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Quad 405 Dual Mono Power Supply

A weakness of most amplifiers is the power supply. This is a reservoir of energy which used to supply current to the amplifier as and when demands are made of it. A primary consideration is a low impedance (resistance to change) over as wide a frequency band as possible. This is easily achieved at higher frequencies but is more difficult at lower frequencies due to the heavier demands made upon the power supply in the bass region as the signals are normally far larger then the treble plus the power supply impedance naturally rises at lower frequencies because of the nature of the PSU capacitors themselves. One solution to the problem is to fit larger capacitors in the power supply - a doubling of capacitance would double the available charge that the amplifier can use, hence increasing bass slam, solidity etc. What can also be done is to split the power supply into two parts, each supplying current to its own amplifier channel. This is known as a dual mono power supply. The advantages are that if the original capacitor values are used the the total charge available to the amplifier is still doubled but each channels demands do not effect the other channels operation.

The NET Audio 405 DMPSU is designed to take advantage of the fact that the 405 transformer has two secondary windings which are used in parallel to feed a single power supply rectifier and capacitor set in a standard 405 MK1 or MK2. 

If the secondary windings are split, each winding can be use to feed an independent rectifier and capacitor set, one for the right channel and one for the left, now creating a dual mono design with each channel having its own 2 x 10000uF power supply instead of both channels sharing a single set of the same value as in the original design. This eliminates the PSU cross talk which occurs in a standard 405 producing much improved imaging, detail and bass response.

The 405 Dual Mono Power Supply is shipped complete with all necessary fixings and wiring to enable this unique upgrade to be fitted to your 405 MK1 or MK2 in just a few hours.

Fitting instructions can be found Here.


4 X 10000uF Dual Mono Power Supply.

Ideal for the 405 MK1 and MK2 as the ultimate power supply and capacitor upgrade. Provides independent left and right power supplies for each channel.

Quad 405 Dual Mono Power Supply Capacitor upgrade includes in a fully built module:-

  • Four Audio Grade 10000uF 63V Capacitors.
  • Now with Schottky Rectifiers.
  • Two bridge rectifiers.
  • One fiberglass circuit board.
  • All fitting screws, solder tags, wiring etc.
  • OFC Silver Plated Copper earth strap 
Total Price excluding P+P = £85.

Quad 405 Dual mono power supply module. As this is a high value item it will be posted by Special Delivery unless requested otherwise.


The OFC Silver Plated Copper earth strap is available separately for customers who have fitted the NET Audio 405 DMPSU but bought the PSU before the earth strap was supplied.

The earth strap connect to the central earth bolt on the PSU to the top M4 bolt on the rear of the heatsink which used to hold the original rectifier on. The strap is 100mm in length.

  Total Price excluding P+P = £1.50.