Wednesday, November 16, 2005

Quad 405 Tansformer rumble ....

Some older 405's have a problem with the transformer. It produces a rumble (not in the speakers but in the transformer itself).

There is no way to fix this problem except by replacing the transformer.

Of course you can order a new transformer from Quad but this is a quite expensive solution. Therefor this alternative: one can fit a toroidal transformer (300VA 2x 35V). This also offers the advantage of better stability and somewhat less noise, limiting the cost to about 90 Euro.

The only problem: to fit it in you will need a special mounting plate. I found one on Ebay in the UK, Stuart Adamson had them made by a steel manufacturer. I also had to move the fuse because it was in the way (see the picture).

But now my 405 works fine again ;-)

PS. The transformer you need is a Toroidal 2x 35 or 2x 36 Volt, 300 VA (not less!). Make sure it will fit in.


A 300VA toroïdal transformer and the mounting-plate are now available in the Dada Electronics Webshop.


Anonymous Anonymous said...

Hello, what is the good voltage for a new toroidal transformer?


3:25 AM  
Blogger Stefaan said...

The ideal voltage of the transformer to get +/- 50 Volt, as foreseen in the original design is:

50V / squareroot(2) = 35,36 Volt.

So 2 x 36 Volt @ 4 Ampere will do perfect.


9:38 PM  
Anonymous Anonymous said...

Merci Stefaan,


2:11 AM  
Blogger KostisK said...

I have a modified 405 with net audio dual psu. My concern is whether the physical dimensions of the toroidal transformer aren't compatible ? Any opinions ?

2:41 PM  
Anonymous Anonymous said...

I wonder if you know what VA rating the original 405-2 transfomer has? (300VA?) Is the transformer in the 405-1 the same as the 405-2, BTW?

6:25 PM  
Blogger Stefaan said...


The original 405 transformer is a double 2x35V 2A transformer so this makes 280VA in total.

The 405-1 and the 405-2 have the same transformer.


6:32 PM  
Anonymous Anonymous said...


Thanks for this useful post, I have transformer noise in my 405-2 :-(

You say 2 transformers would be better for a dual supply.

I can only find:

2x35 120Va 1.71A
2x35 160Va 2.29A

Would a pair of either do the job and would it be better to have the 1.71 or 2.29 amps in the 405.



3:57 PM  
Blogger Stefaan said...

Hi, Joel,

2x 120VA is not enough, it would limit the maximum power and/or the transformer might be overloaded.
2x 160VA is a better idea if you can find them small enough to fit.


4:05 PM  
Anonymous Anonymous said...

Great Post Guys, I had the same problem and I used the transformer from Amplimo 78018 (300 VA) cost : 66 euro.

With two simple tie reps it is fixed in the chasis

6:56 PM  

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