How to include a CV/expression pedal input

[pimpifax]

Hello.

I´m not only new in this forum. Also in (building) electronics. As well english isn´t my mother tonge, so i hope my writing isn´t to bad...

So i already build this PWM pedal which works quite fine.
My second project will be this analog bit crusher. But my Problem is that i want to manipulate the sound while playing. Which means i want to include an input for an expression pedal or better an CV (controlled Voltage) input that is also used with synths. I already have a midi 2 CV converter and this would allow me also to use a recorded process. So:

- Is it possible to include an expression pedal better a CV input?
- Is CV and exp pedal the same anyway?
- Can someone post me a link, a Schematic, or an instruction how i have to do it or how i should be done?

Thanks.

[oskar]

Hello.

- Is it possible to include an expression pedal better a CV input?

Yes.

- Can someone post me a link, a Schematic, or an instruction how i have to do it or how i should be done?

Generally it depends on the function you want to control. It can be really easy. For instance, if the potentiometer is used to give out a control voltage in the first place, or it could be totally screaming hard to achieve and need serious re-engineering.

In your case with the analog bit crusher you could substitute the potentiometer (R9) for some sort of variable resistance like an optocoupler (NSL-32) and have the CV drive the LED.
You could also substitute the oscillator for a VCO like a 4046 and convert the square wave output to trig pulses.
Bypassing the pot (R9) with a pedal with a 1 Meg pot could be almost easy to achieve though but there would be no voltage control, just live pedal action.

[oskar]

Here's a discussion about it:
http://electro-music.com/forum/topic-58146-0.html

A crude example:
http://www.instructables.com/id/Make-a-Voltage-Controlled-Resistor-and-Use-It/

[pimpifax]

Thank you!

I like to keep things open for different possibilities as long as its getting not too complicated! So my plan would be to add two switches in serial. The first one will let me choose between the internal pot and external control. The second one between the two externals. What menas a) the external pot aka expressionpedal or b) the CV aka NSL-32. The only problem is it seems that the NSL-32 is very difficult to find at local dealers here in Vienna, Austria, EU.  I found a online-store in Germany but with shipping i will cost me 10,- EUR for just one piece.  So i will keep on searching. Otherwise i will bite in this sour apple (i don´t know if you say it lkie that in english  ) and pay the money.

I also would have some more questions.
- Is the schematics you posted the same one that i posted? With my humble circuit reading skills i would say yes?!
- Is it correct that the 5V CV input (via jack) has to be connected direct to the LED part of the NSL-32? I mean without any parts between like a resistor or anything else?
- At the resistor part of the NSL-32 there are only two poles instead of the normaly three of a potentiometer. So is it ok that there is only one connection from the NES-32 to the D(iode) 2?

[pimpifax]

There´s another thing. As i said i´m a noob. So i hope i use the right terms.

If i´m right CV goes from -5V to +5V. Which means a dynamic or resolution of 10V. The problem is see is that when the CV goes under 0V (means from 0 to -5V). Than i suspect the LED in the optocoupler won´t work? Which means that i have only the half resolution to work with. If i am correct there are two possibilities. a) just use the half amount. Or b) convert the -5V to +5V into 0V to +10V (with a transistor?). If i´m right which transistor can i use?

[Gurner]

If i´m right CV goes from -5V to +5V. Which means a dynamic or resolution of 10V. The problem is see is that when the CV goes under 0V (means from 0 to -5V). Than i suspect the LED in the optocoupler won´t work? Which means that i have only the half resolution to work with. If i am correct there are two possibilities. a) just use the half amount. Or b) convert the -5V to +5V into 0V to +10V (with a transistor?). If i´m right which transistor can i use?

Is there a voltage  'standard' for CVs?  

You asked in your first post...

" Is CV and exp pedal the same anyway?"

a CV stands for control voltage ...you can easily mod an expression pedal to output a CV, but sometimes they just put out a changing resistance ...so (as with most things!) it depends.

What are you going to be using ...a pedal? a pot? some other circuit as the CV source?

If you aren't tied to any particular variant to control your intended circuit, then why not just use an expression pedal with a 1M pot in lieu of R9?

Re your -5V to +5V question...tie the LED cathode to -5V (same voltage source as the CV generated source), and then send your -5V thru +5V to it 9you obviously need to spec your series current limiting resistor well!) ...job done. You will indeed lose some resolution due to the fwd voltage of the LED (therefore use a red led, which has the lowest forward voltage @approx 2V)

[oskar]

...the CV aka NSL-32. The only problem is it seems that the NSL-32

That was just an example. As a beginner it will still be in reach for you if you are willing to put the energy needed into it.
In reality there are a lot of things that could turn out to disappoint you in the end.

is very difficult to find at local dealers here in Vienna, Austria, EU.  I found a online-store in Germany but with shipping i will cost me 10,- EUR for just one piece.  So i will keep on searching. Otherwise i will bite in this sour apple (i don´t know if you say it lkie that in english  ) and pay the money.

