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Old 12th September 2011, 03:19 PM   #11
Tajzmaj is offline Tajzmaj  Slovenia
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About 405....
Original quad 405 have ground connection on each board. It is connected to the heat sink directly via bolt.....This is power ground which goes to speakers and to the 0V on power capacitors......
The other ,,ground,, goes only to the inpput connector which is isolated from enclosure.....This is signal ground.
Both grounds are connected with 10E resistors. On each board.....
So those ebay boards seems ok to me....if I find right item.....
About drivers. Drivers are mounted on the same heatsink with output transistors at the original amp which ensure termal coupling......and there is one more thing. One of those ,,drivers ,, is in fact output transistor of the small class A amplifier which is boosted with class C ,,dumpers,, and it dissipates a lot of heat. So it would not be good idea to place it on some small heat sink.....
And of course you can earn some oscillations as well....
So my advice is : DO NOT
Best regards, Taj
http://www.ebay.co.uk/itm/2pcs-QUAD-...18165847663265
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Old 12th September 2011, 05:04 PM   #12
nickds1 is offline nickds1  England
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Quote:
Originally Posted by Tajzmaj View Post
The eBay kit is for a 405-1 using an LM301 - its not a good version. They make a big deal about 1% resistors etc. where the whole point of the design is that it doesn't care (mostly) about component tolerances.

They even point out how accurate the 3uH L2 inductor is - in actuality, it should be 2.82uH to balance the bridge.

Odd that they went to all that trouble to make a clone board, then chose an old revision that even Quad themselves heavily updated 20 years ago, let alone everyone else.
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Old 12th September 2011, 07:11 PM   #13
bdm47 is offline bdm47  United Kingdom
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thanks taj for info . my plan was to take board gnd to 0v caps as well as sp-rtn heatsink part of chassis earth ? diagram needed showing connections ? if poss bernard
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Old 12th September 2011, 07:31 PM   #14
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All is now well and no need for any more help. I knew it was something stupidly simple. When I finally sat down and got a look at the circuit diagram I realised that the cloners had managed to reverse the lables for the signal in and earth! I hang my head in shame. I'm really sorry to have used up your time, but at the same time really glad to know that there are some really helpful people out there!
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Old 13th September 2011, 12:33 AM   #15
Tajzmaj is offline Tajzmaj  Slovenia
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At original 405 it was done like that. The centre point of the poer caps goes to the chassis. Speaker returns goes to the centre point. Boards are only bolt to the heat sinks and that's all. No wires no anithing......just bolt. The signal ground goes from board to the input connector....
If you want I can send you a service manual for whole 405 family. Email me...
Regards, Taj
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Old 28th September 2011, 09:53 AM   #16
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I would advice to use the schematic "405-3" by Keith Snook, QUAD 405 Amplifier Information and Modification , http://keith-snook.info/Schematics/Q...olution%20.pdf

Just wish someone could help me make customised circuit boards for it. I have made my own layout accepting alternative sizes of capacitors in order to make more universial.
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Old 19th March 2012, 04:59 PM   #17
Pemo is offline Pemo  Mexico
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Quote:
Originally Posted by ljm_ljm View Post
I made some QUAD405 design. But don't know if I have provided version?

have "LJM" letters ON THE BOARD?
Hi, I'm interested in the Quad 405 you sell.

Is the original Zobel issue solved in your design?

I found a LJM 2010 V2 of your design, is this the right one?

RGDS

PEMO
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Old 19th March 2012, 05:29 PM   #18
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Quote:
Originally Posted by Pemo View Post
I found a LJM 2010 V2 of your design, is this the right one?
That version has very little in common with later designs.... Snook's 405-3 is the schematic to follow if a modern 405 without issues is the goal. As Snook's version uses fewer components, a new PCB could use components more readily availble. Some PCMs can have alternatives, like 5-10-15 mm instead of just 10 mm.

Roger
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Old 3rd April 2012, 10:06 PM   #19
VMAudio is offline VMAudio  Spain
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Quote:
Originally Posted by jaycee View Post
If you get a humm when you join channels, that is a ground loop.

If the 10R resistor which appears to be part of the Zobel network is getting hot, the amplifier is oscillating.

Signal earth should not be on the chassis. Connect that to safety earth. The input sockets should be isolated from the chassis. Connect both signal grounds at one point only, and then connect this point to 0V star earth at the main supply capacitors, via a 10 ohm resistor. Somewhat like this:

Click the image to open in full size.
Please, can you re-display the image?
I can´t watch the scheme of wiring .
Regards VMA.
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