SICK DUCK...quack quack... :)

deadastronaut · August 11, 2011, 06:21:18 PM

continuing my fetish with leds and ldr's and wah's, heres a simple auto quack wah.......'SICK DUCK.'......quack quack....get funky wid it....

phector2004 · August 11, 2011, 06:30:42 PM

Looks good, Rob! A solid, simple design as always

I don't know my filters all too well, but could there be a 3rd pot added adjusting the filter frequency? Or would that need impractical varicaps?

p.s. The title initially shocked me... "did the censoring go away?"

deadastronaut · August 11, 2011, 06:36:45 PM

@phil. yeah the censoring was a close thing....

its open to mods as always...i guess the freq/resonance , pot would be part of the 'T' I guess...someone more knowledgable would know!..anyone fancy chiming in on that?...

Govmnt_Lacky · August 11, 2011, 07:13:47 PM

Sorry for being a little DENSE

What is the purpose of the 386 in this circuit? I see the input going to it but THATS IT??

Is there an output from the 386? Where does it go and how does it contribute to the filter portion?

Also, can you get away with a TL071 or 081 for IC1? Why use a dual op amp there?

EDIT: OK, I see that the 386 is driving the LEDs/Lamps. But my question about the single op amp still stands.

phector2004 · August 11, 2011, 07:18:51 PM

LED driver (for the LDR to ground)

I think the other 1/2 IC could actually do the trick... I don't know how bright it would make the LED, though.
Maybe the output isn't high enough?

vendettav · August 12, 2011, 03:15:53 AM

nice rob. i was actually thinking of doing the same if you remember?

anyways do you think this sounds better than the Nurse Quacky?

Gurner · August 12, 2011, 04:47:54 AM

Nice simple circuit, a couple of comments...

Since the LEDs biasing is 1/2 VCC ...which in turn is totally dependent on the LM386 supply...I wouldn't be using a battery with this one...a wall wart only, else as the battery fades soo too will the LED brightness, which in turn is gonna effect the filter response (also, that LM386/LED combo is gonna be a bit of a battery hungry, so another reason for a wall wart). Also if using a 9V wall wart, then that means there's 4.5V on the output of the LM386 across two LEDS...that's 2.25V forward voltage per LED - you'd need to select your LEDs very carefully.

I wouldn't use this effect as the first effect in my chain...the input impedance is too low for a guitar

Why two LEDS? (is this an amount of light needed type of thing, or just dissapating the 1/2 VCC level on the output of the LM386 across two diodes - if the latter you could just use a resistor)

Just a thought - becuase standardisation across LEDs is going to be hard for everyone to get the same results, it might have been better to have a series resistor in line with the LED, with a variable resistor in parallel (this then would be your depth pot)

nocentelli · August 12, 2011, 05:51:35 AM

Having built the Lightwah, i'd assume the second LED is for visual indiction, i.e. externally mounted on the enclosure. This proves very useful for setting the sensitivity the lightwah: Cover the "controller" LDR completely with your foot, turn up the sens until the LED just lights up, and it is adjusted to work with the local ambient light level.

Joe Hart · August 12, 2011, 07:54:58 AM

I misread the topic. I switched the vowels. There's a joke in there somewhere... what's the difference between an ill waterfowl and... or something.
-Joe Hart

deadastronaut · August 12, 2011, 02:40:01 PM

@gov lacky: yep use a 071...

@phil, dunno about the other half of an 072 driving an led?...(sound to light wise)

@gurner: yep a pot could turn down the led/s instead, ...probably a better idea!..(i only use wallwarts..no batts)

@V.not sure if this is better than a nurse quacky, but i built one of those ages ago, and it didnt quack enough to me....but i did like the attack adjustment on it...

@nocentelli: yep, just for indicator really...i love pretty lights...

@joe: watch out for censorship!...

@all , i just thought i'd throw this up here for anyone to tinker with, i'll get it on breadboard when i get a moment, got a busy weekend

.....but i will tinker with it asap....

deadastronaut · August 15, 2011, 06:35:13 AM

ok had a chance to bread it,

the wah is ok, but when i add the input to the 386 (sound to light) , the wah output signal distorts?...hmmm with no audio output on the 386?..strange....

i guess i'm missing something here?...

vendettav · August 15, 2011, 01:57:41 PM

may be it's somewhat drawing a lot of current or osmehting?

deadastronaut · August 15, 2011, 02:05:18 PM

maybe...funny though jakefuzz just posted an envelope detector on this thread...

http://www.diystompboxes.com/smfforum/index.php?topic=93205.msg800335;topicseen#msg800335

i'll give this one a go and see what happens...

it'll be great if it works ok...like phil suggested earlier

, use the other half of the op amp, its a few more components that id like but hey...if it works fine..it makes sense too!...

deadastronaut · August 15, 2011, 02:54:51 PM

great!...that little circuit jakefuzz put up works great....now for a bit of tweaking on values as i only have superbright leds....

cool......cheers jake...

edit: edit: hmmmm still getting distortion out of the wah....

deadastronaut · August 15, 2011, 03:56:31 PM

OK heres what i have now, still getting distortion out of the wah though, when i connect up the envelope dooby....

@gurner, would it be something to do with input impedance?...like you said earlier?..

would it be something to do with my led and ldr grounds?.....

hmmmm.... weird the wah is really clean on its own...until i add that envelope dooby...

phector2004 · August 15, 2011, 04:23:58 PM

Dumb guess, but have you tried adding a 220uF from DC to ground?

deadastronaut · August 15, 2011, 04:26:07 PM

nope, i did a 100uf...

Gurner · August 15, 2011, 04:42:19 PM

Quote from: deadastronaut on August 15, 2011, 04:26:07 PM
@gurner, would it be something to do with input impedance?...like you said earlier?..

Just to make sure I understand the issue...when you connect up the LED driver part of the circuit (whether using an LM386 or opamp variant), you're hearing distortion....but you're satisfied that the wah circuit is without distortion when the envelope detect is disconnected & when say a torch is manually shone on the ldr?

if so, then as you've already identified the problem is eminating from the envelope detect aspect of the circuit.

Towards isolating the issue - lash up a temporary separate voltage supply to the envelope detect circuit (my suspicion is that the current draw in the envelope detect circuit is causing some issues here)...hurl some major caps onto the +ve pin of the envelope detector IC.

If using a dual opamp consider splitting into two individual opamp IC... again, some major caps onto the +ve pin of the envelope detector IC.

A couple of meandering thoughts.....IMHO a TL072 isn't a good choice of opamp to drive an LED. It's not rail to rail, so if your voltage supply sags when the LED is fully on, then you may get clipping creeping in on the signal half of the opamp. I'd be inclined to use a rail to rail opamp that's also capable of driving heavy loads.

deadastronaut · August 15, 2011, 04:53:20 PM

cheers gurner, yeah its the envelope 'dooby' thats causing it...

ok i'll try and seperate em , or i might try a lm358 opamp then.....or both.... cheers man.

shame i fancied it all on one op amp...

Gurner · August 15, 2011, 04:55:14 PM

Quote from: deadastronaut on August 15, 2011, 04:53:20 PM
cheers gurner, yeah its the envelope 'dooby' thats causing it...

ok i'll try and seperate em , or i might try a lm358 opamp then.....or both.... cheers man.

shame i fancied it all on one op amp...

you might still be able to get away with a dual...I'm only suggesting these ideas for breadboarding towards ID'ing the problem...once we know what's causing it, then we can revist the design.

News:

SICK DUCK...quack quack... :)