Hamptone MK2 Motor Control for Leslie Speakers

MK2 MOTOR SPEED CONTROL 

( Made in the USA! )

The MK2 is based on the same pulsing concept that the MK1D uses, but expands upon it adding several new speeds, and remote operation from an Expression pedal (50K ohms) or a TRS dual footswitch.

The MK2 uses a microcontroller (programmable “brain”) to detect an EXPED (expression pedal) or FS (footswitch) and switch internal circuitry to interpret the two different inputs.

FOOTSWITCH (FS) OPERATION

When a TRS dual footswitch is plugged in to the 1/4″ jack, one switch becomes an ON/OFF switch, while the other toggles between FAST speed and the SLOW speed chosen by the dip switch settings (shown in the left column of the settings table). In FS mode, the unit has 3 speeds, OFF – SLOW – FAST.

EXPRESSION PEDAL (EXPED) 3 SPEED MODES

An expression pedal can also be used, and when any of the 10 valid speeds selected in the FS mode are chose, the MK2 will act as a 3 speed. When the pedal is fully back, the motors are off, 10%-90% position will select SLOW speed, all the way forward selects FAST. The expression pedal should be 50k ohms linear taper.

EXPRESSION PEDAL OTHER MODES

There are 6 additional modes of operation when an EXPED is used: 3 modes with 4 speeds, 10 speed, Pulse width Modulation, and external midi CV mode. The 4 and 10 speed modes divide up the pedal range evenly and switch between the various speeds shown in the right column of the dip switch table. PWM (pulse width modulation) and midi CV are described in detail below.

PULSE WIDTH MODULATION MODE (PWM)

Pulse width modulation is a different concept of changing a motors speed by varying the amount of time each AC cycle is on. The result is smooth speed change in the upper speed range, but limited torque in the lower speed range. The MK2 does not use a tachometer, which is usually present in a PWM system. Therefore, the speed can be less stable, and at slow speed, can stall. The PWM range has been limited to avoid low speed stalling, but the speed at which that can happen may vary from Leslie to Leslie. Therefore the user should use caution when using this mode, if the motors stall, the MK2 will still be pulsing the motors, which is not good for the MK2 or the motors. We included this as a “special” mode. The PWM dip switch setting is only read at power up, and the unit stays in that mode until the power is cycled (turning the unit off for approximately 5 seconds). As the EXPED is moved toward the FAST position, the “ON” time of the motors is increased making them go faster. At a point, the motors will “jump” to full speed. The MK2 has been designed to turn the motors on fully at this point.

MIDI CV MODE

The MK2 can be controlled from an external DC voltage using the circuit shown. The input of the MK2 is not opto isolated, so care should be taken to ensure the input does not exceed 5.0vdc. Though there is over-voltage protection on both the Tip and Ring inputs, but excessive DC voltage, or AC can cause the
microcontroller to go into reset stopping normal function. The MK2 does have an internal power transformer, so its ground is essentially “floating”, and should conform to an external system ground. Refer to the table below for speed vs CV voltage on the RING of the TRS. The TIP must be terminated to ground through a 50k ohm resistor.