Cone buzz

[Mike]

I need some help with my spider bridge Dobro.
Every now and then it buzzes and I don't know why. I took it apart, checked the cone and how it was set up, corrected some of the spider's legs so they have better contact to the cone, checked the tailpiece and adjusted the neck so that it is dead straight now. After that it was really fine... for some time at least.
Today I took the guitar out of the case, started to play and then it happened: it buzzed! Messing with the tension screw did not really help. It has brand new strings on it so it shouldn't be the strings, I think. The funny thing is... after some time of playing the buzzing went away and I don't know why! I don't know when it'll come back either but I'm pretty sure that it will do.
What can it be that makes the guitar buzz? Is there anything I overlooked? Slowly but surely I'm becoming a little desperate.

Thanks for your help

Michael

[LouisianaGrey]

I'd suspect the tension screw. I don't like the sound of the phrase "messing with the tension screw". What did you do? With the strings on & tuned to pitch you should tighten until all of the slack is taken up, then give it between a half and on-and-a-quarter turns.

Gregg McKenna's troubleshooting guide says:

TROUBLESHOOTING BUZZES AND RATTLES
Check everything in this order.

STRINGS...replace old strings with winding coming apart.
BAR PRESSURE... try using a little more bar pressure when you play pushing the bar down slightly harder onto the strings.
TENSION SCREW FOR SPIDER...tighten tension screw through small hole in coverplate palm rest with a small screwdriver until tight, DO NOT OVERTIGHTEN, as this can damage the cone.
STRINGS BINDING IN BRIDGE SLOTS... this mostly would affect the bass strings.Slightly widen affected string slot/s (see section on string breakage near bridge).
TAILPIECE... check tailpiece/strapbutton screw, if loose tighten. Also look at where the tailpiece touches the coverplate at the underneath of the leading edge, it should have a piece of felt or foam rubber on it so there's no metal to metal contact. To know if the tailpiece is what's causing the buzz or rattle try lifting up slightly on the tailpiece (lifting leading edge up off coverplate) while playing. If the buzz or rattle stops when you lift up on tailpiece then you know that this is the problem. To repair, loosen strings completly, remove strings ends from tailpiece then remove the tailpiece itself. Install a small piece of felt or foam rubber to the underneath of the outermost lip of the tailpiece where it touches coverplate. I find a small piece of very thin narrow self adhesive rubber weatherstripping works great. Cut it a little narrower than the width of the tailpiece so it dosen't stick out. Whatever you use, make sure it is soft and that it is not too thick that it will raise the tailpiece higher. Reinstall tailpiece and strings.
COVERPLATE...make sure all coverplate screws are tight and that there are none missing. To know if the coverplate is causing a buzz or rattle, try pushing down on edge of coverplate at various points while striking a string with your other hand. If you are able to get the buzz or rattle to stop then the problem is in the coverplate. Also make sure that the spider bridge legs are not hitting the underside of the coverplate.
SEATING CONE TO SOUNDWELL...slightly loosen string pressure/detune strings. Take a small stick of wood or small screwdriver tip and insert it into one of the half moon slots on the coverplate where the spider bridge legs are visible. Very carefully pry against the spider leg to move the spider and cone assembly as a unit back and forth on the soundwell in a lapping/seating type motion. Alternate direction by prying on each side of the spider leg, this may help to seat the cone on the soundwell. Be very careful not to damage coverplate when prying and do not force anything. Do not overdo. When done, recenter spider bridge legs to middle of half moon slots and retune strings.

