable resistance of the potentiometer with an LDR kind of thing driven by an LFO?  But you'd want to restrict it so the LFO only does one "sweep" from high to low or low to high for the whole deal to work.  

This is not my forte . . .

[EliGold]

Check out the Lera on R.G.'s site:
http://www.geofex.com/Article_Folders/lera/lera.htm

It's essentially a circuit which slowly ramps resistance up and down at the click of a switch.  Instead of using it in a modulating effect to control an LFO, you might adapt it to a panning circuit.  Should be fairly easy.

It only requires a single switch, so if you wanted to have your effect have True bypass, an LED indicator, AND the lera circuit to activate with one switch, check out a 4PDT here:
http://www.banzaieffects.com/parts/switches.htm

I've never dealt with this company, or one of those switches, so I can't vouch for either.  FWIW, I would probably use two seperate switches.

Good Luck,

Eli

[EliGold]

Also,

Here's a link for what seems like the perfect match for the afore-mentioned Lera circuit:
http://www.runoffgroove.com/splitter-blend.html

It even uses a 25k pot which I think the Lera (as it's designed) likes to see.

Let us know what you decide to do and how it works out.

Eli

[sfr]

yeah, that's what I was looking for!  Thanks.  Don't know how I missed that on GEO.   Seems like all I had right thinking about this idea was the LED/LDR part . . .

[gez]

I quite like the look of this design:

http://www.joefus.com/pedals/images/buttons.gif

[R.G.]

I've been thinking about ideas to implement a standard foot switch control, that when hit, would turn the effect on or off with a bit of slide into or out of the effect. Being able to control the length of the "slide" would be nice, and it needn't be a very long one. I just can't really think of how to tackle this at all - does anyone have any ideas?

I've been working on something like this for a long time.

The earlier quoted ideas are all good. Here are a couple more I can add

It is possible to get a panning or slow changeover effect by using series switching JFETs, as in the Ibanez "bypass" circuit. You just have to slow the switching ...way... down with big caps or big resistors or both.

A good slow-change pedal is indeed a variation of an automated panning pedal, as you suggest. One LM13600 and some synth-y control circuits do the job as well.

I've mentioned my idea for a "morphing" pedal here a few times. This would take a few voltage controlled amplifiers (VCAs) and generate the control voltages so the volume would ramp up and down at specific rates to do different things. The actual implementation to get variable up/down rated on fadeovers and various combinations is complex - not because of the VCA/panners but because of the multiple variable control voltages.

I had to step back from analog and go to digital. If you've read the ASMOP series of articles, you can probably guess. Using a PIC microcontroller to control D-to-A converters or digital pots for the VCA's does the trick. The PIC does all the heavy lifting, so that it reads the front panel controls directly, then controls the multiple channels to do what you want.

A few things that you can do this way:
2-Channel  - variable-speed panning
                - variable-speed fadover (your app)
more than 2 channels
                - variable speed morphing between effects loops
                - channel-on-demand fadeover switching between effects loops

The pedalboard can get seriously out of hand this way, but then, hey, that's what we're here for, yes?

[Mark Hammer]

RG,

You sent me a photocopy of an old E&MM article/project of a swell-control pedal, that had voume presets.  Hit the footpedal and it ramps up from volume level A to B.  Hit it again and it ramps down.

I'll see if I can get my scanner back from my son and post it.

Honestly, sometimes I feel like Flanders trying to get back his barbecue from Homer! :roll:

[R.G.]

You sent me a photocopy of an old E&MM article/project of a swell-control pedal, that had voume presets. Hit the footpedal and it ramps up from volume level A to B. Hit it again and it ramps down.

I'll see if I can get my scanner back from my son and post it.

Yeah, I remember that one. It used an OTA with a CMOS opamp feeding a voltage through a resistor to the control pin. The CMOS opamp read the voltage from a cap that was ramped up and down from a preset... I think.

If you don't find it, I still have the original article.

This is one way to do a panner - use dual OTAs and a control/inverted voltage to run them. I suspect that the ramp up/down thing could be made into that kind of panner by adding on a duplicate circuit that used the CMOS opamp to invert the control voltage. It gives you linear voltages instead of exponential, but that's probably OK.

There is a way with OTAs to get exponential characteristics. The control pin looks like a silicon junction to the external signal, even though it's really the input to a current mirror. The current in a silicon junction is an exponential function of the applied voltage, so all you have to do to get exponential operation on a 3080, 3280, or 13700 is to feed the control pin a current limited (1ma max) control *voltage* that ranges from 0 to one silicon drop.

You can get acceptable results with an opamp feeding a normal 0-9V signal into a resistive divider of fairly low value. The resistor divider output impedance is fairly low, and it works pretty well. The other way is to put the control voltage divider ahead of an opamp that has an output that goes to the negative rail and let the opamp drive the control pin directly. You must limit current somehow, because OTA flatly die if you put more than 1ma (3080) to 2ma (13700) into the control pin.

[Nasse]

Has anybody tried a TDA1524 voltage controlled stereo tone/vol/balance control as autopanner or something? If i remember it needs more than 9V, maybe 12 or 15 V single supply, so not so useful for pedals...

