AutoFade Pedal

[effectsbay]

Hello All

I want to build a pedal, but having a hard time wrapping my brain around how to do it. It's a auto fade in/out pedal. Basically, it'll get a signal in, hoping to have two footswitches - one for fade in, the other for fade out. I want a pot to control the duration of the fade. The single pot would handle duration for in and out fades. I've been looking at some trem schematics thinking that is somewhat similar. But I think I might be WAY over complicating things. Am I? Anyone of an idea on how to draw this out?

Thanks!
hank

[R.G.]

There's the Auto-Swell in the old E & MM collection that does this.

[effectsbay]

There's the Auto-Swell in the old E & MM collection that does this.

Hello.. thanks for the reply! What is the old 'E & MM' collection?

thanks!
hank

[R.G.]

Electronics and Music Maker, UK pubs from the 70s? 80? I think Mark has the circuits on hammer.ampage.org. If not, I can find them.

[haveyouseenhim]

I've been wanting to build this effect too, but i cant find a schem or layout. I may just have to settle with a volume pedal.

[effectsbay]

Will the Auto-Swell only swell once? I don't want it to repeat. Click to fade out.. click to fade in.

Thanks!
hank

[haveyouseenhim]

I dont think you will find the one time fade thingy, but i think this is what RG was referring to.

http://hammer.ampage.org/files/StringDamper.PDF

[effectsbay]

This is basically what I want:
http://www.megabeataudio.com/en/products/darthfader

$250 USD is pretty steep for fade in/out.

hank

[midwayfair]

Purely theoretical, but ....

You could do it as a sort of manual optical tremolo. Use a vactrol (or LED/LDR combo) and a pot to control the drain resistance on the LED (controlling how quickly it turns off) and another pot to control the resistance from the voltage (to control how quickly it turns on). A switch could be used to turn on the LED, and then it plunges the resistance of the LDR as the light comes on. Want a switch that also turns on the fade out? Just connect do it so that it flips between connecting the "drain speed" pot (which slows down the turn off) and a really small resistor (~500R-1K) that simply has the LED turn off as normal.

Stick the LDR between two halves of an op amp, and you'll have a nearly dead signal when the LDR is dark and a live signal when it's on.

You could also use a single momentary switch instead and set the drain/swell separately. Then you press the momentary and it fades in, release the momentary and it fades out. Maybe a third pot could be a bypass for the dry signal, allowing you to have a minimum volume. The swells would be an increase in volume.

Edit: Most of us use a volume pedal for this, by the way

Edit edit: I'm sure there's also a way to adapt an envelope pedal, but not really my area of expertise.

[effectsbay]

Edit: Most of us use a volume pedal for this, by the way

Except I need to fade out samples.. while I'm working other pedals during the fade out and transition to the new piece. I want to be able to trigger the fade out on the sample and continue to play without devoting my attention on the vol pedal only.

Thanks!
hank

[midwayfair]

Ahhhhh. I thought you were looking for a ducking or violin swell type effect.

In that case, you might actually need to consider a digital solution. Waaaaay out of my area of expertise, but there are some folks around with some real digital knowledge.

[Mark Hammer]

Electronics and Music Maker, UK pubs from the 70s? 80? I think Mark has the circuits on hammer.ampage.org. If not, I can find them.

I still have the article you sent me way back when, but I don't think I scanned it.  Can't seem to find it on my hard drive though I know it's in the relevant binder.

The String Damper is not really appropriate for the desired application.  Yes, it fades in and out, but it operates on a note-wise basis, and from what I can tell, what is desired is something like the fade out at the end of a tune, where the volume-reduction continues despite the player's dynamics.  If a person had a vigilant soundman, the mixer would do the same thing, but in the absence of a soundman, the goal is to hit a footswitch and let a circuit do the work.

The LERA circuit over at GEOFEX ( http://www.geofex.com/article_folders/lera/lera.htm ) forms the core of what the OP is trying to do.  It switches between a maximum and submaximum voltage, whose ramp-up/ramp-down time is determined by the usual RC timing parameters.  In the LERA, that voltage controls an optoisolator, but other things could be controlled, like FETs or OTAs.  And since fade-in/out time would be potentially longer than ramp-up/down, one assumes that the value of the cap should be larger, like 220uf or so.

[artifus]

i was just looking for that, remembering a metal pick activated swell - there's a thread around here somewhere. found these instead:

http://www.americaspedal.net/fx15/ - http://www.dirk-hendrik.com/temp/dod_fx15.pdf

http://pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

googling 555 envelope generator may turn up other ideas, synth sites will no doubt have various other solutions but the lera looks like a nice and simple approach. also, there was a recent 'soft on led' thread that could be used with a ldr.

