First Build JRM-1DC Single Coil -- ColinS

14/11/2022 Box Open, start trial fit, nice wood but neck fit will need work.

Went through trial fit. All went together. Neck was tight at first but next day fitted well after getting used to being in the warm.

It has a single P90 with a Tune O Matic style bridge, but unlike the video of scale lengthe measurement there is no tail piece, the strings lock directly into the bridge.

I read Gibson uses a principle like this too on its cheaper models, but wider . But a purist would worry that the strings will meet the individual little "nuts" at a very high angle so time will tell whether there will be short string lives. But , hey I bought a $199 kit that was on sale not a Gibson!

Also the "half scale length" --Headstock nut to crown of 12th fret-- is 313mm
The "half scale length" --crown of 12th fret to individual "nut' on the bridge --can be 313mm but only at at full extension . That is , there is no scope for adjustment. Hopefully that's OK.

Ready to start sanding and Tru Oiling it. Nice looking piece of wood so hope I can keep its initial appearance

Is the neck too tight or too loose? If tight, you could wait a bit as often the neck fit is tight after temperature and humidity changes in transport. Make changes now and you may find that things become a bit too loose in a couple of weeks (though it might stay as it is).

If loose, it's a question of how loose. You'll be adding layers of finish to the neck so you don't want a fit now that's very tight or you won't be able to fit it with the finish on.

If it's a question of getting the end of the neck pocket curve to match the end of the neck curve, then I use chalk on the end of the pocket, fit the neck and then remove some wood where there's a chalk mark until the chalk is fairly even across the end of the neck.

You can also use carbon copy paper to do the same thing.

Thanks Simon. It magically fitted later in the day. Your suggestion of humidity etc. Most likely

It will probably get a bit looser then after a couple of days.

One thing that you might want to check is the height of the bridge. The supplied kit bridge is very tall and recent JRM-1 builders have found that they can’t lower the bridge enough to get a good string action. The saddles on the bridge are a lot taller than really necessary which doesn’t help the situation. Lightly clamp the neck in place (if you don’t want to screw it on yet) and run a metal straight edge from the 1st feet to the top of a saddle when the bridge is resting on the body. With the inserts and posts in (don't fit the inserts until the finish is on) I think you can get the bridge sitting almost right on the body so you might just want to stick a bit of card about 1mm thick under the bridge. That will give you an idea of the likely minimum string action you can get. You might be fine, you might have a big gap at the 12th fret.

If it turns out the action is high, the normal quick fix for this is a shim in the neck pocket. This is fine on most guitars, but the fixed height dog-ear P90 is then a long way from the strings, resulting in a relatively weak output lacking in bass.

You can buy or make a shim for the pickup to raise it up from the body to get it nearer the strings. Or you could get a replacement soapbar P90 pickup, which should fit nicely in the pickup rout and which is height adjustable.

You can buy a replacement wrapover bridge. These come in various flavours, from the original (Gibson) plain stoptail, a stoptail with fixed intonation compensation ridges, a similar ridged stoptail but with a moveable section (Wilkinson) for better intonation or a lower height wrapover bridge with fully adjustable saddles.

Or you could complain to Pit Bull. The kit originally came with a set-neck which had a bit of an angle to it which suited the tall bridge (the first picture on the PB website of the kit shows a set-neck body, the rest of the pictures are of a bolt-on). Then it changed to a bolt-on neck. But bolt-on necks almost always sit parallel to the body, and that bit of neck angle has been lost. Unfortunately the I assume the bridge selection wasn’t changed with it.

Quote:

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Originally Posted by ColinS

Also the "half scale length" --Headstock nut to crown of 12th fret-- is 313mm
The "half scale length" --crown of 12th fret to individual "nut' on the bridge --can be 313mm but only at at full extension . That is , there is no scope for adjustment. Hopefully that's OK.

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I'd be making sure there was some scope to extend 316mm from the 12th fret to the nut particularly at the point where the 'Bass E' would touch the "nut' on the bridge...The treble E would be fine at 313mm

As the bridge post holes are already drilled, there isn't really any scope for moving the bridge, so you are reliant on the bridge having it's own means of intonation. As well as moveable saddles, there are normally two screws at the rear of the bridge that press against the posts and will physically move the bridge backwards to assist intonation if necessary. With moving saddles, this shouldn't be necessary. I don't like to use them if at all possible as they make the bridge more prone to wobble.

