Repairs, Maintenance & Upgrades > Preamps, Modifications & Upgrades

The "Miracle Mod" on hybrid wood hammers Pre-1978

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Ben Bove:
I wanted to make a sticky covering the early Mark I action because of the high number of requests of how to improve sluggish action.  The fact is that the Rhodes action is extremely simplified compared to an acoustic piano action - the 2 major components are only the hammer, and where the hammer interacts with the key referred to as the key pedestal. 

A grand piano action


The Rhodes action



This topic is about the improvements originally designed by the Rhodes engineers by use of a Pedestal Bump, a small piece of plastic added to each key, to improve the feel and lightness of the action.  The basic concept is the lack of a "jack," or a fixed point where the key propels the hammer.  An aftermarket recreation of this design is available as the "Miracle Mod" action kit from Vintage Vibe or others, and this guide covers installation and an explanation of why it works.  There are other adjustments throughout the Rhodes that should be made for the most ideal action, however the Miracle Mod creates the greatest initial improvement for sluggish action for pre-1978 Rhodes pianos.

Improvements:
1) Faster action by linearizing hammer throw
2) Decreased hammer bounce

The link below provided by Vintage Vibe shows their videos for installation on action beds. 

http://www.vintagevibe.com/t-kitdirections.aspx
"Miracle Mod Video 1-4"

NOTE: Installation for 1976 - mid 1978 pianos is different and will be covered separately below.

HAMMERS
When comparing the hybrid wood-plastic hammers from 1970 - Sept. 1975, against the all plastic hammer from Sept. 1975 onward, the angles on the hammer cam are a very different shape all together from front to back.  The old hybrid hammer is much more rounded in the back, while the plastic hammer from the factory bump era has almost 2 distinct flatter planes and gives a sharper fulcrum point.  This plays into how to place the bump.

Early hybrid wood-plastic hammer


Later all-plastic hammer



EXPLANATION
The early Mark 1 hammer literally rolls over the pedestal: most of the energy is lost when the hammer is forced up because it's rocking horizontally over the ped.  It lacks a "fixed point."



A bump installed on the pedestal creates a "fixed point" throwing where the energy is concentrated at a small point as opposed to spread over the surface area of the pedestal.  If you can imagine, a seesaw exchanges the energy most efficiently from end to end by having only 1 centered fulcrum - if a seesaw was mounted on a ball, it would take much more energy to rock it back and forth.  The consolidation of energy on one fixed point helps to propel the hammer more efficiently without energy loss from unneeded lateral motion.

the hammer is propelled initially by the bump until it reaches maximum point, then bump's position is out of the way while hammer's back brakes on pedestal.  The Rhodes diagram below actually isn't drawn correctly, you'll notice if you push the key as it looks, the key would sink below the case in the front.  The same goes for the pedestal - the hammer should lay flat with the bump, not straddling the bump and the back.  But you'll get the general idea:


HAMMER BOUNCE
Braking occurs when the back of the hammer lays flat on the pedestal, aimed at stopping the kinetic energy of the hammer from bouncing around after it's thrown.  The pedestal bump effectively fills a gap at the rounded surface of the hammer, extending the length by which the hammer comes into stop contact with the key.  This in turn reduces double striking, as the bump helps to catch the hammer from flopping around in the front after it's thrown. 



INSTALLATION
Every piano is different.  The exact placement on pianos can vary from one Rhodes to another, all dependent on where the hammer curve interacts with the key pedestal.  You can try to nail it on the first try, but I always recommend to test at least 3 keys of varying placements so you can feel the differences and see which location feels best to you.  It may or may not be at the very front of the key pedestal.



1)  Test the keys and see how they feel for lightness
2)  See how they feel for hammer bounce after the initial hit - is there any plunking or hard flopping
3)  See how high the hammer sits when you strike and hold a key - a hammer resting too high in the air is not good and can create escapement issues (hammer rests up against tine). 

If the bump is too far forward, you'll feel a resistance as the hammer curve "pops" over the bump, where the hammer is actually rubbing laterally against the bump.  Once you get the right placement where there's no dragging feeling or popping, and there's no double-bouncing etc, take your model key and replicate placement on all the rest of the keys.  A word of caution though - sometimes an action rail can be out of adjustment (or never adjusted properly from factory).  So put the very lowest key and very highest key in, and make sure the hammer curve is in the same spot for both.  If your lowest key has a curve that sits on the end of the pedestal, then your highest key has a curve that sits further back, then there's a slant from top to bottom in the action, and the bump will interact differently because it moves out of alignment with the hammers. 

Also as a note, the bump on hybrid wood-plastic hammer models is very touchy, as small differences in placement directly affects the angle interaction on the hammer and key.  Remeber that this early action was never designed for a bump, so to get it right you have to find just the right spot. 



