MPX Bus
Preface
HX3 MPX bus is a serial daisy-chained bus for scanning analog controls like drawbars and potentiometers, using shift registers and analog multiplexers on MPX-type analog input boards. Due to the series connection, the physical position of the interface board in the chain determines which "address" (corresponding to the parameter number in the HX3 Manager/Editor) is assigned to the analog controllers. Nevertheless, all drawbars/potentiometers can be assigned to any analog HX3 function via the HX3 Manager/Editor parameter Analog Remap, regardless of their physical position.
MPX bus was introduced with HX3.5 to provide multiple analog inputs in addition to the "classic" 24 drawbar inputs of HX3.1 to HX3.4 boards. While HX3.6 mainboards still provide 24 analog control (drawbar) inputs, HX3.7 no longer provides analog inputs onboard. For HX3.7, external analog input boards have to be connected to the daisy-chained MPX bus.
It is possible to make your own analog input board designs, using our MPX board schematics as a base. However, we recommend DBX6/DBX9/DBX12 (6, 9 or 12 DrawBars multipleXed), ANX8 (8 ANalog multipleXed inputs) and PTX4-25 or PTX4-35 (4 PoTentiometers multipleXed) assemblies for new organ designs as they greatly simplify the installation. These boards carry their own multiplexers/shift register ICs, so they can be daisy-chained via the MPX bus system, a 10-wire flat ribbon cable connected to PL27 MPX on HX3.6 mainboard. Any number of DBX6, DBX9, DBX12, ANX8 and PTX4 modules may be be strung together in any order until the maximum capacity of 64 analog controls is reached. The 24 internal inputs on ANLG UPR and ANLG LWR of HX3.5/3.6 boards can be used independently, so this adds up to a total of 88 analog inputs. HX3.7 is limited to 64 analog inputs.
It is not allowed to wire MPX connectors in parallel (like on I2C bus for digital inputs); however, it is allowed to mix any MPX-compatible analog input boards as long as they form a chain.
Please note: Boards in version 3.6b require a small attenuation adapter between PL27 and the first DBX, ANX or PTX board, otherwise there will be interference in the analog scanning with certain cable lengths. See section Product Changes and Bugfixes.
For schematics please refer to our schematics repository on our update server.
Input Monitor
A very helpful feature of HX3 Manager/Editor is the Input Monitor. You can use it to check the function of all analog inputs by observing raw digital values obtained from the attached MPX interfaces.
By clicking into the input table you will also find out to which HX3 tab the input is assigned. Conversely, when you click on an assignment in Analog Remap, the active field in the input monitor tables jumps to the assigned input.
MPX Boards
MPX Connector Installation
DBX boards are provided with two angled 10-pin headers. All DBX drawbar boards are available without drawbar potentiometers installed on request. Please order drawbar potentiometers and knobs separeately. Insert drawbars into solder pads from bottom of PCB (no silk screen lettering) on desired positions, turn over and place on an even surface before soldering to maintain even spacing.
To be used in tight installations, all DBX boards may be cut along white lines on board without affecting function, using a fine toothed saw blade. This must be done before mounting of drawbar potentiometers.
DBX6 Drawbar Module
DBX6 boards are suitable for ADSR, equalizer or volume control with 4 to 6 drawbars. With 6 drawbars mounted, right bottom chain header position is occupied by last drawbar. In this case, use solder pad wire connections or top mounted headers for chaining boards.
| DX6 input assignment (6 versatile drawbars) | ||||||||
|---|---|---|---|---|---|---|---|---|
| DBX6 Drawbar | R1 | R2 | R5 | R6 | R7 | R8 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6... | |
DBX9 Drawbar Module
DBX9 boards are suitable for classic 9 harmonic drawbar installations on B3- or M100-like organ consoles. They offer additional 3 analog inputs (if needed) for connection of own potentiometers (10k to 47k types suitable). To use these, set "solder blob" jumper JP1 open and JP2 closed (12 analog inputs mode). Potentiometer inputs are available on 6-pin connectors PL2 (not mounted; all 6-pin connectors are wired in parallel, same pinout). The inputs are also available on 5 solder pads marked AIN +9 to AIN +11, as well as GND and VREF (common to all pots).
