QUAD 405 clone

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#161
stef1777 said:
You also need to change the four 560 2W green resistors close to the power transistor. The stock resistors are stick to the pcb. Too hot -> 72°C box closed. Use 3W and it is necessary to raise them by 1cm from pcb.
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Is it ok to use 5W Cement resistors instead of the four 560 2W green resistors close to the power transistor?


Or would 3W Metal Film be a better choice?
 
#162
t-minik said:
Hello stocktrader200, thanks a lot.
I already did the Snook/Ludwig input gain reduction mod ( c2=33uf, c4=150nf, r6=100k).
My concern about R2 is because my input rca aren't connected to chassis earth and I fear about humming or R2 heating.
Will try and see.

Best regards
Click to expand...

Hi, how did ended up your Quad clone building?


To everyone: looking today to give a try to a QUAD405 clone from China. Noticed there are 2 versions, the TO3 version with Mj15024 transistors single sided pcb like ones of @roclite and a two sided one with plastic capsule power transistors from a not so known korean company called KEC like @stef1777 has presented.

Which one I should order? The quality of the pcb is more important than components as I plan to upgrade/mod with to the latest.
Noticed also a version with TO3 with a dual sided pcb.

Thanks for your input!
 
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#165
#166
atupi said:
Hi, how did ended up your Quad clone building?


To everyone: looking today to give a try to a QUAD405 clone from China. Noticed there are 2 versions, the TO3 version with Mj15024 transistors single sided pcb like ones of @roclite and a two sided one with plastic capsule power transistors from a not so known korean company called KEC like @stef1777 has presented.

Which one I should order? The quality of the pcb is more important than components as I plan to upgrade/mod with to the latest.
Noticed also a version with TO3 with a dual sided pcb.

Thanks for your input!
Click to expand...
For the first type, an empty PCB is sold ($ 10) per pair.
There are features with pinout BJT from different manufacturers.
 
#168
It is also common to reduce the gain. See:

Quad 405-2 upgrades


I used OPA228 which I think works quite well in the LJM QUAD405-2.

The original used LM301. There was a later version that used TL071 and also that handled 4 Ohm loads better. The LJM QUAD405-2 is like the later version with the TL071. That is the version I bought.


I am still using the D1047 outputs, however I treat those carefully since I have had those blow in other LJM amplifiers (MX50X2, L20.5). In those other amplifiers I used genuine Toshiba 2SC5200N as replacements.
 
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#170
The LJM QUAD405-2 board (the better version with the TL071) work fine with the gain modification and OPA228. (Or OPA134.) They work very nicely with just those two mods. (They work nicely out of the box too.)

No hiss. But bypass the opamp pins directly from the socket you install to the input ground plane with 0.1uF film and something like 10uF to 47uF electrolytic.

FYI: Don't mix-up the single op-amp pin-out for the power pins with the typical dual op-amp pin-out. If you do and install bypass caps where they would be for a dual (pin 8 to AGND and pin 4 to AGND) then you will get hiss.
 
#172
US4523152A - High-efficiency feedforward-error-correction ...patents.google.com › patent

The present invention relates to a feedforward-error-correction amplifier system comprising a switching circuit, a linear-amplification means, and a summing ..
 
#176
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#177
stef1777 said:
I changed the chemical capacitors and the CBB at input with a better MKP.

If you install a dc protection with anti-ploc, use a floating ground model.

As the LJM protection module or this one : Amplificateur de puissance sonore special, rx 2, double canal, anti impact, protection cc, protection du klaxon, panneau fini | AliExpress

I've cut the original opamp and installed a dip socket.
Click to expand...
Did you tested that speaker protection module? I mean it triggers if "see" DC at input?
 
#178
stef1777 said:
Hello,

For me, I made the following modifications:

- change of chemical capacitors by Nichicon UFGs.
- change of the CBB input capacitor by Janzen Audio Superior Z-Cap.
- change of TL071 by an OPA1611.
- change of a resistor and a capacitor to adapt the input gain.
- change of the 2 power resistors by Matsushita M 3W.

OPA1611AID with Extended 200MA Current Class A Output Single OP AMP Module New | eBay

https://ibb.co/N1WbxbD

https://ibb.co/TgjNKjq

https://ibb.co/J3bvCTt
Click to expand...

I see you did not changed the schematic, only parts with better ones. Did you left the opamp in the original inverting mode?
 
#180
Just wanted to add that I applied almost all the important mods to have this clone much closer to a DCD-Mod3 and I'm quite astonished by the sound.
I'm using 4 ohm speakers and the limiters are still in place but as I not listening to high level there are no issues.
Greatest improvement came when placed C8 (120pf) down to the Tr2 emitter.
Only thing is now I'm using +/- 35V supply but I will do some tests also with 50v.

If I decide to remain to the 35V one what changes I should do, can anyone more knowledgeable advise me? I really don't need too much power, only quality.
The sound is soo liquid, smooth with a laaaarge stereo image. Very happy 🙂
 
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