Or you can hack one up from an LED and an LDR.

- Is the schematics you posted the same one that i posted? With my humble circuit reading skills i would say yes?!

Yes. I believe it is the same. The schematic is the original project that I've seen people build around here.

- Is it correct that the 5V CV input (via jack) has to be connected direct to the LED part of the NSL-32? I mean without any parts between like a resistor or anything else?

You'd need a resistor in series with the LED, but it could be sufficient for your needs.

- At the resistor part of the NSL-32 there are only two poles instead of the normaly three of a potentiometer.

In your case the potentiometer you're substituting for an LDR is wired as a variable resistor. Two of the legs are shorted together. You would be in trouble if you tried to do the same thing with a potentiometer wired in another way. I wouldn't stick around to help you... 

So is it ok that there is only one connection from the NES-32 to the D(iode) 2?

? 4 legs. Two for the LDR which is non-polar and two for the LED. Fool around a bit with ordinary LED's before you fry this much more expensive component.


There might be projects lying around in the world of analog synthesizers that would be worth looking into for you.
Here is another place to find info about Voltage Control:
http://electro-music.com/forum/forum-112.html

Synth kits:
http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY

If i´m right CV goes from -5V to +5V. Which means a dynamic or resolution of 10V.

If that is what you're MIDI to CV converter says, yes.

The problem is see is that when the CV goes under 0V (means from 0 to -5V). Than i suspect the LED in the optocoupler won´t work?

Pretty much. It is even so awful that the LED doesn't do much work until the voltage reach over ~2V.

Which means that i have only the half resolution to work with. If i am correct there are two possibilities. a) just use the half amount. Or b) convert the -5V to +5V into 0V to +10V (with a transistor?). If i´m right which transistor can i use?

You pretty much nail it and you can use just about any transistor for this. BC547 would be a good start. I would solve it with an OP-amplifier instead. Cause that's just the way I roll... 

Is there a voltage  'standard' for CVs? 

There is more than one standard. Most use the 1V/Octave standard.
http://en.wikipedia.org/wiki/CV/Gate

[Strategy]

Hey, I also replied to you on Madbean. I add CV inputs to things when I can. Here's a diagram I made up. I don't want to double post but in a nutshell you can create an "external cv input" by adding a little circuit that translates incoming CV's to variable resistance.

here's my diagram I posted in Madbeans forum.



I still consider myself a novice to an extent but have successfully added CV inputs to my pedals and other projects. It sometimes doesn't work like if you are adding voltage controlled resistance to a pot with a large (250k+) resistance value. Worth experimenting. I use costly vactrol brand optocouplers becuase I'm insane, but many people 'roll their own' using LEDs and LDRs wrapped in heat shrink tube.

I oculd have used a diagram like this back when I was interested inthis! Finally just sort of figured it out trial and error.

If anyone sees something I hsould modify in this hackish diagram please let me know and I'll pick up comments.

Strategy

[pimpifax]

@Garner: As i wrote in my first post i would like to use my midi 2 CV converter which is normally used for analog synths (Midi to CV/Gate. I have the Kenton Pro solo MK2). My mistake that i forget to mention that i´m not only a guitar player. I´m also with old analog synths which are using only CV(/Gate) what was the predecessor of Midi. I alway thought -5/+5V would be the standard but as Wiki says it seems to be wrong at all...

@oskar: Thanks for all the answers. Learning in progress. Although my head is smokeing.

? 4 legs. Two for the LDR which is non-polar and two for the LED...

Yes, but in this case i was just talking about the resistor (LDR) side which has only 2 legs. The problem is that the pot which should be replaced has 3 pins. As you said two of them are shorted. Sorry but i still don´t understand if this would be a problem or if would work though? (I mean in case of replaceing the pot instead of useing Strategys solution.)

I would solve it with an OP-amplifier instead. Cause that's just the way I roll...  icon_cool

In my case it would be only importend for me that the -V from side A isn´t only converted into just +V on side B. It would be necessary that the +V from side A is added. So what i mean is -5/+5V shouldn´t be just +5V at the end. It should be 0/+10V. Can you tell me how you would build such a thing?

@Strategy: Ah... Thx! I see... That makes sense for me and would also be more there where i wanted to go than expected. Because i wouldn´t need an extra switch to use CV and could regulate the center of a CV controlled sweep with the existing pot. So maybe i´ll try this first (additional to the op-amp converter thing if applicable).
But what do you mean with "+/- 200 ohms"? +/- 200 in reference to what exactly?

