Advice for an amateur.. Crackling noise.

[tony311]

Hello, I have posted this on another forum, but I don't know whether they have the patience for an amateur.

I Have succesfully built a few pedals. I recently tried my hand at the Electrovibe from PCBPedal. It all works as it should however as i increase the gain, I get a crackling type sound that is proportional to the volume. Its not a pot causing it and I have run through with the probe but can't quite isolate it, or I don't know how to isolate it. It appears in all aspects of the unit except when in bypass of course.

Am I correct in assuming this would be caused by a transistor issue? I have done the usual of re flowing and checking etc. but its now a bit beyond me.

I would be greatful for any advice.

[bluebunny]

Is this really a test, Tony?  Or a real post?  We can move it to the main forum if you want more traffic.  It's a bit quiet in this dusty corner...

[tony311]

Is this really a test, Tony?  Or a real post?  We can move it to the main forum if you want more traffic.  It's a bit quiet in this dusty corner...

Oh ok so I have posted this in the wrong place? Obviously. I just noticed that. Would be great if you could move it to the correct section

[bluebunny]

No problem.  Sorted.  Enjoy the many forthcoming replies.   

[duck_arse]

... but not this one. no build docs?


the gain pot is in the lamp driver circuit. you set it and then leave it, doesn't matter if it crackles when adjusting if the rest of the circuit works, and if the crackle stops when adjustings stop.

..... I have posted this on another forum .....

there are other forums?

[antonis]

Does crackling occur both for |Vibrato & Chorus mode..??

[Hypernurbs]

You sure you mean the gain pot? not the volume pot?

[Kevin Mitchell]

You sure you mean the gain pot? not the volume pot?

Is that a Gain knob??
Typically in vibe clone-ish things it's a trim, if there at all.
This controls the intensity of the lamp - or rather one side of it's range. If you're getting crackling noises then it's probably a fussy power supply as more current gets allotted to the lamp.

I'm a bit surprised to see a lack of filtering there - these vibes can get pretty noisy. Unless a very low current lamp is specified? Is that a thing?
I typically use at least 1000uF for the lamp supply (18v) and another for the signal supply (15v). It's needed to keep things happy and prevent audible ticking.

I feel that pedalPCB didn't vet this one...

Also, two 2n5088s in darlington configuration for the driver? Haven't seen that before. A single 2n3904 or alternative darlington transistor works fine. - not sure if this is a problem, just something I'd take note of comparing to any other vibe clone.

[bluebunny]

Looking at the build document, the "Gain" control is a set-and-forget trimmer.  If it crackles when you're adjusting it (for the one and only time), then unplug from your amp. 

(BTW, build docs are here.)



Edit: I think I just repeated what the duck said... 

[tony311]

Thanks for all the replys. Yes I am refering to the GAIN TRIMPOT. When I adjust that to get a reasonable level, I get a lot of crackling on the output.

It happens on mainly on the vibrato and the crackling appears to go with the beat of the vibe, so on the louder parts, the crackles louder. I cannot adjust the trimpot to get a reasonable level withouth getting a lot of crackling. It is almost inaudiable to get rid of the crackle.

Hope this makes sense.

[tony311]

Lamp is very low current. 40mA. I do mean the TRIMPOT not the volume. Can I just substitute the 100uf caps with 1000uf caps without causing any other issues?
Is it possible the 2 transistors that are the drivers could be faulty, one or both? would this cause noise like crackling?

You sure you mean the gain pot? not the volume pot?

Is that a Gain knob??
Typically in vibe clone-ish things it's a trim, if there at all.
This controls the intensity of the lamp - or rather one side of it's range. If you're getting crackling noises then it's probably a fussy power supply as more current gets allotted to the lamp.

I'm a bit surprised to see a lack of filtering there - these vibes can get pretty noisy. Unless a very low current lamp is specified? Is that a thing?
I typically use at least 1000uF for the lamp supply (18v) and another for the signal supply (15v). It's needed to keep things happy and prevent audible ticking.

I feel that pedalPCB didn't vet this one...

Also, two 2n5088s in darlington configuration for the driver? Haven't seen that before. A single 2n3904 or alternative darlington transistor works fine. - not sure if this is a problem, just something I'd take note of comparing to any other vibe clone.

[tony311]

I did a bit more probing. If the image attached makes sence, the section in the yellow is clear audio. The audio starts to crackle at the 1uf capacitor onwards. I replaced that capacitor but it made no difference. Unfortunatly I don't understand enough about it to determine why, how, where the audio is being affected from that point on?

[Clint Eastwood]

Is the 1uF cap a tantalum? It seems they can cause crackling when faulty/bad quality. Try replacing it with something else?

[tony311]

Not up there no, the only titaniums are below. These were suggested in the circuit because of some reason I don't understand.