Jumper settings via removing or adding solder blobs:
| Jumper settings DBX9 | ||
|---|---|---|
| Konfiguration | JP1 | JP2 |
| 9 Drawbars on DBX9 | open | closed |
| 9 Drawbars and 1 to 3 Pots on DBX9 |
closed | open |
| Input assignment DBX9 | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DBX9 Drawbar | R1 | R2 | R4 | R5 | R6 | R7 | R9 | R11 | R12 | Next Board | ||||
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8 | +9... | ||||
| Input assignment for B3-like installation (9 drawbars, JP2 closed) | ||||||||||||||
| Input assignement DBX9 + 3 analog inputs | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DBX9 Drawbar | R1 | R2 | R4 | R5 | R6 | R7 | R9 | R11 | R12 | AIN+9 | AIN+10 | AIN+11 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8 | +9 | +10 | +11 | +12... | |
| Input assignment for B3-like installation (9 drawbars) plus 3 additional pot inputs (JP1 closed) | ||||||||||||||
Note: Next Board is assignment of first control of next module in chain (on right side of this module).
The assignment of the 6-pin header for the connection of further potentiometers is as follows:
| Pinout of 6-pin header PL2 | ||
|---|---|---|
| Pin | Function | |
| 1 | Input AIN+9 | |
| 2 | Input AIN+10 | |
| 3 | Input AIN+11 | |
| 4 | (not connected) | |
| 5 | VREF (common pot end) | |
| 6 | GND (common pot ground) | |
DBX12 Drawbar Module
DBX12 boards are suitable for 12 harmonic drawbar installations on H100-, Böhm- or Wersi-like organ consoles. Drawbar positions DB+0 to DB+11 are populated, rightmost position R16 remains empty.
However, it is possible to use DBX12 boards in a B3-like 9+3 drawbar configuration (i.e. 9 upper or lower on left side, one space and 3 pedal drawbars on right side). In this case, do not populate R13 (space), use positiion R16 (rightmost) instead. Note that position R16 (pedal sustain) is handled as input #9 (R13), not #12. In either case, DBX12 only has 12 inputs, not 13. It is not possible to populate DBX12 as 3+9 drawbars (pedal drawbars on left side), as position R13 and R16 share the same analog input! See section HX3.6_Installation_Manual#Typical_Applications for details.
Jumper settings via removing or adding solder blobs. Note: Next Board is assignment of first control of next module in chain (on right side of this module).
| Jumper setting DBX12 | ||
|---|---|---|
| Configuration | JP1 | JP2 |
| 12 Drawbars on DBX12 | closed | open |
| 9+3 Drawbars on DBX12 | closed | open |
| Input assignment DBX12 in H100 configuration | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DBX12 Drawbar | R1 | R2 | R4 | R5 | R6 | R7 | R9 | R11 | R12 | R13 | R14 | R15 | no R16 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8 | +9 | +10 | +11 | none | +12... | |
| Input assignment for H100 like installation (12 drawbars) with R13 installed, no R16 | |||||||||||||||
| Input assignment DBX12 in B3 like configuration | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| DBX12 Drawbar | R1 | R2 | R4 | R5 | R6 | R7 | R9 | R11 | R12 | no R13 | R14 | R15 | R16 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8 | none | +10 | +11 | +9 | +12... | |
| Input assigment for B3 like installation (9 harmonic drawbars plus 3 pedal drawbars) with R16 installed, no R13 | |||||||||||||||
PTX4 Potentiometer Module
PTX4-25 and PTX4-35 boards feature 4 high quality potentiometers, available with or without middle detent. The only difference is the distance from one pot to next (25mm on PTX4-25, 35mm on PTX4-35). Any number of PTX4 boards may be inserted anywhere in the MPX bus chain. A single PTX4 board adds +4 to the input numbering scheme as mentioned above, i.e if the first (leftmost) pot became input #20 (due to some previous DBX boards), the rightmost pot is #23, and next PTX or DBX board (connected to the right) will start with #24.
PTX4 potentiometer boards are not to be used as external potentiometers on additional DBX9 analog inputs. Use separate potentiometers instead.
| Input assignment PTX4-25 and PTX4-35 | ||||||
|---|---|---|---|---|---|---|
| PTX4 Pot | P1 | P2 | P3 | P4 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4... | |
| P1 is the leftmost pot | ||||||
Note: Next Board is assignment of first control of next module in chain (on right side of this module).