*spelligns!*

[edd29]

you may try to look this one  Electro-Harmonix Attack Decay Tape Reverse Simulator

and this one using a metal pick   this is the schematic  http://www.dirk-hendrik.com/temp/dod_fx15.pdf
i just modified the foot swicth in to a metal pick as a swicth.

[effectsbay]

This is what I'm looking for....

Just not soo fancy.. and not soo expensive.

h

[R.G.]

As Mark can tell you, I've been a fan of faders, cross-faders, and what I call "morphers" for a couple of decades. I've built several skunks-works versions of what will be come an N-way morpher. Getting the user interface is hard, the faders are not.

I dug out the article: Auto-Swell, by Clive Button in "The Best of Electronics & Music Maker - Projects Volume 1", which has a copyright date of 1983, and is presumably a collection of articles from earlier years. The Auto-Swell did indeed swell up when the foot pedal was pressed, but reverted instantly to a preset lower level when the footswitch was released. And that's not the project I was remembering.

But it did make me remember the project in more detail. It was one of Penfold's things, in a book of effects he published. It used a VCA setup with a CMOS opamp set up to ramp the control voltage and hence loudness up and down at a preset rate when an up- and down-footswitch respectively was pressed. It's somewhere in the files. Mark, do you remember that one? Seems like I had it in hard copy, not internet gleanings.

Here's the deal: you can make loudness do whatever you want by using a VCA and a control voltage. One of the incarnations of the morpher was a single footpedal with a preset ramp up time and ramp down time on two separate knobs, the footswitch picking out which direction to go, and volume ending at max or min, also preset. Pretty complex for a stage unit, but maybe useful in the studio.

I have a suspicion that the fader/morpher will surface again some day.

[Mark Hammer]

Found my copy of the Auto-Swell.  Worst.... drawing...ever.  Can't tell if it is adaptable.

Don't recall the Penfopd circuit you allude to.  Thought Boscorelli might have something, but no.

Ultimately, this is all leading to a resistor/FET attenuator like we see ih the Orange Squeezer, controlled by a cap charge-up and discharge time.  And since that cap can't drain until we want it to, there needs to be a bi-fet op-amp, a FET, or a cmos switch isolating that charge-up cap so that it hangs onto that charge.  A low leakage cap can't hurt eitherl

Another strategy might be to use counters of some kind (4017?), have each counter output increase in level to some maximum, where it could stay until you want it to continue counting, where each counter step would reduce level.  In theory, you could make it count only u up to halfway, or only start from halfway.  The trick would be inhaving enough steps and smoothing to prevent  audible zippering.

[R.G.]

Ultimately, this is all leading to a resistor/FET attenuator like we see ih the Orange Squeezer, controlled by a cap charge-up and discharge time.  And since that cap can't drain until we want it to, there needs to be a bi-fet op-amp, a FET, or a cmos switch isolating that charge-up cap so that it hangs onto that charge.  A low leakage cap can't hurt eitherl

That's what the CMOS opamp was for in the article. I'll eventually run onto it. Fortunately, all-CMOS rail-to-rail opamps are easy and cheap today. The TLC series works.

Another strategy might be to use counters of some kind (4017?), have each counter output increase in level to some maximum, where it could stay until you want it to continue counting, where each counter step would reduce level.  In theory, you could make it count only u up to halfway, or only start from halfway.  The trick would be inhaving enough steps and smoothing to prevent  audible zippering.

Yes, that would work and perform the ramp-and-hold that's needed. In practice, doing it in software inside a controller will be cheaper and more effective. The controller will do the ramp-and-hold, then output the desired voltage by PWM. A 2Hz to 10Hz LPF after the PWM output would kill any zippering pretty well, I think.

One interesting approach would be to get a controller that can do really high frequency PWM signals, 40kHz or higher, and have the controller PWM simply chop the signal. Once filtered as in CDs and other digital music, the output is a linear volume control with duty cycle; no VCA or other attenuator needed at all. At the high end of this, simply putting the audio into digital, doing the volume change digitally and taking the outputs out works. I'm pretty sure I could make an FV-1 do what the OP wants, but it's counterproductive for my purposes because it's limited to only two channels.

I once read that computers hollow out everything they touch. In the end, once a computer is used, it rapidly becomes more cost effective to have a computer replace everything inside the -whatever- behind the I/O switches/knobs/power outputs, etc..

[artifus]

e&mm auto swell

[Mark Hammer]

Thanks.  See what I mean about being badly drawn? 

The path from TR2's emitter to the input of RV3 may as well be one of those legendary "Family Circus" ramble diagrams.