Noise after shielding

I’m nearing completion on my rc4 build (build diary http://www.buildyourownguitar.com.au...ead.php?t=8523 here) and had the bass wired up and working... spent about a week noodling around on it with a great deal of satisfaction! The only issues were when the switch was selecting both pick ups there was a slight dip in volume and also with both pups selected, when either volume pot was zeroed it killed all sound (below last 10% of travel). The tones were clean and clear and good differentiation between pups.

Since then I have stripped it down to give it another couple of coats of oil, waxed it and copper taped the control cavity, both pup cavities and the back of the scratchplate.

Once I reconnected everything there is a lot of noise unless both tone controls are zeroed. If the switch is set to both pups either tone pot can be adjusted without noise but as soon as the second gets moved - noise. The same volume issue as before occurs when zeroing one or other volume pot with both pups selected.

Wiggling the lead in the jack socket reduces but does not eliminate noise. I’ve rewired this with new wire with no improvement. I’ve also replaced all other hot wires and checked all connections for connectivity. All cavities are soldered together and there is connection amongst all cavities. The wiring is the same as here although I have the volume pots closest to the strings and the tones at the bottom as this makes more sense to me.

I’m considering replacing the jack socket and all pots but any ideas what’s causing these issues?

Thanks

Dave

Had very similar issues, in one case I had a stray earth, had used shielded wire and one of the hots wires was intermittently earthing out, in the other the bridge earth had come lose. Wiggling the lead, if your touching the metal of the jack will reduce the noise as your effectively becoming a conduit to earth.

If you have a multi meter I'd start by checking everything you expect to be grounded is, and there is no stray wires, solder between pot connections.

Almost every wiring problem is an earthing issue somewhere, so Rossco is on the money for start points.

It is possible to kill the kit pots with too much heat. I've wrecked a few bits and piece via multiple wiring attempts. I've also had the jack just up and fail - the insulation between the earth and hot connectors isn't amazing. My local guitar shop sells pots and jacks for around $3-$4 for ones similar to the kit or you can lash out for some Real Parts (or similar) ones for around the $12 mark (I see you are in England... so that's AUD I'm talking)

On my first build I had a few problems with the wiring, which ended up being solved by new pots.

Checking all the grounds with a multimeter is a good start. Had a similar issue and it was a hidden ground. Have you checked the the ground to the bridge/strings?

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Thanks for the replies

I’ve checked for continuity for connection of the components and foiled areas with a multimeter. I’ll check the bridge connection again...

Shielding can only do so much and is effective against only certain types of noise, but is obviously better than not having it. But it does have limitations.

I'd run extra copper tape between the control cavity and the neck pickup on both the body and under the pickguard, so they join up. I normally cover all the underside of a flat pickguard with shielding (I always think a bigger ground plane is better and helps stop interference from a wider range of angles). Unless it's a single piece of copper tape, ensure that you've got continuity to all parts of the cavity and on the pickguard.

I often find that parallel strips of copper tape with an overlap don't have continuity between all the strips, so I normally end up with one or two cross-wise strips that seem to then do the job.

I believe the neck pickup should be a mini-humbucker, so that should be silent without any shielding. If it's noisy, it's either because the signal and ground wires have got crossed somewhere, or because there's something making an awful lot of RF noise close by. Any fluorescent lights (some non-LED low-energy bulbs can give off noise) , dimmer switches, other electrical equipment nearby? Can you test in another room or even a different location?

Never hurts to check the amp mains lead ground connection or the guitar lead. The cheap lead that came with the kit should be thrown away, it is that bad! If you are using that for testing, swap to a decent lead.

With both pickups on, I'd expect a very slight drop in volume, partly as there will be some frequency cancelling from the two pickups sensing different parts of the string, and also because both pickup signals are connected together across both volume pots in parallel, the resultant effective resistance to ground of the pots is halved.

Are you testing continuity at the ring of the jack?