BTW i have thought that for *very* long delays and near infinite repeats you need to put one switch/control before the delay, and maybe other like very slow gate after if noise is problem :oops:

[Nasse]

damn double post

[R.G.]

Has anybody tried a TDA1524 voltage controlled stereo tone/vol/balance control as autopanner or something?

Yeah. Works OK as long as the control voltage change is not too fast.

[sfr]

. . . cause I was busy and all, but I came back to look at it again.  Out of the different options discussed here, the hybrid LERA/pan-pedal thing seemed the easiest to me.  Use LDRs in place of the pots on the panner, driven by LED side of the optocoupler in the LERA.  Well, I hit a snag, of course - all the panning circuits I know of use all three poles of the potentiometer.  I was thinking, no problem, simply use two LED/LDR things (like The ToneGod's "rock n' control article - http://geocities.com/thetonegod/rockncontrol/rock.html ) except I have no idea how to get one LED/LDR to swing the opposite of the first in this instance.    Anyone have any ideas, or should I start pursuing one of the other methods mentioned here?  I guess I'll start googling for more info on the things people have mentioned that I'm not entirely clear on.

 I'm starting to feel pretty dumb - maybe I should just go back to tweaking dist+'s.  

thanks though for all the help everyone.

[Mark Hammer]

You know what would be interesting?  Imagine an automatic fader that you could "prime" with a momentary switch, and then the next note you hit it would morph/pan from one setting to another.  The switch essentially tells the pedal to be "ready" to do something with the next detectable trigger pulse.

Actually, that would be a nifty sort of generic 2-in, one-out pedal that could let you morph whatever you want.  For instance from chain 1 to chain 2.  This differs from a more conventional sort of panner in that the panning is prompted by signal input so that the morph is mapped onto a note/chord and the transition heard across a musical event.  You certainly *could* do this with a volume panner pedal and your foot, but then your foot might be preoccupied with something else.  This sort of auto-morph is different from manual morphing in the same way that auto-wahs are different from wah pedals.

[R.G.]

Here's where the current state of the morpher is in Austin.

After tinkering a long time with miscellaneous analog circuits, I found a combination that seems to work. Consider the OTA. It takes in a differential voltage, and makes the current out be proportional to the voltage difference and also to the biase current. The differential inputs don't have to be analog - they can also be purely high/low relative to one another.

If you tie the (-) input of an OTA to a middle voltage, and feed the (+) input with a signal, then the output current goes positive (out of the output pin) when the + input is higher than the bias voltage, and negative (into the output) when the + input is lower than the bias voltage. If the load on the output is a capacitor, then the output ramps up and down following the + input at a speed depending on the bias current.

Take four OTAs (two LM13700's works), hook them up as noted, gang all the bias current inputs so they all get equal currents from a control pot to vary the currents. Buffer the outputs. You can then feed CMOS logic levels into the inputs, and the four outputs will ramp toward full high or full low at a rate determined by the control pot, which becomes a "ramp speed" pot.

Use four more OTAs (another two LM13700's works) and hook them up as VCAs, and run their individual control inputs from each of the individual control voltages.

Now any channel that has a logic high on its input ramps up to full-on through the VCA at a rate that is dependent on the speed control.

You can do whatever you like with the control logic and VCAs.

One of the things is to use only half of this rig, two rampers and two VCAs to do the subtle switching from the first of this thread. A momentary switch can toggle a flipflop to morph between channels. To do the "get ready" setup for you Mark,  you use a "get ready" flipflop and an envelope detector. The momentary footswitch sets the "get ready" flop, the envelope detector toggles the morphing flop, and the morphing flop change resets the "get ready" flop.

Of course, there is that eight pin $1.25 PIC that could make the get-ready and morph-over more compact, if harder to understand.

The OTA as a variable speed ramp took me 'way too long to come up with. I should have tumbled to that a lot quicker.

[sfr]

wow.  

thanks again R.G.  It's going to take me a while to wrap my head around this, but I've got a direction to go learning in, even if I never have this thing built, I'll have learned something.  (and quite a lot of somethings by the way my beginings at understanding this are starting to spider out into other things)

edit  -

all in a flash, I think I understand it!.  Wow, cool.   Now to grasp the specifics and see if I can't make it work.  Thanks!   I'm still in the dark about a lot of things, but it's pretty cool how much more I've come to grasp in the last few months - used to be anything more complicated than a light switch had me sweating.

[sfr]

If you tie the (-) input of an OTA to a middle voltage,

Would pulling from my 4.5v for suppling power to the OTA be fine here?

Buffer the outputs.

dumb question - but what do you mean here?  use the "buffer output" (pins 8 and 9 from the LM13700 pinout here: http://www.national.com/ds/LM/LM13700.pdf ) or something else?  

Of course, there is that eight pin $1.25 PIC that could make the get-ready and morph-over more compact, if harder to understand.

I've heard R.G. and others mention PIC stuff before - does anyone know some references (either online or books) on PIC in reference to audio?

God, I'll probably have more stupid questions later.  Everytime I think I've got something, I realize I don't have something else I thought I had.  Does electronics ever stop making you feel stupid?