# Hum...not from my guitar?



## bcmatt (Aug 25, 2007)

So, I guess people really get sick of questions about hum, but I thought I would throw this out there.
I built a Ceriatone clone of a Matchless DC30. I am quite pleased with the sound, however, I notice a light humm (which is light enough not to bother me). It gets louder as the amp is turned up, but still not bad. 
Now here is the thing; it gets noticeable when my guitar is plugged in and take my hand off of the strings or metal volume knobs. Then when I touch one of them again the hum is very very quiet again. I had been blaming this on my J5 Telecaster which has a lot of metal on it. However, I had a guy from my church band playing it yesterday with his new Les Paul and he was getting the same thing.
Now, it isn't so bad and if you told me that it would never be fixed, I could accept it. However, I am wondering if this may be linked to the fact that I didn't use a drill to wind my heater wires, so they aren't nearly as tight or even as good amp builders get. You can kind of see them as the red and black twisted wires in this picture. As you can see, there is a lot blocking access to the tube sockets now, but I could be convinced to go in and and reinstall heater wires eventually, if your collective wisdom convinces me that this is likely the culprit. Any thoughts? them.


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## Wild Bill (May 3, 2006)

bcmatt said:


> So, I guess people really get sick of questions about hum, but I thought I would throw this out there.
> I built a Ceriatone clone of a Matchless DC30. I am quite pleased with the sound, however, I notice a light humm (which is light enough not to bother me). It gets louder as the amp is turned up, but still not bad.
> Now here is the thing; it gets noticeable when my guitar is plugged in and take my hand off of the strings or metal volume knobs. Then when I touch one of them again the hum is very very quiet again. I had been blaming this on my J5 Telecaster which has a lot of metal on it. However, I had a guy from my church band playing it yesterday with his new Les Paul and he was getting the same thing.
> Now, it isn't so bad and if you told me that it would never be fixed, I could accept it. However, I am wondering if this may be linked to the fact that I didn't use a drill to wind my heater wires, so they aren't nearly as tight or even as good amp builders get. You can kind of see them as the red and black twisted wires in this picture. As you can see, there is a lot blocking access to the tube sockets now, but I could be convinced to go in and and reinstall heater wires eventually, if your collective wisdom convinces me that this is likely the culprit. Any thoughts? them.


Your pix didn't work!

The hum sounds like standard hum pickup from all the power wires in the walls and everywhere today. In the old days amps had ground reverse switches that often would give a position where the hum pickup on the guitar strings was minimized or totally quieted.

Modern amps using a 3-wire cord don't have this problem. The green wire in the cord grounds the chassis back through the power cord to the master ground of the house wiring.

Does your build use a 3-wire cord? Is the green wire grounded to the chassis?

Now, what about the input jack? Is it directly grounded to the chassis or is it an insulated jack that carries its ground back to the preamp area of the board?

Does the circuit ground eventually get grounded to the chassis maybe back at the filter caps in the power supply or do you have the entire ground return "floating" from chassis ground? If so, this would definitely cause the problem!

As Johnny five said in the movie Short Circuit: "More Input!":smile:

:food-smiley-004:


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## bcmatt (Aug 25, 2007)

Hmm, you can't see the picture? Oh well, it's not important. It's on my building blog anyways:
http://yeomansinstruments.blogspot.com/

My power chord is 3-pronged and it is grounded directly to the chassis right by the PT.

The (insulated) Input Jacks are also all ground wired directly to a rail along the front side of the preamp turretboard (several wires are grounded to this rail) which is wired to the chassis by the PT. Where several other wires are grounded from everywhere as well (including the filter caps). So, it is eventually grounded as well, with nothing in the way. It seems pretty direct to me for grounding.
Assuming that I followed the layout exactly without human error, this is the layout:
http://ceriatone.com/images/layoutPic/matchlessLayout/DC30Ceriatone.jpg

So, do you doubt that it is my less than tightly twisted heater wires?


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## Wild Bill (May 3, 2006)

bcmatt said:


> Hmm, you can't see the picture? Oh well, it's not important. It's on my building blog anyways:
> http://yeomansinstruments.blogspot.com/
> 
> My power chord is 3-pronged and it is grounded directly to the chassis right by the PT.
> ...


Those links worked! And I don't see any obvious problems.

It could be a number of things. The layout is doing the right "star ground" thing, where a common ground for a stage is brought directly back to the common ground for all the filter caps in the power supply, and the chassis ground.

First thing is to unplug the guitar cord from the amp and listen. That will tell you if a lot is being brought in from the guitar.

If it is coming from the guitar, this isn't unusual. Lots of guitars pick up some hum, even brand new ones. There is a website called Guitar Nuts that has some great info about this problem and advice on how to rewire the ground scheme in a guitar to make it quiet as a mouse!

Might be worth a look.

:food-smiley-004:


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## bcmatt (Aug 25, 2007)

Hey, thanks Wild Bill!
So, i unplugged the patch chord from the amp and cranked it and it is pretty quiet. Plugging in the patch chord adds that bit of hum. Then plugging in the guitar adds that extra hum that is louder. Then if I touch the guitar in the right spots, it quiets down to that patch-chord-only volume. 

So, that means I will do some reading on the Guitar Nuts website. I have now bookmarked it and will look into it these next few days. Thanks for the help.


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## Phil Lament (Sep 4, 2006)

If you touch metal on the amp, is it the same as touching the guitar? If so, your amp isn't grounded. Check power cord ground wire for continuity. Or maybe house wiring?


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## Soupbone (May 17, 2007)

*could be*

In the old days I once rewired/configured/sheilded a guitar 4 times because of a stupid traffic light on the corner.

In the end it was the most quiet guitar at the studio, but in that room/house it still had that noize!

Could be anything, the floor of the room, the next door neighbors aquarium, If it doesnt bother you I'd let it go.


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## bcmatt (Aug 25, 2007)

Phil Lament said:


> If you touch metal on the amp, is it the same as touching the guitar? If so, your amp isn't grounded. Check power cord ground wire for continuity. Or maybe house wiring?


Uh Oh. I'll have to look into this. When I touch the amp's metal toggle switches, it seems to stop the hum the same as touching the guitar. I'll look into this some more.


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## Phil Lament (Sep 4, 2006)

Any luck with the hum?


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## bcmatt (Aug 25, 2007)

I haven't really had much time to worry about it lately. But you know, I haven't noticed it in a while. It's certainly not a serious issue. 
I was going to try touching the amp while not wearing the guitar and see if it still quiets down. I'll try that tomorrow if I can get it to hum first.


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