LJM L10-1 class a biasing

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Forman313

Forman313

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Joined 2010
Hi,


I just received a couple of LJM L10 (9418) amp boards with On-Semi NJW0281G/NJW0302G & c5171/a1930.

The plan is biasing them into class a, but I have no schematic or manual what so ever. Just the boards, that came assembled. Must have ordered wrong since I wantet the kit.

I have some old matched (i think) Toshiba 5200/1943 lying around. Would I benefit from swapping the on-semi´s with the Toshibas?
Or should I save them for a different project? I have 8 pairs of them, and I want to build a ~100w class A amp when I get some more experience.

The toroid im planning to use, is a 1000VA 4x32v + 4x44v. I know its a bot high for pure class A operation, so it probably need to transition out of class a at 50-60w?

any help would be greatly appreciated, especially schematic and biasing guide.
 
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AudioSan

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Joined 2009
1000VA devided by 8 sec? so. how is it devided?
you need about 2A bias to hit your 50-60W class A.
with 2*32V sec(+/-41VDC) that is 160+W dissipation pr ch. so 320VA pr ch is minimum.
with 2*44V sec(+/-57VDC) that is 230W dissipation pr ch. so 460VA pr ch is minimum.
with this facts, i realy doubt your transformer is big enough.
 
Forman313

Forman313

Member
Joined 2010
AudioSan said:
1000VA devided by 8 sec? so. how is it devided?
you need about 2A bias to hit your 50-60W class A.
with 2*32V sec(+/-41VDC) that is 160+W dissipation pr ch. so 320VA pr ch is minimum.
with 2*44V sec(+/-57VDC) that is 230W dissipation pr ch. so 460VA pr ch is minimum.
with this facts, i realy doubt your transformer is big enough.
Click to expand...

The 44v windings are just for input stage etc, so in this application they are no good.

I think the 32v windings are 7-7,5A each, so it should do the trick.


Thats 2A bias.. per device, right?

Any limitations in the C5171/A1930 i need to worry about? I not really sure how to calculate the load on these...
 
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AudioSan

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Joined 2009
then its 73mV drop.
0.333*0.22

EDIT: i read 0.73V not mV:) 0.73mV would have been impossible to measure correctly with a standar multimeter.

EDIT 2: heng on. 333mA pr device? is it 6 output pairs? i thought it was 3 pairs. if so, its 2/3=0.666mA pr device. and 146mV voltage drop.
 
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Forman313

Forman313

Member
Joined 2010
AudioSan said:
then its 73mV drop.
0.333*0.22

EDIT: i read 0.73V not mV:) 0.73mV would have been impossible to measure correctly with a standar multimeter.

EDIT 2: heng on. 333mA pr device? is it 6 output pairs? i thought it was 3 pairs. if so, its 2/3=0.666mA pr device. and 146mV voltage drop.
Click to expand...

I meant 73mW .. just a typo.

Its 3 pairs, but I assumed I had to divide it by all the transistors, and not pairs.
 
Forman313

Forman313

Member
Joined 2010
AudioSan said:
its devided by the pairs.
then it's 666mA pr device. a voltage drop of 146mV.
and to actualy do this, you will need some big heatsinks. 0.15C/W pr ch or better.
Click to expand...

I see .. thanks :)

I have a couple of heat sinks from an Alto Mac 2400 lying around. With a 16db papst fan, it should be more than enough.
I wont spend too much money on this project, so im using what ever components I have lying around.

Im trying to save some money so I can build a nice powerfull F5T later. Or maybe a Krell clone.

What do you think about PSU? I have 8 12.000uF Elna for audio.. 4 per channel.
 
Forman313

Forman313

Member
Joined 2010
If its divided by pairs.. how does it figure in with the transistor ratings per the datasheet?

How come the IQ is divided per pair... I mean, there are two transistors? Does the two share the load, or .. ?

This is something I need to read up on .. any suggestions as to where I can find any litterature?
 
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