Hello Erlend Sæterdal,
Is that the same amp that burned in 2013?
Did you rebuild it? Did you build it/rebuild with transistors that you sourced from authorized distributors or the transistors supplied from the kits?
If the rebuild was successful did you stick with 47V DC or did you lower the supply voltages?
I ask since I have only tested my L7 (kit, using supplied kit transistors) at low voltages and after one of my MX50x2's burned (first time connected to +/- 50V) I am wondering if I should stay well below 47V on the L7 and/or buy new transistors from authorized distributors.
Thanks
I tried l20.5 Yesterday. Way better than l12-2 Indeed. My L12-2 will stay in a box for backup if i get issue with the other one.
I am building a 2 channel amp with thoose modules for an old man who built and sold amps his hole life. He is well known in Denmark. I will use a 2 x 33 vac Transformer. I built another one several years ago with same supply and no problems. The 6 channel amp worked fine after replacing one module. In fact it was only one small signal transistor wich was blowned.
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Do you have a website with build instructions/suggested implementations for any of your products?
Is this the most direct way to purchase?
?????-ljm ?????????-???
Which is your favourite amp you sell?
I prefer to recommend mx50se
It's very easy and simple. Best for entry installation. And the effect is very good.
Then you can consider upgrading versions of mx50se, such as l20.5 and l20v10
They are more complex. More space is needed.
then. L15dsmd is also my recommended product. It's a digital amplifier.
But it requires a lot of power. DC + - 50V is required
I have a Chinese Taobao store. But it's not convenient for international sales.
So you can look for more convenient agents. Maybe they specialize in international purchasing.
As long as it is installed normally. The L7 can use up to DC + - 70V.
Mx50x2 + - 55v voltage. There will be no problem.
Don't buy pirated goods. There will be my logo on it. Green PCB
if possible. I'll have a picture if I have time.
I think a capacitor may need to be replaced. It will be better. L20.5
The MX50X2 which burned has your new panda logo and green PCB.
I have attached photos. Are those genuine? The soldering (back) looks rather messy. The blue board MX50SE that I bought was much cleaner.
Two boards from the same order were powered up the first time at +/-50V and one board was fine the other burned badly. Lost four drivers, four outputs, three of four 0.22 ohm, two 100 ohm and two 470 ohm. The board that burned was destroyed in seconds.
Both boards had worked fine at +/-25V (on my initial test setup, low volume).
Attachments
@ljm_ljm , please what is your recommendation about MX50X2 bias ?
I changed D1047 for genuine 2SC5200 i got a long time ago, also replaced the 2.2k fixed resistor with à 2.2k trimmer and set bias to 20mA (3mV through à 0.15R collector resistor).
It seems to works good but i can't measure anything and want to be sure.
best regards
I changed D1047 for genuine 2SC5200 i got a long time ago, also replaced the 2.2k fixed resistor with à 2.2k trimmer and set bias to 20mA (3mV through à 0.15R collector resistor).
It seems to works good but i can't measure anything and want to be sure.
best regards
You should set up an Aliexpress web store!
I would like to build a two channel L20.5 amplifier, it is being well reviewed on a couple of German forums.
The size of the case is not important, but what components would you recommend for a full LJM L20.5 amplifier build?
Which of your speaker protection boards, power supply boards and toroidal transformers would you recommend to run a pair of L20.5 boards at ~48v to 52v?
Do you have a soft start board?
I forget where I read it, but I thought I read that you wrote not to use an SMPS with the L20.5 boards. Why is that? It would seem like a much easier/cheaper build with an SMPS.
Thank you,
David.
Sorry LJM but Class D amplifier as nothing digital inside, it's pure analog circuit.
Other thing, I make the "ASR forum Mod" on my L20.5, one of them (or maybe the two) was "make sparks" at start up, do you have any idea why?
Review and Measurements of L20.5 Loudspeaker Amp | Audio Science Review (ASR) Forum
You show 5 different ways to build an amp with the 20.5 boards,
Which is the best way to build it?
Option 1,
Option 2,
Option 3,
Option 4,
Option 5,
Thank you,
David.
I have some years experience with L7's and they are yet in the main amps I currently use.
I always used green pcb's kits with the LJM logo on them.
Regretfully, any voltage over + - 40VDC means seeing the NCC5551/5401 driver pairs explode in the very moment the mains switch is set to on.
To keep safe a voltage slightly less than + - 40VDC is the choice.
In such conditions L7's can go on for years, allowing nice sound.
I am wondering if I should take a +/-40 VDC approach with my MX50X2 (after one of the two incinerated the outputs/drivers/emitter resistors) during the first few seconds of the first power up at +/-50 VDC. It had worked fine earlier in an easy debug test setup powered at low voltage through LM317/337 at +/-20V.
I have not attached my L7 to high voltage yet so perhaps +/-40 VDC is best but that complicates things since the old defunct receivers I am using have higher voltage transformers.
Does anyone know the relationship for peak output voltage to supply voltage for the L7 and MX50x2? I ask since I am sure 24V and 3A across my speakers will plenty. Does that require supplies of +/- 30V?, or +/- 35V?, or +/- 40V?
I am not trying to measure this myself since one MX50X2 already incinerated and I have concerns about the second which is still working but is back to the low voltage test setup.
Regarding the NCC5551/5401 maybe I should just replace them on the L7 before trying then at higher voltages above the +/-20V of my simple/easy debugging setup? Could I perhaps use TTA004/TTC004? Those are readily available and less trouble than disassembling and repairing a blown amplifier.
Or should I use ON/Fairchild 5551/5401? Is the problem with the NCC devices due to low breakdown voltage or is it that the SOA is too low? (TO-92 too small?)
I am considering replacing the 649/669 drivers and 1047 outputs on the MX50x2 with hFE and Vbe matched TTA004/TTC004 and 2SC5200 because I don't like the bias stability I am observing on the one surviving MX50x2 even at only +/- 26V. One of the inner D1047 got very hot to my fingers last night while the others were much cooler. So something is not right. The heat sink and the angle iron were not very hot. So I wonder if something is wrong with the outputs or drivers.
Perhaps I should simply remove all the drivers and outputs and measure them in my transistor checker before the second board burns up. Could badly mismatched devices cause this? I have also noted that the inner pair of D1047 bias up at significantly higher bias currents than the outer pair.
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@Kozard
Be careful, NC5551 have different pinout arrangement than the 5551 available on western market.
Maybe you would like to check each one's datasheet.
Keeping under +-40VDC is a safety measure that gives peace of mind, good sound and stay away of troubles. The output power is still enough to drive any modern loudspeaker near 90 dB/1W/ 1m.
Needing more power, better watching at other projects or use bi-amplification IMHO.
Be careful, NC5551 have different pinout arrangement than the 5551 available on western market.
Maybe you would like to check each one's datasheet.
Keeping under +-40VDC is a safety measure that gives peace of mind, good sound and stay away of troubles. The output power is still enough to drive any modern loudspeaker near 90 dB/1W/ 1m.
Needing more power, better watching at other projects or use bi-amplification IMHO.