Very notable buzz on overdrive pedal

[mattis03]

Hi, so I'm both new to building your own pedals and to this forum. I built my first pedal today which was an overdrive pedal. I followed a schematic from Wampler pedals, shown below. I first did it on a breadboard, and it worked, but there was this notable buzz. I thought that it might have to do with the breadboard, so I did it on perfboard instead and soldered everything. It worked well but there was still a big buzz, which was really sad because otherwise, it sounded awesome. I did some researched and found out that it might have to do with my psu, mains buzz or something, so I tried it with a 9v battery and the buzz was still there. So my question is if someone might know which direction I should start debugging or something .

[idy]

Welcome to the forum!
That is an OK choice for a first or early project with an opamp. You made your own layout, always a chance for things to go wrong there...

You appear to have taken a knife to the back side to make sure there are no unwanted solder bridges, good..

Buzzing is often faulty grounding. Make sure that each place on the schematic that goes to ground does that.

Have a meter? Give us the voltages on each pin of the opamp. People here like voltages as much as we love pictures...

[GibsonGM]

Is the circuit inside a metal box that is grounded (to the PCB)?  If not, you might be picking up noise from any number of places: lighting in your room, a nearby computer and so on.    Make sure EVERY part that needs to go to ground does actually connect there.

[iainpunk]

welcome to the forum!

how would you describe the buzz? does it sound like a 50Hz hum? (or 60Hz if you live in that part of the world)
i suggest you look at this link:debugging guide

cheers, Iain

[mattis03]

Welcome to the forum!
That is an OK choice for a first or early project with an opamp. You made your own layout, always a chance for things to go wrong there...

You appear to have taken a knife to the back side to make sure there are no unwanted solder bridges, good..

Buzzing is often faulty grounding. Make sure that each place on the schematic that goes to ground does that.

Have a meter? Give us the voltages on each pin of the opamp. People here like voltages as much as we love pictures...

Yes I have a meter, but not to experienced with it. When you say voltages on each pin, how should I measure that?

[mattis03]

Is the circuit inside a metal box that is grounded (to the PCB)?  If not, you might be picking up noise from any number of places: lighting in your room, a nearby computer and so on.    Make sure EVERY part that needs to go to ground does actually connect there.

The thing is that I was thinking about 3d printing the case, idk if I'm crazy for doing that but yeah:). Every time I tried I had the circuit on the floor like 1 m from my tube amp.

[mattis03]

welcome to the forum!

how would you describe the buzz? does it sound like a 50Hz hum? (or 60Hz if you live in that part of the world)
i suggest you look at this link:debugging guide

cheers, Iain

The thing is that the hum gets greatly reduced when I turn down(making it less bright sound) my tone knob on the guitar. So it sounds really good with almost no buzz in that case. I will read, thx.

[GibsonGM]

To measure the pin voltages, set the meter to "DC volts".   Connect the black probe to ground (battery minus here, not always the case).  Use the red probe to take measurements...careful not to short the IC pins together as you do this! 

The buzz may or may not be from an error in the circuit...all the wires in your home radiate noise, basically. And turning it up amplifies it more, whatever it is....

[mattis03]

To measure the pin voltages, set the meter to "DC volts".   Connect the black probe to ground (battery minus here, not always the case).  Use the red probe to take measurements...careful not to short the IC pins together as you do this! 

The buzz may or may not be from an error in the circuit...all the wires in your home radiate noise, basically. And turning it up amplifies it more, whatever it is....

pin 1(output A)= 4.8V
pin 2(inverting input A) = 4.8 v
pin 3(non-inverting input A)=4.37V
Vcc- = 0V obviously
vcc+ = 9.61V
is this what you were asking for?

[mattis03]

Idk if this means anything but every time I touch the ground with my finger most of the buzzing goes away, whilst the effect being the same.

[idy]

pin 1(output A)= 4.8V
pin 2(inverting input A) = 4.8 v
pin 3(non-inverting input A)=4.37V
Vcc- = 0V obviously
vcc+ = 9.61V
is this what you were asking for?

yes, but there are two opamps on that chip. What about pins 5,6, and 7?
The first three look good!

Now, it is common for high gain pedal to buzz outside of a proper shield, like a metal box. Or a cookie tin. Or a foil-lined hand carved cigar box, or a foil-lined 3-d printed box...or can they 3-d print a conductive box?

