Looking for a simple design for long fade-ins and -outs

juni · Joined: Apr 27, 2009 Posts: 4 Location: europe

Hello everybody,
New member here... I'll start with a question but hope to be able to contribute something back to the DIY world as i learn more... Hopefully this is an acceptable entrance.

Anyway....
I've been trying to find a simple design which i could make into a sort of auto-fader. The use would be in live looping set in which i always run out of hand and feet...

The idea would be that a hit of a button would smoothly either bring a channel in or out of the mix, without sacrificing a hand at the mixer or foot on an inaccurate pedal. I've looked at many EG-designs but usually they are unneccessarily complex for my purposes and most importantly won't do as slow fades as i'd wish. It would be really nice if the time could be set to a whole minute or even more. Are this long times even worth considering with an analog circuit?

Any ideas where to look at?

Thanks a lot.

blue hell · Posted: Mon Apr 27, 2009 2:00 pm Post subject:

Those long times would be doable .. 100 k with 1000 uF would give a tau of 100 s and a full fade time approximately 5 times that value. So when you'd charge or discharge a 1000 uF cap your times would be long enough, then you'd use the voltage over the capacitor to control a VCA ... so now the question becomes one of finding simple VCAs I guess where the current flowing into the control input would need to be in the order of 10 uA or less ... maybe an opamp buffer between cap and VCA ...

aaronleese · Joined: Apr 27, 2009 Posts: 3 Location: san francisco

There is also a program called FlyLoops which has an autofade button, which can be mapped to midi controllers and allows you to automatically fade loops in/out with just one button.

check it out:
www.flyloops.com

juni · Joined: Apr 27, 2009 Posts: 4 Location: europe

juni · Joined: Apr 27, 2009 Posts: 4 Location: europe

So is it really this simple?:

Charging the cap: VCA fades in until cap is fully charged.
Discharging: VCA fades out until cap is fully discharged.
+ a pot before cap for adjusting charge time...?

So i would need a button for charging (=fade in) and another for discharging = (fade out).
Simple mind, i still can't fully understand how would i make the connections... Hmm...

Uncle Krunkus · Posted: Tue Apr 28, 2009 4:24 am Post subject:

At the spot that says "Gate In" you just put a switch which one way ties this point to +V. This will charge the cap and bring the output up to +V over time. If you leave the switch in that position it will keep the output high indefinitely (like holding a key down on a keyboard). When you flick the switch the other way, it ties that point to 0V and the cap slowly discharges, and stays there, until you switch it back again.
You still need to hang a VCA(s) off the CV this circuit generates, and route your audio through the VCA(s).

juni · Joined: Apr 27, 2009 Posts: 4 Location: europe