OM/Mandocello Guitar conversions

[Bernie Daniel]

All I know is that I desire a mandocello greatly!!

Bernie - I will watch your Loar conversion with great interest! I have my eye on the LH-700 for my Archtop guitar musings so a Loar cello will be very cool!

Stay tuned!

The way I have this figured now Ken this will be a pretty clean conversion.

I will get the guitar. a spanking new The Loar LH-300 arch top, in mid-week.

It has 6 Grover open backed (1:18 stay-tight or whatever they call them) tuners on it. I have a set of 6 more identical new tuners in hand.

So I will drill hole between 1 & 2 and between 2 & 3 on each side and add four more tuners to the top. (this will be scary on a brand new guitar!!!).

But then I'll make a new bone nut, fix up the bridge (I plan on putting a bone cap on the original rosewood bridge) and notch to take 5 courses, and then modify the tail piece to take 10 strings (5 courses) and it is time to tune it up (famous last words!).

But once I have it up and running and set up I will probably sell it because I really do not plan on taking up the cittern. Of course I could find that I like it a lot more than the mandocello and keep it -- but I doubt that will happen. LOL!!

[Ken Olmstead]

Bernie, cittern huh? might as well play 12 string guitar!

So do these Loar arch tops have the strength to handle the extra load of the cello strings? What will you do for the tailpiece?

[Mike Anderson]

You're not a good reader, are ya?

That's your reply to a request to be cordial???

[Bernie Daniel]

Originally Posted by NotMelloCello

You're not a good reader, are ya?

That's your reply to a request to be cordial???

You can lead a horse to water but you cannot make him drink -- back in my days when I was a rancher we used to talk about folks who have "a burr under the saddle"....

[Bernie Daniel]

Bernie, cittern huh? might as well play 12 string guitar!

So do these Loar arch tops have the strength to handle the extra load of the cello strings? What will you do for the tailpiece?

Yes I think so Ken -- see my comments in post #25 in this string. I think the math works out for it especially if I go to lighter string gauges i.e., less tension.

On the tail piece. After doing four guitar to mandocello conversions I've gained some experience at modifying regular Gibson tail pieces - converting them to trapeze style for mandocellos -- see pics.

But for this cittern I plan to on modifying the existing guitar TP to accept 10 strings. I will use metal pins drilled into the original TP -- I diagrammed it out this weekend and it should work put well and look pretty sharp. IMHO!!

[Bernie Daniel]

Ken & Pete here is how I will start with the string set on new "The Loar" cittern.

First, as a standard guitar with a medium set of strings the total tension on the instrument would be about 190 lbs.

Now, if you converted it to a mandocello and used a set of D'Addario J78's and tuned it to pitch you would generate 290 lbs total tension. From past experience I know that arch top guitars will handle this tension. I've done four myself and they have all held up fine. Others have also done them including you Pete -- A-OK! Right!

So for the new The Loar cittern I am setting a goal of no more than 300 lbs total tension on the instrument. It follows that since it will have 10 strings I want each string to be 30 lbs at pitch.

Then you can just set up a spread sheet with formulas and with the pitches needed (column A) C2, G2, D3, A3 and E4 the associated frequencies (column B) and then with the scale length (25") you can compute the needed string unit weight required (Column C). These can then be matched up going to the D"Addario string data on their website and you can pick a string (Column D) that has the string unit weight closest to what you want (Column E).

Finally, enter the actual string unit weight data from D'Addario data base (Column E) into the equation for string tension and you have calculated the ACTUAL total tension on each string. Multiply this times 2 and you see that using a string set of: 0.066", 0.045", 0.030", 0.020", and 0.013" I will end up with a total tension of 303 lbs at pitch. (BTW: the first four are wound the last plain -- the formula changes for string type).

I feel pretty secure that the top will stand up just fine. So we're off -- the new guitar comes tomorrow!

Here is the chart from my spread sheet:
Column A = "Desired Pitch Designation"
Column B = "Associated Frequency (Hz = cycles/sec)"
Column C = "Calculated String Unit Weight Needed (lbs/in)"
Column D = "Best String Match (D'Addario string code)"
Column E = "Given String Unit Weight (lbs/in)"
Column F = "Actual Tension Achieved (lbs)"

A........B................C...................D... .............E.....................F
C2.....65.41.......0.000914346 .......PB066........0.00087718........28.781

G2.....98...........0.00040733.........PB045...... ..0.00041751........30.750

D3....146.83......0.000181455........PB030........ 0.0001866.........30.851

A3....220..........0.000080826........PB020....... .0.00008106........30.087

E4....329.63......0.000042674........PL013........ .0.00003744........31.197

Total tension = 303.3 lbs

Formulas: T = (UW x (2 x L x F)2] / 386.4
UW (unit weight) = (T x 386.4) / (2 x L x F)2
Where:
T = string tension (lbs)
UW = string unit weight (lb/in)
L= scale length (in)
F = frequency (Hz = cycles/sec)
use a constant of 326 for wound strings.

