Shielding a Hollowbody Bass

[Gilmourisgod]

I'm in the works on a hollowbody bass build, more or less a modded copy of a Ric 4005, and it occurs to me I have no idea how to shield it. It will have two single-coil pickups, so I assume I'll get some hum. I have two fairly large cat-eye F Holes, and a rear control cavity cover plate, so acess should be pretty good. My first thought is to get some thin sheet brass, braze or solder it together and build a little box to house the pots and at least some of the wiring, but somebody must have done this before. Suggestioms? Examples? I seem to recall some oddball basses out there with a similar "box" approach, but most hollowbodies I've seen were just unshielded. And Noisy!

 

[ctmullins]

Hey G! I’ve done this once or twice. First, shielding won’t address single-coil hum. It will address electrostatic buzz. Even though it’s nearly impossible to build a complete Faraday cage that fully encloses your electronics, you can still achieve significant noise reduction by shielding as much of the underside of the top as you can. Make sure it’s properly grounded of course. Also use shielded wire to connect everything, and make sure its shield is also properly grounded.

Or just install EMGs…..

 

[Aloe]

ime the only thing you can do is to shield under the pickups. then if it's still noisy, the next step is replacing the pickups, it can be a massive difference.

 

[Gilmourisgod]

Yeah, the few YT videos I've found adressing the subject seems to weigh heavily on using shielded coax wire, wih no attemt to create a shielded "box" within the body. I can think of several ways to do that, (the esiest to simply create a wood enclosure inside the body that can be copper foil lined) but it might make any future attempts at wirng, like swapping pickups, nightmarish, trying to pull wire in and out of the "box".

 

[Gilmourisgod]

D'oh! Idiot Alert! I had forgotten that the Retrovibe Toasters I bought for this build are HUMBUCKERS. This is what happens when my bulds go on "hiatus" for 6 months... I forget stuff.

Retrovibe Replacement Hot ’69 Rickenbacker® Style Toaster® Humbucker Pickup 4-wire for coil tap – Retrovibe

Do I need to do any shielding with these pickups? Maybe shielded wire is more than enough? Figuring out how to wire these to their maximum potential is a bit of a mystery to me so far, have to find a good idiot-proof diagram....

 

[Aloe]

Do I need to do any shielding with these pickups?

no experience with exactly those, but I've experienced noisy humbuckers in an archtop guitar. shielding improved things a bit, but a set of Duncans made it silent.

so... it depends. it might be not required or might improve things.

 

[ctmullins]

Humbuckers address 60-cycle hum, not electrostatic buzz.

Shielding addresses electrostatic buzz.

You really need both.

I say start with the shielded wire and see how bad it is.

 

[Matt Liebenau]

The thing with making shielded wire as effective as possible is to do everything with shielded wire. The connections to any switches, between pots, to the output jack.

 

[BassicJazzy]

My Ovation Elite Acoustic has a box to shield the electronics, and even the battery is held in separate closed metal box. Of course, that's just a piezo p'up.

 

[klyph]

The danelectro basses from the sixties had the pots and switches enclosed in a “pouch” made of copper tape stuck to the underside of the top or the pickguard. They even touted this with a sticker on the headstock that read “totally shielded”. I don’t know if they tried to shield the pickup or not.

I wonder if it’s possible to make a faraday cage inside a hollow body out of chicken wire or something similar? I guess that would have to be deployed early on in the build…

 

[klattman]

The thing with making shielded wire as effective as possible is to do everything with shielded wire. The connections to any switches, between pots, to the output jack.

Worked for me using shielded wire and grounding all shield and using on all connections. Made my guild starfire dead quiet. Unbelievable considering the hum before my fix made it unusable (you could hear it while playing and it created interference with notes being played).

 

[Basvarken]

On my semi-acoustic long-scale bass that the Czech company BaCH built they painted everything on the inside with shielding paint.
The bass doesn't have a controls cover on the back. So they really went in the F-holes with a brush and painted as far as they could get ;-)
They even painted inside the upper F-hole, where no wiring or electronics are. Most likely to make it look symmetrical ?

 

[micguy]

Hey G! I’ve done this once or twice. First, shielding won’t address single-coil hum. It will address electrostatic buzz.

This has been said here a couple of times, but really it can't be said enough - no amount of shielding will make a soloed single coil pickup quiet. To make a quiet bass, you need hum cancelling pickups AND good shielding.

 

[alexclaber]

and a rear control cavity cover plate

I really wish all hollow body basses had this!!!

Have you considered a dummy coil for noise cancellation? I was chatting with someone recently who swapped some humbuckers for single coils in his bass (so it has a mix of humbucking and single coil pickups) and he put a dummy coil in the cavity on a push-pull pot. Rather cunning!

 

[micguy]

My Ovation Elite Acoustic has a box to shield the electronics, and even the battery is held in separate closed metal box. Of course, that's just a piezo p'up.

One of the most bizarre things I ever experienced was an active guitar I built that, at one point, had radio frequency interference issues. I lived rather close to a huge AM radio antenna farm, and one day, I had AM radio coming out of my (previously silent) guitar. Oddly, it was far better sounding than most AM radios - very good fidelity of the unwanted signal. The thing didn't have too many components, but at one point I had changed them all, and the AM radio persisted in coming through.

So I tried (in desperation) a different battery. Silence. Swapped the battery back and forth a couple times so be certain, but yes, somewhere in that battery was a poor contact acting as an RF detector. If you're trying to shield against interference (electrostatic and.or RF), yes, even the battery should be shielded. Another takeaway is that and active bass has to be done right, or someday you may have RF issues - active electronics (and batteries) can be RF detectors, passive circuits don't do that.

 

[micguy]

Have you considered a dummy coil for noise cancellation? I was chatting with someone recently who swapped some humbuckers for single coils in his bass (so it has a mix of humbucking and single coil pickups) and he put a dummy coil in the cavity on a push-pull pot. Rather cunning!

For a dummy coil to work well, it needs to be matched in terms of hum pickup and impedance to the pickup. There is a way of doing this that gets a you an essentially perfect match:

 

[BassicJazzy]

For a dummy coil to work well, it needs to be matched in terms of hum pickup and impedance to the pickup. There is a way of doing this that gets a you an essentially perfect match:

View attachment 7312746View attachment 7312747

Everything about this bass is so cool it just blows my mind. From the rear mounted second p'up to the through-body stringing, but the capper is the position markings on the side of neck. Awesome!

 

[scuzzy]

I have done shielded wire on a friend's semi hollow guitar, with humbuckers, and it worked great.

 

[Aloe]

So I tried (in desperation) a different battery. Silence. Swapped the battery back and forth a couple times so be certain, but yes, somewhere in that battery was a poor contact acting as an RF detector. If you're trying to shield against interference (electrostatic and.or RF), yes, even the battery should be shielded. Another takeaway is that and active bass has to be done right, or someday you may have RF issues - active electronics (and batteries) can be RF detectors, passive circuits don't do that.

hm, interesting, I might revisit one bass that's still picky to some EMI, probably the one from high voltage lines.

if I have a separate battery box, should I shield the wires in between it and control cavity?

 

[micguy]

Everything about this bass is so cool it just blows my mind. From the rear mounted second p'up to the through-body stringing, but the capper is the position markings on the side of neck. Awesome!

When a Physicist/Engineer/Bassist builds a few basses, gigs with them constantly, and tweaks ad nauseum, eventually interesting solutions to various problems pop up.

I play on some very big, dark stages (at least in the back where I am - the singers being far way from us means we don't get much light when the lighting is "moody" - the position markers are a lifesaver at those times.