Guitar amp kit (problem with noise and humming)

[bzblues]

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: https://www.youtube.com/watch?v=7n-21zF ... nZditowski

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!

[thetragichero]

no idea what kit or amp you're talking about
posting a schematic and gut shots would get you the best responses

[xtian]

I saw your post on thegearpage also. We're a tube-amp shop, here. You might try on MEF: https://music-electronics-forum.com

[bzblues]

Sorry, I forgot post the schemantics and to mention the name! It is a simple kit from Misukdig called "little Rebel Amp"

Here is the schemantics if anyone is interested. I'll check the other forum! Thank you!

[pompeiisneaks]

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: https://www.youtube.com/watch?v=7n-21zF ... nZditowski

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!

Looking at the schematic, the bass pot has an X on the first pin, meaning it should NOT be grounded. This may be the cause of the hum, a loop is being created when it's near 0.

Disconnect the bass pot lug 1 from ground and see if that resolves the issue.

basspot.png

Edit: had wrong pin number

basically it's working as a variable resistor instead of a potential divider.

~Phil

[bzblues]

Hello! you mean like so? attached picture

[pompeiisneaks]

I'm not sure. The circuit board should leave the right one 'not connected' I was assuming you meant you connected the pin to ground directly. Per that picture I'd almost expect it to be the red wire not the green one, because usually looking at a pot from that back side is 3, 2, 1 from left to right, you would almost need to double check that the circuit board has a connection (or not) to ground on any pins, if so then the creators of the board made a mistake. What you should see is that two of the three should connect to different points in the circuit like the schematic shows and the third has no connection.

I'm not 100% sure, maybe the board already has this handled and it's unrelated?

~Phil

[pompeiisneaks]

It looks like there's a possibility it's already handled... I zoomed in. You might want to contact the seller or as mentioned by xtian look at a solid state amp group to get more detail.

In that close up it looks like the right most connection has no traces going away from it, but that's just a guess.

~Phil

[bzblues]

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. You say that the pots should no be grounded? (sorry, I'm super very much new a this and its all a bit confusing)

I've contact the seller but he's not giving any answers. All he said was "Put a 100 ohm resistor right after the 9V pin in the DC jack. Did that and it killed off the signal.

​​​​​​​
Thank you! ​​​​​​​

[pompeiisneaks]

Sorry that's about my best shot. Yes it looks like that would be pin 1 in my understanding of the pictures. In theory you could leave it disconnected, not sure why he even did that, other than to help people avoid wiring the bass wrong.

Sorry, but I don't know a lot more about troubleshooting solid state amps, that's about the limit of my understanding.

~Phil

[sluckey]

Your schematic shows the proper input jack wired correctly. But the layout shows an incorrect input jack. A correctly wired jack would look like the attached pic. The jumper is important. If your jack only has two solder lugs then get a Switchcraft 12A and wire it as shown in the attachment.

BTW, when you suspect the kind of noise you have is coming from inside the amp you should disconnect anything from the input jack. Also rule out outside interference such as fluorescent lights.

[bzblues]

Sorry that's about my best shot. Yes it looks like that would be pin 1 in my understanding of the pictures. In theory you could leave it disconnected, not sure why he even did that, other than to help people avoid wiring the bass wrong.

Sorry, but I don't know a lot more about troubleshooting solid state amps, that's about the limit of my understanding.

~Phil

No worries! every information is appreciated!

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.

[pompeiisneaks]

Sorry that's about my best shot. Yes it looks like that would be pin 1 in my understanding of the pictures. In theory you could leave it disconnected, not sure why he even did that, other than to help people avoid wiring the bass wrong.

Sorry, but I don't know a lot more about troubleshooting solid state amps, that's about the limit of my understanding.

~Phil

No worries! every information is appreciated!

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.

Yeah grounding the pot is going to give the ground a signal loop up through that wire back into the signal path, this is why on the schematic it's shown as an X it should not be connected to anything at all, left hanging in the air. The board creator maybe just assumed that might confuse people so he created a non connected solder point so it would reduce confusion. Adding a 100 ohm resistor to the 9V pin gives your power supply nearly a dead short and will not help for sure.

~Phil

[bzblues]

Your schematic shows the proper input jack wired correctly. But the layout shows an incorrect input jack. A correctly wired jack would look like the attached pic. The jumper is important. If your jack only has two solder lugs then get a Switchcraft 12A and wire it as shown in the attachment.

BTW, when you suspect the kind of noise you have is coming from inside the amp you should disconnect anything from the input jack. Also rule out outside interference such as fluorescent lights.

Hello! I replaced the jack but it didn't make any difference. The noise is there with or without the guitar connected. The place that I live in its not that well isolated, but still, the problem is from the amp.

[bzblues]

I've been told that maybe I should put a Filter but I have no idea what kind of filter. Maybe this one?

https://es.aliexpress.com/item/32949654 ... web201603_