Major hum

jjucius · Post by **jjucius** » Sun May 26, 2013 10:37 pm

I get hum and squeal from my dumble build with no guitar pluged in and the tone of the hum changes as I turn the presence control. I just cant figure it out. it's probably staring me right in my face. but any help would be appreciated.

amplifiednation · Post by **amplifiednation** » Sun May 26, 2013 10:45 pm

Pull the negative feedback off of the speaker jack and see if it continues

jjucius · Post by **jjucius** » Sun May 26, 2013 11:38 pm

It quits when I do that but the sound is nasty

ayan · Post by **ayan** » Mon May 27, 2013 12:10 am

This is a possibility: if you had the feedback loop backwards, maybe you had positive feedback which would explain the squealing. You pulled the loop and the squealing stopped but the sound was nasty because the amp is running open loop -- I do not like that sound either. Get the feedback from the other side and you may get the negative feedback you need around the power amp -- you may have the ground and lead reversed on the speaker jack, or you may have been feeding the feedback to the wrong side of the PI.

Gil

jjucius wrote:It quits when I do that but the sound is nasty

jjucius · Post by **jjucius** » Mon May 27, 2013 1:03 am

I switched the OT primary wires on the power tubes and it did the trick (cant belive I didn't see that) now I just have some buzz but I noticed I need to clean up my grounds. also i'm using the chassis and iron from a peavey triumph 60 and the wires coming from the PT i'm using for the bias voltage has a center tap, anyone know if I should ground it or leave it hang. Thanks for all your help.

ayan · Post by **ayan** » Tue May 28, 2013 3:30 pm

You can do either on the bias winding center tap, however, know that if you ground it you'll have to modify the circuit because you will end up with approximately half of the DC than you get if you leave it floating.

Gil

PS: Glad reversing the feedback did the trick for the squealing problem!

jjucius wrote:I switched the OT primary wires on the power tubes and it did the trick (cant belive I didn't see that) now I just have some buzz but I noticed I need to clean up my grounds. also i'm using the chassis and iron from a peavey triumph 60 and the wires coming from the PT i'm using for the bias voltage has a center tap, anyone know if I should ground it or leave it hang. Thanks for all your help.

JazzGuitarGimp · Post by **JazzGuitarGimp** » Tue May 28, 2013 4:31 pm

Major Hum and Colonel Buzz are from the same battalion you know...

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