Guitar amp kit (problem with noise and humming)

bzblues

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Hello everyone.

I've built 3 of these kit amps so far and I always have the same problem.

The section of the bass potentiometer in the circuit board acts strange. When I turn the pot down to "0", there is a loud hum, like its not grounded, WICH IT IS! I had the exact same problem in the previous two.

Also, when I connect the DC power supply, the humming noise appears very loud, even more when I turn the bass potentiometer. When the amp is using the 9V battery, the noise reduces drastically, but its there in the background. I'll attach a video for you to see what its going on:

I've tried to do the start point grounding, but nothing, I grounded to the PCB aluminium plate below and to the plate in the control panel and nothing. I built this enclosure of aluminium but NOTHING, absolutely nothing seems to resolve this issue. I've also tried different DC power supplys and NOTHING.

Please, if anyone can help, its driving me crazy not beeing able to fix it. And believe me, I've had checked and re-checked every solder joint, every component, everything is in its right place!
 

Pick_n_Strum

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Have you tried it in different outlets / locations in your home? Could be an issue with dirty power.

Also agree with Jon Snell - thinking about this issue more from a pedal standpoint, hum is often bad grounding.

Odd that all 3 would have the exact same grounding issue, unless it's more of a design flaw.

EDIT: Also just looked at the schematic - is it just me or does it look like it's showing lug 1 of the bass pot NOT grounded?

Also, this guy has the same problem:

https://reverb.com/item/4757892-little-rebel-miniamp-2-w
 
Last edited:

wabashslim

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Odd that all 3 would have the exact same grounding issue, unless it's more of a design flaw.
Also, this guy has the same problem:
https://reverb.com/item/4757892-little-rebel-miniamp-2-w

Design flaw it is, unless everybody's using inadequate wall warts.

Also just looked at the schematic - is it just me or does it look like it's showing lug 1 of the bass pot NOT grounded?

Obviously intentional. Just like your guitar's tone control.

I could use one of these minis myself, I've got an empty small chassis already drilled for half a dozen pots and a couple cabs to install it in. I'll build in a power supply to avoid the warts.
 
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Jon Snell

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It is only a ground wire missing. Spend a bit of time checking everything that should be is ground.
I would pay particular attention to the virtual earth and the single 10u capacitor. The op amps like a balances supply. Screenshot 2020-11-11 at 07.58.12.png
Balance the earth with two 100uF capacitors, one from +ve to earth and the other from earth to ground.
The ground IS NOT EARTH but VIRTUAL earth. Don't get confused!
Screenshot 2020-11-11 at 07.58.12.png Screenshot 2020-11-11 at 07.57.52.png

Did you ground the unused lug on the bass pot by mistake?

Edit; more info.
 
Last edited:

bzblues

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It is only a ground wire missing. Spend a bit of time checking everything that should be is ground.
I would pay particular attention to the virtual earth and the single 10u capacitor. The op amps like a balances supply. View attachment 784455
Balance the earth with two 100uF capacitors, one from +ve to earth and the other from earth to ground.
The ground IS NOT EARTH but VIRTUAL earth. Don't get confused!
View attachment 784455 View attachment 784456

Did you ground the unused lug on the bass pot by mistake?

Edit; more info.


I've been getting practically the same answer about the grounding of the pot. I can see that in the bass pot part of the PCB there is no connection to anywhere in the 3rd lug (looking from the back of the pot from left to right). The rest of the pots have a connection for this lug in each one of them (sorry, I'm super very much new a this and its all a bit confusing)


Thank you!
 

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  • little rebel PCB.jpg
    little rebel PCB.jpg
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Jon Snell

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The schematic is available with a purchase of the kit.
Back to basics;
Does the master volume work correctly and make the hum reduce?
Is there hum with no guitar lead plugged ?
Are you using a 9volt regulated DC power plug?
 

bzblues

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The schematic is available with a purchase of the kit.
Back to basics;
Does the master volume work correctly and make the hum reduce?
Is there hum with no guitar lead plugged ?
Are you using a 9volt regulated DC power plug?


Hello

1) Te master volume works propperly, it minimize the hum, but not completly
2) There is hum with ot without guitar.
3) I'm using a regulated power supply supposedly. The seller told me that it was regulated, noise free, commutes at 40Hz, etc. Not doing a thing, the hum is still there.

The electricity of the apartment that I live in its not that well "Isolated" it think. I have a Roland Street Cube that I use with a DC power supply of good queality and still makes a bit a humming, but with the Little Rebel Amp, its a whole other thing, it is unplayable.
 

wabashslim

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Here's the manual in German w/ schematic & layout ...
 

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  • Little-Rebel-2W-Guitar-Amplifier.pdf
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Jon Snell

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If you temorarily bridge R6 with a piece of wire and the hum stops, the hum is coming from the stage before. In which case link out R3. If it stops the issue is the input socket wiring.
If it makes no difference, then the hum is coming from the tone/volume control section.
 

bzblues

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Have you tried it in different outlets / locations in your home? Could be an issue with dirty power.

Also agree with Jon Snell - thinking about this issue more from a pedal standpoint, hum is often bad grounding.

Odd that all 3 would have the exact same grounding issue, unless it's more of a design flaw.

EDIT: Also just looked at the schematic - is it just me or does it look like it's showing lug 1 of the bass pot NOT grounded?

Also, this guy has the same problem:

https://reverb.com/item/4757892-little-rebel-miniamp-2-w


Yup, it seems that it is not grounded. So, I remove that wire that is connected to the PCB and solder it to the metal plate below the circuit to ground it. Didn't work, when I turn the pot down, it makes a sound like a screaming burning monster (cool horror movie effect for sure). The seller told me to solder a 100 ohm resistor to the 9V lug, but IT KILLED THE SIGNAL COMPLETLY! nothing comes out and the LED is dimm.
 

bzblues

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You need to fault find.
As I suggested, start isolating portions of the circuit to find out where the issue comes from and then you can fix it.
Until then it is like piddling against the wind.

I'm not sure or don't have the knowledge to do that. Not sure where to begin...I'm very much new in this. I'll try to figure it out.
 




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