Fender Rhodes Key Height and Dip Specs

Started by GrovisOtis, October 13, 2011, 04:16:52 PM

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GrovisOtis

Hello,

I am currently rebuilding my Fender Rhodes piano from scratch and was wondering what the proper key height and key dip should be?  I have not found any spec online for key height just for the dip. I am a piano technician and was wondering if the standard Key height and dip (44-46mm height and 10mm dip) can apply to the rhodes or if I am just making it worse by putting it to these specs.

Any information you could provide would be very helpfull!

Thanks,

Grovis

Cormac Long

AFAIK.. its only the dip distance that's important. Once that is adequate, additional shimming is only required for leveling the keys.

I think this is because of the way the hammer rests on the pedestal block. That keeps it in position and when you press a key, the same hammer arm will ultimately reach the braking position and prevent the key from dipping further. So additional height increase on the balance pin will give you scope for more dip that you really don't get to use as the braking prevents it from raising further.

Hopefully you'll get a much more informed answer here.. but the above is what I've pickup up along the way.
Regards,
   Cormac

Forum Administrator
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pianotuner steveo

 Grovis, the way you adjust dip in a Rhodes also affects the key height. I am a piano tech also, and you do not adjust the dip the traditional way in a Rhodes. The front rail felts are only to prevent noise, there shouldnt be paper front rail shims under them. You adjust dip by shimming the back rail cloth. This takes care of dip and height at the same time.

I thought it was silly at first, but it does speed things up.

Basically shim the back rail cloth so that the dip is 3/8 or 7/16 ( whatever your preference), When it is correct, the key height is correct, then adjust your harp/ escapement.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

Edd_K

Steve...If you'd be so kind, please give us more details about how to shim the backrail cloth to set the key dip and height.  It would be much appreciated.

Thanks in advance,
EK

pianotuner steveo

#4
You can change the back rail cloth, they come in different thicknesess, but also, you could add shims under the present cloth if it is too thin and is in good condition. Shimming each key (on the balance rail) is possible, but is time consuming because you have to be sure they are all level in the front.

The back rail cloth gets glued down with any wood glue. Technically you should only glue down the half of the cloth closer to the front of the piano, but I don't think it really matters. The original thought here was that hardened glue under the back edge of the keys may cause clicking, but really, the cloth is thick enough to prevent this.

You need to measure the dip first. Press down any white key and measure 3/8" (or 7/16" for a lighter feel) from the top of the depressed key to the top of a white key that s next to it.

If dip is too shallow, the action feels 'choked' or heavy. If it is too deep, it can make the action feel too light, and cause all kinds of escapement issues.

The fronts of the black keys should remain above their neighboring white keys slightly. If they get buried , then you will need to add paper front rail shims under the green front rail felts on THE BLACK KEYS ONLY. In some wurlitzers, there is a screw under the black keys to raise that does the same thing.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

GrovisOtis

Thanks so much for the advice, seems like a good method.  So when you are doing this, you only proceed with only the felts under the keys and no paper punchings?

Thanks!

Grovis

prtarrell

If replacing the back rail felt,  duplicate the original thickness.   Determine if the balance rail is straight by  stretching a string from the ends of the rail in between the two rows of pins.  If it sags,  shim it.   A slight arch in the middle is OK.   Place a white bass key, a middle keyboard white key, and a treble white  key on the action frame.  Observe how they fit:  the balance rail pins,  the front rail pins,  the case front rail  (key slip in acoustic pianos) in both the at rest position and the depressed position.  Observe how the end keys relate visually to the  cheek blocks.  Secure the name rail (Rhodes aluminum rail with red felt on the bottom).  There needs to be a little space between the key top and the felt. The key height at the front of the piano is changed by felt and paper punchings on the balance rail.  This process is  fitting the keys to the key frame and case.   Put in all the other white keys and with a straight edge or stretched string, level  the white keys. When you do this the harp should be installed to make the bridal tapes slack therefore not pulling up on the keys.  When done,  get your eye down at one end of the piano and observe the line formed  by the key top lips. It should be perfectly flat or with a slight arch in the middle of the keyboard.   The  key dip is determined by the distance between the pedestal felt and the hammer assembly.  Fixed,
unless you change the relation of the back aluminum rail to  the action frame back rail. In the depressed position the keys do not touch the felt front rail punchings.  Measure the white key dip with a dip block.   To set the black key height place a coin ( a quarter is about right) on the white keys adjust the black keys with punchings in the depressed position.  You can further check the black key height by by  putting the coin on top of the dip block to check the height in the rest position.  If you have done  everything correctly,  the top surface of all keys between the balance rail and the pedestal should be smooth.  Perfection in white key leveling is best done with a flat metal bar.