The best antennas for picking up RF noise are the pickups and the strings, I think. So best bet is you have a bad ground to the bridge or one of the pickup shielding wires.

I have heard a ground loop can also cause this if you have components with multiple paths to ground, but I have never actually had this problem. Best to check the easy stuff first ;-)

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I didn’t get chance to check anything yesterday but all cavities have a soldered wire connecting them. Also, when I have been checking continuity with a multimeter I’ve just been taking random points between any of the cavities and getting a bleep. Should I be looking for readings and if so what? #certainlynotapromultimeteruser

For good foil shielding, you should be reading one or two ohms at most. My experience is that if sections aren't properly connecting, then I get 'overload' indication on even the high ohm settings on the multimeter, showing no connection at all. Beeping is an indication of good continuity, so I wouldn't worry too much about sections that beep.

The other thing to check is that the foil has a good connection to ground. It should be connected to ground by the pots on the pickguard touching the foil there, and the foil on the pickguard making contact to the foil in the cavities by contact pressure with the pickguard on. Which is why I like as much overlap on the body and pickguard of foil as possible, and use all the space under the pickguard. But worth checking for a connection from the back of the pots to the foil on the pickguard, just in case the pots have some form of insulation preventing a through connection (unlikely but better safe than sorry).

Your in good company, don't worry. The great thing about these forums is that you can learn as you go.

Everything that is grounded has to get to the ring on the jack, so I think it's a good idea to clip one lead to that. The continuity that you are checking needs to be continuous to there.

Do all the things Simon has suggested with your foil. Test to make sure that everything that should be grounded is continuous all the way to the jack, by beep or very low (near 0) ohms.


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A higher ohmage is acceptable as shielding still works (supposedly) up to about 1 megohm, but I always feel that lower is better. And with copper, you should be looking at a very small reading.

Quote:

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Originally Posted by Simon Barden

A higher ohmage is acceptable as shielding still works (supposedly) up to about 1 megohm, but I always feel that lower is better. And with copper, you should be looking at a very small reading.

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That's good to know. I usually get a reading that is not 0 but very close. Never higher than 2 ohms, and usually less than 1 even using aluminum HVAC tape.



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Most low-cost multimeter leads have a reasonable resistance, and often just touching the probes together can give a 0.1-0.2 ohm reading. For a good, accurate, low resistance reading, you need a more specialised meter; but these often use a higher driving voltage so aren't ideal for delicate electronics.

I'm sure my multimeter isn't one of the best that China has ever produced but here are some sample readings... (Some took a few seconds to settle down)

test probe to probe 0.1 - 0.2Ω
Isolated foil to foil (probes about 10mm apart) 0.5Ω
Isolated oil to foil (probes about 60mm apart) 0.7Ω

With the jack socket removed from the body:
Jack ring to switch 0.4Ω
Jack ring to Bridge tone pot body 8.46Ω
Jack ring to Bridge volume pot body 8.46Ω
Jack ring - Neck tone pot body 8.46Ω
Jack ring - Neck volume pot body 8.46Ω
Bridge body - jack ring 0.8 - 0.9Ω
Bridge body - jack ring (ring connected to cavity foil) 0.7Ω
Bridge volume pot body - neck volume pot body 0.5Ω
Bridge tone pot body - neck tone pot body 0.6Ω
Bridge body - control cavity foil 0.7 - 0.8Ω
Bridge body - neck volume pot body 0.5 - 0.6Ω

all of the above registered a connectivity beep

With the guitar still open I plugged it in with a loose jack socket - still quiet with both tones zeroed, still noisy (although not as bad as before) when opening the tone pots.

Any alarm bells?

Reassembled and to recap the scenario...

Neck pup selected, tone off - ok

Neck pup selected, tone open in any position - noise

Bridge pup selected, tone off - ok

Bridge pup selected, tone open in any position - noise

Both pups selected, both tones zeroed - ok but slight volume drop. Zero either volume kills all volume (in last 10% of pot travel).

