LJM L20 V9.2 main amp

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#23
Transistors seem to be good ones. The link I bought the kit is this: https://www.aliexpress.us/item/3256...t_main.17.709b1802eDrr7d&gatewayAdapt=glo2usa and choose "Type 1", you have to buy everything, but at least you get 2 bare PCVs. The price is good if you consider you get all transistors. Be aware the 2N5551s included in the kit have a pinout different from the one we all know, the base is not at the center, it is BCE. The PCB is made to fit this different pinout. Usually, when you buy a board the transistors are good ones. But if you buy transistors on eBay, you probably get fakes, almost sure!
 
#25
Hi marigno,
Many thanks for the link! You confirmed what I had located.

Pin out different = fakes. In the garbage they go without testing. They will be copy of a JIS number. Therefore I don't care, mystery device. The same for the outputs. They are either original 2SC manufacture, or KSC manufacture (licensed). Otherwise they are fakes and cannot be trusted. I'll use MJW devices for outputs. Let's be honest, if the parts were any good, they would have their real numbers.

I refuse to use anything for myself that I wouldn't use in a repair for a customer. Vice-versa as well. So while the kit may be a good price, maybe it isn't - depending on devices. Like everyone out there, I hate wasting money. The diff pair will also be closely matched and bonded together.
 
#26
Usually, the fakes have a lot lower VCEmax. The final pairs have a VCEmax of around 280V over 140V on the datasheet, so you can be sure they are original. The different pinout doesn't mean it is a fake, it is only a different production. I learned it back in 1980 when I lost my mind after a BC337 BCE. I found all transistors in the kit to be more or less the same and could select the ones to put in the diff, the bad is that the PCB doesn't allow to couple them physically and thermally.
 
#27
I have original 2N5401 and 2N5551 transistors. They have a specific pinout, so if those are marked as the 2N numbers, they are fakes. Period, end of story.

Why not just put the real part number on them?

I would probably use real Japanese numbers given the pinout.

Fakes often have lower Ic max, lower voltage, lower beta and may have a peaked beta vs Ic curve. Overall, they are completely unknown. All you can be sure of is that they are not the number marked on the case. Sorry, I want to know exactly what I am using. Changing the number means they are hiding something. If they are not licensed and do not publish complete curves, the parts are garbage.
 
#28
Here is the updated schematic (mainly for R213 and Res), and the component list.
The 5551 are from CDIL, their name is NCC551, and are identical to the 2N5551, but BCE pinout.
 

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  • L20 Component list.pdf
    L20 Component list.pdf
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  • L20 Schematic.jpg
    L20 Schematic.jpg
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#29
Hi marigno,
Now why am I so sceptical? That datasheet does appear to be more believable than most do, for sure.

It is nice that they provide curves. Has anyone actually checked to make sure they do adhere to those curves? Additionally, if they are equivalent, why is the pinout different?

My personal feeling is that they are a common part with either a European number, or original Japanese number. I have a good stock of the real deal. Of course I can't use them in that amplifier, I would be forced to use another known part. JIS probably.

I've been so long in this business I know there are good reasons for things being the way they are. That's why I don't simply believe a claim if I see a strong departure from how that part type should be. For example, using those parts where an original goes is not possible. So using the same or similar part number and claiming equivalency is a farce.

This design should then (using that layout) call out a Japanese number, or European number with the same pinout. Then you know what you have. Honesty, sorry lacking these days. Those parts are common to another part they were already producing. Therefore, not the same part as claimed. Maybe for the price they figure it is close enough, but if the characteristics are not exact, they may not work in all circuits.
 
#33
This is a new un-touched board. I have another pair made up into a stereo amp, and all I did was to remove and replace C1 the input cap for a 10uF MKP type. I note these new latest boards use a 33uF solid electrolytic type (I think?) so I would perhaps not even change this. I did not add an output coil either. However when I get round to using these new boards, I might add one, but not likely to change anything else...... PS: I am currently builing an L12-2 V4.2 amp for comparisons
 
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#35
marigno said:
8 OP total or 8 transistors total a channel?
I will build the real thing using a 140V total PSU, expecting an output power of about 200W/8Ohms. I know this way there is a transistor becoming hot, but I don't remember which one, perhaps T219, I'll find out.
I ordered the soft start and the speakers protection boards, to verify if I can fit 2 x 500VA toroids and all the rest in a 2U cabinet 360 x 300mm internal space.
Click to expand...

I wouldn't use 140V (-70-0-70). Mine popped at 64-0-64 after about 10 minutes of nice audio. So sad.
 
#38
Marigno suggested some nice modifications. I would just like to note that the added output choke should not have a parallel resistor placed inside the coil. The resistor acts like an iron core and this can cause increased distortion in the coil.
 
#39
Hi PANDINUS,
The resistor acts like an iron core and this can cause increased distortion in the coil.
Click to expand...
I'm sorry, that simply is not true. The core of most resistors is ceramic. If you are concerned about the resistor leads, not enough material to be concerned about. The resistor damps the coil, which is why it is used in the first place.
 
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