Rhodes Chroma Aftertouch System User manual

POLYPHONIC AFTERTOUCH SYSTEM
FOR RHODES CHROMA
Installation Manual

Introduction
Thank you for purchasing a Rhodes Chroma Aftertouch System. This
product adds polyphonic aftertouch functionality to any Rhodes
Chroma. Our aftertouch system uses high quality force-sensing-
resistors 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. We noticed that 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 were located under the keys, which
gives a signicant 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 diculty, 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)

• Phillips Head Screwdriver
• Awl, Center Punch, or other tool for starting screw holes
• Soldering Iron
• Solder
• Ruler
• Pencil
Tools Required For 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 ac-
cess 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 dierent 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
Installation

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 14-
pin 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 aects 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 marked).
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