No input signal, only output.

[deadsnake]

Hi I´ve been trying to debug this circuit but had no luck doing it (i´m not a geek at this). I´ve built this wah wah circuit and I´m only getting the output signal and not input.

Well you might be confused since " how can you have an output with input?", the circuit is not shielded yet and I´m getting a little bit of hum, when I turn the wah on I can notice the output signal frequency changing.
The humming is quite weak so have to turn the volume a little bit more to clearly notice it. Everytime I turn the pot knob I can hear a sound similar to a seashell going back and forth close to you ear (you know what I´mean right?).

I´ve checked the whole circuit and I looked for some missoldered joints which could cause shortings or unwanted traces.  I checked the resistors values about 3 times and the caps too.

I don´t have a multimeter at hand and I don´t know how to use the audio probe. Well If somebody taught me I would aprecciate.

Well I´ve made one but I don´t know what sound I should be hearing.

Do I need to have my guitar plugged in? I'm asking this because it´s quite hard to play guitar and look for signals at the same time.

[Connoisseur of Distortion]

cd player works. just make a little converter with a cap in there. simple!

[SISKO]

Hi deadsnake!!.
                  well.. as you said, the circuit is working, voltages are right and all that stuff (I'm telling you this because its NORMAL to hear that noise in Wahs  
So.. (almost) definitely your input its grounded. You may shorted the input jack or the inputs points at the PCB.. i would desolder those parts and see if that fix it.

I don´t have a multimeter at hand and I don´t know how to use the audio probe. Well If somebody taught me I would appreciate.

Check the FAQ section
-------------------------
What do you need to learn how to use Multimeter or Audio Probe?

Do I need to have my guitar plugged in? I'm asking this because it´s quite hard to play guitar and look for signals at the same time.

Of course you need..

OK i hope its works
Bye
SISKO

[deadsnake]

Many thanks I aprecciate it. I got another question though, I´ve got the PCB layout and the original Schem if you think it´s easier to follow, what components could block my input signal?

The schem is a bit different from the layout, I followed the layout truthfully.

this is the layout



check this pcb layout I did a green trace over the part that I think it´s grounded.


and the schem is in pdf format
http://www.morleypedals.com/pwaes.pdf

I'm going to double check my soldering and see I accidentally soldered a trace that was not supposed to.

[twabelljr]

    Pull the IC and battery. With a cable plugged into the input, measure the resistance from the cable tip to input ground. It should read O.L.. ( no continuity). The input should not short through the voltage divider under normal conditions.
What do you measure?

[Andre]

Are you sure you got the IC placed in the right direction?
If the orientation of the text on the IC is the same as on the parts layout you got it the wrong way around.
The square island is pin 1.

[deadsnake]

The IC is right altough at first I thought the square meant it was the positive pole(just like thw caos). I don´t have a multimeter that can read the resistance between the input and the gnd. But I can try to check that using a probe I think. Maybe a strong signal would mean it has no resistance.

[SISKO]

The squeare means the pin number 1, but i (still) think that your input its grounded, try to remove the  input jack and the .1uf cap at the input.. those are the only components that could be worng..
Try to replace that cap with another of the same value..

Bye
SISKO

[deadsnake]

I just bought a multimeter and a new caps I going to replace those and I´ll se what I get many thanks

[deadsnake]

It seems that I´m getting a really weak input signal.
I tried turning my amp on and touching the tip of the cable and I got a loud noise.
I then tried using plugging this cable into the circuit´s output and plugged another cable to the input and I did the same thing.
I got the same sound but way softer.
What can I change on that PCB so I can get a stronger input signal.

[deadsnake]

I just did some V reading on the IC and this is what I got.

1 - 5,23
2 - 5,22
3 - 4,96
4 - 0
5 - 9,73
6 - 9,12
7 - 9,11
8 - 9,62

Am I supposed to get 0V at pin 4? looking at the PCB layout what could have gone wrong?

[gaussmarkov]

i took your pic and coloured in the ground.  this should help a bit.  it shows how pin 4 of the ic should be 0v, just as you got with your dmm.  this picture also shows how to correct your original suggestion about what is grounded.



have you tried using an audio probe to trace your signal?  these are simple to construct and really effective.  i think this will show that your input signal is probably just fine.  and it will help you find the spot where it isn't.  see the debugging page linked at the top of every page on this forum.

keep us posted on what you find out! 

[twabelljr]

  Pin 5 voltage seems too high. Like your 10k resistors are not grounded and dropping the voltage like they should. I would check in this area first. I think voltages should be closer to this:

[deadsnake]

I did my probing and  I was amazed how such a simple thing could make wonders.

this is what I got from doing it




You are the best man.

[johngreene]

So far things look normal. You need to continue from Pin 1 of the IC though.

Double check the DC voltages too, as twabelljr pointed out, Pin 5 is much too high. It's as though the 10K resistor to ground on the far right isn't there or is a really large value.

--john

[deadsnake]

I´m going to check those V´s at those points as soon as I get back from a wedding I just want to forward those msg so you can foward it at time I´m traveling tommorow.

Here is what I got I thinks there is nothing left to probe.


I might not know what I´m talking about but, is it normal to have no signal at those traces? I was about to take some os those components out and reaplace them.

[deadsnake]

I really aprecciate everybody's help so far. I would like to one day help other people too.

[gaussmarkov]

+1 re twabelljr & johngreene:  and use your dmm to read the values of both 10K resistors on the right and make sure the one on the outside is properly soldered to the ground trace.  maybe check continuity by placing one probe on the bottom lead of that resistor and the other probe on another lead that should be grounded?

you're gonna fix this ckt, man.  i can feel it! 

[deadsnake]

Man you are the best!!!
Just like you said the problem was on that 10K res on the far left. It had cold soldering. You know I saw it, it was looking suspicious but I ignored it, that old way of thinking ..... "It's probably not the problem". You are a prophet just like you said

you're gonna fix this ckt, man.  i can feel it! 

Well the problem was either that or this .0047uF it had a small soldering drop over it´s lead. And the lead was not piercing the PCB and not touching the soldering on the other side. Well I fixed this and I then notice using the probe that I was getting output. I going to thank you guys how many times I have to. Thank you again. I´m going to post a build report as soon as I get the mechanical part of my wah pedal working. I´m doing it from scratch. 

Att. Jr.

[deadsnake]

Man you are the best!!!
Just like you said the problem was on that 10K res on the far left. It had cold soldering. You know I saw it, it was looking suspicious but I ignored it, that old way of thinking ..... "It's probably not the problem". You are a prophet just like you said

you're gonna fix this ckt, man.  i can feel it! 

Well the problem was either that or this .0047uF it had a small soldering drop over it´s lead. And the lead was not piercing the PCB and not touching the soldering on the other side. Well I fixed this and I then notice using the probe that I was getting output. I going to thank you guys how many times I have to. Thank you again. I´m going to post a build report as soon as I get the mechanical part of my wah pedal working. I´m doing it from scratch. 

Att. Jr.