Debugging Noise

[bhcarpenter]

Apart from visually inspecting joints and verifying components are correct, what is the recommended way to track down noisy components in a build? A few of my FV-1 builds are significantly noisier than others, and there has to be a better way to debug this than to just start replacing components until it goes away.

 

[Cybercow]

Will you please describe the "noise" in detail?

FWIW, I've run into a few bad date codes for TL072CP dual opamps. They are . . . .

KNOWN BAD TL072CP DATE CODES:
18MDSHY
14AP8NM
07A5L8QM

Two of them came from Tayda. The other from a "reliable" source on eBay. They all exhibited artifacts of increased distortion on natural fade-outs of a signal. When no signal was present, there was no noise detected. But when a plectumed signal was applied, as the amplitude decreased during the natural decay of the amplitude envelope, unwanted distortion was introduced into the signal. When I replaced them TL072IP dual-opamps from a different source, (this time they were from StompBoxParts - and I tried SmallBear and Mouser too), the previously heard distortion was gone.

 

[Brett]

I'll preface what I'm about to tell you by saying that it's probably not going to be a ton of help...

The FV-1 platform is digital and digital pedals can be sensitive to your power supply or how you have them hooked up.

Are you daisy-chaining these FV-1 pedals with each other? With analog pedals? With pedals that have voltage doubler circuits in them?

Are all of these FV-1 pedals noisy when they are the only pedal between your guitar and amp using an isolated power supply?

Can you describe the noise that you're hearing in more detail?

 

[bhcarpenter]

I’ll try to get a recording of the noise. For power I’m either using a Strymon Zuma or Voodoo Labs Pedal Power II. No Daisy chaining. I’ll try to get a recording of the noise, but I think I was hoping for more process guidance than advice for a particular case. I guess it depends on what kind of noise you’re experiencing?

 

[bhcarpenter]

Here’s an example with an Arachnid build. I have a similar issue with an Organ Donor.

Caveat: I have not yet started debugging, and it’s entirely possible that there’s wrong value components. Or that I fried the FV-1 when soldering it. I guess I’m looking for a “teach me to fish”

Dropbox - File Deleted - Simplify your life

www.dropbox.com

 

[MichaelW]

Here’s an example with an Arachnid build. I have a similar issue with an Organ Donor.

Caveat: I have not yet started debugging, and it’s entirely possible that there’s wrong value components. Or that I fried the FV-1 when soldering it. I guess I’m looking for a “teach me to fish”

Dropbox - File Deleted - Simplify your life

www.dropbox.com

Yikes, that's not right, shouldn't be that noisy. My Arachnid is actually dead quiet.

 

[eh là bas ma]

what is the recommended way to track down noisy components in a build?

An audio-probe, following signal path according to schematics, until you notice something that sounds like your noise :

Misc > Audio Probe : DIY Fever – Building my own guitars, amps and pedals

[DIY Fever] Audio Probe - very simple contraption that helps with debugging audio circuits

diy-fever.com

I am currently considering this build, because audio-probing is sometimes the only way, and it would make the process quicker and easier :

Signal Tracer/Injector Pen V6.2 kit, 19,90

Audio Probe Tool

www.musikding.de

 

[Cybercow]

Yikes! That a LOT more noise than what should be happenin'. I'd follow the audio-probe suggestion.

 

[bhcarpenter]

An audio-probe, following signal path according to schematics

I'd follow the audio-probe suggestion.

I always get a ton of noise (sounds like 60hz hum… or maybe DC offset?) when using my audio probe, which is why I didn’t consider that as an option. But this makes me think that maybe my audio probe is broken?

I’ve been using this one. Can’t remember where I got it.

 

[eh là bas ma]

always get a ton of noise (sounds like 60hz hum… or maybe DC offset?) when using my audio probe

Sounds like it's not correctly grounded ? Noises like that, when it's grounded, occur to me when the tip is in contact with the table, or the enclosure, etc.

Any ground point on the build will do, a jack ground works... alligator clip on the ground probe, makes it a lot much easier to have a steady ground connection.
Edit 2 : ...and it's a good idea to insulate the clip with some tape on the outside, in case it touches something close.

I would expect popping noises at the beginning of a test, when the tip gets gets in contact with a pad, to probe it. Or if the tip is moving on the pad, that's all.

Edit : your probe seems like the electrolytic cap has a big value ? I used a 100n film cap on mine, not sure if that's an issue, though.
Like we are all used to say in Normandie : "maybe it is, and maybe it is not".

 

[bhcarpenter]

Ok thanks all! It sounds like the answer to my original question is “trace the signal path with an audio probe.”

For the particular Arachnid in the example above, I started debugging tonight. This one was indeed a case of incorrect component value. I had installed a B100k as the Mix pot instead of B10k. All seems well now!

Now to debug the other one. And my audio probe.

 

[jhaneyzz]

Build an Audio Probe - Diagnose Problems

Audio Probe This is very simple yet very useful tool for debugging new pedals. You need one 1/4″ mono plug, one 100nF capacitor, all...

guitarpedalbuilders.blogspot.com

 

[The Gator]

Yeah i questioned to myself about the cap as well. Not the size in farads, but shouldn't it be an electrolytic cap?

 

[bhcarpenter]

I think my audio probe troubles were due to installing the cap backwards.

 

[Cybercow]

An audio probe does not have to use an electrolytic. A film cap of 100n is sufficient. Just be sure it can handle any voltages to which it is exposed.