GLUE
For testing the 3 positions on your keys, you may choose to use contact cement so the bumps can be removed after the test. 
Superglue should be used in the end for final installation of the bump and felts.  Reason being, with a contact cement or other higher-volume glue substance, it can fill up the gaps where the felt covers over the bump, and create a sort of slope to the felt.  The felt should be wrapped very tightly over the bump so that it can create the greatest affect.  When the bump is secured with superglue, the felt should then be superglued with a decent amount of pressure applied directly to the area just before the bump.


FELTS ON HAMMERS
September 1975 to Mid-1978 pianos - All plastic hammers, white felt on hammer cams, bare wood pedestals

There are 2 ways to go about a bump modification on these pianos:
1) Leave the felts on the hammers, and install the pedestal bump on the bare key pedestal
2) remove the felts from the hammers, and install the pedestal bump with felts on top of the key pedestals.

Both CAN work, but it's my suggestion to remove the felt from the hammers, and do bump / felt on the keys.  Here's an explanation to why:

From what I can tell, the way the felts were installed at the factory on these models were to line up the felts with the BACK of the hammer cam.  This means any variance in the length of the felts would vary at the hammer curve.  Not good - this is the critical dimension.  So all pianos over these years can be different - some would take the bump on key alone just fine, some with shorter felts would come into what I refer to as a "stop-lock" scenario where the bump collides with the felt in ideal placement - locking the hammer from moving. 



For the key below, placing the bump further back on the key to match the felt, results in the hammer resting very high and slams up against the tine in resting position - the note will thud and not ring. 



CLICK THE VIDEO BELOW FOR DEMONSTRATION:


It takes a lot longer to install the modification incorrectly, remove it and then install it correctly a second time.  For that reason, I really recommend doing bump and felt both on the keys.  It provides for a smooth stroke with the bump UNDER the felt, and prevents any collisions.

CONCLUSION
In my opinion, if you like a lighter and more efficient action it's necessary to have a bump mod.  Through discussions with CBS Fender sources - the bump was originally designed and is present in most of the 1960s Silvertop pianos.  It was removed during the early 70s as deemed either too difficult to manufacture or too difficult to calibrate.  After many technicians in the field began modifying pianos with this method, it was later reintroduced on all pianos mid 1978-1984, including Mark 1,2,3,4 prototype, and Mark 5.  That being said, of almost 20 years of Rhodes production the bump has been factory installed in one way or another for about 12 of those years.

Examples

1967 Silvertop Rhodes pedestal bump metal clip


An original Mark V key pedestal with factory wood bump.


1972 Mark 1 piano with new Pedestal Bump modification


1978 Rhodes piano with felt bump modification (this has been debated as a factory modification, in that before they were able to design the wood bump this might have been done at the factory.  This is seen regularly in identical fashion on early 1978 pianos)


FINAL ADJUSTMENTS
Again as all pianos are different, certain pianos will need minor adjustments after the bump mod is installed.  All the hammers should sit slightly higher than before which is normal.  Depending on how installation goes, you may need to globally raise the harp slightly with a shim at the left, or left and right support blocks.  I recommend all users to experiment raising the harp slightly to see if any double-striking or bark improves - quickest way is to throw a credit card under the harp on the left side.  Should you need to raise the harp, you may also have to adjust the strikeline - the forward and backward location of the harp (search forum). 

DAMPERS:
If a piano naturally has tight bridle straps, the bump modification can make your dampers incapable of stopping the tines.  The bump mod slightly lifts the hammers into a higher resting position, which in turn pulls the damper straps a little bit.  If they're very tight, it'll pull them away from the tine in resting position.  The simplest solution is to bend the ends of the damper arm up.  You want to make sure the bend is after the bridle strap point towards the end (if it were before, it would mess with how the bridle strap interacts).  It's best performed with two hands - one holding the damper arm at the bridle strap point, and the other hand bending the end up.  This also prevents a bend in the very back where the damper arm connects to the action rail.  Too high of a bend up will result in hard-strike notes deadening out, as the tine collides with the damper felt.  Not enough of a bend and the damper felts still won't be able to stop the tines.  Also, double check how they all react with the sustain pedal when finished so that damper arms function properly with sustain.

With your faster action, happy 32nd-noting!

Rob A:
Fantastic post. Well done. This is a significant contribution.

Mark II:
I'd like to second Rob's statement.

Well done, thanks a lot.

Mark II

gunnar:
This post would have been so helpful when I did the bump mod on my '77 piano...I left the felts on the hammers and after some slight alterations to the harp position, it works a treat and it made a huge improvement on the action.

Great post!

james:
Indeed. I'm glad I have my piano torn apart right now so I can start rebumping it.

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