Questions re string stiffness jig

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Questions re string stiffness jig

Post by kiwigeo » Tue Oct 28, 2014 5:32 pm

Trevor,

Okay I've managed to bodge up a string stiffness measuring jig as per photos and text in section 4.7.3.1 of "The Black Book". Questions:

1. How is the upper section (with locking nut and brass anvil) fixed to the lower base of the jig? Im using clamps on my jig.
2. is there an ideal distance between underside of the string and the top of the brass anvil that the fret presses against? Should this be close to a typical action measurement?
3. The string is tied to a length of what appears to be cord which runs over the pulley and down to the weights. What exactly is used on the jig in the book?
3. What range of weights are required to tension up classical strings and steel strings?

Cheers and thanks

Martin
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Tue Oct 28, 2014 8:41 pm

And one more question: The Arctec undersaddle pickup Im using terminates in a 2.5mm TS male plug. I plan to chop off the 2.5mm plug and replace it with a 3.5mm plug to go straight into the mic input socket on my HP 250 laptop. Will a 3.5mm TS plug go straight into the laptop soundcard with no problems?
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Wed Oct 29, 2014 9:15 pm

kiwigeo wrote:Trevor,

Okay I've managed to bodge up a string stiffness measuring jig as per photos and text in section 4.7.3.1 of "The Black Book". Questions:

1. How is the upper section (with locking nut and brass anvil) fixed to the lower base of the jig? Im using clamps on my jig.
2. is there an ideal distance between underside of the string and the top of the brass anvil that the fret presses against? Should this be close to a typical action measurement?
3. The string is tied to a length of what appears to be cord which runs over the pulley and down to the weights. What exactly is used on the jig in the book?
3. What range of weights are required to tension up classical strings and steel strings?

Cheers and thanks

Martin
Question 2 has been taken care of. I bought a bricklayers (synthetic) line and it seems to have minimal stretch.
Martin

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Re: Questions re string stiffness jig

Post by Trevor Gore » Wed Oct 29, 2014 9:28 pm

1) Mine is screwed down with a couple of countersunk screws such that the anvil/fret are dead centre of the string span

2) I use ~5mm, basically classical action, but still linear for SS action

3) Exactly what you've described. For steel strings I have a brass block with an axial hole through which the guitar string passes and a transverse screw which clamps the string. A ring goes through the other end of the block from the guitar string and the polyester VB chord is tied to that.

4) (or 3) again if you're numerically challenged :mrgreen: ) Can be read off the packages of D'Addario strings or as published on the D'Addario website. The range is up to ~18 kg (180 N) for steel strings and 11 kg (110 N) for classical strings. I just hang weights on until the string is at pitch

5) My new laptop is an HP and I haven't had to change the wiring from what it was on my Toshiba. Hot to T, ground to S. R can be NC, 2nd channel or bias voltage for electret mics, from what I've seen. I plug straight in and it's fine for getting a frequency measurement.
kiwigeo wrote:Question 2 has been taken care of. I bought a bricklayers (synthetic) line and it seems to have minimal stretch.
Now Martin, I know you find numbers a challenge... :D

It doesn't matter if the polyester chord stretches or not, so long as it's not like a piece of shock chord. I just use VB (Venetian blind) chord. The locking nut device is "locked" when the measurements are being done, so the VB chord isn't "in the circuit".

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Re: Questions re string stiffness jig

Post by kiwigeo » Thu Oct 30, 2014 8:53 am

Thanks alot Trevor,

How the anvil/fret section is attached to the base is a bit unclear in the photos. The assembly appears to slide along over the ruler so I couldnt see clearly how it was fixed once it was at the right position.

For different scale lengths I assume youd reposition the lock nut assembly or make up a whole new anvil/locknut assembly?

Once I finish the jig and get it working Ill post up dimensions and materials for others interested in making the jig.

Numerically challenged? I'm more numerically traumatised....my brother is a Maths teacher.
Martin

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Re: Questions re string stiffness jig

Post by Trevor Gore » Thu Oct 30, 2014 2:26 pm

kiwigeo wrote: For different scale lengths I assume youd reposition the lock nut assembly or make up a whole new anvil/locknut assembly?
I have the scale length set permanently at 650mm, the rated scale length, and then mathematically scale from there for actual scale length (otherwise you have to test for every scale length). The simple Mersenne formula is used for scaling, as that was proved to be plenty accurate enough and is what gets used in the rest of the intonation calcs.

