3-legged dog help:

waky · February 11, 2009, 10:47:42 PM

well i built a 3-legged dog yesterday, when i first ran it i missed the jumper between pins 8 and 9 so the chip got pretty hot, after i fixed it the sound comming from the effect was some horrible squeal/static... i know for a fact its not the 4049 because i swaped a fresh chip and got the same noise. the noise diminishes alot when i touch the strings of the guitar but when i touch them i get no sound from the effect.

what may be causing this?

by the way the gain pot doesnt do anything and the volume pot makes it squeal differently, could an electrolitic be damaged from the first error?, could it be a ground loop? (i dont really know what that is, can someone explain?).

im using a "cd4049ube"

Paul Marossy · February 12, 2009, 10:03:58 AM

Is your battery brand new? If you use an old battery that is putting out a low voltage, that circuit will squeal like a son of a gun. Been there, done that.

Not sure about the quirky touching the strings and your effect goes away part, though...

waky · February 12, 2009, 12:23:01 PM

the battery is putting out 9 volts, the effect doesnt dissapear the squeal dissapears. the thing is that i dont get any distortion =/. only a VERY faint sound of the strings disorted horribly xD

Paul Marossy · February 12, 2009, 12:27:47 PM

Huh, that is even more weird. OK, so what layout did you use? The one at ROG? Did you ground all of the unused pins?

StephenGiles · February 12, 2009, 02:45:03 PM

http://www.youtube.com/watch?v=b5yqoqBUeqs

Maybe our Bonzo can help

suprleed · February 12, 2009, 03:33:37 PM

The touching the strings thing is odd. Almost sounds like a grounding problem. I would go thru and double check that all your ground connections are correct versus your layout e.g. circuit board, jacks, power etc.

waky · February 12, 2009, 08:41:54 PM

hmm i only grounded the pins that appeared grounded an rog... some were left open yes i though it was grounding issue too but i have checked ALOTmy grounding, there arent many ground connections anywhere =/ the drive pot is still useless.

should i ground all pins that are unused?

Paul Marossy · February 12, 2009, 09:23:33 PM

Quote from: waky on February 12, 2009, 08:41:54 PM
hmm i only grounded the pins that appeared grounded an rog... some were left open yes i though it was grounding issue too but i have checked ALOTmy grounding, there arent many ground connections anywhere =/ the drive pot is still useless.

should i ground all pins that are unused?

My understanding is that all pins that are not being used are supposed to be connected to ground. Check out the layout at www.runoffgroove.com

waky · February 12, 2009, 09:56:35 PM

i did .. xD i thought pins 10, 12, 13 15 and 16 were left open.. ill try what paul said and i'll get back to ya.

still open for suggestions

StephenGiles · February 13, 2009, 09:37:40 AM

Quote from: StephenGiles on February 12, 2009, 02:45:03 PM
http://www.youtube.com/watch?v=b5yqoqBUeqs

Maybe our Bonzo can help

Well, we love our dog!!

Paul Marossy · February 13, 2009, 09:41:06 AM

Quote from: waky on February 12, 2009, 09:56:35 PM
i did .. xD i thought pins 10, 12, 13 15 and 16 were left open.. ill try what paul said and i'll get back to ya. still open for suggestions

Which layout did you use, the PCB or that RadioShack perfboard thing? I used the RadioShack perfboard to build mine.

Looking at this page, http://www.runoffgroove.com/3leggeddog.html, I see Pins 10, 12, 13, 15 & 16 not connected to anything, which differs from what you stated above. I seem to remember something about the unused pins needed to be sent to ground, but perhaps I am thinking of another circuit...

waky · February 14, 2009, 11:21:00 PM

right so i got my stompbox to work, only one problem... the drive pot at minimun gives a distortion (with synth like sounds on higher notes, is this normal?) when i start turning the knob up i get this weird oscillation, pitch changes as i move the pot around, it only works ok at the minimun setting, i have wired lugs 1 and 2 ?

Paul Marossy · February 16, 2009, 10:40:12 AM

Quote from: waky on February 14, 2009, 11:21:00 PM
right so i got my stompbox to work, only one problem... the drive pot at minimun gives a distortion (with synth like sounds on higher notes, is this normal?) when i start turning the knob up i get this weird oscillation, pitch changes as i move the pot around, it only works ok at the minimun setting, i have wired lugs 1 and 2 ?

Something is still not right, it shouldn't be behaving like that.

waky · February 16, 2009, 11:24:52 AM

yeah i was wondering if i should plug the third lug of the drive pot to ground? or some other wiring to prevent the oscilation

.

im not sure of what to do =/... i figured that the reason it didnt sound at first was because i had the volume pot connected to ground, so to anyone who builds this in the future dont connect volume pot to ground!

anchovie · February 16, 2009, 11:35:50 AM

Quote from: waky on February 16, 2009, 11:24:52 AM
i figured that the reason it didnt sound at first was because i had the volume pot connected to ground, so to anyone who builds this in the future dont connect volume pot to ground!

How can you say that? You can't go dishing out "advice" like that when you haven't got your circuit working properly. Just because you have sound coming out of your circuit doesn't mean that it "works" - from what you describe this neither sounds nor functions like a 3-Legged Dog!

Almost every volume control ever made will have lug 3 connected to ground, it's the whole principle of it working as a voltage divider to attenuate the signal.

Have you checked all of your soldering for shorts? Did you cut the tracks in the places indicated on the layout?

Paul Marossy · February 16, 2009, 11:44:29 AM

QuoteAlmost every volume control ever made will have lug 3 connected to ground, it's the whole principle of it working as a voltage divider to attenuate the signal.

+1

waky · February 16, 2009, 12:02:25 PM

uh... well im embarrased.. you are right i shouldnt be giving advice away =/... and yes i checked all that...

about the drive pot, on minimum (0 resistance) it has distortion.. as soon as i flip a little bit the pot i get the oscilattion (it stops when i play on the guitar, but the distortion becomes kinda of a synth sound, and as soon as the strings mute the oscilation begins again)

Ripthorn · February 16, 2009, 01:53:29 PM

I had a similar problem with my red llama a while ago (about the drive pot causing a nasty oscillation). Turns out I had one of my resistors in a feedback loop around the inverter in the wrong place (before a junction instead of after). It's any easy thing to miss.

Paul Marossy · February 19, 2009, 11:40:02 AM

Also, are you sure that you have the right CD4049 chip? I remember that in this circuit, you need to use the CD4049UBE chip vs. the CD4049 buffered version...

gez · February 19, 2009, 02:30:21 PM

Re the unused inverters: it's only the inputs that need to be tied to one of the rails (usually ground).

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