THE FOLLOWING STEPS REQUIRE REMOVING THE COVERPLATE
To remove coverplate, loosen up strings and remove ends from tailpiece. Disconnect from tuners if you are going to be replacing strings. Remove the 12 screws holding the coverplate to the guitar top. CAUTION, make sure you have a good screwdriver that is the right size for the screw head and work slowly and carefully so the screwdriver dosen't slip out of the screwhead and destroy your guitars finish. The tailpiece dosen't have to be removed to remove coverplate but it might be a good idea to remove it to install a piece of felt or foam rubber to the underside of it at this time if it dosen't have it already and to make other troubleshooting steps easier. Once the coverplate is removed you can lift out spider and cone assembly as a unit.
8. CONE...when lifting cone out from guitar see if it is binding anywhere on the wood from the guitar top which may be preventing it from properly seating on the soundwell. If it is binding, trim wood slightly where it is hitting. A router works best for this but don't try it unless you are confident about doing it. Make sure your router base is protected from scratching the guitars finish. If cone is only mildly hitting on wood from guitar top you can trim a little material from the edge of the cone itself with a sharp pair of shop scissors. DO NOT REMOVE TOO MUCH MATERIAL. The cone should fit into the guitar body without hitting anywhere.
9. SOUNDWELL OR CONE MOUNTING SURFACE...make sure it is completly flat and free from any bumps or rough spots that will prevent cone from seating properly. Run a piece of medium grit sandpaper over cone mounting surface to smooth before putting guitar back together.
10. INSIDE OF GUITAR BODY... blow out or vacumn any dust or debris from inside the guitar body.
11. LEVELING SPIDER...remove spider bridge from resonator cone by removing tension screw that sits between the 2 wooden bridge saddles. Take a full sheet of 100 or 120 grit sandpaper and lay it flat against the bench grit side up. Run the spider bridge over the sandpaper back and forth while holding the sandpaper sheet down with your other hand or you can stick sandpaper down to bench top with double sided tape. The purpose of doing this is to take all the roughness of the spider casting off the bottom of the legs where they contact the cone so they all touch solidly to the cone surface without any gaps. After sanding for awhile inspect the legs to see if they all have sanding marks on them. If they don't that means the leg/s without the sanding marks is/are high. To repair, slightly rap high leg down very carefully with a small hammer by holding affected leg over the side of the bench and gently rapping end of leg with hammer to bring down. CAUTION, be very careful, the spider bridge casting is very brittle and by hitting too hard you can break off one of the legs.You only need a gentle light rap to adjust a high leg. Continue to run spider over the sand paper until there is sanding marks on all the bottoms of the spider legs where it contacts cone.You may have to repeat this process several times by adjusting high legs and sanding until all the legs have sanding marks on them, this will ensure that the spider sits level on the cone. DO NOT OVERSAND. If resonator cone is dirty now is a good time to clean it. Clean with a little soap & water and papertowel dry, then reinstall spider to resonator cone by installing and tightening tension screw. Make sure tension screw head is large enough to span the bridge insert channel and dosen't just turn down inside it. If your screw head is too small and you've been having problems with buzzes and rattles, there's a good chance your tension screw isn't holding the spider bridge down tight enough. Get a larger headed screw at the hardware store the same thread diameter as the old one to make sure the spider bridge will be firmly secured to the cone. Now is the time to fix any obvious problems while you have the guitar apart.

PUTTING GUITAR BACK TOGETHER... before putting guitar back together. check the following things.
1. TOP OF SOUNDWELL... for smoothness, remove any rough spots or dried glue chunks with sandpaper.
2. RESONATOR CONE...make sure cone is clean, not damaged, and fits into guitar opening without binding.
3. NECK SPLINE SCREW...if your guitar has a neck spline, make sure neck spline screw is tight.
4.COVERPLATE...check the back side of your coverplate to make sure there are no burrs along the screw holes that will dig into the finish or prevent coverplate from sitting flat against guitar top. Remove burrs with fine sandpaper or small file
5. INSIDE OF GUITAR BODY... make sure it is clean without any loose debris left inside.
6. REPAIR ANY STRIPPED OUT SCREW HOLES...now is the time to do it while coverplate is off.
7. WOODEN BRIDGE INSERTS...check to make sure they are tight in the bridge channels. If they are loose, glue them into the bridge channels with a little wood glue. Make sure you install them correctly with the back angle facing the tailpiece.
8. NUT...make sure nut is securely fastened, if loose reglue into nut slot.
9. SPIDER BRIDGE...make sure there are no legs cracked or broken and that the legs have been leveled as explained above. Also ensure tension screw head is wide enough to span bridge channel and screw is long enough.
10. CLEANING/POLISHING GUITAR BODY...with guitar apart now is an excellent time to polish your guitar if needed. Use only a high quality guitar polish and a soft cotton flannel cloth. NEVER USE FURNITURE POLISH.


