To these interested in the real subject of this conversation:
May I suggest you to go back to the previous page and read really important information in the post #120.
During the next week I plan to present further important information regarding the problems with L20.5.
May I suggest you to go back to the previous page and read really important information in the post #120.
During the next week I plan to present further important information regarding the problems with L20.5.
Hello friends,
Meanwhile, I have spoken to Billy and I must say, this was a fruitful exchange. He has explained me the nature of the problem and possible solutions.
Now, please, refer to the schematic in post #3.
To repair the damaged board or improve its reliability, you have to:
1. Replace R13 and R20 with higher resistance
2. Replace the yellow 104 capacitor with something better.
I have successfully recovered one of the boards by replacing resistors with what I had available: quality 0R22/7W and much better 104 capacitor.
I have also re-soldered and tested all output transistors. One transistor was damaged and one 01R resistor has shown megaohm resistance.
I have tested the bord on dummy load at low wattage and it works now.
The lesson learned: something causes sudden high current inrush into the output stage and it usually damages one half of the output. The result is extremely high voltage at the output, almost the value of the rail.
I suggest cautious evaluation of the board before connecting it to the speakers because this kind of failure would most probably destroy your speakers.
I have also tried to repair yet another board but this time I couldn’t apply the same cure. Measurements at the bases of the output transistors indicate that the signal doesn’t reach the output stage, indicating that the problem must have been somewhere in the previous stages. I might get back to this problem later on.
Below you may observe at the snapshot below one board without modification and the other after the repair. All credit for the presented method go to Billy, I just followed his instructions.
I wish you all a pleasant Sunday afternoon.
Meanwhile, I have spoken to Billy and I must say, this was a fruitful exchange. He has explained me the nature of the problem and possible solutions.
Now, please, refer to the schematic in post #3.
To repair the damaged board or improve its reliability, you have to:
1. Replace R13 and R20 with higher resistance
2. Replace the yellow 104 capacitor with something better.
I have successfully recovered one of the boards by replacing resistors with what I had available: quality 0R22/7W and much better 104 capacitor.
I have also re-soldered and tested all output transistors. One transistor was damaged and one 01R resistor has shown megaohm resistance.
I have tested the bord on dummy load at low wattage and it works now.
The lesson learned: something causes sudden high current inrush into the output stage and it usually damages one half of the output. The result is extremely high voltage at the output, almost the value of the rail.
I suggest cautious evaluation of the board before connecting it to the speakers because this kind of failure would most probably destroy your speakers.
I have also tried to repair yet another board but this time I couldn’t apply the same cure. Measurements at the bases of the output transistors indicate that the signal doesn’t reach the output stage, indicating that the problem must have been somewhere in the previous stages. I might get back to this problem later on.
Below you may observe at the snapshot below one board without modification and the other after the repair. All credit for the presented method go to Billy, I just followed his instructions.
I wish you all a pleasant Sunday afternoon.
Attachments
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I have been using the newer board with bipolar electrolytics and on semi transistors for more than a month now.
Dual mono in a 2he Dissipante. Shortest possible wire runs I could come up with.
Zero problems. Absolutely noiseless, with source turned on, headphones connected directly to the output. Does not get too hot or stay cold.
No modifications made and no components changed.
Will post pics when I get back from holidays.
Dual mono in a 2he Dissipante. Shortest possible wire runs I could come up with.
Zero problems. Absolutely noiseless, with source turned on, headphones connected directly to the output. Does not get too hot or stay cold.
No modifications made and no components changed.
Will post pics when I get back from holidays.
L20.5
The biggest problem is actually getting the later boards they have been available for about a year but even when sellers show the newer board in the ad they aren't guaranteed to send the new board I have purchsed what I thought were the new boards and despite the pictures in the ad showing the later boards it has always been the older boards they have sent. These sellers clearly have a lot of older boards and will do anything to sell them so be careful and ask for a picture of the actual product you will be receiving.
The biggest problem is actually getting the later boards they have been available for about a year but even when sellers show the newer board in the ad they aren't guaranteed to send the new board I have purchsed what I thought were the new boards and despite the pictures in the ad showing the later boards it has always been the older boards they have sent. These sellers clearly have a lot of older boards and will do anything to sell them so be careful and ask for a picture of the actual product you will be receiving.
What are the differences between the old and new boards?
How can you tell the difference?
Thank you,
David
Hi David,
The new boards are easy to spot due to all the power connectors being all at one end of the board. I will put a picture up as soon as I get settled in I have just got back from another couple of weeks in hospital and need a bit of time to sort things out. I should have the picture up by tomorrow.
