Quad 405 thingy

[Jonboy]

Barry has just told me off for willy waving so here is a pic of my beast, the story goes that it was built by a Quad engineer to power ESL's and based around two 405 amplifiers but having one large transformer, it also has 4 soft start relays, you can use one side of the amp or both sides to bi-amp, two imputs and four speaker outlets with toggle switches at the front to set it how you want, as you can see it not the prettiest thing in the world but it does sound rather nice for a solid stater.
It came to me a couple of years ago along with a pair of ESL 63's that have now been sold on

[Barry]

Barry has just told me off for willy waving so here is a pic of my beast, the story goes that it was built by a Quad engineer to power ESL's and based around two 405 amplifiers but having one large transformer, it also has 4 soft start relays, you can use one side of the amp or both sides to bi-amp, two imputs and four speaker outlets with toggle switches at the front to set it how you want, as you can see it not the prettiest thing in the world but it does sound rather nice for a solid stater.
It came to me a couple of years ago along with a pair of ESL 63's that have now been sold on

I take it all back - it is bigger than the commercial 405 amplifier. What are the numbers and issue of the circuit boards? Have any mods been made to the circuit boards?

Nice one!

Regards

[DSJR]

There looks to be two transformers in there as well.....

Nowt wrong with the 405 circuit once fettled (Quad went through at least 7 versions of the amp board to get to mk2 form and the earlier versions can have all sorts of lovely things done to improve them. As long as the thing doesn't run hot you won't go wrong...

[Jonboy]

Yes there are two trannys, the numbers on the three of the circuit boards are M12565-7, 405-2 and one board has M12565-3, does this mean three are the later boards with one perhaps not?
As for mods i couldn't tell you

[Barry]

Yes there are two trannys, the numbers on the three of the circuit boards are M12565-7, 405-2 and one board has M12565-3, does this mean three are the later boards with one perhaps not?
As for mods i couldn't tell you

Jon,
Are you sure the first quoted number is not M12368-7 ? If so, then this is same as the original board (M12368-5) but with a change of track layout and changes to the values of some of the components:

R2 10R from 2R2
R4 22K from 10K
R5 4K7 from 10K
R9 220R from 180R
R19 (3K3) removed
R23 1K2 from 3K3
C9 (330p) removed
C18 47n added
FS1 and FS2 interchanged


M12565-3 was introduced at sn. 59001. Other 405's with this board are sn. 57301 to 57600. This board incorporates the clamp circuit, which was previously fitted separately, as part of the amplifier board. Voltage limiter is now a link. Other circuit changes resulted in a re-designed board layout.

Regards

[quad405]

I like it, I like it!

[Jonboy]

I have just checked those numbers again Barry and they are as i said.
These are the only numbers i can see on the boards near the heat sinks unless you know a different place but this would probably mean stripping them apart

[Barry]

Jon,

My information came from the 'Quad 404 Power Amplifier Service Data' section of the Quad handbook for service engineers.

Since my last post I have found reference to the circuit boards M12565-7. They are quoted on the Quad 405-2 circuit diagram M12333 Issue 9. I cannot, as yet, tell you the serial numbers of the 405-2 to which they apply, but as the last Issue was 10, they would be fairly late versions. For both the M12565-3 and -7, the output protection circuit was integral with the board and both used a thick film network comprising four transistors, six resistors and a diode, referred to as N1 and N2 and essentially replacing the circuitry around TR5 and TR6 of earlier versions, used in the 405-1.

Regards

[Marco]

Hi Jon,

Your amp may not look pretty, but it's giving off a good sounding vibe to me!

Oi loikes it

Love those big blue caps - what kind are they?

Marco.

[Jonboy]

sorry Marco i can't look up anything at the moment as i'm currently sitting sipping red wine in the middle of France writing on a borrowed laptop, the sun is shinning, birds are singing, it's sheer bliss to be away from the manic flat out pace of life in England