pianotuner steveo

Grovis, as prtarelll said, only the black keys may need the paper punchings to prevent the fronts of the black keys from getting burIed between the white keys in the rest (up) position.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

benzeene

Hey All,

I'm getting in a little late on this one, but have related problems:

I was initially instructed to set the "key dip" by measuring key down from key up - on the front of the key and shimming as necessary to reach the optimal 3/8 measurement of displacement.  In doing so, here was my result:

1.  In the low use area of the keyboard - very low range and highest note - the keys looked pretty normal and played well.

2.  In the mid to upper register the keys would push all the way down till they struck the wood in front of the key with the lip of the key top.  When not played, the key was lower than the low-use range by nearly a half - giving a hug dip in the key hight in the middle register.

So, clearly setting the dip without considering the rest of the problem did not suffice.

Back to square A

So I removed the keys again, and removed the hammer combs and damper assemblies entirely - so I could get a look at the problem.  In reading comments above, I thought that maybe I had a problem with the back rail felt being worn or damaged.

Turns out, not so.

Placing the keys back in, however, did result in an obvious problem:

The key pedestals were significantly different hight following the same ranges as outlined above. When the key was fully depressed - actually when resting from gravity - without the hammer to balance against, the pedestal felt was nearly a half inch lower in the middle ranges!  This, by measuring from the action rail (where the keys are mounted) to the pedestal felt.

Obviously, the key pedestals on all keys should be roughly equal, or depressing the key in the middle of the keyboard will not have the same physical affect as playing one at the very bottom.

Since all hammer assemblies - as clear as I can make out - are identical, we need to insure that the distance from the back rail and the throw of the key itself are pretty doggone close.

One other twist:

I noticed that the back rail is not flush with the case - having a upward bow in the problem middle range.  An obvious problem, but one that doesn't hold much hope of repair, I'm afraid.

So, now I'm shimming the center rail, such that the key pedestals are roughly the same distance from the action rail.  Not sure how it will come out, but thought I'd share that.  Should have a clearer idea if this helped soon.

Stay tuned...

All best,

Ben Dowling
Ben Dowling - pianist, composer
www.bendowling.com

Member of Korg voicing team (projects include M1, T Series, Wavestation, Oasys PCI, Oasys and more...)

Rhodes Stage Mark 1 (1978)
Mason & Hamlin A, AA
Korg Oasys
Prophet 5
etc.

Rob A

Welcome aboard, Ben. Nice having you in the community.


Abraham

#10
I'm having kinda the same problem. I found my front rail pins where already shimmed behind the green felts. Even that way, they were so low that most of the keys -mainly on the lower range- didn't even touch them, being the key dip set by the hammer travel alone. So I had to shim them further for the keys to really stop on them. Shimming on the back would only affect the hammer start positions but not travel ending positions, so this won't even affect strike line nor escapement, it would just help lighting the action, as the hammers would have less distance to the strike point.

Only shimming the front rail pins I was able to lower the hammer ending positions, to increase escapement by reducing keydips. I made sure my whole action frame is not crooked (as the outer crate seems to be off a bit) and I know this is weird but, who knows... If I dont shim the lower & mid range then I have to raise the bass side of the harp assembly for the escapement to be enhough.

Also I have inspected the hammer tips heights, which seems to be in bounds, so I still couldnt figure out whats wrong.

Being that said, I would also appreciate some info about key height on rest position, if any of you could take measures.

Didn't anyone here ever happened to find the same issues? You NEVER had to shim the front rail Steve??
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

pianotuner steveo

#11
I did not say that I never added punchings to the front rail, I said that according to the service manual, and several people on this board, that is not the 'approved' method for Rhodes pianos.

I am a piano tech,adding or subtracting punchings (shimming) is the way I was taught to do it, so I prefer that method. Allegedly, the keys are not even supposed to touch the front rail felts in the down position like in wurlitzers and acoustic pianos.

Also- shortening the strike distance does not make the action lighter.
If anything, it would make it feel more 'choked'

1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

Abraham

Sorry, Im just triyng to figure out myself how the thing works... as I dont have all the experience you could have and I have no other options than doing this myself. There aren't much of those around.

I'm courious about front rail felt washers expected measures, mine could have been replaced at some point.

