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-   -   Quad 405 Mk 1 (http://www.diyaudio.com/forums/solid-state/81888-quad-405-mk-1-a.html)

bulgin 21st June 2006 06:49 PM

Quad 405 Mk 1
 
Hi All

A few weeks ago I bought a Quad 405 Mk 1 for peanuts and to add to my other Quad dinosaurs, or so I thought... It has been in storage elsewhere for at least 10 years and over the weekend, I decided to find out what gives, after all the negatives I read about it.

I took off the top plate and saw a virgin amp with everything clean, just like Huntingdon made it. I have a couple of restored 33 pre's but decided to use my workhorse Kenwood Ci Basic as a pre-amp, after making up an interconnect with rca phonos at one end and a 4-pin din at the other.

I don't know if my expectations were too low but I was actually pleasantly surprised - no crackles of pops, just surprisingly dynamic in sound - not bad for the 5 tenners (UK) I paid. And it packs a nice wallop too.

Later, I will try another pre or Quad's 33 to see what's up.

bulgin

Zombie 22nd June 2006 06:50 AM

Q33
 
Wise choice to avoid the 33...

AndrewT 22nd June 2006 07:31 AM

Hi,
an amp that has aluminium electrolytic capacitors in it may need a bit of tender care before switching it on after long storage.

Apparently the oxide insulator degrades with time when insufficient voltage is across the terminals.

To recover the caps a process called reforming is advised. this builds up the insulator between the plates to ensure that excessive leakage does not damage the cap at switch on.

bulgin 22nd June 2006 12:30 PM

Quad 405
 
Hi Zombie, AndrewT

I know all about that (the caps) vulnerability at startup after storage and took a reckless chance (which I shouldn't have!), not knowing how to feed regulated ac to the amp. Fortunately, all is well by the looks of things.

Would you have any idea on how to go about this, please?

bulgin

sreten 22nd June 2006 12:40 PM

Hi,

Its a good idea to replace all the electrolyics in an old amplifier,
power supply and signal electrolytics, upgrading in the process.

:)/sreten.

Zombie 22nd June 2006 02:04 PM

Net-Audio.co.uk
 
has some interesting upgrades...

sreten 22nd June 2006 02:46 PM

I meant upgrading the quality of the capacitors, not modding the amplifer, :)/sreten.

Zombie 22nd June 2006 02:59 PM

Modifying?
 
Some of the kits at net-audio replace old elcos with new and better ones...why not change the opamp for a better one while at it?
The double PSU kit is not a mod, just an upgrade to the 306 and 606 level.
Would replacing the original PSU caps with 15000uF+ be a mod or an upgrade?
Would changing the 120p ceramic to a silver mica be a mod? Or make the upgrades Quad itself did to the 405-1?
Nope.
But I would consider the Snook and Ludwig suggestions to be "mods"...
Happy solstice
Thomas

AndrewT 22nd June 2006 03:08 PM

Hi Bulgin,
you need to remove the electrical connection from at least one terminal of each electrolytic to allow connections from very high source impedance and DC voltage supply. And then monitor leakage and charge rate over a few hours. Quite a time consuming process and you must be careful to NOT accidentally short a charged capacitor risking internal damage and to yourself.

bulgin 22nd June 2006 06:39 PM

Quad 405
 
Thanks Guys!!

I know about those dangers. My local expert sage for years on old timer amps has unfortunately moved away and 'gone fishin'. Time to read more electronics books and do the jobs myself, I guess. Replacing caps and changing stuff to make these old amps better and more convenient to use, I've done before.

Regards to all

bulgin


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