POLYPHONIC AFTERTOUCH SYSTEM
FOR RHODES CHROMA
Installation Manual
Introduction
Thank you for purchasing a NEA Rhodes Chroma Aftertouch System.
This product adds polyphonic aftertouch functionality to any Rhodes
Chroma. Our aftertouch system uses high quality force-sensingresistors that were designed for human touch applications, making
them ideal for use in aftertouch systems. Each key’s aftertouch
sensitivity can be adjusted, allowing for uniform response across the
Chroma’s keyboard, which can require as much or as little pressure as
your tastes require.
The original aftertouch system for the Chroma required that the
sensors be mounted to that back rail, which due to the mechanics of
the Chroma keyboard, required more force than should have been
necessary to engage aftertouch. The Chroma keyboard has the same
style of keys as the Prophet T8 and Synclaviers, which both have
fully adjustable, great feeling polyphonic aftertouch. The sensors in
these two synths are located under the keys, which gives a signicant
mechanical advantage. (Requires less force to activate aftertouch)
We decided to adapt the circuitry and mechanics from these synths
into a system for the Chroma. We were able to take advantage of the
Chroma’s keyboard mechanics to make our aftertouch system feel
great.
This kit is easy to moderate in terms of difculty, and can be installed
in about 3 hours. We hope you enjoy our product.
Kit Contents
• Aftertouch Sensor PCB (2)
• Foam Balance Rail Punchings (70)
• 3/8” #4 wood screws (80)
• 14-Pin DIP Connector Cable (1)
• Nylon Cable Tie (2)
• 12-Pin 1” FFC Connector (1)
Tools Required For Installation
• Phillips Head Screwdriver
• Awl, Center Punch, or other tool for starting screw holes
• Soldering Iron
• Solder
• Ruler
• Pencil
Installation
To begin the installation process, start by removing the lid and the 4
screws that hold the front panel in place. Flip the lid up to allow access to the keys. Remove all of the keys and set aside.
Clean any dust and debris from the keybed.
You will see two sets of guide pins, each with a different type of felt
ring (Fig. 1). The thick, green piano felts are the front rail punchings,
and the thin felts are the balance rail punchings. Remove the felt
balance rail punchings, being careful to leave any paper punchings
(used for key leveling) behind (Fig. 2 & 3). Replace the felt punchings
with the punchings contained in the aftertouch kit (Fig. 4).
Figure 1 - Front and Back Rail Guide Pins and Punchings
Figure 2 - Removing Balance Rail Felts
Figure 3 - Paper Spacers Remaining
Figure 4 - NEA Quick-Recovery Foam Punchings
The aftertouch kit contains two PCBs (Fig. 5 & 6). One PCB has a 14pin DIP cable connected to it. This is the Lower Sensor Board (Placed
beneath the lowest 32 notes on the Chroma keyboard). The Lower
Sensor Board must be connected to the Upper Sensor Board using the
12-pin 1” FFC connector. J2 on the Lower Sensor Board should be
connected to J1 on the Upper Sensor Board. Solder the FFC connector
on the bottom side of the PCBs (Fig. 7). Fold the cable as shown in
Figure 8.
Figure 5 - Lower Sensor PCB With 14P DIP Connector Cable (Note that trim-pot is only populated on Lower Sensor PCB)
Figure 6 - Upper Sensor Board
Figure 7 - Soldering FFC Connector
Figure 8 - Proper Folding of FFC Cable
Place the aftertouch assembly onto the base of the keybed as shown
in Figure 9. Do not screw the assembly into place yet. The assembly
should be oriented so that the sensors are closest to the front rail, and
the back edge of the PCBs is ush with the balance rail. Fold the DIP
connector cable as shown in Figure 10, and be sure to secure the cable
so that it will not be in the way of anything such as other keys or the
lid. Plug the 14-pin DIP cable into J22 on the Chroma I/O Board.
Take note of the pin numbering on the DIP connector (Fig. 11). Pin 1
on the J22 on the Chroma is indicated with a small dot. Be sure that
you orient the connector correctly.
