Reso-electric dobro kit - any improvements possible?

[Graham Bartlett]

My partner just bought me this reso-electric kit, which is basically a cross between a dobro and a Les Paul. No idea which forum it fits into, but I'm going to guess here.

http://www.guitarkitfabric.co.uk/Catalo ... r-pawlonia

The body and neck are assembled already, so a lot of the hard work has been done. Which is good for me, because in spite of the copy of Cumpiano on my bookshelf, I never did get round to building my own from scratch. :/ I'm basically picking up at the finish/paint/varnish stage. But I'm wondering if there's anything I can do to improve on it.

The body is strange. The structural part of the body blank is basically solid, routed and drilled for the resonator soundwell, pickup, controls and wiring. A couple of traditional grilles cover wells in the cutaway horns which again are not connected to the soundwell, but presumably help to lighten and balance it. And then there's a pretty arched back attached, with kind of a chamber between the back and the main body, but with no aperture to the soundwell.

I expect I'll use it acoustically as well as electric. With that in mind, is the instrument missing a trick by all these chambers being unconnected? And the top/body is only routed just enough to accommodate the resonator - would there be mileage in making that deeper, or would that just weaken it too much?

Or should I just build it as-is and not overthink it...?

[Freeman Keller]

Graham, first welcome to MIMF and second, that is an interesting guitar. I'll make a few random comments that may help you think about how you want to build it. First my (minor) credentials - I own three resonators and work on them from time to time. Mine are all acoustic and cover the three basic styles of cones

Yours is a "spider bridge" (like the one on the back right). The cone sits in a little shallow depression with a metal spider on top - the spider is attached with a single screw thru the center of the cone. The string energy is imparted to the cone thru that little tension screw (that is an important part of setting them up, but I'm getting ahead of myself).

Spider bridge resonators have the sweet singing long sustaining sound that we associate with bluegrass "dobro" (think Jerry Douglas, Cindy Cashdollar, Josh Graves). They are usually, but not always, played with a slide or "steel", but certainly they can be set up to be fretted. Like any acoustic guitar, amplifying them can be somewhat problematic - there are various sensor that have been installed in the saddle or on the cone.

Most acoustic resonators do have a hollow body and large air chamber just like an acoustic guitar, but there have been resonators built with solid or semi solid bodies (google "reso electric"). These are primarily electric guitars - they often have a lip stick or other pickup between the cone and end of the neck. The problem with that is that it is a magnetic p/u so the sound tends to be more like an electric guitar - certainly it is colored by the cone but it will be different from the acoustic guitar. It looks like your kit has an undersaddle piezo pickup as well as the magnetic - that should give you more of the cone sound.

There will be some compromises when building a guitar that will be played with a slide and fretted. Most slide players like relatively flat fretboards, most electric players like some radius. Since yours is pre fretted you'll need to take whatever they give you and radius the saddle accordingly. Most of the time resonators have very little string compensation built into the scale length - you don't stretch the strings with a slide so they don't go sharp. However if you fret them, they do go sharp. Therefore compensation becomes a compromise. Again, yours will be set for you by the location of the center of the cone - they may have shifted it (compensated) or not. If I know a little more about how you plan to play (and if you check that measurement) I might be able to help you.

Another part of the geometry that is a compromise is action height and neck angle. Slide player tend to like a slightly higher action (and stiffer strings), fretted favors lower action. I compromise with mine and set the action just a bit higher than my other acoustic guitars and run slightly heavier strings. I also tend to tune my resonators to open G or D. If you plan to tune up to A or E you may want to consider lighter strings.

Action on a resonator is largely set with the neck angle. You have a tiny bit of wiggle at the saddle but not much. My guitars all have necks that can be taken loose and shimmed to change the angle - they have neck sticks like a banjo. Your neck is "set" into the body implying to me that it is glued in like a Les Paul. That is going to be very critical to get playable action. I'm going to suggest that when you get to that point of the build that you take some very careful measurements of the guitar's geometry with the neck clamped in place and the cone in the well - that along with knowing how you want to play it will help me advise you.

My suggestions before you go any farther - put the cone and spider in the well with the saddle slot straight across the guitar. Clamp the neck into the pocket. Measure from the nut to the 12th fret and to the center of the saddle slot. Give us those numbers.

Put a straightedge on top of the frets and take a picture of the end of it relative to the saddle slot. Something like this - I have a saddle in the slot and strings on but what I'm looking for is where the fret plane hits the metal part of the spider

Lastly, tell us how you plan to string, tune and play the guitar.

[Graham Bartlett]

Thanks Freeman. I hung out here a little about 10 years back, but a child and a divorce kind of stopped any further progress in the instrument building direction! Nice collection you've got there.

I've got a National copy (Regal) myself already, so I'm pretty familiar with the basic care and feeding of these creatures. I've not had to make one from scratch before though. Mostly I use open G, although with a second instrument I might leave one in open D and see if I can get a bit more mileage on that. I use a mix of slide and fretted playing, and mostly fingerstyle.