Both pups selected, either tone open in any position with the other zeroed - ok

Both pups selected, bridge tone fully open, neck tone zeroed -ok. Decrease neck volume - noise

Both pups selected, bridge tone zeroed, neck tone fully open - ok. Decrease bridge volume - noise

For all above scenarios, touch any pot spindle and get noise (no knobs fitted so far)

???

Your jack ring to pot body readings are high, indicating a poor solder joint somewhere. Those readings should be right down in the 0.4Ω region. But it's hard to understand why as the jack ring to switch reading is low when the switch is grounded from the neck tone pot, and that is reading 8.46Ω!

Can you take and post a picture of the wiring with the scratchplate off and showing all the connections so we can see exactly how it's wired now. I've been going by the build picture on the cardboard template, which obviously is missing a couple of connections.

Thanks Simon, here you go. When I originally wired it I used the colours supplied and as the Pit Bull wiring diagram but have replaced the hot wires with red ones.

Attachment 29918
Attachment 29919

For clarity, the end of the red wire connected to the switch is not touching the switch body tab.

Something's gone wrong with the photos. Can't see or link to them.

Also for info, the vol pots (nearest straight edge on scratchplate) are As and the tone pots Bs.

Going by the photos I can see and the description of the fault it looks like the signal and ground connections on the jack are reversed.

Nil sound when either volume is at less than 10% would be normal with this wiring scheme.

It's personal preference for every builder but for consistency and clarity on all my builds I prefer to use Black or Green or bare wire for all earths/grounds, with Reds and Yellows and Oranges as signal wires. And White and Blue wires for DC voltages when they enter the scene. Obviously there are plenty of times where this just can't happen or it simply doesn't matter.

Is the cap leg on the 2nd tone pot going to the outside lug instead of the middle? It looks like it may be, but it's hard to tell from the photos.

Also, is it possible the tip of the red wire poking through the switch lug is brushing the switch body tab? Again, difficult to tell from the photos. And, the hot lug on the jack looks close to brushing the copper shielding in the 2nd pic, but again it hard to tell. Plus, all the ground connections on the back of the volume pot are a touch gnarly, so there could be a bit of noise in there.

Thanks Marcel. Sorted!

heh that red wire suckered me completely Marcel... ‘ok, hot red wire to jack hot, that’s fine’ oops.

Glad it’s working. Is all the noise gone?

Yes thanks WeirdBits 😀

All controls working independently without noise... The only minor things are still when zeroing either of the volume pots when both pups selected kills all volume, and with both pups selected with both volumes fully open there is a slight volume dip compared to solo’d pups... however, I’ve noticed that if i knock the neck volume down a notch then the volume boosts back up to same volume as when either pup is maxed out. Not issues, just oddities.

The build is now officially finished (whoop!) and I’ll try to get pics up on the build diary later today.

Thanks to all of you for your help.

Mute when zeroing either volume in middle position is normal for LP style 2 vol 2 tone with switch wiring like yours. Working as intended.

No noise when one volume pot zeroed with both pickups is standard with that wiring arrangement. It's what I'd call 'Gibson' wiring and all twin pickup Les Pauls, SGs, Flying Vs etc. have the same issue. One reason there's a pickup selector switch! for when you only want one pickup on! I think the Rickenbacker wiring method prevents this, but it is more complicated circuit and needs a different type of selector switch.

The 'both pickups on' volume issue is down to phase cancellation, and lowering the output of one pickup reduces the cancellation, actually making the output louder in this instance! If the pickups were fitted in slightly different locations on the body, you'd get another set of output interactions which may result in a thinner and quieter, or louder and thicker, mixed sound. And changing the pickups for ones with different tones is also going to give a different mixed position sound.

If it really bothers you, then I'd suggest playing through a compressor, set with just enough compression to help balance the levels.