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NET Audio 405 MK3 Amplifier Boards - Designed to get the very best from your 405

The NET Audio Quad 405 MK3 circuit boards have recently been updated and with the addition of the new NET Audio Schottky Dual Mono Power Supply (SDMPSU), the fully upgraded 405 MK3 sounds better than ever. Open, clear, balanced unfatiguing sound designed to get very high performance from your partnering equipment.

The Quad 405 MK1 and MK2 can be upgrade to a very high level of sonic ability but to go further by simply modifying the original Quad boards has its limitations. For higher levels of performance to be reached new NET Audio 405 MK3 amplifier boards have been designed which still uses the famous Quad Current Dumping principal to keep with the traditions of the original 405. The boards are the same size as the Quad boards and the mounting holes are identical so the NET Audio 405 MK3 boards will easily slot straight into a 405 MK1 or MK2 chassis without any mechanical modification required to the chassis.

The new NET Audio 405 MK3 boards have bee designed to obtain increased levels of detail, tighter and deeper bass response, cleaner treble and better imaging with increased load driving ability than the best 405 MK2 full upgrade that NET Audio has done. A 405 MK2 special was constructed as a one off design to take the standard 405 full upgrade to a level of performance higher than any board modification could acheive but was not a practical proposition for commercial sale. The new MK3 had to beat the 405 Special substantially to be worthy of sale as a NET Audio 405 MK3 and to guarantee a genuine leap in 405 amplifier performance.

The output stage on the NET Audio 405 MK3 uses 30A On Semiconductor Darlington transistors to do the "dumping" and high performance On Semiconductor MJE15031 transistors as the high performance class A amplifier which feed them. These two outputs are summed and then fed to the speaker, each low and high current output delivering its own portion of the audio signal. There are no current limiting circuits on the output so that the NET Audio 405 MK3 can drive difficult loads down to 3 ohms on transients and still be within the safe operating area of the transistors. The design, however,  is not intended for continued high power use (disco etc) into low impedance loads (few Hi-Fi amps ever are), as the heat sinking on the 405 is not sufficient for this, but has been designed for normal domestic use as an amplifier of very high quality used to drive speakers which may dip to 4 ohms instead of the 8 ohms with the original design.

The Quad type "crowbar" speaker protection is still retained on the MK3 boards in case any potentially speaker damaging fault does occur. This prevents your speaker drivers from being damaged in the unlikeley event of amp board failure.

The full upgrade includes a full chassis rewire including the speaker, power supply lines and mains wiring with high quality PTFE insulated Silver plated stranded OFC copper wire and fitting of all new connectors for the input (phono) and speaker outputs (gold plated speaker binding posts).

To power the boards, the NET Audio Dual Mono Power Supply (now the new Schottky version) is fitted so each board is run from it's own set of power supply capacitors instead of the original 405 which shared the power supply between the two channels. Please see here for further details.

Board fitting instructions can be downloaded here.

Full NET Audio 405 MK3 Upgrade instructions can be downloaded here.

Simply put, this is the best commercially available 405 replacement board and upgrade kit available bar non.

A review of the original is available from Hi-Fi Insight here and here

Specifications:-

Input Sensitivity 1.5V RMS

Power output: Greater than 100W RMS into 8 Ohms at 240V Mains Voltage

Distortion into 8 ohms in standard 405 chassis with NET Audio Schottky DMPSU and AD843 Opamps

50Hz

1W 0.0095%   10W 0.0041%   100W   0.003%

1kHz

1W 0.0085%   10W 0.0045%   100W   0.0036%

10kHz

1W 0.011%   10W 0.0095%

Damping Factor >200 at 1KHz

 

NET Audio 405 MK3 Circuit Board


 

NET Audio 405 MK3 Boards

The NET Audio 405 MK3 amplifier boards are configurable for the variances between the MK1, MK2 and the latest graphite MK2 405s with the power switch and phono sockets on the rear panel so that the new MK3 boards can be fitted to any Quad 405 by simply removing the original Quad boards and then fitting the new NET Audio 405 MK3 boards using the same connectors on the wiring loom without any soldering being required.

NET Audio 405 MK3 Boards consist of

  • Two NET Audio 405 MK3 amplifier boards fitted with OPA604AP Opamps
  • Fitting instructions in downloadable PDF format

Total Price  = £230

 

  • If you require OPA627AP Opamps instead of the standard fitment OPA604AP then please add them to you order with the Add To Cart button below. This applies to the Full Upgrade Kits also.

    • Two Burr Brown OPA627AP Opamps to be supplied instead of the OPA604AP

    Total Price  = £26


    NET Audio 405 MK3 Full Upgrade

    The full upgrade consists of two NET Audio 405 MK3 boards fitted into you 405 MK1 or MK2 chassis and a NET Audio 405 dual mono power supply. Your 405 will be completely stripped down and the full upgrade fitted for you at NET Audio and fully bench tested once complete. All internal wiring is replaced by PTFE insulated, silver plated copper wire.

    NET Audio 405 MK3 Full Upgrade consists of

    • Two NET Audio 405 MK3 amplifier boards with OPA604AP Opamps
    • One NET Audio Dual Mono Power Supply
    • Full set of silver plated OFC cables used to wire DC power and speaker outputs.
    • Transformer directly wired to the mains inlet socket (and fuse) at your required mains voltage.
    • Two phono sockets wired with OFC  input wires
    • Gold Plated Speaker Binding Posts
    • Full bench test once the upgrade has been completed

    Total Price  = £400


    NET Audio 405 MK3 Full Upgrade Kit

    The full upgrade kit consists of two NET Audio 405 MK3 boards, full assembled and tested with accompanying wires to fit into you 405 MK1 or MK2 chassis and a NET Audio 405 dual mono power supply. Your 405 will need to be completely stripped down then the new modules and wiring fitted by yourself.

    NET Audio 405 MK3 Full Upgrade Kit consists of

    • Two NET Audio 405 MK3 amplifier boards with OPA604AP Opamps
    • One NET Audio Dual Mono Power Supply
    • Full set of silver plated OFC cables used to wire DC power and speaker outputs with crimp terminals fitted.
    • Transformer wiring to connect the mains inlet socket (and fuse) at your required mains voltage
    • Two phono sockets with OFC  input wires
    • Gold Plated Speaker Binding Posts
    • 2m of 0.8mm Silver Solder
    • Tube of Heatsink Compound

    Total Price  = £335


    NET Audio 405 MK3 Monobloc Conversion

    The NET Audio 405 MK3 amplifier boards can be fitted to any MK1 or MK2 405 amplifiers to convert them to a Monobloc, one per channel for stereo use. The complete full upgrade conversion is fitted, minus one channel and its power wires, with one single phono input for signal and two pairs of speaker binding posts for speaker connections - either single or bi-wired. The Monobloc version produces 115 W RMS into an 8 ohm load (measured at just over 115W RMS continuous - mains voltage was 239V AC at the time of measurement)

    NET Audio 405 MK3 Monobloc Conversion

    • One NET Audio 405 MK3 amplifier board  with OPA604AP Opamps
    • One NET Audio 405 Mono PSU board
    • Full set of silver plated OFC cables used to wire DC power and speaker outputs.
    • Transformer directly wired to the mains inlet socket (and fuse) at your required mains voltage.
    • One phono socket wired with OFC  input wires
    • Gold Plated Speaker Binding Posts x 2 for bi-wired or single wired speakers
    • Full bench test once the upgrade has been completed

    Total Price  = £285 per amplifier.  Out of Stock

     

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