ANX8 Analog Input Module
ANX8 boards feature 8 additional analog inputs for connection of built-in potentiometers, drawbars, pitch/modulation wheels and other analog controls. Any number of ANX8 boards may be inserted anywhere in the MPX bus chain, with PL9 "NEXT BOARD" pointing to end of chain. A single ANX8 board adds +8 to the input numbering scheme as mentioned above, i.e if the first (leftmost) pot became input #20 (due to some previous DBX boards), the rightmost pot is #27, and next PTX or DBX board (connected to the right) will start with #28.
8 separate inputs are available on 3-pin headers PL1 to PL8. Connect pin(s) marked "REF" to end of potentiometer, pin "GND" to start, pin "AIN" to wiper.
Note: Next Board is assignment of first control of next module in chain (on right side of this module).
| Input assignment ANX8 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| ANX8 Input | PL1 | PL2 | PL3 | PL4 | PL5 | PL6 | PL7 | PL8 | Next Board | |
| Input # | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8... | |
For convenient wiring, analog inputs are also available in groups of 4 inputs (PL11 with inputs +0 to +3, PL12 with inputs +4 to +7):
| Eingangsbelegung ANX8 PL11, PL12 | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ANX8 Input | PL11-1 | PL11-2 | PL11-3 | PL11-4 | PL11-5 | PL11-6 | PL12-1 | PL12-2 | PL12-3 | PL12-4 | PL12-5 | PL12-6 | Next Board | ||
| Input # | GND | +0 | +1 | +2 | +3 | REF | GND | +4 | +5 | +6 | +7 | REF | +8... | ||
Chaining DBX6/DBX9/DBX12, ANX8 and PTX4
Connect first DBX6, DBX9, DBX12, ANX8 or PTX4 assembly to PL27. The leftmost control HX3.6/HX3.7 "sees" in the chain is external MPX analog input #0 (assigned by parameter #5024). The number counts up to the next DBX/PTX board connected to the daisy-chain connector. I.e. if you chain a DBX9 and a PTX4 (in this order), the leftmost (first) potentiometer on PTX4 becomes control #9, assigned by parameter #5033 (#0 to #8 used up by DBX9). Adding a DBX12 will start at #13, assigned by parameter #5037, and so on.
Your chain now looks like this:
| HX3.6 PL27 | cable | PL1/7 DBX9 PL3/8 | cable | PL1 PTX4 PL2 | cable | PL1/7 DBX12 PL4/8 | etc. |
| Input # | 0 1 2 3 4 5 6 7 8 | 9 10 11 12 | 13 14 15 16 17 ... |
Note: PL1 (top left, bottom mounted) and PL7 are internally connected in parallel, as well as PL3 (top right, bottom mounted) and PL8. These connectors may be used alternatively (see HX3.6_Installation_Manual#Installation_Alternatives for details).
As mentioned before, DBX6, DBX9, DBX12 or PTX4 can be arranged in any order as long as they form a chain from one board to another. Parameter assignment always starts at #0 (parameter #5024) for the leftmost control in the chain. It is possible to skip individual drawbar inputs by setting its assignment parameter to "254 - Not assigned". This may be useful for empty spaces in the drawbar lineup, for example between harmonic and ADSR drawbars or upper and pedal drawbars. All DBX boards are available without drawbar potentiometers mounted, so you may configure them as required by your installation.
Typical Applications
A typical organ configuration (9 drawbars per manual, 3 for pedal) using DBX12 may look as follows:
| HX3.6 PL27 | cable | PL1/7 DBX12 with R16 (PL4/8) | (=) | (PL1/7) DBX9 PL3 | cable | PL1 PTX4 PL2 |
| Input# | 0 1 2 3 4 5 6 7 8 -- 10 11 9 | 12 13 14 15 16 17 18 19 20 | 21 22 23 24 |
or, depending on installation (to keep cable length short):
| HX3.6 PL27 | cable | PL/7 PTX4 PL2 | cable | PL/7 DBX12 with R16 (PL4/8) | (=) | (PL1/7) DBX9 PL3 |
| Input# | 0 1 2 3 | 4 5 6 7 8 9 10 11 12 -- 14 15 13 | 16 17 18 19 20 21 22 23 |
A H100-like installation may look like this:
| HX3.6 PL27 | cable | PL1 PTX4 PL2 | cable | PL1/7 DBX12 with R13 (PL4/8) | (=) | (PL1/7) DBX12 with R13 (PL4/8) |
| Input# | 0 1 2 3 | 4 5 6 7 8 9 10 11 12 13 14 15 | 16 17 18 19 20 21 22 23 24 25 26 27 |
Note: PL1 (top left, bottom mounted) and PL7 are internally connected in parallel, as well as PL3/PL4 (top right, bottom mounted) and PL8. These connectors may be used alternatively (see HX3.6_Installation_Manual#Installation_Alternatives for details).
