Quad 405 Information Page

Original sales brochure

This is a link to the original Quad 405 sales brochure.

http://www.quadesl.org/Amplifiers/amplifiers.html

http://stereophile.com/interviews/522/

MAC MOD 405
The respected audio designer Steve McCormack (USA) soon realized that the basic concept of the Quad 405 ("Current-Dumping") was great, but the idea was destroyed by crummy parts and a drastic protection circuitry. In consequence he offered a modification kit for the 405. The ultimate Mac Mod were mono amps. The modification contained the following changes :

· Current Limiting removed

· Improved IC fitted (LM 318)

· Faster Drivers ( Motorola MJE 15031 )

· Faster Output Devices ( Motorola 2N3773 )

· Improved Resistors (metal-film 1% by Resista Mk3 or Corning RN-60 )

· Improved Capacitors (Wonder Caps, Wima, dipped mica)

· Improved Wiring (Audioquest) and Plugs (Tiffany)

The Mac Mod 405 surpasses the original 405 in every respect : It was a great sounding amp which could compete with the most advanced high end amps in these days. Harry Pearson of the "Absolute Sound" magazine wrote an enthusiastic review about it. I still regard it a pity that Quad-UK did not overtake the Mac Mod as standard, because the improved 405 is an exceptional amplifier. The only caveat about the complete Mac Mod is, that the ultimate version (= mono amps) has too much power for the delicate ESL-57 (protection circuitry mandatory !), though power output is quite right for the ESL-63.

Bernd Ludwig Text File and Schematic

This page is an extremely comprehensive Quad 405 modification document (plus other related info) that was very kindly sent to me by Bernd Ludwig. Please remember all audio equipment contains high voltages so only undertake modifications if you know what you're doing. Version June 2005.

Mono-block instructions

This is a link to a two page instruction for mono-blocking your 405 or 405-2. By monoblocking the amps, you will get double the current capacity, but still retain the 100 watt at 8 ohm output. I have several mono-blocked amps, and they do sound better. My B&W Nautilus 805 speakers are bi-amped and my matching Focal transmission line subs are mono-blocked. So I use a total of 8 channels of Quad 405-2 amps for my stereo listening. Do not even ask how many channels for my whole home theater system!!

The Canadian version of the amps did not come with a variable input voltage selector. They came fixed at 110 volts and had a more robust wiring and also an extra set of fuses. Click on the picture to the left to see the Canadian version of the power supply and how to wire it.

This is a pdf file of redrawn schematics from http://www.dc-daylight.ltd.uk/index.html showing the evolution of 405 and 405-2 schematics.

Here is a link to the 405-2 modifications page at http://www.dc-daylight.ltd.uk/Valve-Audio-Interest/QUAD/QUAD-405-2-Modification/QUAD-405-2-Mods.html

This is a pdf file for the 405 Owners Manual

This is a pdf file for the 405-2 Owners Manual.

405-1 pdf file schematic

405-1 hi-res schematic jpg

405-2 pdf file schematic

405-2 hi-res schematic jpg

This is an article by Max Dubious titled "Pooging The Quad 405: Chicken Salad from Chicken Bleep. It is a nice article on updating the venerable Quad 405 and 405-2 amplifier.