John's Organ Works

MIDI Keyboard Stacks
MIDI Pedalboards
MIDI Encoders and Decoders
Miscellaneous Sales
Our Selling Policy
Place an Order
Contact Us
The Virtual Pipe Organ Explained
John's Blog

Do Not Feed!
Organ Grinder

KS4B - Base Unit for Four Keyboard Midi Stack


base unit

The KS4B base unit fits beneath the KS2 two keyboard MIDI Stack and converts it into a four-keyboard stack. Perfect for Salisbury Cathedral or the Silver Octopus 70 stop Willis! The base units adds two further keyboards, each with its own USB connection to the computer. The pistons of the base unit are wired to two 9-way D-connectors which plug into the auxiliary piston ports of the upper unit. 

The upper stack simply stands on the base unit, located by metal fingers. It can easily be lifted off again, whether to conveniently transport the whole in two parts, or to use the upper part independently as a two-keyboard stack.

The base unit is guaranteed for one year.  See Our Selling Policy for the terms of our guarantee.

The rest of this description applies to the two units assembled as a four-keyboard stack.


Features at a glance
* four full-size 61 note keyboards
* 8 pistons per keyboard
* semi-weighted touch
* substantial bolted MDF chassis - no wobble!
* upper three keyboards progressively inclined for comfort
* requires no external power supply and no batteries (draws power from USB connections)
* requires no MIDI-to-USB converter
* non-scratch feet (which may be removed if stack is to be bolted down)
* option to connect two expression pedals
* option to add music stand
* finished in black  (goes with anything!) Other colours available.
* can be transported in boot and back seat of most cars (after being separated)
* fully compatible with Hauptwerk (keyboards compatible with Miditzer)
* a generic pdf User Guide is available on our Downloads page
* needs 5 available USB ports

Computer requirements
The stack should work with any reasonably up-to-date computer whether PC or Mac. The necessary drivers may already be installed. If not, they can easily be downloaded free from the M-Audio website ( If in doubt, go to the M-Audio website, select your operating system and check that drivers are available for the following devices:
* Keystation 61
* Ekeys

The stack is not in itself a musical instrument. It only works in conjunction with suitable software (eg Hauptwerk or Miditzer). Obviously, your computer must also meet the requirements for your chosen software.

Note: You will need 5 free USB ports to connect the stack (and you may need a further 2 for the Hauptwerk dongle and a MIDI pedalboard.) If your computer does not have enough ports, you can use a USB hub to expand it.

Physical dimensions
Overall width (side to side)                880 mm
Overall depth (front to back)              610 mm
Height with feet                                 360 mm
Height without feet                            350 mm
Length of keys                                  137 mm
Vertical separation of keyboards           70 mm
Keyboard overhang                             22 mm
Inclination of second keyboard              2.5 degrees
Inclination of third keyboard                   5 degrees
Inclination of top keyboard                     7.5 degrees
Bolt down sockets (with feet removed)  4 X M4

Keyboard touch
The keys are taken from M-Audio Keystation 61 MIDI keyboards and have exactly the same touch, which the manufacturer describes as “semi-weighted". We wouldn’t claim that this touch is completely perfect from an organist’s point of view -  the contact point is a little too low - but in our opinion it still provides a perfectly workable solution and an enjoyable playing experience.

The 32  pistons can be configured to do almost anything in Hauptwerk. Most obviously they can be used as combination pistons, but they can also carry out menu commands. Particularly useful ones are to advance the registration sequencer, or to start and stop the built-in recording. The pistons are not numbered, but they are grouped for ease of identification.

The pistons cannot be used in Miditzer  (but you can use your computer keyboard for this purpose).

 Swell pedal connection
The rear panel of the KS2 upper stack includes two stereo jack sockets to which standard keyboard expression pedals can be attached. Useful if your pedalboard has no swell pedals (or not enough). Simply bolt additional expression pedal(s) to your pedalboard and pass the lead(s) up to the back of the stack.

 Auxiliary piston ports
The auxiliary piston ports of the KS2 upper stack are used to process the pistons of the KS4B base unit. It is not possible to attach additional pistons (such as toe pistons), except when the upper part of the stack is used independently.

 MIDI output channel
Each MIDI output is on channel 1 which is suitable for Hauptwerk. For a small additional cost, one extra piston can be fitted to each keyboard to select the output channel (1 - 16). This is necessary if the stack is to be used with certain other software, including Miditzer and jOrgan. It is not required for Hauptwerk use. Piston output is always on Channel 1


Place an order

Return to MIDI keyboard stack page

Return to home page