What "pushes" in a PP system?

[Jeffrey]

Hello everyone,
I have been trying to understand the mechanics behind the Emmons Push-Pull system, but am not having much luck. I get how an all-pull, and a pull-release work, but not the push-pull. Is there something actually "pushing", or is it more like just releasing tension and allowing the string to lower?
It's that unique Emmons PP sound that's got me curious. Can anyone explain how it works, and how it differs from the all-pulls? I appreciate the help!

Thank you,
Jeffrey

[Georg]

Much the same as for Pull-Release, a Push-Pull has rods that "push" against spring-loads holding the changer in neutral, to release string tension and lower tone. See http://www.steelguitar.com/maps/changerPP.html

The "famous" PP sound is only achieved when changer is perfectly tuned, as the changer-parts literally vibrate against end-plate, rods and mechanics when strings are excited. The PP sound is the result of "metal vibrating against metal and body in extremely narrow gaps under the right tension", causing a "growl" sound through the entire construction that gets "injected" back to the strings and adds to their tone and sustain. When that changer is well-tuned the PP sound is wonderful with rich harmonics and increased sustain, but if it isn't well-tuned it doesn't sound like much.

Most PP-sound lovers will probably get angry when I refer to the PP as a "rattler", but after having studied the PP mechanics (on paper) back in the early 70s and test-played a few well-tuned PP PSGs relatively recently, I stand by that "term".

[Jeffrey]

Georg,

Thank you for the reply, and for the link. I've never had the good fortune of being able to crawl under an Emmons. From pictures found on the net I could see the springs and the rods. But, until seeing drawings of the fingers, I couldn't quite get my head around how all of it was working. I'm not sure if it was a lightbulb or an all-day sucker that appeared over my head when I seen how simple it all was! My copedant doesn't require any complicated rodding, so I've always liked the pull-release for it's simplicity. But I've got to say, this push-pull intrigues me. Thanks again.

Jeffrey

[Jeffrey]

The link that Georg Gave me (see link above), in order to understand the mechanics of a push-pull changer, made sense to me... At first. But something about it has been bugging me, so I went back to it again last night. Now something's not making sense, and I was hoping someone could clear it up a bit?

From the animated pics I can see how a PP pulls, and I can see how a PP pushes. But what I don't get is how one finger, such as the one for an E, can both push AND pull? I can't imagine an Emmons not raising and lowering the E's. I have to be missing something? And it's a pretty important something, too .

Thank you,
Jeffrey

[Georg]

A PP has a "dominant raise", which means it can raise and lower the same string, like the E strings, but not "split" between raise and lower - raise will take precedence.
Believe it or not but mechanically the Push-Pull changer is pretty limited, which is why various variants of the All-Pull changer has taken over on PSGs.

[Jeffrey]

Hi Georg,
I've already set my mind to building an all pull system, so my questions regarding the PP are purely to satisfy my curiosity. I hope you don't feel that I'm wasting your time. My mind is generally a mess and sometimes i cant even sleep for trying to solve a puzzle.

But I've gotta be honest... I still can't get my mind around this raise/lower thing. In the drawings it seems that if a finger were set up to raise AND lower the same string, it would just fight itself and nothing would move. I guess that either I need to get my hands on one, or find a more in-depth drawing. One things for sure... I'm not gonna get any sleep tonight!

Thanks Georg,
Jeffrey

[burt]

Jeffrey,
The PP finger is in fact two segments, side by side.
One segment has the string going over it, the other one doesn't.

The segment that doesn't have the string going over it is the one that is 'pushed' when activating a lower.
It is held tight up against the body of the steel by a spring, and can only move in one direction.

The other segment rests on an adjusting screw that runs through the lowering segment.
This screw sets the 'open' position of the raise finger.

Thus, to tune a PP:

Press a pedal and raise the finger till it touches the body and can't go any further, and tune the raised note at the keyhead.

Release the pedal, and tune the open note using the aforementioned screw that is in the lowering segment.

Activate a knee lever to push the lowering segment back. This will also cause the raise segment to go back also, due to string tension.
Tune the lowered note with the adjusting screw that is in the endplate

http://usera.ImageCave.com/steelie/Misc/Open1-copy.jpg

http://usera.ImageCave.com/steelie/Misc/Raise1-copy.jpg

http://usera.ImageCave.com/steelie/Misc/Lower1-copy.jpg

[Georg]

No time-waste here
Curiosity is a good thing, and time passes for us all no matter what.


Note that the string is attached to the raise finger, and the lower finger is spring-loaded to not allow raise finger to return past the "neutral" position when raise is released.

The two animations clearly shows that the raise finger moves to raise independent of the lower finger, and then returns to rest against the adjustment screw on the lower finger. As long as the lower is not activated it stays in "neutral", so that's the position the raise finger returns to after a raise.

The lower finger when lowered let the string-tensioned raise finger follow lower finger all the way down to the lower adjustment screw in the end-plate, but only if there is enough slack on the raise-rod to allow the raise finger to follow the lower finger down.

Pulling on the raise-rod and pushing on the lower-rod at the same time for a string, will take up all slack in the raise-rod and pull the raise finger towards its "fully raised" position, so in such a situation it doesn't matter that the lower finger gets pushed towards the lower adjustment screw since the raise finger can't follow it down.

If you have followed the animations and my description so far, you will see that there is no conflict between simultaneous raise and lower. The raise moves free of the lower and the string gets raised, hence the term "dominant raise".

[Dave L]

What is confusing to me in the images here http://www.steelguitar.com/maps/changerPP.html#
is that in the raise pull there is a spring and stop collar on the bottom pull rod towards the key head.
in the lower diagram there is a spring and stop collar on the upper push rod towards the changer end.
are these two separate bell cranks?
or is the spring stop collar configuration on both at the same time just not shown for clarity?
which then it seems they would constantly be fighting each other.
Burts explanation of tuning makes sense as well as the concept of the system, just confused as to the actual implementation of the mechanics.

[Georg]

Dave, they are shown as separate bellcranks.
The rod for raise just passes through the bellcrank for lower - use it for support, and the rod for lower passes through the bellcrank for raise.