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
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
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.
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.
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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
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
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
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
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
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.
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.
And about double psu....and stuff.
Quad 405 is veteran, classic......so I like to leave it in ,,original ,, condition. No holes drilling, no cutting......that is why I leave only 2 big smoothing cans inside. I wasn't happy when it shows up that I will break that nice vintage wiring....
If you want to have better Quad 405 than build a clone......because when you repair and improve everything than it will run just too hot.....and you will place 2 fans at the front
Regards
Quad 405 is veteran, classic......so I like to leave it in ,,original ,, condition. No holes drilling, no cutting......that is why I leave only 2 big smoothing cans inside. I wasn't happy when it shows up that I will break that nice vintage wiring....
If you want to have better Quad 405 than build a clone......because when you repair and improve everything than it will run just too hot.....and you will place 2 fans at the front
Regards
And about double psu....and stuff.
Quad 405 is veteran, classic......so I like to leave it in ,,original ,, condition. No holes drilling, no cutting......that is why I leave only 2 big smoothing cans inside. I wasn't happy when it shows up that I will break that nice vintage wiring....
If you want to have better Quad 405 than build a clone......because when you repair and improve everything than it will run just too hot.....and you will place 2 fans at the front
Regards
160,000 or so of these were made - they are not rare & valuable jewels. Some people may like them to be completely original, but I quite like the idea of making a few subtle changes to (so far as people say) radically improve the sound quality without changing the overall character too much.
Its an amp that lends itself well to simple mods & playing around with.
Cheers
I completely agree with you. Amp is intended to play music ......and 405 is not so rare. But some radical modifications simple just aren't worth to bother with. Those which needs a lot of mechanical modifications. Why? Because at the end you will discover that when you replace output transistors you need to replace supply capacitors.....and than you will discover that amp will worked better wit one more pair of output transistors....and than the power transformer will need to be replaced. After that you will discover that maybe one more pair of output transistors will give better results.....but from the beginning the heat sinks are too small and transformer is too big now.........so never ending story. I went through all these phases...
And after that discovered that most serious limitation for 405 is small enclosure which enables radical procedures. Amp is quite old design but revolutionary for it's time. And it was intended to drive esl speakers and mostly for 8 ohm loads.....
On my opinion there is absolutely worth to replace capacitors and op amps. To replace vintage and overheated output transistors is also nice idea. But not with something ultra modern and fast......
At the ens. This is how at the end modify 405 circuit. 6 output transistors 1000VA toroid and huge cap block for each channel. And this fan cooled heat sink is also from one of my diy 405......
Nice sounding amps all of them. Almost the same character. 405 sound clear and punchy.
Regards, Taj
And after that discovered that most serious limitation for 405 is small enclosure which enables radical procedures. Amp is quite old design but revolutionary for it's time. And it was intended to drive esl speakers and mostly for 8 ohm loads.....
On my opinion there is absolutely worth to replace capacitors and op amps. To replace vintage and overheated output transistors is also nice idea. But not with something ultra modern and fast......
At the ens. This is how at the end modify 405 circuit. 6 output transistors 1000VA toroid and huge cap block for each channel. And this fan cooled heat sink is also from one of my diy 405......
Nice sounding amps all of them. Almost the same character. 405 sound clear and punchy.
Regards, Taj
Attachments
Yet another Quad 405-2 rebuild
Following on from my ramblings earlier in this thread, I've started documenting what I'm up to on this at NMdS Electronics Index
Its a "stream of conciousness" (or stream of something else...), so no apologies for style etc., but any feedback (no jokes please) on the content would be welcome.
Photos etc. will be added as work proceeds - as I write this I have all the bits except the speaker posts.
Cheers
Following on from my ramblings earlier in this thread, I've started documenting what I'm up to on this at NMdS Electronics Index
Its a "stream of conciousness" (or stream of something else...), so no apologies for style etc., but any feedback (no jokes please) on the content would be welcome.
Photos etc. will be added as work proceeds - as I write this I have all the bits except the speaker posts.
Cheers
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Bit more on this:
New PSU section and testing using my HP 8903B & other kit...
Driving the HP 8903B over GPIB with Pete Millet's VEE-based s/w( HP 8903 Software ) from a W7 box. New PSU, lots of decoupling. 100W dummy load, quick test adapter box and fan + thermocouple to stop it cooking. The 8903B looks boring as when its under GPIB control the front panel doesn't update much. My one has all the I/O on the back as it was originally used in an ATE.
The intention is to characterise both channels before & after the mods to quantify the net effect of the changes.
Write up (work in progress) here: http://www.desmith.net/NMdS/Electronics/QUAD_upgrades.html
New PSU section and testing using my HP 8903B & other kit...
Driving the HP 8903B over GPIB with Pete Millet's VEE-based s/w( HP 8903 Software ) from a W7 box. New PSU, lots of decoupling. 100W dummy load, quick test adapter box and fan + thermocouple to stop it cooking. The 8903B looks boring as when its under GPIB control the front panel doesn't update much. My one has all the I/O on the back as it was originally used in an ATE.
The intention is to characterise both channels before & after the mods to quantify the net effect of the changes.
Write up (work in progress) here: http://www.desmith.net/NMdS/Electronics/QUAD_upgrades.html
Attachments
Finished! Grief. At last, a project actually finished...
Very very happy with the results...
Quad 405-2 upgrades
I've also made an LTspice simulation of the 405-2 which, contrary to my general experiences with SPICE, actually seems to somewhat reflect reality (perhaps because I took the trouble to get the models right). i.e. change component values and move stuff around in the deck, and it appears to reflect the real world. If anyone is interested in that side of things, let me know...
Cheers!
Very very happy with the results...
Quad 405-2 upgrades
I've also made an LTspice simulation of the 405-2 which, contrary to my general experiences with SPICE, actually seems to somewhat reflect reality (perhaps because I took the trouble to get the models right). i.e. change component values and move stuff around in the deck, and it appears to reflect the real world. If anyone is interested in that side of things, let me know...
Cheers!
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