I had no white felt washers on the level rail, but paper shims intead, and I wonder what effect could this have. I'll be buying those from vv but I dont know wich height is the correct. Also, this would increase key height and reduce escapement. And escapement is yet too small, so I don't know.
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

pianotuner steveo

#13
Abraham, you need to set all these specs in a certain order, or else you will go around and around trying to get it right.

1. Level the keys ( the white felts)
2. Set the dip
Once the keys are correct, then move on to the action.
3. Set strike distance- hammer tip to tine at rest position- ( shimming harp height) make sure dampers work.
4. Set escapement to 3/8"... this will have a slight affect on above, you need to set it so both are good
5. Set strike line ( front to back harp position for best tone) this actually can be done almost at any time without affecting the others
6. Adjust voicing to your liking
7. Tuning
8. PLAY IT!

The white balance rail felts go ON TOP of the paper punchings

1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

Abraham

#14
Thank you Steve.

My piano didn't have white felts but only paper shims on the balance rail. If I put white felts on, key height increases to a point where there's a gap under the keys. I know this is not what's expected.

So we have a 1976 suitcase, plastic hammers with -originally- white felts below and bare flat pedestals. It seems that, at some point someone applied the old-fashioned miracle mod as described in the service manual. Maybe they took wrong measures, so hammers may be resting too high because of the bumps not being in the right spot, and causing all that mess.

So that I'm ordering a miracle mod kit and I would reset all pedestals, getting rid of those white felts. Then we'll see what's happening...
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

sean


Hey Abraham,

Make sure that you are intimately familiar with the Rhodes Service Manual (read it twice):
     http://www.fenderrhodes.com/org/manual/toc.html

And also read all the Technotes at http://www.fenderrhodes.com/service/technotes.html
(If you hit the "oopsie" 404 message on any of these links, just replace the ".org" in the URL with a ".com" and the technote or schematic will appear.)

By all means, your piano should have little white felts around the pins on the balance rail for each and every key.  There should also be one or a few thin paper punchings (rings) under these felts to make sure that all the keys are the same height (nice and level across the whole keyboard).

(When you say that these felts cause "a gap" - what do you mean?  Do you mean that it raises the front edge of the key so that it is a tiny bit above the front edge of the piano case?  Oh well, the suitcase top doesn't have the biggest front lip.)

You want the felts on the balance rail.


The big green felts around the guide pins are completely unimportant.  They should not be stopping your keystroke.  In the Rhodes action, what is supposed to stop your keystroke is the key pedestal raises up and pushes against the hammer cam and arrives at the "stop-lock" position.

See http://ep-forum.com/smf/index.php?topic=4666.0

The stop-lock position is shown clearly in this diagram

It is a shame that the keyboard museum is no longer online, because the little Rhodes action animation that used to live at http://www.keyboardmuseum.com/v_teach/rhodestone.html was awesome.

Sean


AFeastOfFriends

I'm a bit confused as to what key dip is. Isn't it the distance between a depressed key and a key at rest?

sean


Exactly that.  The distance that the front edge of the key moves down when depressed.


http://www.fenderrhodes.com/org/manual/ch4.html#4-1

pianotuner steveo

#18
Yes,key dip is the distance of one white key depressed next to a white key that is not depressed. It should be 3/8". - 7/16". Too shallow makes the action feel choked, or heavy, too deep makes the action light, but causes escapement problems.

Dip on the black keys is correct when the front of the black key is still slightly above the neighboring white keys when depressed. If the front of the black keys are buried under the whites or flush with them, the dip is too deep. If they are too deep, then you have to use front rail punchings under the green felt punchings on the black keys.

Abraham, when I said the white felts, I did not mean on the pedestals or hammers, I meant the balance rail round white felts. Those are for leveling keys

1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

Abraham

Thank you guys.

Thank you Sean for such a complete explanation, and yeah, there's a GAP between the key bottom and the crate lip, which doesn't seem normal to me, I'll take pictures. This may be caused by key pedestals being too tall because of a bad placement of pedestal felts. I'll be ordering new ones and posting results as soon as I get those delivered.

Thank you Steve, you're always there to help...! I know you meant the balance rail felts, not the other. What I'm saying is I don't have any of those, but just paper shims. I have to go shopping some of them also, then I´ll post results here. Everything points to, pedestal set too high because poorly applied "miracle" mod, or else hammers stopping too high because of... well... who knows... (tips too tall, damaged hammers/supports...).

Then I´ll be ordering:
- balance rail felts
- new hammer tips
- new pedestal felts + miracle mod bumps
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

benzeene

OK All,

I've just successfully completed fixing my action issues with my '78 Rhodes Stage Mark 1.

