Quad 405-2 vs 303

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V9977

Well-known member
Joined
Nov 22, 2004
Messages
170
Location
Athens, Greece
Have been a/b testing these two amps which have been in the familly for years.
They have been used in a pro context for thousants of flight-hours and have just
finished renovating them. Both in very simmilar condition and opperate correctly.

The 303 sounds so much more 'impressive' it is unreal.

I don't get it...
 
What's your load like? The 405 series has some weird behavior when the load strays from resistive. Supposedly the 405-2 cleaned a lot of that up but there apparently were still issues.

Peace,
Paul
 
Thanks for reply.

I thought all speakers presented a load which strayed from resistive quite bit?

Tried them both with JBL4401 and Westlake LC3w12.
They were a bit underpowered for the Westlakes (esp. 303) but the difference was massive
and everyone prefered the 303 by miles.

Now, wether that is closer to the true representation of the mix is a totaly different matter..
 
How far did you go with your renovations? More than just a recap and bias?

My 405 (Mk I) needed a recap and I decided to go further. I carried out Bernd Ludwig's upgrade mod on mine. I didn't try any fancy opamps, just a 5534, and the difference was night and day, like a veil had been lifted. The main difference seemed to come from reworking the input stage for less gain and better bandwidth.

I have a couple of 303s too, which I have recapped and replaced the trimmers. The difference with the 303 wasn't nearly as obvious as with the 405, although after the recap the 303 was way quieter and more phase-coherent.

 
I've always been a big fan of the Quad 303. A fantastic amplifier and a great company.
These are the kind of amplifiers that work continuously for 15 years and sound really good.
I've come across them in all kinds of places.
When I did some work at Abbey Road in the 80's the monitors (JBL) each had a 303 working in 'balanced' mode. Sounded great.
Generally these amps only go wrong when a capacitor blows or a transistor gives up the ghost - in which case it's best to replace ALL the transistors - as it's DC coupled throughout and if one goes they generally all go.
It used to be a simple matter to phone up Quad in Huntingdon and they would send the parts by return. However, I haven't done that for a while so I don't know if some of the parts are obsolete now.

As regards the 405. The early versions of this so-called 'current dumping' amp were not great - principally because they used a 301 op amp in the front end. The low slew rate of this chip made for a very 'tizzy' sound. It was improved when they replaced the chip with a TL071.
But overall, I personally think the sound of the 303 is much better.
 
Hi,


  i agree with Barclaycon, 303 is great. Personally, I have never like 405s of either incarnation that much, but the later mark II is an improvement.


  KIndest regards,


    ANdyP
 
while I haven't had the chance to compare, the 405 with the Bernd Ludwig mods sounds great here powering a pair of NS-10...

as has been stated above, the amp before the mods was basically unusable.
 
520F is a great amp. I have a friend who uses one on his mains (Tannoy SGM10). Never usually more than half-way up on the level controls and lots of clarity.

I use my modded 405 on my Tannoy 15" Golds and my 303 on the NS10s. Both are sounding excellent. I have another modded 405 on my home system. Still, if I was offered a 520F in place of the 405 I wouldn't say no.

 
The 405 was something of a classic, and as Peter Walker used to publish all his designs in "Wireless World", the number of clones produced was huge - so much so that one of the local transformer manufacturers used to have an off the shelf "Current Dumper" power transformer in their catalogue. They lent themselves well to "Souping up" - extra power transistors, higher rail voltages etc and they seemed to be absolutely bombproof.
M
 
mobyd said:
The 405 was something of a classic ... they lent themselves well to "Souping up" - extra power transistors, higher rail voltages etc and they seemed to be absolutely bombproof.


And so the 520 was born. They added a discrete input stage and put the opamp in the feedback path, but the advantages of current dumping (absence of crossover distortion, better reliability) were kept from then on.

 
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