I did forget to mention in my types of replacement bridge that the plain stoptail bridge needs the bridge at at angle, with the bass-side post hole about 4mm further back than the treble. The kit looks to have the post holes equidistant from the pickup rout, so isn't suitable for the JRM-1. If you do think about a replacement, check whether it's designed for angled or straight installation.

Many thanks, Simon.

I'm not super happy with the bridge generally. The angle of the strings from the anchor points to the notches is very high, higher than Gibson uses on it original design, I expect broken strings , we'll see!

Ill check the points you raise when I get the neck on, I've just finished Tru-Oiling and am giving it a week in the warm before I assemble. I like the wood parts but in retrospect wish I'd had a closer look at the mechanicals.

Thanks GavinI393,

I dont think I can get 316mm on Low E (12th to bridge nut) without plugging and redrilling bridge fixing hole further out,

Ill double check this when I assemble again when oil has cured/dried fully. Then Ill have a word with Pit Bull if it is deficient.

If the low side of the bridge needs to move back a bit to intonate the low E string, then there is that grub screw adjustment available on the rear of the bridge. Though I prefer not to use it, and just move the saddles, it can give up to 3mm extra adjustment.

It’s probably what Pit Bull will also say.

The need (or not for copper shielding of cavities

I am about to wire up my single P90 pick up and the two potentiometers on my JRM 1DC.

I notice that none of the Pit Bull instruction videos (which all deal with more complicated electronics,multiple pick ups/switches and potentiometers) show any attempt to line the cavities with copper to reduce hum.

I can understand this given that the connecting leads supplied with the kits are of sheathed wire. But copper sheet is advertised and Ive bought a quantity.

What is other people's experience , have you found copper sheet shielding useful, needed or an unnecessary complication?

Thanks.
ColinS

Ah, Ive put the copper in anyway. its a bit like wallpapering a ceiling, hard to do neatly but it does flatten down eventually. Ive soldered an earth lead to the copper in the pick up rout and led that back to the pot rout. see how that goes.

I must admit the guitar does look pretty fabulous with 13 coats of Tru Oil.

Any one got any experience with the twin humbucker Les Paul style model with the pick ups and bridge offered as standard??

It is useful, especially with single coils and even more so with P90s with their large wide coils.

It won’t stop all hum, but it can cut down the level quite considerably.

But to be effective, the copper needs to be grounded and it needs to enclose as much of the electrics as possible. You can’t do too much about enclosing more of the pickup cavity than just the bottom and sides, but in the control cavity, you can also stick it on the underside of the cavity cover. On guitars/basses with pickguards that mount or surround the pickups, you can cover the underside of the pickguard as well.

The copper will be automatically grounded where it touches the pots, but for separate pickup cavities, you’ll need to run grounding wires out from already grounded shielding areas. I use thin wire and stick the bare ends down with more copper tape. For cavity covers and pickguards, you can ground by copper to copper contact, which means running the foil up and over the cavity recesses, and for pickguards, over the top of the body, but underneath the pickguard so it can’t be seen. Ideally run it on pickguards to screw areas so the copper surfaces are firmly held together at those points. Large areas of plastic tend to warp slightly, so trusting to a couple of small areas in the middle of a pickguard to make contact isn’t the most reliable of methods.

Because the shielding is grounded (it really doesn’t do much for noise if it isn’t) then beware of signal wires touching it with the result of no audio output. A single loose whisker of wire can result in silence. So be careful with your soldering and minimise the amount of exposed signal wire. Use heat shrink where possible. Use insulating tape over the foil where contact may be made once you put a cover or scratchplate on. Especially take care around the jack socket area as the spring contacts will move outwards when a plug is inserted, so it’s often safest to avoid shielding the hole around side-mounted jacks (and definitely use insulating tape in Strat jack socket cavities).

If you need more copper foil, you can find cheap rolls of shielding tape around 25-30mm wide on eBay or Amazon if you can’t find it locally. Also sold as slug-repellant tape (same product, different name). Just make sure it has conductive adhesive. The majority of tapes do now, but don’t assume and avoid anything that doesn’t state it explicitly, otherwise you may need to solder the strips together to get continuity.

