Replacing an expression pedal with an automated device

[danoisefactory]

In a more simple way (just a LFO speedknob to control the speed of which the resistance rises and drops) , could this work to control the amount of feedback in a feedback loop (in case of Krok for instance).

Replacing the pot (250k) with an LFO and another something which acts like the pot would?

Cause i'd like to do that with a fuzz with an internal feedbackloop. (I built a MXR Distortion+ with feedbackloop, which is fun, should have an expresion pedal for the loop to be honest, but i'd like it to be more  randomly chaotic...).

And then maybe extend the feedbackloop with a octave up within the feedbackloop. or a ringmod...

Oh, and just a though that just occured to me. If i would change the pot in my crybaby, to a dual pot, i could use one of the pots as an expression pedal, right? (if the pot would fit that is...). That would really save me some space... Not to mention buying or building the whole pedal.

[expanoncolin]

In a more simple way (just a LFO speedknob to control the speed of which the resistance rises and drops) , could this work to control the amount of feedback in a feedback loop (in case of Krok for instance).

Replacing the pot (250k) with an LFO and another something which acts like the pot would?

Cause i'd like to do that with a fuzz with an internal feedbackloop. (I built a MXR Distortion+ with feedbackloop, which is fun, should have an expresion pedal for the loop to be honest, but i'd like it to be more  randomly chaotic...).

And then maybe extend the feedbackloop with a octave up within the feedbackloop. or a ringmod...

Oh, and just a though that just occured to me. If i would change the pot in my crybaby, to a dual pot, i could use one of the pots as an expression pedal, right? (if the pot would fit that is...). That would really save me some space... Not to mention buying or building the whole pedal.

Yes, you certainly have the idea.  The caveat though is that an LFO is a modulating voltage, a voltage that goes up and down.  A feedback loop works simply on resistance - all it is is a pot.  You can't replace a pot with an LFO because, well, an LFO is just a modulationg voltage, but you can use that voltage to control a resistance - that is what the H11F3 we have been talking about is for.  But in your case, the resistance is larger, so you'd want to use an LED and a photocell...  take the output of the LFO through a 1k maybe resistor, then optocouple it to a photocell and you should get some nice modulated feedback.

I think crybaby's use special pots and it's hard to fit other things in there, but I'm not sure.  You never know until you open the box and look.

-Colin

[Xanthene]

Modding is great. It really brings out the creativity out of everyone. Colin, I'll try to figure out why my voltage is the way it is tonight and I'll get back to you. I'm using a 9v but could it be that something is draining it? Possibly a short somewhere? Also, just to make sure I have this all figured out, does the "out" and vb create the signal, or is it "out" with ground? I'm unsure.

[expanoncolin]

Modding is great. It really brings out the creativity out of everyone. Colin, I'll try to figure out why my voltage is the way it is tonight and I'll get back to you. I'm using a 9v but could it be that something is draining it? Possibly a short somewhere? Also, just to make sure I have this all figured out, does the "out" and vb create the signal, or is it "out" with ground? I'm unsure.

The LFO oscillates around Vb, that is, Vb is the voltage that the LFO oscillates around, it goes from maybe 1V to 8V (+/-3.5V from 4.5V, which is what Vb should be).  It is Vb referenced.

It is strange that your power supply is at 7V, yeah, something else might be shorting it or draining too much... is the LFO the only thing you're powering?  Test the power supply with nothing connected to it.

-Colin

[Xanthene]

So, what is the "out" in the schematic? The center pin on the 1K pot, that is.

[expanoncolin]

So, what is the "out" in the schematic? The center pin on the 1K pot, that is.

That is what you should connect to the buffers.  It is the output of the LFO.  It is the oscillating frequency.  The 1k pot mixes between the square wave and the triangle wave, but the resistance from the 1k pot makes it bad for driving the H11F3 directly.

-Colin

[danoisefactory]

>> But in your case, the resistance is larger, so you'd want to use an LED and a photocell... take the output of the LFO through a 1k maybe resistor, then optocouple it to a photocell and you should get some nice modulated feedback. >>

Ok, so use the LFO to control the brightness of LED (with voltage) which in turn changes the resistance of the photocell. brilliant!.
Do i still need to buffer the signal from the LFO to the LED?

Should it be a bright led or just any normal LED? Or does that depend on the photocell? Guess i'll just have to socket the LED to find out the differences. So i'll just figure that out myself.

On the LFO: can I make the schematic so that it just uses the triangle? cause a squarewave is more a sort of on-off while a triangle is more graduall rising and falling of voltage.
Although an on-off  might be cool as well. Forget it, i'll use them both.

If I remember well (it's been a while since i opened up my crybaby) the crybaby uses a gear on the pot. So with some modding it should work. But you do have a point. I'll go hunting for cheapo wah's to mod into a wah/expression pedal thing.

