Hi Postpunk and welcome back from vacations.
Excuse me for joking in my previous message, but I couldnt resist. This situation isnt funny but everything seems to be extremely ridiculous. (Almost) Everyone is repeating: carefully, purchase just the boards with Panda logo, all other are fake. What the Hell???
We are having here a major fireworks of LJMs fake devices. Can you imagine that: a device with declared VCBO 160V is smoldering at 42V. Who sells here fake devices?
OK, enough rant - now back to the business as usual.
For you solution is straightforward: at Reichelt there is a pair 2SC3263/2SA1294. Devices are product of Inchange (China) but I trust Reichelt judgement. Currently I am using exactly that pair and it works perfectly but I want more. On Monday I intend to order FJA1343/FJA4213 from Farnell . In my opinion this should be a perfect match with guaranteed performance.
How the hell one can build a 'Blameless Amplifier' from a pile of junk? No Way.
Replace everything, including resistors. I will do that.
I am grateful to LJM - with his boards and fake components I have learned perfectly how to de-solder and re-solder. I deserve a PhD degree in that area, Thanks to him.
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I am somewhat relieved that others have had the same experience otherwise I would not understand why I have lost so many LJM amplifiers. However I have lost zero after replacing the outputs and drivers. (Except replacing the semiconductors everything else remains the same such as load, power supply, heatsink, wiring, chassis, etc.)
I have had good experiences with replacing the D1047 and B817 with Toshiba 2SC5200N and 2SA1943N which are readily available.
And two days ago one of the two L20 V7 started to smoke... (That one still had the original D1047 and B817.)
I have had good experiences with replacing the D1047 and B817 with Toshiba 2SC5200N and 2SA1943N which are readily available.
And two days ago one of the two L20 V7 started to smoke... (That one still had the original D1047 and B817.)
Thanks Kozard, I indeed apreciate your valuable contribution to this theme and to the entire community.
Please note that FJA4313 is exactly the same as 2SC5200, just in diferent package. Outstanding characteristics of these devices are high linearity for low THD, high spéd and low capacitance.
Thanks and pleasant week end.
Hello Dave,
I really don't know the answer to your question but I'd assume that there will be no audible difference.
What really matter is time because with each day we are running out of viable options. Here at Farnell Europe I can get only Sanken 2SA1386, whilst 2SC3519 is out of stock. Mouser, surprisingly has nothing. But Farnell has both FJA4313 and FJA4213, but in very limited number, so I will hurry up, before they run out of stock. I trust both Farnell and Fairchild (ON-Semi) so why not.
TT Electronic was Mousers supplier of 2SA4313 and 2SC3519 until 2016 when they have discoutinued that product line because of decreased demand. We are really running out of time and options.
So hurry-up Dave.
PS: @postpunk: don't bother with Reichelts Insemi devices. The lower price isn't worth risk.
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Ah, yes, these two should have been 2SA1930 & 2SC5171, but he has silently "upgraded" them with inferrior KTC4370/KTA1659. Initially, I have purchased the adequate Inchange 2SA1930 & 2SC5171 pair. Now I have decided to replace them too with adequate ON-Semi MJE1530 / MJE1531. If you do the same, dont forget to isolate them with mica tabs from the heat sink.
By the way, I have found even better alternative for output pairs: NJW3281G / NJW1302G which have symmetrical characteristics in complementary configuration. I already have replacements for small input transistors (I did that already), so I need only an idea what to do with 2SD669. I already have an Inchange version but I want to make ON-Semi only amplifier to make sure noting interesting happens in the near future. For the sake of safety and peace of minds.
Regards.
I used TTC004 (and TTA004) to rebuild my MX50X2 for both driver and bias devices.
I think it is a reasonable choice there. I would be careful here (L20.5 or L20) since more is being asked of the driver here (current and power dissipation) compared with the MX50X2 or MX50SE.
It would be nice to find a larger driver.
I think it is a reasonable choice there. I would be careful here (L20.5 or L20) since more is being asked of the driver here (current and power dissipation) compared with the MX50X2 or MX50SE.
It would be nice to find a larger driver.
Thanks guys.