And best to use a multimeter to check for continuity between strips. Even with conductive adhesive, I’ve sometimes had to run a crosswise strip of tape over the top of overlapping parallel strips of tape in order to get continuity from one end of a pickguard to the other.

Regarding copper foil... I ordered a custom pickup one time and for some bizarre reason didn't get them to pot it in wax. (it was an option...) (D'oh!)It was taking off uncontrolably at times with undesirable feedback. I used copper foil to shield the pickup cavity and a portion of the pickguard (strat style). When I play it live it helps with squealing while leaving a reasonably resonant and open sound (jury's out for me on how potting a pickup affects the tone).

Without doing before and after tests you’ll never know exactly how potting affects the tone of a particular pickup. A lot will depend on just how the pickup was wound as to the degree of microphony a pickup has to begin with. I have seen some videos of before and after tests on humbuckers, and there was a difference, but very slight and far less than the difference you could get by changing the speakers in your amp.

If you assume that the coil wires are held tight at the ends of the coils so they can’t vibrate there, then the maximum single length of wire free to vibrate is in the order of 50mm or so, which will be less in most instances due to wires crossing over each other. So a very short vibration length. The wire tension won’t be anything like as much as a guitar string, but the wire is so very thin its mass per unit length is very low. It all results in a high-pitched resonant frequency. At low volumes/low gain, you’ll have a number of lengths of coil wire resonating in sympathy with higher string harmonics. As this coil wire is moving in a magnetic field, it induces a small current in itself which will add a very small amount of higher frequencies to the basic pickup sound.

Turn up the volume and/or increase the amp gain or add in a drive pedal and you can get enough acoustic feedback going for those loose turns to continue to resonate, even when you stop playing. So you get that uncontrollable high-pitched squeal that’s now unrelated to any note you are playing.

Wax pot the pickup and depending on the degree of wax potting, the coil turns are either completely stopped from moving, or just some of them are. So partial wax potting (it all depends on how long you leave the pickup in the wax bath for the wax to penetrate the windings) can give some extra high-end air to the sound and allow louder volumes and more gain before feedback occurs, whilst full wax potting allows all-out loud metal mayhem.

With a high degree of scatter winding and a high wind tension you can get unpotted pickups that remain squeal-free until you use very high gain levels. The more the wires cross each other, the shorter the lengths of wire left free to vibrate. The higher the tension, the higher the pitch and the smaller the amplitude of the vibration will be. So you can push the resonant frequencies up to areas where the guitar speaker is falling off in frequency output, and the resonant signal is less anyway, and you can generally make them squeal free up to loud volumes and/or gain levels.

The trouble with high-tension winding is that the wire is far more likely to break in the process, so it's not something you'll get that often from large-scale pickup manufacturers. So they will generally pot their pickups just to be sure.

It is fairly easy to wax pot or re-pot your own pickups. You just need a temperature controlled heating bath and a ideally a mixture of 90% paraffin wax and 10% beeswax (or so I've read). There are plenty of cheap body waxing heating baths available on the internet, you just need one big enough to drop a pickup into. Temperature control is important as you just want the max above its melting point. Too much hotter and you can damage winding insulation and the plastic on the bobbins.

You'll need to carefully remove any tape wound wound the coil before dipping, (so you'll need to get some more to replace it afterwards). It's then basically a question of immersing the pickup in the melted wax and waiting until all the small bubbles of displaced air stop appearing. Then pull it out and wipe off the excess wax and let it cool. Always wear protective water/wax-proof gloves as the wax is hot and will burn!

Just finished and played this guitar, enormously pleased with it. Haven't yet checked intonation but like playing it.

I ain't pretending that its as good as the v expensive American Fender Tele I sold recently because that guitar was a pointless extravagance given my lack of skill, but this simple single P90 guitar does the job well enough for me -- so far.

I'm sufficiently pleased to have just ordered the twin humbucker single cut mahogany body kit. But this time I ordered it with the Grover tuners and bone nut in anticipation that it may be worth upgrading ancilliary parts later. Tru oil brilliant on the mahogany

7 January 2023

Ive now been using this guitar for a few weeks now. Enormously pleased. Intonation v good in spite of my earlier fears

+1 for Tru-oil looking nice on mahogany.