'78jmp humming loudly.Any suggestions on a fix.

[Jonathan Wilder]

Sounds like it may very well be a grouding issue...as if someone has been in there before with things apart and didn't re-ground stuff the way it should've been grounded.

Pull the V1 valve out and see if the hum disappears.

 

[bennieusmaximus]

Nope,the noise still stays ther with v1 out of the socket.Been pokin around a little bit with a chop stick and found when tapping any part of the v2 socket it makes a thumping sound.the other valve sockets do not do this.I willl probably get sone sockets and replace that 100k resistor going across the socket pins.Someone has definetly been here before.the amp has kt88's and ceramic power tube sockets.That may be all they did though.the thing worked good up untill a month ago and sounded good.I know if I can get it goin again it will be my go to amp.No ground isssues found at this time.thanks for your help I really appreciate it.Gota leave for awile taking my kids to toy story 2.

 

[Jonathan Wilder]

Nope,the noise still stays ther with v1 out of the socket.Been pokin around a little bit with a chop stick and found when tapping any part of the v2 socket it makes a thumping sound.the other valve sockets do not do this.I willl probably get sone sockets and replace that 100k resistor going across the socket pins.Someone has definetly been here before.the amp has kt88's and ceramic power tube sockets.That may be all they did though.the thing worked good up untill a month ago and sounded good.I know if I can get it goin again it will be my go to amp.No ground isssues found at this time.thanks for your help I really appreciate it.Gota leave for awile taking my kids to toy story 2.

By "ground issues" I meant that the preamp more than likely isn't properly grounded.

When you replaced the filter caps, when you did the one under the board did you jump its negative to the chassis AND connect a black wire from the preamp filter cap negative to the ground buss on the back of the pots?

 

[bennieusmaximus]

When I replaced the cap that the board covered there was only one wire going to ground,and that was the ground for the cap.No other ground was going to this point.Should I put a ground from the preamp cap to this point?This noise was an issue before the caps.I decided to replace the caps even if this didnt fix the problem.Figured it needed it anyway.plan to do the same to th JMP combo also.

 

[bennieusmaximus]

Ok,so I looked at the schematic and took a ground wire from the ground buss that goes all the way across the rear of the pots and took it to ground.took the loud humming away.Now only vol 1 has some buzzing when turning it up loud,but that was there when I got it.any suggestions on that would be helpfull also.thanks for the help.

 

[Jonathan Wilder]

Ok,so I looked at the schematic and took a ground wire from the ground buss that goes all the way across the rear of the pots and took it to ground.took the loud humming away.Now only vol 1 has some buzzing when turning it up loud,but that was there when I got it.any suggestions on that would be helpfull also.thanks for the help.

You're never gonna get an amp to be "completely 100% hum free" at high volumes. Some hum at loud volumes is unavoidable and that's just how it is. But it sounds like you killed your ground hum issue which is good.

 

[bennieusmaximus]

Yea I just clipped the cap off vol 1 pot and that noise just went away also.

 

[Jonathan Wilder]

Yea I just clipped the cap off vol 1 pot and that noise just went away also.

Yeah that will kill some brightness but in all honesty those amps are WAY bright with that cap installed anyway. Lots of people pull them off.

 

[charveldan]

Works wonders.

 

[bennieusmaximus]

charveldan,You were reading my mind!Any tone sucking or any other issues with these?

 

[charveldan]

charveldan,You were reading my mind!Any tone sucking or any other issues with these?

No issues, good pedal, i use it upstream of my Wylde OD & OCD, the sensitivity threshold works well, if you have a very faint clean signal you might have to back off the knob a touch.

I use the Wylde OD for most rock and use the OCD as a clean boost, the ISP works well, got mine off Ebay.BTW there a hum without the Gate with the OD pedals on, but if your jamming nobody will know.