Bill
The new boards are easy to spot due to all the power connectors being all at one end of the board. I will put a picture up as soon as I get settled in I have just got back from another couple of weeks in hospital and need a bit of time to sort things out. I should have the picture up by tomorrow.
Bill
I'm a little ticked off then, I ordered these boards just in the last couple of months directly from LJM.
Are you sure?
The ones with the connectors on the end of a (c) date of 2017
and the ones with the connectors in the middle of the board have a (c) date of 2018
There are also "in between" versions. I received the one with the connectors in the middle but with D1047 and B817. One of the two incinerated instantly without a signal. The other side was perfectly fine.
I removed all the outputs and found one of the B817 was shorted. That board with the burned up B817 ran fine with just one genuine Toshiba 2SC5200N and just one genuine Toshiba 2SA1943N installed. I fortunately had a very small fast fuse for first power up and the only damage was the one B817. I prefer good current limited lab supplies for first power up...
I have not had time to get back to that project but my conclusion at the time was that the D1047 and B817 supplied are junk. Is there more to the story? I have replaced D1047 and B817 with Toshiba before on other LJM too...
I removed all the outputs and found one of the B817 was shorted. That board with the burned up B817 ran fine with just one genuine Toshiba 2SC5200N and just one genuine Toshiba 2SA1943N installed. I fortunately had a very small fast fuse for first power up and the only damage was the one B817. I prefer good current limited lab supplies for first power up...
I have not had time to get back to that project but my conclusion at the time was that the D1047 and B817 supplied are junk. Is there more to the story? I have replaced D1047 and B817 with Toshiba before on other LJM too...
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So Toshiba 2SC5200N(S1,E,S) and 2SA1943N(S1,E,S) are good alternatives for the NJW0281G and NJW0302G no one has right now?
What about using Sanken 2SA1386 and 2SC3519?
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I think the quality and true capability (vs the datasheet claim) would be far better with genuine Sanken. The 2SA1386 and 2SC3519 should be a good upgrade in quality. With my experience with blown D1047 and B817 with the LJM amplifiers I think it is a quality or fake issue. Every time one side went and the other was fine. Once replaced with Toshiba everything was solid.
I am planning on trying the full set of 4 pairs of Toshiba (genuine) 2SC5200N/2SA1943N. I might possibly try a full set of 4 pairs of Sanken 2SC6145/2SA2223 on one board and see if I can measure any difference at all. Right now I am side tracked with a variety of other projects, however.
Because of the shorting D1047 and B817 I ordered the L28 (different designer, but like L20) which came with 4x pairs of Toshiba TTC5200/TTA1943. However my initial distortion measurements were disappointing. I don't know if I will put the time into trying to figure out why. (Much worse than my L20 V7, or Quad405-2 or uPC1342V.) At this point I am interested more in down selecting the design and then doing the final build with the best components.
And if you are repairing a board don't get the output transistors from AliExpress or Ebay or Amazon. Go with a real authorized distributor. I ordered several batches of 2SC5200/2SA1943, D1047/B817, TIP35/36, TIP41/42 and TIP142/147 online. My conclusion is... ...don't do it! Go with a real authorized distributor. The same warning goes for the drivers too!!!
I am planning on trying the full set of 4 pairs of Toshiba (genuine) 2SC5200N/2SA1943N. I might possibly try a full set of 4 pairs of Sanken 2SC6145/2SA2223 on one board and see if I can measure any difference at all. Right now I am side tracked with a variety of other projects, however.
Because of the shorting D1047 and B817 I ordered the L28 (different designer, but like L20) which came with 4x pairs of Toshiba TTC5200/TTA1943. However my initial distortion measurements were disappointing. I don't know if I will put the time into trying to figure out why. (Much worse than my L20 V7, or Quad405-2 or uPC1342V.) At this point I am interested more in down selecting the design and then doing the final build with the best components.
And if you are repairing a board don't get the output transistors from AliExpress or Ebay or Amazon. Go with a real authorized distributor. I ordered several batches of 2SC5200/2SA1943, D1047/B817, TIP35/36, TIP41/42 and TIP142/147 online. My conclusion is... ...don't do it! Go with a real authorized distributor. The same warning goes for the drivers too!!!
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Hello Dave,Eagerly waiting...
Give me, please, few more days. What I want is to present what options do we have regarding replacement of parts of unacceptable quality and what options exist to attain comparable THD values without sacrificing other important parameters. Today I have received yet another board which I would like to compare to L20 boards.
Meanwhile, have a pleasant ongoing week end.