Wah Pedal Retrofit from Anderton.

[QSQCaito]

Hi! as you probably read im about to build my own Wah, from scratch, including inductor. And i was going to do it remote, just as shown here :


What i'd really appreciate much is a starting point, to know that this worked using "X" ldr and "X" pot..

Because i have totally no clue of values of ldr and/or pot..
Regarding the pot, it can be 5k 10k 25k 50k and 100k, any of them, without complication.. and ldr.. i can get well, most of the common values.. and i can still search for others


thanks a lot

bye bye

DAC

[Mark Hammer]

There is a whole stack of factors that Craig omitted from the original article (which I have at home).

The LDR retrofit is very similar to the way the Orange Squeezer works.  In the OS, the 82k input resistor and the FET to ground form a virtual pot.  As the FET's resistance changes from maximum R, the "pot gets turned down".  Here, the LDR and the 100k resistor form a virtual pot.  In this case, the "pot gets turned down" as the LED shines brighter and reduces the resistance of the LDR.

Here is where it gets tricky.  If the LDR's resistance varies from 10meg to 1meg, or even 100k, then the "pot" hasn't really been turned down very much has it?  Conversely, if the LDR varies from 100k to 200R and even the slightest hint of light in the LED brings it down to 10k in a hurry, then it is as if you have a 110k pot that never really spends much time above about 1/10 to 1/4 of the way.  If the 100k fixed resistor that forms the other leg of this virtual pot were changed, the action of this pot might be very different.  E.g., with a 500k/470k fixed resistor, changes to a 10meg LDR will have more impact, and so might those of a much lower resistance LDR.

Ultimately, though, several factors will determine whether this retrofit will work:
1) A parallel resistance with the LDR which will set the maximum value that this leg of the virtual pot can have.
2) The current-limiting resistor that determins how bright the LED is allowed to get.
3) The brightness of the LED which determines how easily a couple of ma will push that LDR.
4) The value of the control pot that also serves as current limiting resistance between V+ and the LED.

Pretty much the only thing you *don'T* have to worry about are those two caps.

[QSQCaito]

  This is the third time i read, and can't get to fully understand what you wrote

Is it there anyway to know, at least which pot and ldr should i use, to get an aporximate value of a regular wah pot, working in a range of 0-100k?

I know this needs calibration, and i can play with the current limiting resistor for the led, and the parallel resistance with the ldr(which is not included in that schem, right?)


Thanks a lot!

Bye bye

DAC


EDIT: I was checking the web pages of some suppliers that i bought, and i was watching i could get CLM8200-2 LED+LDR+LDR AXIAL  - 100 - 5KΩ-10MΩ  I think this works like a regular pot, could this be used??

thanks a lot!!!!!

bye bye

dac

[Mark Hammer]

To make some things simpler:

1) When Anderton wrote this article, very few LEDs were more than 300-500mcd in brightness, so a 2k2 resistor seemed fine.  Now, it is easy to get LEDs with a 5000mcd rating.  Putting a 2k2 resistor in front of these will not produce the same performance as what Craig wrote about in 1980 or so.

2) You may have to make the 100k resistor connected to the LDR either bigger or smaller in value to get a good feel.

3) You may have to place a fixed resistor in parallel with the LDR to get a good feel.

[QSQCaito]

Cool, really thanks lots! Half od my problems solved..

The other half is
Which value of pot and LDR should i use?

thanks a lot

bye bye

dac



EDIT: I was checking the web pages of some suppliers that i bought, and i was watching i could get CLM8200-2 LED+LDR+LDR AXIAL  - 100 - 5KΩ-10MΩ  I think this works like a regular pot, could this be used??

[QSQCaito]

One last quesiton and i'll stop bothering, has anyone built this project succesfully?
bye yye

thanks lots

dac

[QSQCaito]

bump for a last attempt, if not i will give up

bye bye

thanks

dac

[John Lyons]

If I'm not mistaken I beleive Paul Marrossy here Diyguitarist.com  has done the anderton retrofit. Check his site or PM him here.

John

[QSQCaito]

If I'm not mistaken I beleive Paul Marrossy here Diyguitarist.com  has done the anderton retrofit. Check his site or PM him here.

John

Thanks a lot, i'll proceed to.

Bye bye

DAC

[dist]

Hi. If you res my thread Remote wah you would see that i managed to get it working yesterday.
I pref boarded the layout and is planing on making an PCB with some improvements. I'm gonna add pads for an trim pot to adjust the resistance before the led.

About led/ldr.

Tried it first with an vtl5c2 optocupler, witch I'm not recomending for this project. When taking the pedal back to heel position it kinda delayed the movement if you know what i mean. First i move the pedal, then it reacts. But with this http://www.banzaieffects.com/Audio-Opto-Coupler-pr-17349.html it worked like a charm.

Later after i posted this i tried the real old fashion thing with an ultravhite led and an univibe photocell and it worked even better. Actually got an wider range than my wah (ibanez blubber) had originally. As for the remote part of the layout i didn't need any board, just wire everything directly to the pot. The original pot from the wah. 9v+ to the first lug, the cap from lug 1 to 3 , lug 3 to gnd ( the jack) with 9v- (you can do the 9v- cirquit breaking here if you want to) and the center lug of the pot to the jack. Now i can use an standard guitar cable to controll my wah.

