Trouble Finding Ground Hum Problem (Pics)

[railhead]

First off, this is my first ever build, so the organization and soldering "technique" leave much to be desired.

That said, this is a simple AB switch and it works 110% perfect -- until I plug in 9v DC. When I do that, it hums like there's no tomorrow. Since I used insulated jacks, I took a ground and put it underneath the nut of the LED bezel. What else do I need to do? Could I have screwed up the DC jack (I actually melted part of it)? Here's a pic (be nice!):



I just noticed one of the legs of the black wire looks like it's not secured, but the hidden side is smoothly soldered.

Where did I screw up?

[syndromet]

 

I took a ground and put it underneath the nut of the LED bezel.

Try removing that connection. Bet that will help you some. As long as you're only using 9v to power the diodes, you don't have to connect the power ground to the signal ground, and you should reduce your chances of getting groundloops.

[railhead]

I'll try that in a second -- but what if I want or need to use it without power? Will it still be grounded since I'm using insulated jacks?

[railhead]

Nope, that didn't do anything -- still hums like a motherscratcher.

[oskar]

1. The topmost signal wire runs close to the DC-input wires. Fold them away from eachother.
2. I'd connect the DC- to ground. Also having ground electrically connected with the metal parts of the case would be a good idea.

[CGDARK]

Do you use this to AB two amps? If yes, the ground loop may be produced by the amps and your power supply not by the box.

CG

[railhead]

Yes, this pedal is splitting 2 amps.

How would go about resolving that loop issue, then?

[CGDARK]

First, test the box using just one amp. If no ground loop, then you know that the ground loop if from the amps. To avoid that, you will need a circuit with a transformer on one of the outputs. This will cut the hum very efficiently. Check the ...updated hum free splitter/A/B/Y   at http://www.geofex.com/ to give you an idea of how it is done.  You will only need one buffer and one transformer circuit. If you need help let me know.

CG

[GibsonGM]

Are both amps plugged into the same power circuit? (wall outlet).  They should be.
+1GCDark

[railhead]

Okay, here's the breakdown...

1. Both amps are into the same power strip.
2. With no 9v, the pedal works perfectly.
3. Send to 1 amp with output A, leaving output B empty. Add 9v. If the used output jack (output A in this example) is the active one, I get the hum -- switching to output B (the empty jack) kills the hum. If I do the same thing using output B, I get the same result, so basically, the output that has a plug inserted hums when activated. So, when both are plugged in, I get constant hum.

Could it be the power jack, since I kinda melted it? Did I hook it up properly with the center lug going to the switch? What's the middle lug used for (anyone know where there's a layout explanation for one of these, BTW?)?

Ideas?

TIA,
Maury

[CGDARK]

Could it be the power jack, since I kinda melted it? Did I hook it up properly with the center lug going to the switch? What's the middle lug used for (anyone know where there's a layout explanation for one of these, BTW?)?

Ideas?

TIA,
Maury

The dc jack is wired correctly. I just emailed you the diagram.

CG

[CGDARK]

I think the problem is in the switch wiring. I'm doing a tracing of each wire and I will let you know what the findings are.

CG

[CGDARK]

The switch wiring is OK. The only thing that I found is that the power ground is not connected to the signal ground. I know that this (sometimes) don't need to be tied up, but just to be sure test the box joining the two grounds at the center pin of the switch.

CG

[railhead]

You'll have to bear with me since a total n00b...

Which lug is "power ground" -- the center (unused) lug on the DC jack? I thought the "big" lug in the middle of the jack was/is the power ground(just wanting to clarify).

The "signal ground" is what's already coming from the switch's center lug, right?

So, if I'm understanding correctly, I need to try putting a leg between the large lug on the DC jack and the center pin on the switch?

[railhead]

SWEET -- that fixed the hum!

Now let me ask this: WHY?!? I was making my version of the Fulltone AB Switch and he didn't do that:

[railhead]

Okay, there's one more hum issue that has to have something to do with grounding: there's still a very slight hum/buzz in the background, and when I touch the top of the switch with my finger, it goes silent.

Do I need to go ahead and run a leg from the signal ground to the shell like I had before?

[MetalGod]

Try powering the pedal with a battery instead of the external power supply - I reckon that would give you less hum.

Also, it's 99% certain to be ground loop hum and your layout can't fix that.  Try removing the ground connection on one of the jacks - that will break the ground loop.  If that doesn't fix it you're gona have to make RG's isolated A/B box.  I made his old opamp version and it worked very well - the new transformer version is suppposed to be better again.

[CGDARK]

Okay, there's one more hum issue that has to have something to do with grounding: there's still a very slight hum/buzz in the background, and when I touch the top of the switch with my finger, it goes silent.

Do I need to go ahead and run a leg from the signal ground to the shell like I had before?

Sorry, but I was out for a moment. Yes, you can try it.

CG

[slacker]

Do I need to go ahead and run a leg from the signal ground to the shell like I had before?

yeah that should do it.

[railhead]

I'm at work now (ugh) so I can't try this -- but I'll give it a go when I get home.

But why does my version need this extra "work" if the Fuller's didn't (seen in the pic above)? The only thing I'm doing different is using the insulated jacks -- so I can see why I need to run a ground from the signal ground to the shell. But why do I need to tap the DC jack onto the switch if he didn't?

Thanks again!
Maury