[Eddie Sheehy]

A couple of extra pounds of thrust and you could put a Mandocello in orbit...

[Ken Olmstead]

Wow Bernie, looks like you got it all figured! What is that Gibson tailpiece from? Should be a cool project!

[Bernie Daniel]

A couple of extra pounds of thrust and you could put a Mandocello in orbit...

Edddie -- I just ran my program for your 26" scale mandocello for a set of J78's and it comes up to about 318 lbs total tension!

For a 24.75" scale like my Gibson it is 288 lbs -- that extra length makes about a 10% increase in total tension --30 lbs!

It adds up fast because tension is a function of (2 times the scale length) quantity squared!!

[Bernie Daniel]

Wow Bernie, looks like you got it all figured! What is that Gibson tailpiece from? Should be a cool project!

Ken I made that from a standard Gibson tail piece, some 1/8 brass round stock and my soldering gun! I wish I still had some decent lead-based solder left!

I've made three of them now so maybe I am getting a little better at it. I had the engraving done at a local trophy shop using Old English Script -- that part cost $20!

[Ken Olmstead]

Ken I made that from a standard Gibson tail piece, some 1/8 brass round stock and my soldering gun!

I've made three of them now I am getting better at it. I had the engraving done at a local trophy shop using Old English Script -- that part cost $20!

You mean a regular mandolin tailpiece?

[tkdboyd]

I have been wanting an Octave Mandolin pretty bad and this thread has me thinking. A Guitar Center The Loar's archtop LH-300 is priced at 599.99, and the conversion set up would be around $400.00 or so? If there was someone out there willing to drill into a new guitar. I know this is about Mandocellos, but a GBOM for $1000.00 sounds like a good deal?

[allenhopkins]

...the MDC805 had been discussed on this forum dozens of times over the years - we know all about its good points and bad points, e.g., from the wide fret board to the weak tail piece and on to the fact that it also about the most reasonably priced GREAT acoustic mandocello out there….

Opened the case on my MDC 805 Saturday and found chaos; the tailpiece had let go at the hinge. Off to the repair shop…

Still think it's a great guitar-bodied mandocello, but Saturday's dance was done with the Gibson K-1.

[Eddie Sheehy]

The Monterey Archtop Bouzouki conversion just arrived. A little tweaking of the bridge to set the intonation and she was up and running. The body is rough looking but I like the sound and the scale is great for GGDDAADD tuning. The action is a tad high on the upper frets so I may sand the bridge down a bit.
While I'm tempted to tune it to GGDDAAEE and play it like an OM, that scale is just a bit too much... but then again I've played longer scales...

It definitely has the volume for jams...

[Bernie Daniel]

You mean a regular mandolin tailpiece?

Yes the part that comes down at a right angle and has the 3 holes to screw it to the tail of the mandolin is cut off then bent forward and curled around to make a hinge for the trapeze. I made up a crude diagram:

[Eddie Sheehy]

Very creative, Bernie. Kudos.

[Bernie Daniel]

I have been wanting an Octave Mandolin pretty bad and this thread has me thinking. A Guitar Center The Loar's archtop LH-300 is priced at 599.99, and the conversion set up would be around $400.00 or so? If there was someone out there willing to drill into a new guitar. I know this is about Mandocellos, but a GBOM for $1000.00 sounds like a good deal?

Doing an octave would be the same as a mandocello -- and depending on how fancy you wanted to get you might get away with less than $400 in modification I suppose -- esp. if you do it yourself.

For example if you moved the four octave courses to the center 1.5" of the fret board (both nut and saddle) it would play well and you would not have to make a new octave fret board and slim down the neck. But you would not have a treble side extension either.

Then: 1) change out the tuning machines -- $60 + labor= plug old holes with black pegs, drill new holes and install mando tuners - you would have to decide how clean you would like to fill the old guitar tuner holes -- on thing easy is to glue a hard wood peg in the hole and top it off with a MOP dot! ;
2) make a new bone nut ($4 + the labor to shape a new nut then figure out the inter-string and inter-course spacings;
3) try to reshape the guitar bridge saddle to support octave string set -- again you would utilize the center section of the bridge saddle and figure out spacings.
4) come up with a plan to modify the tail piece to hold 8 strings -- there are several ways to do that.

