MKS-40 Power and Case


Rack Mount Case Rather than attempt the metal work for a keyboard replicate of the Jupiter or a desktop unit, a 2U rack case is the best design as it has the deep space needed for the electronics and a new front panel can be easily fabricated at a reasonable cost.

The solution chosen is a RS Pro Ventilated 2U rack mount case with ventilated aluminum sides and steel external panels. The ventilation ensures the circuits can remain cool without resorting to a DC fan. The rack mount case has a grey powder paint, and the low height of the top and bottom panel lips provides the maximum space for the PANEL PCB. The case has a depth of 360mm which provides lots of space for the PSU and circuit boards.

The case was bought at an early stage to check the panel dimensions and component layout. It is a tight fit at the front!

Front Panel A 2U custom aluminum panel has been designed and Beta Layout have done the manufacturing. I have kept to a plain anodised aluminum, which is 3mm thick and holds the printed text the best. A black panel is possible but more expensive. I have not tried to emulate the originals colours and fonts, as this is not an exact replica of the Jupiter 4. The panel has CNC drilled holes for the components, countersunk screw holes for mounting the PANEL PCB to the back and to mount the panel to the case.

Whilst one of the first items to be designed, it was the last to be bought to ensure the fit is correct.

Rear Panel The RS Pro case has been drilled at the rear for;

  • MIDI IN
  • Audio Outputs L and R (XLR’s)
  • IEC Power Inlet

Power Supply  The original Jupiter 4 power supply provided +5V at 1A, and +15V and -15V also at 1A.  The -15V rail needs to be accurate, as it it is used as a reference voltage to various critical areas; ADSR clock generator transistor pair, VCO tune and pitch DAC. Roland specify this rail must be accurate to +/-10mV.

The MKS-40 uses -10V precision voltage references in the VCO and ADSR Clocks, with suitable resistor adjustments. The pitch DAC has been upgraded to 12-bit with its own precision voltage reference. Roland also moved to precision power rails in the Jupiter 8.

A modern switched power supply will be used; either the Meanwell RPT-60C or the more powerful LPT103-M, depending on the -15V current consumed. A lab power supply will be used during development, then a decision on which PSU to use can be made on total current consumption.

The power rails are provided to the Processor, Motherboard, Assigner and Chorus boards connect directly using a star network and thick cables. The Voice cards get their power from the Motherboard and the Processor PCB provides power to the Panel PCB.

The Jupiter 4 experienced a few issues with the pitch and power cabling/traces. From serial number 871600 the GND and -15V on the Assigner board were hard wired back to the power supply and the D7 and C4 connectors were hard wired to avoid pitch issues in the Portamento circuit and VCO. There were also extra power supply decoupling caps added on the trace sides of some boards.

The MKS-40 pays carefully attention to these original issues by using a star network and large cables to the main boards, as well as extra decoupling caps as part of the PCB design.

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