Quad 405-2, 34 & FM4...

[nickds1]

Managed to get these three in VGC (almost pristine) at a boot fair (aka garage sale) for pretty much nothing (like USD 15 for the lot) - never owned Quad before, so eager to get them up and running.

However, what "upgrades" should I look at doing? Opamp changes etc. Is it worth re-capping the 34 and/or the 405-2?

No cables came with them - Therefore I also need two interconnects (FM2 & 405-2 to 34) - any recommendations for a good source (there are some cheapies on eBay but of unknown quality).

Ideas and input very welcome as I really want to listen to these at their best!

Many thanks

[nickds1]

...should have added I also need some of the sticky rubber pads that go over the screws in the plastic feet of the 34 & FM4... obviously, I can make some, but originals/decent after-market spares would be good.

Thanks

[tunneldiode]

Wow, I wish I lived in the US, if you can get all of that kit for $15-
It would all cost an arm and a leg in the UK.

Personally, I don't go in for audiophool uvavu nonsense, so I would just get the service data, and give them a once over.
On the 405; R7 and R8 should be checked, as they can (and do) fail.

If you are keen on upgrading, there are some ideas here:

www.keith-snook.info/QUAD-405-mods.html

As for cables, I made my own.

[nickds1]

Originally Posted by tunneldiode

Wow, I wish I lived in the US, if you can get all of that kit for $15-
It would all cost an arm and a leg in the UK.

See my flag! I live in Kent. The actual cost was GBP 10 for the set at a local boot fair. The guy was clearing his dad's house and patently didn't have a clue.

Thanks for the link - I had seen that site, however there seem to be a whole raft of possibilities around for these devices...

Cheers

[AndrewT]

Some folk make their own luck.

I should learn to do that !

[Tajzmaj]

Hi. Replace op with opa604....and add 2 100n caps across supply legs. Otherwise it will oscillate. Replace all electrolytic capacitors is also good idea. In 405 closed enclosure becomes quite hot....and check output transistors and drivers. If they are not all the same replace them with some new devices. But not too fast otherwise it will oscillate again. Mj15024 is good enough for output and Bd242 for driver.....If you need service manual contact me and I will send you pdf.
Regards, Taj

[nickds1]

Originally Posted by Tajzmaj

Hi. Replace op with opa604....and add 2 100n caps across supply legs. Otherwise it will oscillate. Replace all electrolytic capacitors is also good idea. In 405 closed enclosure becomes quite hot....and check output transistors and drivers. If they are not all the same replace them with some new devices. But not too fast otherwise it will oscillate again. Mj15024 is good enough for output and Bd242 for driver.....If you need service manual contact me and I will send you pdf.
Regards, Taj

I have all the docs, thanks - your suggestions seem to be the same as Bernd Ludwig - the latest version of his doc that I have found is version 13 on the DaDa Electronics download page " Quad 405 Upgrade Instructions Bernd Ludwig V 13 2009".

Cheers

[Tajzmaj]

I have 405 my own......and I modify it such way. Bernd Ludwig is guy with lots of experience with those amps and all his suggestions make sense. He doesn't believe in ,,myths,, and legends all solutions are practical....Some are maybe to radical....cut the trace......and similar but if you want you can try. Because I build a lot 405 clones some with only 2 transistors like original and the others with 6 transistors I try a lot. And see a lot of unwanted things on my scope.....About opamp...I get nice results and very low hiss with opa27. But whatever you change it sounds very very similar all the time. Little aggressive when you crank it up...The most significant difference which i noticed was when I rebuilt my original 405 and later replace old 10000 uF caps with new 22000 units from epcos and replace all supply and output wires with some more heavy duty. It is funny how tiny are original.The gretz rectifier should be replaced with some 35A unit too. I get significant improvement in bass response. Those ideas about changing input cap and so on are on my opinion stupid because the amp will deliver flat response to 20Hz so....but be careful in my amp one of those input caps was defective so I replaced it with 0,68uF Wima unit. About changing the input sensitivity.....I never tried but if you use source with low output noise than everything is ok + you can use quad just with passive preamp containing selector switch and volume pot. You need only 0.775 volts for full power if I'm correct. So cd player will deliver more than enough drive voltage.
Nice and interesting amplifiers. And reliable. Just don't short the outputs. And don't use it to drive big lazy speakers with low Z. You will overheat it.
Best regards, Taj

[nickds1]

Doing the basic Bernd L mods, but was wondering if a dual PSU is worth the trouble, and specifically if using schottky diodes is worth it, or whether a simple pair of 20A bridges would do...

Further, many folk seem to put 100n caps across each diode. Any benefit?

Cheers

[Mooly]

100nf across the diodes can be a very real benefit in some instances. As the diodes come into and out of conduction a small burst of RF can be generated... I have experienced this first hand myself in an Hitachi product and also a friend with Leak (I think it was) tuner where it caused a constant harsh buzz.

Trouble is what works best and also first identifing the problem.

To play safe a single cap around 0.1uf perhaps in series with a 1 ohm 1watt carbon (not WW) resistor placed across the input to the bridge is as good as anything.