And why use a wah? i still have a joystick lying around, which has two pots in it, so i can use it for two expressions. Bit more difficult to play with on stage, but still,  i'm gonna use that as well. Guess that will be a separate project on its own, building a lot of different expression pedal / things. (I als have this steering wheel lying around...).

Anyway, first i'll try that LFO tot LED photocell.

Thanks for the info!

[expanoncolin]

>> But in your case, the resistance is larger, so you'd want to use an LED and a photocell... take the output of the LFO through a 1k maybe resistor, then optocouple it to a photocell and you should get some nice modulated feedback. >>

Ok, so use the LFO to control the brightness of LED (with voltage) which in turn changes the resistance of the photocell. brilliant!.
Do i still need to buffer the signal from the LFO to the LED?

Should it be a bright led or just any normal LED? Or does that depend on the photocell? Guess i'll just have to socket the LED to find out the differences. So i'll just figure that out myself.

On the LFO: can I make the schematic so that it just uses the triangle? cause a squarewave is more a sort of on-off while a triangle is more graduall rising and falling of voltage.
Although an on-off  might be cool as well. Forget it, i'll use them both.

If I remember well (it's been a while since i opened up my crybaby) the crybaby uses a gear on the pot. So with some modding it should work. But you do have a point. I'll go hunting for cheapo wah's to mod into a wah/expression pedal thing.

And why use a wah? i still have a joystick lying around, which has two pots in it, so i can use it for two expressions. Bit more difficult to play with on stage, but still,  i'm gonna use that as well. Guess that will be a separate project on its own, building a lot of different expression pedal / things. (I als have this steering wheel lying around...).

Anyway, first i'll try that LFO tot LED photocell.

Thanks for the info!

You will likely need a buffer to get reliable results from the LFO using the mix pot.  If you use a toggle (replace the switch with an SPDT toggle, the pull being the center lug) you don't need a buffer, then it just switches from tri to square.  Breadboard first!  Then find out which LED works the best, and what current limiting resistor you need.

-Colin

[Xanthene]

I was only able to find 4N32 Optocouplers. I'm pissed as all the stores I went to had no idea what I was looking for. It just goes to show that dumbasses are everyone lol.

[Xanthene]

If these won't work. Is there any other way to do this? I can't find these H11F3 around anywhere.

[expanoncolin]

If these won't work. Is there any other way to do this? I can't find these H11F3 around anywhere.

In that resistance range, not easily.  Photocells typically have max resistances of 100-1000k.  You could do it with a FET but that is very hard to set up.  H11F3's are fairly rare, special purpose.  You need to buy them on the net.  I think at the moment they are cheapest from Mouser.

-Colin

[Xanthene]

Now I'm having trouble finding non polarized capacitors. The one I have is bipolar, I'm thinking that means non polarized. Electronics stores down in Toronto are no help either. It's like non of this stuff even makes sense to them, I don't understand this electronics twilight zone. "What do you mean electronics?"

Colin, can you explain this capacitor issue I'm having? haha

Thanks man. I hope to soon be able to complete this project and not feel like a total...you know, dumbass.

[expanoncolin]

Yeah, it is hard to speak electronics to anyone other than those who are doing exactly what you are doing...  Such is the wide world of electronics I guess though.  

This is what polarized electrolytic capacitors look like:


Note the band with - signs on it, showing that it is polarized and that side is the - side and the other is the + side.  Nonpolarized will not have a band like that on them.  The other common type of capacitor that is polarized is the tantalum capacitor.  They normally look like this:

They are less common.  Note the +, showing that it is polarized and that that side is the + side.

Almost every other capacitor you will run into is nonpolarized.

Did you ever sort out your voltage problem?  Did you test it with nothing connected?

-Colin

[Xanthene]

I was running it with a 9Volt Battery but I'm going to use an AC adapter instead. 9V 500mA, that should work right?

I think the batteries I was using were old and dead? Are opamps sensitive? Could it be damaged and not working properly?

I find it odd about the capacitors because the only thing I can find are polarized. But I think I may have actually bought some non polarized ones and was just unsure. Thanks for the help Colin.

[expanoncolin]

I was running it with a 9Volt Battery but I'm going to use an AC adapter instead. 9V 500mA, that should work right?

I think the batteries I was using were old and dead? Are opamps sensitive? Could it be damaged and not working properly?

I find it odd about the capacitors because the only thing I can find are polarized. But I think I may have actually bought some non polarized ones and was just unsure. Thanks for the help Colin.

Anything that doesn't look like the two I sent you wouldn't be polarized, most likely.  



Some there are polarized like I posted, the rest aren't.

The op amp could be damaged.  What kind are you using?  If you hooked up power backwards, they normally fry pretty quick.  Check the voltage with nothing connected, thenw ith things connected again.  If it is 7V in one case and not the other, something is awry, same goes for if it is 7V in both cases.

-Colin