Just to fill you in, I had taken most of the approaches that involved measuring and shimming the balance rail felt to achieve equal "key drop."  None of the approaches worked for my problem. 

My issue was related to different parts of the keyboard having obviously different key drops - the very top and bottom seemed to be around the optimal 3/8 inches, but the center (heavy traffic) area was far less.  When at rest the keys in the middle of the keyboard were very close to the front rail.

So, it would have seemed obvious that correcting the key drop would have sufficed.

It did not.

I decided to really look at the problem.  In my reading here, I got the impression that the back rail felt might be an issue - maybe worn etc.  Unfortunately (or fortunately it turns out) I had to remove all the hammers and damper assemblies in order to examine the back rail.  I found the back rail to be in acceptable condition, and certainly not bad enough to cause the problem.

But I did notice something that was very important:  The pedestal "throw length" (for lack of a better term), was drastically different over the various ranges of the instrument.  Since I had just removed all the hammer assemblies, I knew that the hammers were identical in all ranges, and that the physics of the key action system should also be identical - if the action was to respond and play the same in all ranges (something all us pianists strive for).

There were other problems as well:  There was a gap between the back rail and the case in the troubled ranges as well.  But I decided that all other problems were subservient to the big problem:  All pedestal throws should be identical.  If they weren't we would never achieve good playing feel across all ranges.

Taking this as the crux of the issue, I did the following:

1.  Examined the keys that were responding in the way I would expect.  In my case, this was the lowest and highest note on my 73 keyboard.

2.  With hammer and damper assemblies out of the piano, the key gravity would place the keys in the depressed key position (the weight of the hammer itself is the counter-weight).

3.  In the above mentioned depressed hammer position, I measured the location of each pedestal for each key against the action rail (on which the hammers are installed).  The action rail is the machined aluminum part of the piano, which I considered to be the one unchangeable aspect of the instrument.  It doesn't change shape with age...

4.  I replaced all the center (balance) rail felts with new ones from a piano supply house.

5.  Then, using LOTS of shims, I shimmed each key on the balance rail, until all pedestal felts (for each key) were equal across the entire instrument - when measured against the action rail.  My theory was that the distance the pedestal traveled up and down against the action rail was the most important feature of the action.  If it wasn't equal, there would not be consistency between different ranges of the instrument.

6.  I paid no attention to the felts under the key guides (front rail).  They will not come into play when the hammer assemblies are reinstalled ( for reasons gone into elsewhere).

7.  I did use a piece of wood and a hammer to tap on balance rail guide pins as needed to fix problems of unevenness right to left (some of my keys were tilted one way or the other).  Just little taps were enough.

The result of the above is a keyboard that plays properly and feels good across the entire instrument.  Incidentally, the key drop also now measures correctly (which makes sense if you think about it).

So, a couple of comments:

A.  Measuring the key drop - in and of itself - is not an appropriate fix for my specific problem.  It might work in most cases, but clearly not in all.

B.  The physics of the problem needs to be considered carefully in order to address the specific problem with your instrument.  We know that the action rail is not changing shape.  We know that the hammer assemblies are identical in the stage mark 1 circa 1978 (probably in all, but I don't know that).  So the physics of the action itself needs to be addressed in order to fix or optimize the situation.  Look at the problem from that perspective, and I think you'll side step difficulties.

C.  The key drop measurement should end up being correct by using the above strategy if the keys are not damaged.

D.  THIS THING IS A TOY!  You just can't compare the Rhodes action to a piano.  No comparison.  It's a design that works by some accident of fate.  The damper system is as crude as it gets.  The good news is that through trial and error, they pretty much got it right.  Mine plays just beautifully now.  Never thought it would.

Anyway, I hope this is valuable to someone out there.

Peace and love,

Ben Dowling
Ben Dowling - pianist, composer
www.bendowling.com

Member of Korg voicing team (projects include M1, T Series, Wavestation, Oasys PCI, Oasys and more...)

Rhodes Stage Mark 1 (1978)
Mason & Hamlin A, AA
Korg Oasys
Prophet 5
etc.

Abraham

So, If I'm understanding everything you said, you adjusted the balance rail to level the pedestal ends, instead leveling the front lips of the keys. It makes sense but, doesn't this make the keys uneven by the player's side?

