Fade out tone with capacitor?

[pokus]

Hey there,
usually I use capacitors for coupling and filtering. But now I want make use of its storing characteristics.
I built up a feedback path from the collector of a transistor to another. Made of a switch and a resistor. It has a nice sustain effect whether there is a additional cap in it or not. But now when the switch is closed I want the effect to fade out just a little and not break up immediately. Just like a LED fades out when you have a big cap connected between + and gnd on a breadboard or something and remove the power.
But I guess it's a problem that only one side of the cap in my feedback path is connected when the switch is opened, as I tried so with a 220uF one. So the cap doesn't discharge. Even put a large resistor in parallel to the switch. Didn't bring me anywhere near.
Has anybody a solution how I can make it work?

[Digital Larry]

Schematic?

[pokus]

Don't really have one. It's basically just the Muff feedback mod.

[Kipper4]

Here's a leg up.

The muff mod is described here about 1/4 way down the page.

http://www.kitrae.net/music/Big_Muff_Mods_and_Tweaks_Page.html

[MaxPower]

Elektor's 301 circuits has a circuit in which a capacitor affects the attack and release based on the cap size. It's a square to saw converter but it may give you an idea.

I'll post the circuit name/number when I get home or tomorrow.

[pokus]

Ok, as I realized capacitors don't really store AC voltage, I thought of something else.

Why not use an opamp in unity gain mode. The non-inverting pin connected to the collector of Q3. Output and inverting pin to collector of Q1 trough a coupling cap. V+ pin to +9V through a switch and a big cap between + and -. V- to gnd.
So the cap will make the opamp work for a short time even the switch is opened.
But some questions came to my mind.
Isn't the output from the collector of Q1/Q3 changed by the opamp when it's off, cause it has to be constantly connected?
How to proper bias this thing? Does it pop when I open/close the switch?
And most important ..am I right at all? 

Here's a schematic of a Big Muff, in which I added the two points that should be connected.






Appreciate any kind of help.

Update: The first picture had the wrong points. It's right now.

[MaxPower]

You might want to look into envelopes (attack, release, that sort of thing). They're not just for synth.

The elektor circuit is number 101 btw.

[pokus]

Hey,
thanks for your answer. That's quite a cool idea. I did some research and simulating, but realized there's also the question how to make it fade out with a switch as it only alters the fade in/out of single amplitudes alone. (don't know if thats the right term). It should really be more of a kind fading out to the original tone rather than fading out of single tones. But it's also possible I misunderstood something.

Like I mentioned, I now put in an unity gain opamp with a large capacitor from V+ pin to gnd and the switch between +9V and the V+ pin. The output connected to Q1 with a coupling cap. The non-inverting pin biased and coupled from Q3.
It kind of has the effect I was looking for and when the switch is opened it doesn't really change the original tone.
But two things bother me:
Sometimes when the switch had been opened, you could hear the opamp sort of "dying". Some weird noises mixed with the fading out tone.
Second there is a pop when I close the switch.

Any suggestions how to get rid of that problems, or even another way to do it?
Can it help, in regards to the pop, to put a constant way larger resistor between +9V and V+ and only make a small parallel resistor switchable?

[garcho]

another way to do it?

for switching:

extremely important reading: http://www.muzique.com/lab/pop.htm

and: http://www.geofex.com/Article_Folders/box_pop.htm

also: https://sound-au.com/project145.htm


for electronic (as opposed to electromechanical e.g. potentiometer) volume control:

use the envelope follower (IC1B) and VCA (LM13700) sections from this for something like a noise gate? not sure what you had in mind: http://moosapotamus.net/ideas/penfold-fuzz-unit/

maybe read up on VCAs here: https://sound-au.com/articles/vca-techniques.html

[anotherjim]

Not sure if you need an envelope control for this, that is if you want to be able to bring the feedback in and out gradually rather like taking the guitar closer to the speaker cab.
A momentary footswitch that enables a gradually increasing LED brightness that shines on an LDR in the feedback path might do it?