accidental cure for detuning on U12

mickd · Post by **mickd** » 18 Sep 2002 2:51 pm

The topic of detuning (typically seen on U12's) caused by cross shaft torsion has been raised many times (see, for example this ).

Briefly, if you raise a string and then raise it some more via a 2nd (compound) change, the string will return sharp when you release the 2nd change (e.g hold down the A pedal, then operate/release the lever that does the string 9 B to D raise - the C#'s are now sharp).
Similarly, if you lower and then lower more, it will return flat (e.g with the E's lowered, apply/release Pedal 6 - string 8 comes back flat).

The consensus was to replace aluminium shafts by hardened steel, which have less torsion.

So, I ordered 2 replacement shafts from Sierra - one for the A shaft and one for LKR (which lowers the E's).

When I finally got round to installing the new shafts, I got confused and ended up replacing the Pedal 6 shaft instead of the LKR one (duh)

I was running out of time so I tried it anyway, and to my surprise, the LKR/P6 problem had now gone away !

This doesn't make sense to me - can anyone explain this ? Since I changed the wrong shaft, the torsion problem should surely have been just as bad as it was before - and yet the detuning has completely gone

(the 'A' pedal shaft is another story - but I'll start a separate thread on that later)<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by mickd on 18 September 2002 at 03:53 PM.]</p></FONT>

Jim Smith · Post by **Jim Smith** » 18 Sep 2002 3:16 pm

You got me!

Either that or my theory just got blown out the window.

Wayne Cox · Post by **Wayne Cox** » 19 Sep 2002 11:11 am

MickD, I've got one that is just as bizarre to me. I own a Sierra S-12U. When I lower strings 4 and 8, 1/2 tone, strings 5 & 6 go sharp, according to the tuner, yet the over-all chord comes out in tune.?!*#%$&!
Remember the old adage: "Don't look a gift horse in the mouth"! Still I wonder...
W.C.

Jim Smith · Post by **Jim Smith** » 19 Sep 2002 11:23 am

Wayne, what you're seeing is cabinet raise. Lowering strings removes tension from the cabinet just like raising strings adds tension.

mickd · Post by **mickd** » 19 Sep 2002 1:36 pm

Wayne - I get that effect too, but for me it falls into the category of a 'tuner problem' not an 'ears problem'. Like you said - it stills sounds ok.
But that torsion problem did NOT sound good - and I'm not complaining that it's gone, just puzzled

Jim - I'm sure the theory is basically sound. I'm hoping someone can expand it to explain my case though..

Wayne Cox · Post by **Wayne Cox** » 20 Sep 2002 8:16 am

Re: Jim,
Thanks Jim! That makes perfectly good sense; cabinet raise! Guess I'm not too old to learn something new. Fact is, I've owned only one pedal steel, through the years,that had virtually no cabinet drop or raise. It was basically a good instrument,but I personally was not happy with the tone,so I sold it. The manufacturer later improved the tone quality of the instrument without compromising structural integrity. Then,for personal reasons,he quit building steels. It would not be appropriate for me to name him or his instruments here,still he was very close to perfection. He proved that it can be done.
W.C.