OK, I ended up to get my original Quad 405 board restored. Tested with 20KHz square wave. The output signal is rounded as you mentioned that the original circuit includes a lowpass filter. The wave is still extremely clean, no overshoot and ringing.
Yeah, my point is that not all clones are built the same. Here is the example I call it bad square wave.
I don't have the two main sizes to measure here (of whats available on the internet). I think one is 126x90.3 and the other which is a direct copy of the DaDa high end boards is 120x83 which is likely the original Quad 405 dimensions as the DaDa boards are a physical straight swap for the OEM boards. I have a few of the DaDa copy boards but they are 500 miles from here!
The 126x90.3 ones will be the same as the plethora of LJM copies that come with the black anodised heat sinks. I built a few of those some years ago and measured the passive components, they were all within the stated tolerances. I binned the transistors as I had a lot of spare bonafide components back then and did not want to take the risk. I had not owned an original Quad 405 for over 15 years then so could not have said they would have fitted, I doubt it. The thing is why would anyone with a working Quad 405 want to fit Chinese copy boards unless they were the copies of the Dada boards that are faithful to the recognised tried and tested mods that originated with Ludwigs work and evolved through Snook and De Smith?
The DaDa copy boards are definitely the ones to own, there are no grounding errors built in and zero need to break tracks or solder components on the rear, "higly sought Class A dynamic biasing 80W amplifier PCB" (sic), LJM uses the worst possible translation software.
From elsewhere on diyaudio: Copy using "higly sought".
DaDa board.
Only C8 on the copy is a 1% Polystyrene cap.
Last edited:
The dada boards are good, i purchased a pair a few years ago, cost me about £300, they've gone down now to £140 think it's because all the cheap chineese boards coming in is forcing dada to lower their prices. On the website photo it looked like the opamp was socketed but when the boards arrived the opamps were soldered down which is disappointing. I also purchased net audio quad boards previous to that and the dada boards were slightly better. I've also owned original quad 405 and 405 II amps which have a nice rounded sound which people like, high reliability, won all kind of awards, best amp in what hifi, and still sell for about half of the RRP, which is impressive for a 70's amp.
I've owned the 405 and 405-II ljm boards and they are the best in terms of bang for your buck, for £30 it's difficult to find fault, and with the right mods they are excellent.
Also on my hifi journey i found the best boards i owned which are the fm acoustics fm300a, cost me £112 for the pair, they have blown everything away, even my £4500 bryston 4b is being challenged. Recently I purchased the aiyima A07 because of rave reviews on the asr website and to check out class-d technology that some people are raving about, but the aiyima turned out to be disappointing, same goes for the topping pa5 II
I've owned the 405 and 405-II ljm boards and they are the best in terms of bang for your buck, for £30 it's difficult to find fault, and with the right mods they are excellent.
Also on my hifi journey i found the best boards i owned which are the fm acoustics fm300a, cost me £112 for the pair, they have blown everything away, even my £4500 bryston 4b is being challenged. Recently I purchased the aiyima A07 because of rave reviews on the asr website and to check out class-d technology that some people are raving about, but the aiyima turned out to be disappointing, same goes for the topping pa5 II
They come in for a lot of stick on diyAudio with a few folk questioning the sanity of a person wanting to own one or its modified variants along with the usual accusations of the potential owner not having a quality "ear" or enjoying nostaglia at the expense of performance. I like them, they are solid and best of all easy to repair with no potentiometers to set.
I would like to populate the last 6 DaDa copy boards that I have left, I sold the first built pair to a Quad owning friend. I thought they were at my place in England but my friend tells me they must be here, I will look. I have a Mouser BOM and am disappointed to see the opamp OPA627 can no longer be purchased (from a reputable supplier) as a DIP through hole package which means finding a SOIC>DIP adaptor that hasn't got long leads. I dread soldering surface mount components, I have only a Weller TCP and its no fun when you have 63 year old eyes.
Last edited:
Have you got a link to the dada copy boards.
There are a ton of popular replacements for the opa672. The sparkos or burson discrete are much better. You will need to reduce the 3.3k resistor in the opamp power supply
There are a ton of popular replacements for the opa672. The sparkos or burson discrete are much better. You will need to reduce the 3.3k resistor in the opamp power supply
I have sparkos discrete but have not had the time to try them out. I did speak to stefaan from dada when i purchased his boards and he recommended the discrete. I searched around and found quite a few posts on other forums in which people had tried discrete with good results. Changing the op amp does make an improvement but i found upgrading the transformer to a modern toroid with high current output made more of an improvement than all my other mods put together. These old quad amps love current. That would be my first mod
I have indeed found a sleeve of PCB's here and not in England. An image of the difference in size between the extremely common Chinese copies of the early model and the DaDa board that is a physical straight swap. Green is obviously the DaDa, blue the common LJM clone.
I have highlighted the discrepancy of the power transistor spacing, the black heatsink is the one that comes with the common LJM clones and as you can see there are no holes visible on the left side of the image.
I have highlighted the discrepancy of the power transistor spacing, the black heatsink is the one that comes with the common LJM clones and as you can see there are no holes visible on the left side of the image.
Attachments
I would just buy the boards from dada, support the developers it is their hard work after all
Also the 405-2 china clone boards are very good if modded correctly and after lsitening to them both there really isn't much in it
Also the 405-2 china clone boards are very good if modded correctly and after lsitening to them both there really isn't much in it
Thanks! As you say the ljm 405 is poor, 707 is much better.
What are the main improvements of 707 against 405, Is there a great deal of difference. Can you please expand
Concerning the bootstrap capacitor at the centre of the board, I closest value I have is 300uf, would this be okay to use, can you see any problems
Thanks! Found i right at the bottom of my spare parts box, been there for years, i can't even remember where it came from it's been that long. Can you see any problems with using it ? It is 100 volts rated
Thanks! I live in a small town and there are no electronic shops near me, so everything i buy is mail order from the net. If i order a capacitor it will probably take a few days to arrive, so i am wondering if i can use the 300uf cap for a few days, and i am wanting to find out what the risks are. The 300uf measures well on the esr meter and looks healthy, but what will it do to the amp ?
When you have a chance you might want to get an assortment of good Japanese electrolytics like Panasonic FM in a few capacitance values and helpful voltages such as 63V. Also perhaps a couple values of WIMA film capacitors. Get them from authorized distributors if you want real ones.