REASSEMBLY PROCEDURES

INSTALL RESONATOR CONE AND SPIDER BRIDGE ASSEMBLY...into guitar body, make sure it fits without binding. Also ensure bridge inserts are facing the right way and the back angle is facing toward the tailpiece.
INSTALL COVERPLATE...reinstall the same way it came off, make sure if there were any wear/ scratch marks from the tailpiece and string ball ends that you locate that end again where tailpiece will be so you won't see the scratch marks. When installing coverplate, you may have to slightly push down on coverplate while starting the screws because it may have a slight warp to it. I find the best way is to push down with one hand and start 4 screws at various intervals around coverplate screw flange and run those 4 screws down which will draw the coverplate down flat to the guitar top. After these 4 screws are tightened you can then install the remaining 8 screws tightening down in a clockwise sequence. CAUTION, make sure again that your screwdriver dosen't slip out of the screw head and damage your guitars finish, work slowly and carefully.
INSTALL TAILPIECE STPAPBUTTON AND SCREW...Did you install a piece of felt or foam rubber to underside of tailpiece leading edge where it touches coverplate?
STRING UP GUITAR...install 1st and 6th strings first, next install 5th - 2nd strings to the tailpiece and connect to the tuners. Cut new strings long enough past its respective tuner to get 3 - 4 full wraps around tuner post. I'm not going to comment on how to tie or connect to tuner post because it seems everybody has their own way of doing it. Put a piece of masking tape over the tailpiece slots to keep the ball ends of the strings from popping out of the slots until strings are tightened. Once everything is connected bring up strings evenly until almost tuned, then final tune each string. Never fully tune one string while leaving all the others loose. When replacing an individual string, detune that one string loose before cutting it, Never cut a fully tuned string under tension. New strings will have to be retuned several or more times because they stretch and need time to settle in.

[Mike]

Thanks very much for the very detailed troubleshooting description.

"Messing with the tension screw" was probably the wrong expression. I chose these phrase because around here (southern Austria) not too many people have a clue about resonator guitars and for them the tension screw is the ultimate cure... and the only cure as well.
I always do it just like you said. I screw it it in until it's not loose anymore and tighten the screw between a half and a full turn.

I'll probably have to go throug the whole process again.

Thanks for your support

Michael

[LouisianaGrey]

I assume the bridge is at 90 degrees to the strings and there's enough break angle behind it. Once you get the buzz (does it happen on a particular string or on a particular note, by the way?) it's a good idea to play while pressing on various bits of the instrument, including the strings behind the nut and between the bridge and the tailpiece. Resos tend to get buzzes a lot and they are very hard to diagnose, especially the intermittent ones. It's usually a matter of going through everything one thing at a time. I've even managed to cure a buzz that wasn't caused by anything obvious by just slackening the strings, leaving the guitar overnight and then bringing it back to pitch. I still have no idea what that problem was.

[Mike]

What is the break angle behind the strings?

The buzz happens on open strings... mainly on the low E string. But it does not happen all the time and I don't know why. It goes away without doing anything... maybe some Voodoo!

[LouisianaGrey]

If you regard the strings as being at 180 degrees then the break angle is the angle that they diverge from that behind the bridge. If it's too shallow then the cone doesn't get driven properly. It's a more common problem on biscuit bridge instruments and doesn't usually cause problems on squarenecks of any kind because of the string height. Biscuit bridge instruments in particular benefit from as little break angle as you can get away with without the instrument buzzing. However, spider bridge instruments can take more of an angle than biscuit bridge - the spider bridge cone seems to benefit from more downward pressure on the strings.
I would say the angle should be at least 5 degrees. I f you think it's a problem the quick test/fix is to string the guitar with the strings under the leading edge of the tailpiece and the ball ends on top. This increases the angle, hence the downward pressure. It's not something I recommend generally, despite what some people in guitar stores will tell you, I regard it as a temporary fix for the specific break angle problem.