I'll give this a try and post results. My action is REALLY messed up.
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

Abraham

Ok I have done some progress... I put a new back felt for the keys to rest a litle higher, and this corrected the keydip to reasonable values. This didn't correct the tine stopping issue but made any sort of improvement, just not enhough

Then I moved onto the pedestal felts just to confirm I was right about that "miracle" they made... I have cut them all out, then I re-applied right sized bumps and new thinner red felts. The results are what I would call a miracle...

Still I need new balance rail felts to get this job completed, but this already shows a big improvement.

Thank you for your comments!!
196x Hammond L100
1976 Rhodes MKI '73 Suitcase
1976 Wurlitzer 200-A EP
1981 Casio VL-Tone (Yeah!)
199x Kawai CX-21D Upright
20xx Clavia Nord Electro 2

benzeene

Provided that the back rail is more or less even and the keys are not warped, adjustments to the balance rail should normalize both the key up/key down "throw distance" of the pedestal (as measured against the action rail) and the keys evenness at the same time.  The good news is that I found this to be so.  It may be that I was lucky, but conceptually it makes sense.  Primarily, my approach seems to be the right emphasis for my problem.  Please keep us all posted on your progress, as someone will be helped by this discussion.

Not sure what the "tine stopping" issue is, but - if it's what I think it is - it sounds like a shimming of the harp might be in order.
Ben Dowling - pianist, composer
www.bendowling.com

Member of Korg voicing team (projects include M1, T Series, Wavestation, Oasys PCI, Oasys and more...)

Rhodes Stage Mark 1 (1978)
Mason & Hamlin A, AA
Korg Oasys
Prophet 5
etc.

David Aubke

Quote from: benzeene on January 01, 2012, 08:20:58 AMNot sure what the "tine stopping" issue is, but - if it's what I think it is - it sounds like a shimming of the harp might be in order.

The tine stopping issue
Dave Aubke
Shadetree Keys

shmuelyosef

Quote from: Abraham on December 09, 2011, 08:13:33 AM
Thank you Steve.

My piano didn't have white felts but only paper shims on the balance rail. If I put white felts on, key height increases to a point where there's a gap under the keys. I know this is not what's expected.

So we have a 1976 suitcase, plastic hammers with -originally- white felts below and bare flat pedestals. It seems that, at some point someone applied the old-fashioned miracle mod as described in the service manual. Maybe they took wrong measures, so hammers may be resting too high because of the bumps not being in the right spot, and causing all that mess.

So that I'm ordering a miracle mod kit and I would reset all pedestals, getting rid of those white felts. Then we'll see what's happening...
You raise an interesting question that I have wanted to ask for some time:
When you raise the harp, the proper strike line does move. On my piano (Mark 1 Stage 73 from 1972 or thereabouts...it's closed at the moment and can't remember the date code), however, I have limited range of escapement motion. It is on my 'to do' list to install brass threaded inserts into the maple standoffs and turn the harp mounting holes into slots to give me some range, but the little that I have tried suggests that the harp frame is really hard steel. Also need to manage the filings real carefully or they get all over the pickups and make a real mess...sigh.

Anyone ever done something like this to their harp to make adjustment simpler?
"When I read about the evils of drinking, I gave up reading" --- Henny Youngman

1973 Fender-Rhodes Stage 73 Dyno > 1912 Mason & Hamlin Model A > > Nord Electro 6HP 73 > DSI OB6 analog synth > Rondetti concert accordion > dozens of melodicas, saxophones, clarinets, flutes, drums, amps...help...I'm awash in GAS!!

pianotuner steveo

No offense, but it sounds like doing that would take far more time and effort than just adding shims and readjusting strike line when needed. Maybe you can just mark the strike line position that you prefer with a marker so it lines up the same every time?

1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
2017 Yamaha P255
2020 Kawai CA99
....and a few guitars...

lukevintage

Returning to the original question for key dip, is it fundamental that the back rail cloth/felt is level and in good condition? Naturally, this would mean that the keybed is level too. If there are any inconsistencies in the keybed, would shims or thicker felt be required? I noticed that ep services sells 10cm lengths in varying thicknesses (1.5mm, 2, 3, 4, 5, 6).
Does that mean that Key Dip is ONLY corrected by ensuring the correct height of of the Back rail cloth/felt, which in turn produces the correct escapement?
I ask since the escapement in the centre keys on my Rhodes Mk1 73 '79 is good, where the key dip is good too. Escapement on the bass notes is extended as is the key dip.
Therefore, should I check the wood on the keybed is level? If not level, should I sand it down or build it up with shims and then add a new thick felt? Or should I ignore wood and shims and instead apply different felt thicknesses?