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Re: Questions re string stiffness jig

Post by kiwigeo » Thu Oct 30, 2014 3:52 pm

Okay understood thanks Trevor.
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Thu Oct 30, 2014 8:22 pm

Got the 3.5mm plug wired to the pickup and plugged it into the laptop. Fired up G-tune and it seems to show a bit of noise but no real meaningful response when I pluck the string. I may have damaged the pickup or my soldering job might me suspect. Too tired to f***k with it any more so its going to sit on the bench for a few days while I do other things.

G-tune has been discontinued according to the window that comes up when opening the software. They instruct to download Peterson Strobosoft....which they were involved in developing. Ive ordered Mac and Windows versions of the software which is a few days away.

I pondered over buying a bunch of weights from a sports shop to tension the string up but in the end I hung a bucket of water off the end of the rig and it tensioned the string up nicely. The advantage of the bucket of water is I can fine tune the weight of same by adding or taking out water. Got the idea from watching them load test a rig crane with a huge water bag last time I was at work.
Martin

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Re: Questions re string stiffness jig

Post by Trevor Gore » Fri Oct 31, 2014 10:22 am

G-Tune is still down loadable (or was a few days ago), though they hide it a bit. It's the free version, which works fine, but iirc you can still get a license which will allow you to do a few more things (like keep the calibration, etc.)

You might need to apply "microphone boost". On an HP laptop you might have an app called DTS Audio Control Panel (Start/Control Panel in Win 7) which will allow a boost, but likely also available via the Speaker icon in the tool tray (double click or "wrong" click). G-tune also has noise suppression.

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Re: Questions re string stiffness jig

Post by kiwigeo » Mon Nov 03, 2014 7:33 pm

Trevor Gore wrote:
You might need to apply "microphone boost". On an HP laptop you might have an app called DTS Audio Control Panel (Start/Control Panel in Win 7) which will allow a boost, but likely also available via the Speaker icon in the tool tray (double click or "wrong" click). G-tune also has noise suppression.
Unfortunately Ive got a laptop loaded with Windows 8.0. It's a good reminder why I made the change to Mac.... :?
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Sat Nov 08, 2014 8:25 pm

Okay Ive managed to get the jig "working". I ditched the Artec pickup and stuck in a K and K under saddle pickup. I'm also running the pickup into a pre-amp and output from that is going into the mic input on the laptop.

Couldn't get G-tune to give sensible values bit Strobosoft is giving values that match readings on a hand held tuner sitting next to the string.

Next job is to get a full set of strings and run them on the jig.
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Thu Nov 13, 2014 7:52 pm

Here's the completed jig. Ive got a Savarez high tension in the jig at present. There's about 6Kg tension on the string to get it close to target pitch.
Notes:
1. I have a K and K undersaddle pickup installed and its going into the laptop via a pre-amp to match impedance and boost the signal. The K and K comes with a 1/4" female socket so I wired that up and ran into the 1/4" input on the preamp.
2. I'm using the frequency counter feature on VA but Ive also got Peterson Strobosoft running as a check along with a manual tuner sitting next to the jig.
3. Ive found that plucking the string close to the anvil gives the best result on the freq counter. If you pluck too hard the counter will measure one of the harmonics rather than the fundamental.
4. Ive used a bucket of water as a weight. This allows easy fine tuning of weight. The downside....I have mozzies in he workshop and today I noticed a few wrigglers in the bucket. Might have to add some frogs.
5. The locking nut assembly has a piece of bone saddle inserted to bring the string action at the anvil up to around 6mm.
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Re: Questions re string stiffness jig

Post by Trevor Gore » Thu Nov 13, 2014 11:12 pm

That all looks pretty good, Martin!

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Re: Questions re string stiffness jig

Post by kiwigeo » Fri Nov 14, 2014 3:55 pm

Trevor Gore wrote:That all looks pretty good, Martin!
That was the easy part. Onto the maths next. There'll be a few questions coming on same :?
Martin

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Re: Questions re string stiffness jig

Post by kiwigeo » Sun Nov 16, 2014 10:04 pm

Most of Sunday spent buried in a copy of Stroud's "Engineering Mathematics" reading up on polynomial equations.
Martin

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