[Mike]

My Dobro isn't a squareneck, sorry for the misunderstanding!

I think the break angle is okay... I guess this is rather a constructional issue than a matter of setup, isn't it. I still got the original tailpiece and everything so it should be okay.
But running the strings under the tailpiece could be something that could really help...hm...I'll think about that. What about the string gauge? Currently I'm using John Pearse 13s. Are they okay? Or should I use heavier ones?

Thanks so much!

Michael

[LouisianaGrey]

The gauges of the wound strings are pretty much the same as they would be for a heavier set, so I don't think that would help if there's a problem with the low E. It's a cheap experiment, though, and trying a different brand may make a difference. Resophonic guitars are mysterious beasts. For roundneck guitars I usually fit Newtones.

[Michael Messer]

Hi Mike,

Pete has given you excellent advice.

I gather from the fact that you play round neck Dobro, that you tune in low tunings DGDGBD and DADF#AD? Whereas square neck players generally tune up to GBDGBD. Dobros don't buzz as much as Nationals, but all resophonic guitars do buzz occasionally. You just have to find how to play around them, or tweak the guitar to get rid of them. Only yesterday I was at the BBC recording a live session for Radio 2 with my beloved 1937 twelve string National Havana, when it started to buzz and cause problems! I push & pulled a few things, which at first made it worse....then a bit more tweaking and prodding and it settled down. The final recording wasn't totally free of unwanted buzzes, but it adds character to the music! So it happens to everyone who plays these machines.....ocasionally they buzz!

Try heavier gauge strings on your Dobro - 15 to 56 Newtone Messer Nationals should do the job. You could try heavier - 16 to 59, but you shouldn't need to. In addition....I haven't seen your guitar, but it sounds to me like the buzz is coming from the cone. Try spinning the spider round a bit so it contacts with a different part of the cone, then do the screw up until it hits that sweet spot....tight enough not to buzz and loose enough to sing. Hard to explain, but I know when it's right.

Shine On,
Michael.

[Mike]

That's right, I play in DADF#AD. I used to play in open E but I've been told that it would be better to use open D instead. Better for the neck.

Yesterday I removed the cover plate and strung up the guitar. No buzz! Okay, this usually means that it has something to do with the cover plate and/or tailpiece. (And the cone appeared to be set really well. I'm so proud of my work! ;D) So I decided to put some electrical tape on the rim of the coverplate. Somewhere on this homepage I've read that Amistar does this with their guitars as well. (By the way... you got an amazing homepage. So many nice and friendly people!) I think the tape-damping thing worked. Yesterday I payed the guitar for the whole afternoon and no buzzing!
Today I picked it up and I noticed a buzzing sound. >:(First I was p%#~ off but then I realized that the guitar was just out of tune. I tuned it up and everything was fine again. All-clear. I think I've managed to ... let's say... get the problem under control. I probably didn't solve it completely but I've come to the point where I can say that I can live with it. And the guitar sounds amazing now. It is really loud and got all the sweet sounds at the same time. ;D

Nevertheless I will try your strings. Can't wait to hear them.

What did you do to get your Havana working? Or is this a professional's secret?

Thanks for all the help,

Michael

[Michael Messer]

Hi Mike,

The tape & various other methods of making gaskets does get rid of buzzes, but it can also affect the resonance of the instrument. The perfectly set up resophonic guitar should not have any tape, felt, paper, etc... stopping the resonance travelling through all the parts. I have seen Amistar's electrical tape and I have to say that I am not impressed. The first one I ever saw was for a review and it was gasketed everywhere. In the old days National used paper & card occasionally, but I have always removed it and improved the sound. Felt & paper under the cones is a different thing and was done to create a certain tone.
However.....if you have put tape around the coverplate and the guitar doesn't buzz....just leave it alone! If it ain't broke....don't fix it. I have to say that from your description I think your problem is coming from the cone/spider and not the coverplate.

How did I get my Havana working at the BBC on Thursday - actualy I didn't, I played around the buzz. When I got home and checked it, al the buzzing had gone! I think it was a little BBC Poltergeist ;D

Shine On
Michael.