Korg Monopoly PSU replacement

About Korg Monopoly PSU (power supply unit) replacement

Problem with the old PSU

This new PSU was made to replace the old Monopoly PSU. Unfortunately the original PSU has a lot of disadvantages and design issues that decrease the reliability of Monopoly synthesizer:

  • Heat! The biggest problem in these units. Monopoly synth has too many heat sources inside:
    • VCOs heating inside SSM2033 chip and on the SSM2033 chip (resistor)
    • heating circuit KLM-357 with power transistors that produce heat
    • 50/60Hz transformer (gets too hot!)
    • Linear regulators that produce PSU voltages +5V, +15V, -15V
  • Less efficiency, under 30{eb681a58ecc476759952a50a8a7c167279151df38e58f2598760f2d2e5f4f286}.
  • Higher weight (around 1,1kg)
  • Interference of 50/60Hz hum with tone signal. Note that mains transformer and power cables are located close to the filter board when the synth’s panel is closed. This is especially audible at higher amplification levels when no tone is playing. If you put the synth’s panel up you will see the noise is getting lower. It is because transformer/cables are now more far away from the filter board

Basically the biggest problem is that original voltage linear regulators need at least 4 to 5V of dropout voltage (Vin-non-regulated – Vout-regulated) to work properly. This causes unnecessary losses. So changing of linear regulators is necessary.

Another biggest problem is the mains transformer that radiates 50/60Hz noise and that is totally underrated. It’s dimensions should be bigger. But the most critical is that this transformer produces unnecessary high voltage that is further rectified and comes to the input of linear regulators. The transformer should be changed.


Solution: NEW SMPSU with LDO regulators

After analyzing of the whole PSU system in Monopoly the decision was to build a tailored Switched Mode Power Supply Unit (SMPSU) with LDO (Low Drop Out) regulators to get clean and noise-less supply voltage.





Benefits of a new Monopoly PSU:

  • Heat problem was reduced by means of using of a modern AD/DC converter topology. Modern LDO regulators make possible to achieve much less power losses because of very low drop out voltage (typically 1,5V).
  • An [AD/DC converter] instead of a [mains transformer + rectifier + filtering caps] allows very effective using of LDOs because a relatively high ripple voltage of transformer+rectifier+filtering-caps is eliminated
  • Tailored dimensions, the PSU is installed instead of an original Linear regulator board KLM-376
  • Not necessary to set the -15V and +5V voltage, it is already within desired range (-15V +-10mV, +5V +-20mV)
  • Lower noise, no mains hum interfering with a sound signal
  • Massive metal shielding of a AC-DC converter part that physically separates low voltage cables from the mains voltages. It further reduces the EMI emissions.
  • Higher overall efficiency, more than 70{eb681a58ecc476759952a50a8a7c167279151df38e58f2598760f2d2e5f4f286}
  • Low weight, around 0,3kg
  • Star grounding
  • Full drop-in replacement for an old Monopoly PSU (that consists of a mains transformer, KLM-376 and KLM-372 boards)


FOR SELL: Replacement Korg Monopoly PSU kit

  • 1x completed and tested PSU board incl. shielding & incl. original connectors
  • 1x insulator plate
  • 8x DIN 934 M4 nut
  • 4x DIN 7985 M4x12 screw
  • 3x DIN 125 M4 metal washer
  • 2x earthing cables incl. soldering eyelet


PLEASE NOTE! We sell a fully working and tested PSU with few additional parts (see list above) to mount the PSU into the synthesizer. The following installation is an example. We are not responsible for health injuries and material damages that can cause bad installation of this PSU. Only a qualified tech should make this PSU swap! You are doing the PSU swap on your own risk.


Installation instructions

Be sure the power cord is DISCONNECTED from the wall socket!!


Remove old PSU components, „prolong“ the mains cable inside the synth


Install the insulator plate, see instructions on the pic


Install the PSU, fasten it with 4x M4 DIN934


Connection of mains cable and mains switch and mains earth
Both black switch wires are interchangeable 


Two thin black earth wires: one is connected to the KLM-356 shielding, the second one to the rear jack assembly

On the pictures above supply connectors for all synth PCBs (CN31…35) are already connected. Don’t plug them when turning the PSU for the FIRST time!

Now, when everything is installed, double check everything!! Plug the mains plug into the powerpoint and turn on the switch. Check all supply voltages: +15V, +15V, +5V. If they are present, turn off the switch and unplug the mains plug. Connect all connectors (CN31…35). Ready!

Pricelist (in EUR) & ORDERING

Please, place an order via E-mail! Normally we response within 12 hours.