[oskar]

You have one thread at freestompboxes and one at madbeanpedals. Same thread.
http://www.madbeanpedals.com/forum/index.php?topic=10155.0
You really don't care about other peoples time?
I have no intention of explaining things to you that might have been explained already in some other thread. Bye!

[pimpifax]

Hhm... i don´t really understand why you imputate me that i don´t care about others time?? That´s not true! I highly respect the help from other people and also spend a lot of my time in (german) forums to give others people help! For me is aksing in more forums like aksing more people for help in real life. So why should this be not ok as long as you share the information at last?? Whatever. I send you a PM...

[Mark Hammer]

I see 861 posts here from oskar, and 5 from pimpifax.  I suspect oskar has a deeper sense that a posted query here will inevitably provide a useful response, even if it takes a day or two, than pimpifax does.  So, I don't blame pimpifax for thinking that he won't catch a fish unless he has 3 different fishing poles baited.

Let's move on.

Pimpifax, keep in mind that voltage control is only one way to have real time control.  It has advantages for synthesizers because sometimes a person needs to synchronize many things at once.  So, if an envelope generator connected to a VCA, and another one connected to a filter, both have to track the velocity of a keypress, then a CV allows for one common source (the keyboard) to send the same control signal to different places at once.  Because those CVs are assumed to be something that can be re-assigned to control different parameters, they need to be standardized so that the "receiving" circuit knows what to expect.  This is why analog synthesizers have 0-5V, or 0-10v, or other CV "standards".

But CVs are only one way to have real-time control, and for guitar sometimes you don't need anything that complicated.  As has been pointed out, an expression pedal could simply vary the current going to an LED, and the LED adjusts an LDR.  The LDR then changes some parameter of a circuit.

If what you are trying to change only involves a resistance to ground to change it, then there can be many simple ways of doing that, many of which do not require anything as complicated as a calibrated CV system.

[pimpifax]

Thanks for understanding! I really don´t meant anything bad...
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The real goal would be for me to use both. An expression pedal when i want to play on the fly. But also use a CV input to recreate a process out of my DAW via the Midi 2 CV converter. Especially because i wan´t to use reamping. Beside i want to use the bit crusher also with my synths. I could use (a) switche(s) to change the different control sources. At least it doesn´t have to be perfect. It just should work. And if i have to be creative and do a little workaround it would be also fine. But as i said. After all the possibility to recreate the process of sound changing would be great!

I think if oskar (or someone else) would tell me the op-amp thing to change the -5/+5V (or -15/+15V) into +1/+5V (or +1/+30V), which i would combinate with a manual or prebuild optocoupler it would be quite perfect. At least could try it and see if it works...

[chemosis]

does all the pots on ada flanger give out control voltages?? and if so what do i need to add cv to speed pot of ada flanger?? i look at the old paia phalnger and castle phaser and say "damn i want those cvs on my ada"!

[blackieNYC]

You woke up an old thread for this one, but I'm surprised that geofex.com hasn't been mentioned - How To ... Expression Pedal. It's in that long list on the home page somewhere. 
Something jumped out at me when I saw the OP's link above - the first comment poster there says he was happy with it when he used a reverse log pot for the one modulation control. I don't know about the viability of putting alternate pots in expression pedals. Maybe it's easier than I think.
But if the pots in the Ada are log, you'll want to duplicate that in the CV method or simple pot-switching. (How did the OP do with this?)

[chemosis]

i was wondering about pedals that are already control voltage pedals like ada flanger,funk-a-duck etc. can u just add a stereo jack to the pot and expect it to work??? i would love to look at the pedals that can bee more easily modded for cv like maybe the ada flanger

[chemosis]

hey thanks for the help though.

[ElectricDruid]

Is there a voltage  'standard' for CVs? 

There is more than one standard. Most use the 1V/Octave standard.
http://en.wikipedia.org/wiki/CV/Gate

The 1V/Oct is the common standard for Pitch CVs indicating note frequency - but that's not what we're talking about (unless you want to be able to alter the sample-and-hold rate at musical pitches?!) Other CVs (from LFOs or Envelopes) can have different ranges. +/-5V (10Vpp) is pretty common for LFOs, oscillator outputs and bipolar signals, and envelopes and other unipolar signals tend to be either 0-10V or 0-5V output. 0-5V is steadily becoming more common as it interfaces better with cheap microprocessors. You could have a look to see what standard the Moogerfoogers use, since they're very much aimed at this sort of stuff - I think they went with 0-5V, but don't quote me.

Adding a LDR in parallel with the pot is only one way to approach this. You could also replace the pulse-generating oscillator with a simple voltage-controlled oscillator design. A 7555 timer would do the job for something like this.

HTH,
Tom