Now the one big downer to your idea (IMO). The arch top guitar is mandocello size so you are dealing with a 24.5" scale -- very long for octave tuning and then you essentially have a mandocello-sized octave mandolin. Not ideal IMO.

So now you have to make all the big stretches and have all the discomfort and awkwardness of those mile wide frets and dealing with 5ths that you should not have to "put up with" on an octave! Something to think about.

[Bernie Daniel]

The Monterey Archtop Bouzouki conversion just arrived. A little tweaking of the bridge to set the intonation and she was up and running. The body is rough looking but I like the sound and the scale is great for GGDDAADD tuning. The action is a tad high on the upper frets so I may sand the bridge down a bit.
While I'm tempted to tune it to GGDDAAEE and play it like an OM, that scale is just a bit too much... but then again I've played longer scales...

It definitely has the volume for jams...

Whoohoo! That is quite a little beast there -- it will be a hoot to hear it! Congrats! I do like all that nice tortoise binding!

[Bernie Daniel]

Opened the case on my MDC 805 Saturday and found chaos; the tailpiece had let go at the hinge. Off to the repair shop…

Still think it's a great guitar-bodied mandocello, but Saturday's dance was done with the Gibson K-1.

Sorry to hear that -- when this happened to a some members a couple of years ago I thought that Eastman had came up with an improved tail piece? It was discussed in detail on the Mandocello enthusiast forum -- on Facebook as I recall.

[Pete Braccio]

Hey Bernie,

I've been writing these replies from my phone, so haven't been going into a lot of detail. However, I don't think that I topped 210 total string tension ever on my conversion. I'd be concerned with shooting for 300 lbs.

I put together an Excel spreadsheet to do string calculations (based on the formula in the D'Addario string tension PDF). I'll see if I can post it.

Pete

[Bernie Daniel]

sorry duplicated post!!

[Bernie Daniel]

Hey Bernie,

I've been writing these replies from my phone, so haven't been going into a lot of detail. However, I don't think that I topped 210 total string tension ever on my conversion. I'd be concerned with shooting for 300 lbs.

I put together an Excel spreadsheet to do string calculations (based on the formula in the D'Addario string tension PDF). I'll see if I can post it.

Pete

OK thanks Pete! Let's see where the difference are. I'm doing the same thing -- Excel spread sheet with the D'Addario formula and string data.

The numbers I am getting are pretty close to what D'Addario gets for the individual strings as listed on its J78 package (see the pic below).

Here are the formula I am using for string tension:

T (tension) = [UW x (2 x L x F)2] / 386.4

Where:
T = string tension (lbs)
UW = string unit weight (lb/in)
L= scale length (in)
F = frequency (Hz = cycles/sec)

Note: D'Addario claims you have to use a smaller constant (i.e., 326) in the denominator for the tension calculation on wound strings -- instead of 386.4 -- I think this is some kind of error in their string manual and I decided to ignore it. If you use 326 the numbers are not even close to being correct.

Looking at the D'Addario package for J78 (pic below) you see that adding up the tension for the four strings comes to 144.2 lbs. if you multiply that times 2 (8 strings) you get 288 lbs on a 25" scale on a mandocello with J78's when tuned up to pitch.

[Bernie Daniel]

OK. I see the string tension numbers in post #31 for the cittern have a systematic error! It looks like I used the smaller D'Addario constant (i.e., 326) instead of 386.4. I realize this problem after I had done all the cittern computations and forgot to go back and correct them -- so the tension values in post #31 are revised downward (less tension per string) as per the table below:

Here is the chart from my spread sheet:
Column A = "Desired Pitch Designation"
Column B = "Associated Frequency (Hz = cycles/sec)"
Column C = "Calculated String Unit Weight Needed (lbs/in)"
Column D = "Best String Match (D'Addario string code)"
Column E = "Given String Unit Weight (lbs/in)"
Column F = "Actual Tension Achieved (lbs)"

A........B................C...................D... .............E.....................F
C2.....65.41.......0.000914346 .......PB066........0.00087718........28.28

G2.....98...........0.00040733.........PB045...... ..0.00041751........25.94

D3....146.83......0.000181455........PB030........ 0.0001866.........26.03

A3....220..........0.000080826........PB020....... .0.00008106........25.38

E4....329.63......0.000042674........PL013........ .0.00003744........26.34

Total tension = 255.91 lbs

Formulas: T = (UW x (2 x L x F)2] / 386.4
UW (unit weight) = (T x 386.4) / (2 x L x F)2
Where:
T = string tension (lbs)
UW = string unit weight (lb/in)
L= scale length (in)
F = frequency (Hz = cycles/sec)

[Ken Olmstead]

Looks like computer code or something!

[Eddie Sheehy]

Looks like computer code or something!

Nope. Computer code I understand...