Figure 9 - Test Fit of Aftertouch Assembly
Figure 10 - 14 Pin DIP Cable Placement (Best to fold and run ribbon underneath bender chassis. Tape ribbon down to keep at)
Figure 11 - 14 Pin DIP Cable Plugged Into Chroma I/O PCB J22 (Note pin number markings on PCB and Header)
Turn on the Chroma and press SET SPLIT-35 to enable polyphonic
aftertouch. Edit a sound so that pressure is routed to pitch, resulting
in a pitch bend when aftertouch is applied to a note. Place a key back
into the keybed as shown. Press the key and use your nger to press
on the aftertouch sensor associated with that note. (Remember that
the assembly is not screwed down yet, so you can just slide the pcb to
the side and access the sensor you want to test.) Verify that aftertouch
is working. Adjust the SENS ADJ on the Lower Sensor Board if
needed. (This is a global sensitivity adjust and affects all keys.)
Place one black key on each octave back into the keybed (Fig. 12). We
need to align the assembly so that the keys line up with the sensors.
Use black keys to do this. Be sure that the back edge of the PCBs are
ush with the balance rail, and be sure that the sharps are directly
centered over the sensor strips (Fig. 13). When you are happy with the
alignment, use an awl or center punch to mark the holes as shown in
Figure 14 (only the 6 holes closest to the sensors need to be used). Use
12 #4 screws to secure the aftertouch assembly to the keybed (Fig 15).
Figure 12 - Alignment of Sensors With Keys
Figure 13 - Alignment of Aftertouch Assembly With Balance Rail
Figure 14 - Marking Screw Holes With Awl
Figure 15 - Screwing Aftertouch Assembly Into Place
Note that now the active portion of the sensors is located directly
underneath keys at the same point on all of the black keys (Fig. 16).
This is typically 1.5” from the key front (Fig 17 & 18), but can vary
slightly, so measure this distance on your keyboard to make sure it’s
the same. Mark the black keys as shown in Figure 19. Use an awl to
mark the center point of the key, then screw a #4 screw into the key.
Be sure to drive the screw all the way up to its head as shown in g 18.
Figure 16 - Location of Sensor & Key Contact Point
Figure 17 - Correct Location of Screw on a Sharp Key
APPROXIMATELY 1.5”
Figure 18 - Correct Location of Screw on a Sharp Key
Figure 19 - Example of Starter Hole Marked With Awl
APPROXIMATELY 3.75”
Figure 20 - White Key Screw Location (Side View)
CENTERED
APPROXIMATELY 3.75”
Figure 21 - White Key Screw Locarion (Bottom View)
Now place the key into the keybed and play that note. Apply
aftertouch pressure. Notice that the screw under the key comes into
contact with the protective foam strip over the aftertouch sensor.
Adjust the height of the #4 screw so that it only comes into contact
with the aftertouch sensor when aftertouch is engaged. If it comes
into contact with the sensor too early in the keystroke, aftertouch will
engage too early, and will engage when playing notes at high velocities.
Both of these are undesireable. If the screw comes into contact with
the foam too late in the keystroke, then too much pressure will be
required to engage aftertouch. The height of the screw determines the
point in the keystroke that the aftertouch starts. You want this to be
the same on every note. Adjust this on every black key.
Now place a white key into the keybed. Find the correct distance
for the location of the screw for the white keys, about 3.75” from key
front (Fig. 20 & 21) Apply the #4 screws to the white keys as shown
in Figure 20. Repeat the aftertouch calibration procedure described
in the previous step. Adjust all keys until there is uniform aftertouch
response across the entire keyboard.
Figure 22 - Black Key at Rest
Figure 23 - Black Key Depressed (No Aftertouch Engaged)
Figure 24 - Black Key Depressed (Aftertouch Engaged)
Figure 25 - Key Travel During Normal Key Stroke (Note how close screw comes to the sensor foam without actually touching it.)
Figure 26 - Back of Key Hitting Back Rail Felt During Keystroke
Figure 27 - Back of Key Pressing on Back Rail When Aftertouch is Engaged
(This is what allows the screw to come down on the sensors in a controlled way, which makes the aftertouch response feel good under the ngers.)
Figure 28 - Compression of Balance Rail Foam Punchings When Aftertouch is Engaged.
Test all keys to be sure that the pressure response is even from note to
note.
If you would like more “squish” to the feel of your aftertouch, we also
have custom foam front rail punchings that replace the green felt
front rail punchings. The Prophet T8 and Synclavier both used foam
punchings on the front and balance rails. It is a matter of taste. The
foam punchings have the added benet of making the action quieter.
If you need a set of foam front rail punchings for the Chroma, they can
be purchased separately on our website.
When you feel that the aftertouch response is uniform across the
keyboard and the sensitivity is to your liking, you are ready to close
the lid and play the Chroma.
Please contact us with any questions regarding this product.
New England Analog LLC
Longmont, CO, 80501
720-442-9698
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