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Topic: Question on Hysteresis |
Mark McCornack
From:
California, USA
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Posted 24 May 2023 3:25 pm |
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Greetings... I have a question regarding hysteresis as related to string pitch on a pedal steel guitar. Since this is a technical question that PSG designers and builders would encounter, I thought the builders forum would be an appropriate place to ask it.
As I understand it, this is a phenomenon whereby a string which is raised or lowered from a resting state does not return to its original pitch. For example, if the E string (4) is lowered to an Eb then the lever is released, it will "return" to a note slightly sharp of the original E. When raised with an F lever and "returned" it will be slightly on the flat side. This is counter intuitive to me to as the term hysteresis as defined in magnetics (hysteresis loop) has the opposite effect.
Can anyone here explain this phenomenon with regards to the pedal steel and maybe elaborate on what can be done to mitigate it? |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Mark McCornack
From:
California, USA
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Posted 25 May 2023 8:44 am
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Georg... Thanks very much for forwarding that information to me. I hadn't given this cause much thought, but kind of assumed it was related to nut roller binding/releasing. The bridge would have never occurred to me as a culprit. The part about Lloyd green abandoning the E to Eb of the 4th string due to hysteresis was quite interesting. Seems like a big sacrifice, but Lloyd did pretty OK without that change  . My guitar is less than 2 cents hysteresis on this particular change, so not too bad.
Over the tears, I've always found your Forum posts very insightful and interesting to read. This was a nice bonus, and thanks again for the reply
Cheers, Mark |
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Jim Palenscar
From:
Oceanside, Calif, USA
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Posted 27 May 2023 8:08 am
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| I have read Georg's response and wonder why, if it is on the changer end of the guitar, keyless guitars tend to have less hysteresis than keyed guitars? I have read that all metal exhibits this phenomenon and rarely returns to the exact pre-change tension. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 27 May 2023 8:36 am
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I have only tested one keyless, and it had all the friction-related hysteresis at the bolt the builder had placed in nut-position. Made a bit worse by my choice of string-set - Jagwire L G Series (with wound 6th), but no slip/hang tendency on the bridge/changer on that particular keyless PSG.
FWIW: although I used a whole set of methods to pinpoint the hysteresis area on each of the PSGs I have tested, anyone can quick-test by applying thick crease on the string(s) and string-contact surface(s) where they think the problem is on their own instrument, and play it. Grease will reduce friction to an absolute minimum … for a minute or two. Should be long enough to check by ear.
Just make sure to get (wash) the grease completely off those strings and surfaces before taking the PSG out for a job, as otherwise chances are that it will be highly unstable/unreliable with regard to hysteresis. |
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Jim Palenscar
From:
Oceanside, Calif, USA
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Posted 27 May 2023 8:56 am
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| Also I would think that the clearance that both the nut roller as well as the changer scissors and fingers must have in order to function on the axles would also play a role. |
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Mark McCornack
From:
California, USA
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Posted 27 May 2023 10:45 am
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For my particular guitar (Zumsteel-Encore), the issue is not a showstopper. I am only observing 1.6 to 2.0 cents change on the E(string 4) when raising to F or lowering to Eb and returning. It seems pretty well balanced in that respect.
I also tried cleaning up the nut roller and changer contact area followed by a light application of 3-in-1. Neither of these made a measurable difference in the hysteresis. Again, it's fortunately a minor issue on this guitar.
The measurements getting into the tenths of cents is really overkill in terms of picking the fly-s**t out of the pepper, but I have a good stable means of making these measurements. I made a signal generator that allows me to dial in a note, octave, and offset from ET (in tenths of cents with firmware as shown). The signal generator triggers an oscilloscope that has the steel's pickup output tied to a viewed channel. It's very easy then to dial in a "zero beat" observation on the scope. Just monitor the change required in the signal generator (i.e the scope trigger source) to freeze the output phase of the steel.
Tenths-of-cents has little merit in terms of useful human perception of musical pitch, but I think there is still some academic merit in seeing what incremental design changes hold (if any) "quantifiable" pitch change.
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 27 May 2023 11:50 am
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| Mark McCornack wrote: |
| Tenths-of-cents has little merit in terms of useful human perception of musical pitch, but I think there is still some academic merit in seeing what incremental design changes hold (if any) "quantifiable" pitch change. |
A "slight" overkill, yes  . But can be good if one feels like documenting tuning-deviations for an instrument under stress. I use to rely on a frequency counter for that; with 4 digits after comma in the relevant range. Total overkill, but does not hurt and I do not have to write them all down.
I am generally more interested in seeing how parts of a PSG move – absolutely and relative to other parts, with varying tension. For that I have used tiny mirrors fixed with putty or glue, and a fixed light-source, in effect creating a set of amplifying light-meters. The reflections definitely "dance" more on some PSGs than on others when pedals/levers are pushed. |
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Allen Merrell
From:
Georgia, USA
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Posted 27 May 2023 12:08 pm
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I have an Encore that is the same on E lower but on raising the E to F it is dead on. I had this same issue with my Bud but was able to correct it by a very slight adjustment on the return spring. It took a little playing around with the spring but I was able to get it dead on. I messaged Doug E about the Encore and he said it sounded like it needed lubeing but I gave it a try and it had very little effect. The return springs on my Encore are non adjustable. I am considering making springs and plate that would allow me to adjust this return. This is an interesting discussion can't wait to see what the fix is. Georg, thanks for your article.
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72 ShoBud 6153 D10, Encore, Nashville 112, Boss Katana, Spark 40, GT001, ProFex II,Jackson Pitch changer (Love this bender) |
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