@Kozard: in fact, I was inspired with your work on these boards. I have started thinking about the alternatives when you've mentioned Toshiba output transistors and mysterious high mortality of these boards.
Now, I have insight into the real value of these boards:
Fully populated (Chinglish: completed boards) are worthless because of all these fakes built-in. Bare boards have achance to become good amplifiers, however, at high cost.
However, specifications of boards are totally deceptive: how can one achieve 250W per channel with transistors that can not survive 42V? Are they seling arc welding machines?
But the worst about these boards are more comprehensive measurements. THD is just one parameter, not that good as declared, but, neglecting other aspects of audio quality is yet another show-and-hide story.
Finally, have you noticed that high frequencies are quite exagerated whilst bass seems somehow rachitic? Why? Hint: THD is based on measurements of higher frequencies, above and including 2KHz. And not all of them, just integer multiples of the base frequency. Think about this.
@Kozard: in fact, I was inspired with your work on these boards. I have started thinking about the alternatives when you've mentioned Toshiba output transistors and mysterious high mortality of these boards.
Now, I have insight into the real value of these boards:
Fully populated (Chinglish: completed boards) are worthless because of all these fakes built-in. Bare boards have achance to become good amplifiers, however, at high cost.
However, specifications of boards are totally deceptive: how can one achieve 250W per channel with transistors that can not survive 42V? Are they seling arc welding machines?
But the worst about these boards are more comprehensive measurements. THD is just one parameter, not that good as declared, but, neglecting other aspects of audio quality is yet another show-and-hide story.
Finally, have you noticed that high frequencies are quite exagerated whilst bass seems somehow rachitic? Why? Hint: THD is based on measurements of higher frequencies, above and including 2KHz. And not all of them, just integer multiples of the base frequency. Think about this.
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I had originally hoped that it was a good implementation of the Blameless Amplifier. However I am finding that considerable assembly is required.
As for measuring (low levels of) THD I am finding that is not a simple task. Where the measurement is taken and how the wiring done is not trivial. I am not finished sorting out my measurements but I am finding that a well done amplifier PCB layout can be easily messed up (in terms of THD) by rectifier/filter boards and speaker protection boards that join returns together in multiple places. For example, my uPC1342V board has an obvious star ground layout on the PCB and you can measure 0.0015 to 0.003% THD between the feedback point and the star ground on the board. But if you use a rectifier/filter board that is designed as the star ground point and then also a speaker protection board that joins the returns of multiple channels together you can measure 0.02% THD. (I am currently in the process of sorting this out. I will at least go to an isolated (per channel) protection board. However for the best performance I might just build it as two mono blocks.)
In other words a single channel with a single power supply and no protection board is currently measuring 10x lower THD. Perhaps that is how it was measured with the AP?
As for measuring (low levels of) THD I am finding that is not a simple task. Where the measurement is taken and how the wiring done is not trivial. I am not finished sorting out my measurements but I am finding that a well done amplifier PCB layout can be easily messed up (in terms of THD) by rectifier/filter boards and speaker protection boards that join returns together in multiple places. For example, my uPC1342V board has an obvious star ground layout on the PCB and you can measure 0.0015 to 0.003% THD between the feedback point and the star ground on the board. But if you use a rectifier/filter board that is designed as the star ground point and then also a speaker protection board that joins the returns of multiple channels together you can measure 0.02% THD. (I am currently in the process of sorting this out. I will at least go to an isolated (per channel) protection board. However for the best performance I might just build it as two mono blocks.)
In other words a single channel with a single power supply and no protection board is currently measuring 10x lower THD. Perhaps that is how it was measured with the AP?
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Here are a few pictures of my final build of the L20.5.
No noise can be heard with headphones connected to the outputs, even with source switched on. Believe me I did not think it was possible to accomplish that. I have invested silly amounts of time in trying different layouts, cases and blowing stuff up.
I am now working on getting a single supply build as noiseless and well behaved as possible.
No noise can be heard with headphones connected to the outputs, even with source switched on. Believe me I did not think it was possible to accomplish that. I have invested silly amounts of time in trying different layouts, cases and blowing stuff up.
I am now working on getting a single supply build as noiseless and well behaved as possible.
