Differences between Quad 405 and 405/2

Does anyone know the technical differences between the 405 and 405/2 ? I'm just curious as to what design revisions were made on the later "Mk II" version. Sean
Check out this link which will give you an idea of what changes were incorporated in the 405 and giving it the status of 405-II.


Hope it helps
Thanks very much for the link. I appreciate the info and "leg-work" : )

For those interested in such things, here's a "clickable link" for your convenience : ) Sean
>Quad 405 upgrades / mods
One major difference which I happen to know that exists between the two is that the earlier model was not capable of handling the 4 Ohm speakers but the newer 405II was improved in a way that it was able to handle 4 Ohm speakers as well.

I remember having read a very interesting article long time back in which the Quad 405 was compared with a Naim amp. Two speakers were used one having 4 Ohm impedence and the other with 8 Ohm impedence.

The Naim sounded terrific with the 4 Ohm speaker but Quad was not sounding good. After this test the speakers were switched and the result was otherwise. Quad with the 8 Ohm speker sounded terrific but not the Naim.

Those who had conducted this test were very surprised at the results as no one was expecting it would turn out that way.

I had a 405II and 34 in pristine condition which I sold to a good friend who is now driving the Rogers LS3/5a's and is very happy. The Rogers as you know are 11 Ohm speakers and they are a piece of cake for the Quad 405II in terms of handling.
I have a review of the original 405 in a 1979 "Audio" magazine. While the amp was rated rather strangely in terms of many of the spec's, it went measurably down in power output going from an 8 ohm to a 4 ohm load. From what i can remember, we are talking about a 25% reduction in power output whereas in theory, it should have been a 100% increase. I wonder how the 405 II stacks up in comparison ???

Funny thing is, i was just communicating with someone that is using a 405 to drive a large set of E-stat's that drop down to about 1 ohm or so. They told me that the 405 was doing a better job / would play louder with the E-stat's than their multi-thousand dollar mono-blocks that are rated for over three times the power. All i can say to that one is "go figure"..... : ) Sean
Yes I can figure! Let me give you some feedback on the 405II based on my personal experience.

I had these Maggies sometime back and was running the 405II to drive them, a friend of mine bought the Krell 300i and was very keen to check how it sounded on my Maggies. We spent the whole day comparing the amps and guess what the 405II was the winner! He himself was of the opinion that the Krell was a bad match for the Maggies (older version MG-1c circa 1987). The sound from the Quad was smooth and non-fatiguing whereas the Krell was harsh and unmusical. The other think we noticed was that the 405II could play the Maggies much louder. Go figure!

Quad 405 drives the electrostats wonderfully as it was meant to drive the Quads own ESL-63 and it does a fine job. Some say that The Quad is a good match for all the speakers which are voltage dependent rather than current dependant. I am not technically qualified to comment on that but you know better so you can figure it out yourself what it would mean technically.

One thing I must say here, the specs sometimes are very deceiving, hearing is believing. I have all the faith in my ears and they never deceive me no matter what the specs say. I hope it continues to be that way for sometime to come as I am at a stage in life where I am really enjoying the music.

Happy Listening!
The main difference between the 405 and 405-2 are in the current limiting circuit which was redesigned in the 405-2 to allow higher current into low impedance loads. There is also a diode added to partialy bias the output transistors.The 405-2 also features a better input opamp.
That is correct as I understand and have read elsewhere that 405-2 is able to handle a 4 Ohm load but not the 405.