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Coil Tapped Humbuckers -> Buzz


Daniel Schmolze
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I'm trying to wire up a couple humbuckers with a push-pull pot for coil tapping. Everything seems to be working, but I'm getting an annoying buzz. It goes away when I touch the bridge or random wires in the control cavity. I'm pretty new to guitar electronics, and I'm not completely confident that I'm following the diagram correctly (http://www.guitarelectronics.com/product/WDUHH3T2206). Could this be a grounding problem? I soldered all the grounds to the back of the bridge volume pot -- this is what you're supposed to do, right? Also, for the humbucker wires in the diagram that are connected, I soldered the ends together and then soldered on a longer wire to connect to either the switch or the back of the bridge volume pot.

Thanks.

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I'd never suggest touching wires in the cavity while the guitar is plugged in. But since you're around to speak of your adventure, methinks you survived fine.

It sounds like a bridge grounding problem, to me. Single coils traditionally make more pronounced HUM than HUMbuckers, but if it were a bridge grounding problem, you'd probably hear it without switching to coil split. If this is the case, I'd check the wire (that should be) coming from your bridge/trem, and make sure it's properly grounded.

Nice diagram, btw. Dual coil tap? If I could get that to work with a PRS switching system, I'd be all set :D

There are a TON of tutorials on grounding, if you take a gander at the search feature, too.

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I wouldn't worry about the buzz. From my experience, it's normal for the guitar to buzz if you aren't touching the strings/bridge/ground circuit. But I play with my hand resting on the bridge, so I never have problems with the buzz "coming on".

I'd never suggest touching wires in the cavity while the guitar is plugged in.

If something were miswired and you got shocked inside the cavity, it would shock you anyway if you touched the strings. 1/2 watt pots at 500k aren't enough to keep 120v AC off your bridge... :D

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Does it still buzz when you're NOT touching stuff inside the control cavity? Does the hum get better or worse when you're touching the bridge/strings (assuming the bridge/strings have been added to ground)? If there's no buzz when not poking around, and the hum is reduced when you touch the strings, you've probably done it right. Otherwise, it could be a ground issue-- either a loop, or depending on the severity of the buzz you may have even wired your output jack in reverse. :D

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Does it still buzz when you're NOT touching stuff inside the control cavity? Does the hum get better or worse when you're touching the bridge/strings (assuming the bridge/strings have been added to ground)? If there's no buzz when not poking around, and the hum is reduced when you touch the strings, you've probably done it right. Otherwise, it could be a ground issue-- either a loop, or depending on the severity of the buzz you may have even wired your output jack in reverse. :D

It gets better if I touch the bridge, strings, or stuff in the control cavity, but worse as soon as I let go. I tried switching the wires on the output jack, and I got a much louder buzz, so I'm pretty sure it's not that.

One thing I'm a little confused about is the use of shielded vs. non-shielded wires, and I think this could be the source of my noise issues. Right now I have four non-shielded wires running from the pickup selector switch to the control cavity (two to the volume pots, one to ground, and one to the output jack). These should probably be shielded, right? But I'm not sure where I would attach the two parts of a shielded wire.

Thanks.

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It's rather typical to have hum be reduced when touching the strings, etc. Even humbuckers can pick up noise; adding your body to the ground (by touching the strings) offers a not insubstantial amount of shielding, which in turn reduces the hum.

In my apartment, the noise is awful. I can't use even humbuckers in a fully-shielded guitar without problems. That's just the nature of the beast in my particular living situation. You might be in a similar situation. <shrug> You're right that if the hum got worse by reversing the output jack, it was correct all along. And even though I have my coil splits set up to "cancel" some hum in tandem, the noise is definitely louder when they're tapped.

Not sure what else to suggest. I don't think you'll get appreciably greater hum reduction by shielding those 4 lengths of wire. There's all kinds of unshielded wire in most people's control cavities. If your entire cavity is shielded, you'll be better off. But it might be just your environment. Fluorescents, dimmer switches, and CRT computer monitors are all potential sources of hum-causing interference. In my case, add to that proximity to a mains junction and a phone junction box, plus proximity to a cellular network node, and it's absolutely unbelievable. I should be wearing a tin foil hat. :D

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When you use a coil-tap circuit the humbuckers are acting as single coils so of course they lose their hum-cancelling properties. I always reverse the wiring of the bridge humbucker, then when the coils are tapped, if both are selected they work together again as 2 single coils cancelling out the hum. Dies that make sense?

If the hum you speak of is an earth hum then this post is irrelevant (however good practice) and you need to see if there are any fridges, fluorescent lights or dimmer switches in the vicinity of where your amp is plugged in - as this will be the cause of the hum!

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