[Kevin Mitchell]

Lamp is very low current. 40mA. I do mean the TRIMPOT not the volume. Can I just substitute the 100uf caps with 1000uf caps without causing any other issues?
Is it possible the 2 transistors that are the drivers could be faulty, one or both? would this cause noise like crackling?

Upping the filter caps will only help the circuit. They essentially act as a voltage reservoir so if/when current demand spikes (nature of an LFO) the supply will sit happy, rather than dry up and wait to refill if there's even enough to meet the demand.
-That's my dumbed down explanation and I'm sticking with it 

I would actually draw your attention to the last phase shift stage as that's where you've highlighted the problem. As you see, it's not everywhere in the signal path but right towards the end. So I wouldn't worry about filtering or the LFO design just yet - but I do predict the desire to improve this once you get it going - please let the forum know if it does prove to be noisy after we fix the obvious problem.

I would inspect & replace a possibly bad capacitor first - but I don't think it's a tantalum as it sits.
I guess those electros are the 1uFs in the signal path? Check out any in your red section. Use the probe again to find exactly where the problem first shows up if you can - not having schematic designations on the PCB makes this a bit of a pain so you'll want to use values to identify where you're probing in comparison to the schematic.

[tony311]

I would firstly like to thank you for your assistance and patience. Other forums I have been on, the people seem to be fairly abrupt to those of us that are not completley electronically up to date.

I have highlighted where the crackling noise starts. It actually first appears on Q9 transistor. On the first leg of it. I changed this transistor as well as the one beside it and two capacitors that feed into it, one is a 47uf and the other was a 1uf. I was very careful but this made NO difference. I seem to have this issue a lot where I change things and it ends up not being the issue. The crackle also appears on C17, but this feeds into the two diodes and it part of the power supply so I guess it should not have audio on it anyway? This is where I have got myself into trouble with other electronic builds. I start assuming it is that part or the one proceeding it and start replacing parts, achieving nothing and lifting tracks.
Anyway I did change C17 anyway.
So now I am out of ideas. I have changed 5 parts and made no difference. I have highlighted where the problem first starts in Red and the parts I changed in Yellow.

Just an update, I thought I would also change the two diodes beside the charge pump ic. Of course this made no difference and the crackle still starts at that transistor. I don't think changing components at random is going to solve much.

Lamp is very low current. 40mA. I do mean the TRIMPOT not the volume. Can I just substitute the 100uf caps with 1000uf caps without causing any other issues?
Is it possible the 2 transistors that are the drivers could be faulty, one or both? would this cause noise like crackling?

Upping the filter caps will only help the circuit. They essentially act as a voltage reservoir so if/when current demand spikes (nature of an LFO) the supply will sit happy, rather than dry up and wait to refill if there's even enough to meet the demand.
-That's my dumbed down explanation and I'm sticking with it 

I would actually draw your attention to the last phase shift stage as that's where you've highlighted the problem. As you see, it's not everywhere in the signal path but right towards the end. So I wouldn't worry about filtering or the LFO design just yet - but I do predict the desire to improve this once you get it going - please let the forum know if it does prove to be noisy after we fix the obvious problem.

I would inspect & replace a possibly bad capacitor first - but I don't think it's a tantalum as it sits.
I guess those electros are the 1uFs in the signal path? Check out any in your red section. Use the probe again to find exactly where the problem first shows up if you can - not having schematic designations on the PCB makes this a bit of a pain so you'll want to use values to identify where you're probing in comparison to the schematic.

[cspar]

Did you test the ldr's to make sure that they are similar in response and correct for the circuit or just pull them from a bag?

If that first one is wonky for the circuit.... that could pose a problem right there.

Also are you testing the completed board with it enclosed? The circuit needs to be isolated from any light source other than it's own to function properly.

You can punch a hole in a shoebox for the wiring and use a little electrical tape to shield the light.

[tony311]

Did you test the ldr's to make sure that they are similar in response and correct for the circuit or just pull them from a bag?

If that first one is wonky for the circuit.... that could pose a problem right there.

Also are you testing the completed board with it enclosed? The circuit needs to be isolated from any light source other than it's own to function properly.

You can punch a hole in a shoebox for the wiring and use a little electrical tape to shield the light.

The LDR's are all the same brand and same ones. I have a little cap that sits over the light and ldrs so that stops the light. The crackle actually goes to the beat of the throb/vibe.... I havent tested the LDR's as such.  I do have two spare ones exactly the same. So I will see if i can work out if any of the LDR's are faulty?

I just replaced LDR 1. No difference. Probing I found LDR4 was crackling, so I replaced that with no difference?

[tony311]

Well I have given up with this one. I have replaced everything. Even silly things like jacks etc. The crackling is still there on Vibe and Chorus. So something somewhere just doesn't add up. I even tried an audio source from cd. Same thing, worse actually.