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.
Stefaan
A 300VA toroïdal transformer and the mounting-plate are now available in the Dada Electronics Webshop.
Hello, what is the good voltage for a new toroidal transformer?
ReplyDeleteSeb
The ideal voltage of the transformer to get +/- 50 Volt, as foreseen in the original design is:
ReplyDelete50V / squareroot(2) = 35,36 Volt.
So 2 x 36 Volt @ 4 Ampere will do perfect.
Stefaan
Merci Stefaan,
ReplyDeleteSeb
Stefan,
ReplyDeleteI 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 ?
kostis
Hi!
ReplyDeleteI 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?
Regards
Hi,
ReplyDeleteThe 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.
Stefaan
Hi,
ReplyDeleteThanks 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
and
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.
Thanks
Joel
Hi, Joel,
ReplyDelete2x 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.
Stefaan
Great Post Guys, I had the same problem and I used the transformer from Amplimo 78018 (300 VA) cost : 66 euro.
ReplyDeleteWith two simple tie reps it is fixed in the chasis
http://www.amplimo.nl/index.php?page=shop.product_details&flypage=flypage-rin.tpl&product_id=72&category_id=10&option=com_virtuemart&Itemid=134&lang=en