So I would try to put into something. And make sure that the jacks (at least) make sure the box is grounded. Then tell us how much it buzzes.

[bluebunny]

Welcome.  You definitely need to do something with the unused opamp, otherwise it's probably going into hypersonic oscillation meltdown.  Probably not contributing to "buzz", but worth sorting out.  Connect pin 6 to pin 7, and connect pin 3 to pin 5.  Then it becomes a well-behaved unity buffer.

[GibsonGM]

^ This  Might or might not help the noise issue, but like idy said, it needs an enclosure.   Make SURE all ground points are connected   Really, really sure   

[mattis03]

Welcome.  You definitely need to do something with the unused opamp, otherwise it's probably going into hypersonic oscillation meltdown.  Probably not contributing to "buzz", but worth sorting out.  Connect pin 6 to pin 7, and connect pin 3 to pin 5.  Then it becomes a well-behaved unity buffer.

Ok thx.

btw

Pin 7 = 1,44V
Pin 6 = 1.08V
Pin 5 = 1.07V

And I'll triple check the ground;)

[iainpunk]

Idk if this means anything but every time I touch the ground with my finger most of the buzzing goes away, whilst the effect being the same.

i suggest checking if there is actually a ground on your amp and/or equipment. most amps need a good ground if they want to stay hum free, especially with a gain pedal. are all jacks connected right, both the signal and ground? for some reason i see people who forget to ground one of the in/out jacks for some reason.

cheers

[pinkjimiphoton]

Idk if this means anything but every time I touch the ground with my finger most of the buzzing goes away, whilst the effect being the same.

thats cuz YOU are the antennae, and touching the ground point grounds YOU.

this is pretty normal in any kind of high gain circuit. you mention it being on the ground about a meter from your amp, and yeah, its gonna hum like crazy.

usually there's wiring and crap running under the floor, and you're gonna pick up every bit of interference around you until you put a faraday cage around that sucker.

fuzz/overdrive/distortion etc literally HAS to be in a metal enclosure that's properly grounded.

a 3d printed enclosure will be fine for effects that aren't gainy, but no good for dirt boxes.

so i wouldn't worry about it. get a metal box, install it, and odds are the problem will completely disappear.

[amptramp]

C3 appears to be backwards.

Check the grounding but putting the entire unit in a grounded enclosure is a good idea because your gain can go up to 501.  Anything you pick up on the input is going to be amplified hugely.

When the tone control slider is moved to the left, it connects C29 to C3, you may get oscillation because most op amps do not behave well with a capacitive load.  You need something like 1000 to 2000 ohms either in series with either C3 or C29 to avoid oscillation.  There is a lowpass formed by the output impedance of the op amp and C3 and C29 in series and this causes a phase lag in the feedback that causes oscillation.

As others have said, the other op amp in the package should have the output tied to the inverting input and the non-inverting input connected to the junction of R32 and R33.

And welcome to the forum!

[duck_arse]

one thing about your metal bodied DC jack is that you can't use it with a metal case and negative ground - it will short your supply and nothing will work. you'll need to isolate the DC jack from the metal of the case or get a plastic-bodied jack as replacement. the metal one will be fine until you box the circuit.

and welcome.

[pinkjimiphoton]

C3 appears to be backwards.

Check the grounding but putting the entire unit in a grounded enclosure is a good idea because your gain can go up to 501.  Anything you pick up on the input is going to be amplified hugely.

When the tone control slider is moved to the left, it connects C29 to C3, you may get oscillation because most op amps do not behave well with a capacitive load.  You need something like 1000 to 2000 ohms either in series with either C3 or C29 to avoid oscillation.  There is a lowpass formed by the output impedance of the op amp and C3 and C29 in series and this causes a phase lag in the feedback that causes oscillation.

As others have said, the other op amp in the package should have the output tied to the inverting input and the non-inverting input connected to the junction of R32 and R33.

And welcome to the forum!

good catch, c3 is not capable of blocking the dc in that configuration, and may well be damaged from being backwards. curious if it gets warm or hot while playing?

would definitely cause a "buzz"!!

[PRR]

> curious if it gets warm or hot while playing?

If wired as shown, but with output DC grounded (a worst case), there's at-most 4.5V across 10K or a half-mA, thus less than 0.0025 Watts. That's not hot.

IMHO, little chance the e-cap is ruined, but better safe than sorry.