Installation Alternatives
DBX boards may be chained (connected to each other) by using bottom-mounted 10-pin headers (left and right side of board), top-mounted 10-pin headers or wires soldered to solder pads. We supply 2 angled 10-pin headers with each board; you may use straight headers when space allows this installation.
Instead of using flat ribbon cables, adjacent DBX boards may be chained using solder blobs and 6 short pieces of wire (marked as "=" in table above) where boards "butt against each other". Solder pads on left and right sides provide easy connection from one board to next one by DGND, VCC5, SRCLK, SRIN/OUT ANLG and NRST pads (VREF3 remains unconnected, as well as additional potentiometer pads!).
Also boards may be cut along white lines if no space is allowed from one drawbar to next on different board. If needed, cut the board before mounting the drawbar potentiometers. The boards provide additional solder pads for chaining by wires even when board is shortened. However, the row's last DBX board should retain PL3 (DBX9) or PL4 (DBX12) as you may want to add more DBX or PTX4 boards in the future. Again, plan carefully before mounting drawbar pots or cutting boards!
Dual/Secondary DBX Drawbar Sets
Classic console organ installations mandate dual drawbar sets for each manual. Using dual drawbar sets with DBX bus system differs from old DB9-MPX installations. In new DBX/MPX installations, all drawbars can be "seen" by the firmware, even the inactive ones (they are just skipped when drawbar set is not active). Set parameter #1503 to 3 (DBX mode) and assign all inputs which are primary drawbars with Upr1 or Lwr1 values, while secondary drawbars become Upr2 and Lwr2 values (128 and up).
Secondary drawbars will be activated when drawbar Voice preset on particular manual matches number in "System Inits" parameter #1505 (2ndDB Select Voice Number), otherwise they are skipped and primary drawbars become active.
Mixing DB9/DB12 and DBX Drawbar Sets
As internal inputs on PL31/PL32 can be used as drawbar inputs even in DBX configurations, existing DB9/DB12 and even DB9-MPX drawbars connected to PL31/PL32 (assigned by Analog Remap #5000 to #5023) can still be used, either as primary or secondary drawbar sets.
- When old DB9-MPX drawbar boards are connected to PL31/PL32 as secondary drawbar sets, set parameter #1503 value to 2 (DB9-MPX mode). In this case, do not use secondary drawbar assignments Upr2 and Lwr2 for inputs (parameter values 128 and up) in "Analog Remap" section; Upr2 and Lwr2 assignments will be ignored.
- When old DB9-MPX drawbar boards are not used, set parameter #1503 value to 3 (DBX mode). In this case, secondary drawbar assignments Upr2 and Lwr2 for inputs (parameter values 128 and up) can be used in "Analog Remap" section.
Product Changes and Bugfixes
Please note: Boards in version 3.6b require a small attenuation adapter between PL27 and the first DBX, ANX or PTX board, otherwise there will be interference in the analog scanning with certain cable lengths. The adapter is connected to PL27 with the "HX3" side, the DBX output then leads on to the analog controllers. This adapter was included with the HX3 mainboards. If you are converting an HX3 MIDI expander, for example, you can request the adapter free of charge. It is not required for boards with the revision number HX3.6b2.
Depending on component tolerances and cable lengths, this problem may also occur with damping board, HX3.6b2 or even HX3.7. A capacitor of 100pF (PICOfarad!) from pin 7 of PL1/PL7 (or SRIN_DATA) to pin 9 or 10 (VCC or GND) on any ANX/PTX/DBX9/DBX12 board should help. To simplify the installation, you can solder a 100p capacitor of SMD size 0805 from pin 7 to pin 9 of PL1 or PL7 (far left, seen from the front). MPX boards obtained from 1/2025 and on will have this capacitor already installed.