Mounted in rack with true bypass system thing.

Hope this helps. Annyone interested in the PCB layout?

[QSQCaito]

Oh thanks a lot, this will sure help a lot... gotta take a look at your post, ill later add more comments..


thanks a lot!!

bey bye

dac


PS: doesn't the "audio opto coupler" has any markings.. of what model is it or something??

[dist]

PS: doesn't the "audio opto coupler" has any markings.. of what model is it or something??

Nopes. Just the dot that marks the negative side of the led. sry.  But the white led uniwibe thing works great. And the its relay funny to have it on pref with tied together with yellow electhical tape and turn the light on and off.

[QSQCaito]

Im fully interested in the pcb layout..   I wonder if the CLM8200  LED + LDR - AXIAL  - 220 - 2.8KΩ-10MΩ

would work.. it rises to several ohms..

you ended up using 10k pot right??

well..thats it

thanks a lot..

bye bye

DAC


EDIT: I should end up, totally, having a ressitance between 0 and 100k, right?? as normal wah pot..?
after done all the anderton "mini circuit" to make it remote?

[dist]

No. the 10k resistor was when i tried using the vol retrofit as an pot. Didn't really work well. Than i tried the MUTCH simpler  Wah retrofit. And it worked.

When shopping for led/ldr things i would recommend buying several different that you think might work, They are not that expensive.

I'm adding some links. One if for an word file containing images and info, and one if an zip file with the eagle (free PCB programhttp://www.cadsoft.de/) layout.



http://home.online.no/~erlendg/layouts.htm

[Mark Hammer]

Note that the wah retrofit was a proposed solution to scratchy pots some 25 years ago or more.  It is now possible to buy a) better or equivalent pots with longer lifespans, and b) substances that will "de-scratch" a pot and extend its lifespan.

So, unless there is some specific reason you wanted to try this circuit out (e.g., remote control of a wah), there are other simpler and more predictable routes to pursue.

[dist]

Note that the wah retrofit was a proposed solution to scratchy pots some 25 years ago or more.  It is now possible to buy a) better or equivalent pots with longer lifespans, and b) substances that will "de-scratch" a pot and extend its lifespan.

So, unless there is some specific reason you wanted to try this circuit out (e.g., remote control of a wah), there are other simpler and more predictable routes to pursue.

We are talking about remote here...

[Mark Hammer]

Oops, you're right.

Well then, carry on.

[QSQCaito]

So.. i have to : Find the apropiate pot, buy several LDR's, buy a trim(used as variable resistor) pot to control the led resistance, and i also have to use a trim to put between the 2 lugs of the LDR..

The trim of the led, will be 5k.. that should be ok, right?(put a resistance before, low, to avoid burning led if i turn all the pot)

The trim across the LDR.. any value you think might work?

For the pot value, i'll get a 100k, and then try to determine which value of pot should i use.

For the ldr.. i can get an ldr that goes from 1.3, to 100k, which is like the wah pot.. do you think this will work? If not.. i should get like a 500k max 1M max 10M max LDR?? always starting from 0?

One last bonus question : i should get a final total resistance of 0 to 100k.. or i should put it in the wah and test??

thanks a lot!!!!!!!1

sorry for too much questioning

bye bye

DAC!

[dist]

Use the pot from the wah to get the right travel. Wah pots have a special taper. not like Any log or audio pots..
I'm gonna use a 2k2 trim and 100k resistor. The 2k2 res that i use now works OK so i only want to adjust somewhere around that range. And the resistor is intended for safety so you dint burn your led thats right,

For the ldr.. i can get an ldr that goes from 1.3, to 100k, which is like the wah pot.. do you think this will work? If not.. i should get like a 500k max 1M max 10M max LDR?? always starting from 0?

One last bonus question : i should get a final total resistance of 0 to 100k.. or i should put it in the wah and test??

The univibe photocell i use is 16-33k on. As you might notice, when using a pot in the wha pedal you don't use it entire range, only about 30% of it. so this would do.  You also have sort of an "wah area" adjustment possibility by actually moving the pot in the wah by loosen the pressure element and turning the pot by hand before fastening the pressure element again.

Putt it en the wah and test. I couldn't get Any logical readings of my ohm meter, but i sounded good int the wag any ways.

Hope this helps.

[QSQCaito]

thanks i'll buy that 1.3 to 100k ldr.. first, and try if i can get good results.. about the taper, i'll buy a 100k, but it's no Log-antilog, as the wah pots, is just linear, it's a silde pot.



This can be faked out of a lineal pot, but it has some consequences.



here is an excel(which btw i can't open) that helps calculate how the pot travel will be.

http://www.pisotones.com/Potes/TaperRes_English.xls

I'll just buy the 100k slide.. then test.. post faults if any.. see what can be done.. and just keep on testing..
my ambition won't be defeated

bye bye

thanks

dac