Agreed on the neck. My Regal is not quite intonated properly for fretted playing - it could do with a shim between the body and neck (and a corresponding one on the bracing strut through the body, of course) to get that right. One of these days I'll get round to that. I had to replace the bridge shortly after I'd bought it, because the original (cheap!) one warped. Elderly Instruments were very good and posted me a new National one, but of course I had to fit that myself. Like you say, it's a compromise. I fell in love with a Gretsch Bobtail in a shop last year - couldn't afford it, of course. I may set this kit up lower though and keep it for fretted playing, so the action can drop a bit lower.

As you say, the neck for the kit is glued, so I absolutely don't want the same issues with that. The kit instructions suggest clamping and then fitting the bottom E before gluing, to help when fixing the neck in place. With my experience on the Regal, I'll be doing the top E too, checking how much the bridge/cone needs to be rotated to cover both, and gluing the neck accordingly.

All advice gratefully received!

[Peter Wilcox]

Good post by Freeman, Graham. I've only built a couple of resos and worked on a few more, all square necks, so take what I say with a grain of salt. Action is not critical on those since they're not fretted and the strings lie a cm or so above the neck. In your case, the action will be important. When you set the neck, I would measure the bridge height first with the strings off, then with strings on and tuned up. The string tension will depress the cone slightly, but I'm not sure how much. I think you should try to have about 3/8" or so of saddle above the bridge. Of course, the way they've manufactured this may dictate otherwise.

If you are planning on playing this acoustic also, I think you should try to connect the fake sound holes to the cone chamber with as large a tunnel as possible. It looks like the cone now sits in a sealed chamber, which will impede its movement and volume production, especially in the bass frequencies.

I modified a spider squareneck to electric by putting an under-saddle piezo in, and putting a preamp into the side of the guitar. It sounds OK, but has lost some of the nasal tone. I don't know how your piezo will sound without a separate preamp.

Freeman, if you have any corrections to my points, please post them.

[Graham Bartlett]

Thanks Peter.

That was my initial thought about opening up the chambers. My thought after that though was that with having built loudspeakers, I know the bass response depends on a sealed box and any ports. Passages between the sound well and the fake sound hole wells will effectively become ports. Even joining through to the chamber between the main body and the back is going to create a Helmholz resonator in the same way as a sound hole on a flat top does. (I'm an engineer, by the way. So i can see challenges with opening things up. The question I guess is whether those challenges are worth having a go at, or whether the result will screw it up completely!

[Freeman Keller]

Peter and Graham, I pretty much agree with your thoughts. My experience is with acoustic instruments - I did play a Reso-Electric a long time ago and I thought it was an interesting instrument, but frankly I wasn't all that impressed for the kind of music I play (delta blues mostly). The Res-Electric only had a mag pickup (I think it was a lipstick) and my feeling was it didn't have a lot of cone sound.

I certainly don't think it would hurt to open the area into the sound holes - they are just decoration without. All of my instruments are acoustic and approximately the size and air volume of a triple ought - how much that affects the sound is really hard to say. I do know that there are different internal designs for spider bridge instruments - sound wells that go to the back of the guitar vs some that are more open - and people hear a difference. I don't know what to expect with this one.

I continue to be concerned about the set neck on this one. Once that is glued in place the only adjustment is sanding and notching the saddle. The cone will depress very slightly, not as much as a biscuit bridge, and the saddle will have to be radiused to match the fretboard - I just think that the setup will be really critical.

There are a few other little things that give me pause - how do you get the wire from the piezo UST to the electronics (seems like you will need a hole in the cone which might be a source of rattles? I see it has prewired electronics - I know that most piezo's are very high impedance where magnetic pups are pretty low and it seems to work better to bring the piezo out to a separate preamp or DI (Peter, how did you do yours?). I can't tell if they drilled holes for the wire from the mag pickup and a string ground - don't forget those.

Carry on and report back.

[Peter Wilcox]

Re piezo installation: I drilled a hole in the guitar top just at the edge of the cone seat, but hidden under the cover, and brought the wire over one of the legs of the bridge to it. Here's the thread:

http://www.mimf.com/phpbb/viewtopic.php?f=10&t=4989

[Freeman Keller]

Ingenious. I was thinking a hole thru the cone which would just open a can of worms (or rattles).

[Graham Bartlett]

I haven't really looked at the electronics side. There's a bag of bits, but it doesn't have a battery compartment so I'm assuming it just relies on switching between piezo and humbucker. That at least I can sort myself though - the day job is more software than electronics, but a schematic on the scale of guitar electronics which fits in one page and doesn't have voltages that need warning signs will be a welcome break.

Yes, gluing the neck is the biggest worry for me too. It'll be a little while before I get that far though - need to sort the finish first.

Thinking about opening up those holes though, I reckon I'll just build it as-is to start with and see how it goes. Then I've got a baseline for comparison before I take a drill to things. I need to do some sums on internal volumes anyway, to work out how big those holes should be.

Thanks guys.

[Peter Wilcox]

Graham - is there a schematic for the electronics? Without an active circuit, I don't see how the piezo and magnetic pickups can be combined without significant deterioration of the output signal, unless there is a switch to use one or the other, not both combined. I don't see a switch or push-pull pot in the parts pics.

Also, how can that piezo pickup be installed without blocking access to the cone tensioning screw? And I don't see the saddle(s) either, though hopefully they came with your hit.