FirstWatt J2

[Melon Head]

I hope not.
But as usual I was thinking of parralleling output pairs (I have 4Ohm speakers).

[Zen Mod]

Originally Posted by Tea-Bag

Do we need matched pair in Mu follower design?

naah .......

even if matching can't hurt

[zhoufang]

Originally Posted by Magura

They were matched within 10mV, mounted on a copper bar.....trust me, we have the same idea, I just had it a while ago

Thermal runaway just seems hard to control with those critters.


Magura

Thanks for the information, it certainly saved me from burning some LUs.
If Thermal runaway was so bad, then we will need a design that help to ensure equal sharing of current.
It is such a pity that it cannot be paralleled out of the box.

[mos57]

This morning i have called an italian distributor for Semisouth devices.
Hi tell me that now they are going to sell Power jFet with 100 mOhm SJEP120R100 type, that is a little big (17A vs.15A) (i think this is also ok).
They send me a quotation for 10 pieces.
Prices is 35 Euros each plus shipping charge from Usa (about 50-60 Eu).

Francesco.

[GuidoR]

Hi.
I also called the italian distributor.
For 100 pcs the price is lower.
Note that the price is w/o VAT (so consider +20%).
The all-in price is - again - in the surroundings of EUR 35, matching included (if a GB will be organized, due to the - relatively - low quantities, the matching is not only advisable but -AFAIK- mandatory!).

Stay tuned!

GuidoR

[woody]

Now are we sure Nelson is using the SJEP120r in the J2 ? If you refer back
to the verry first of the article he talks about the larger 30A device with a
power rating of ~270W and a cost of $60. Yes he shows a graph using
the SJEP120r in the F2 so which did he use? Rember the 120r is only rated
at 136w.

[zhoufang]

Originally Posted by Magura

They were matched within 10mV, mounted on a copper bar.....trust me, we have the same idea, I just had it a while ago

Thermal runaway just seems hard to control with those critters.


Magura

What do you think if we put a source resistor to each device in a group?
Have you tired it?

[mos57]

Originally Posted by woody

Now are we sure Nelson is using the SJEP120r in the J2 ? If you refer back
to the verry first of the article he talks about the larger 30A device with a
power rating of ~270W and a cost of $60. Yes he shows a graph using
the SJEP120r in the F2 so which did he use? Rember the 120r is only rated
at 136w.

30 A and 1200 V are referred in general about maximum capability for these series devices, i think. But i think Nelson use the "little" devices with 125 mOhm SJEP120R125, because in his circuit (source grounded amp) is suitable a little input cap device. On other hand, you can read at 6moons that J2 employ just this component (at the end of this page view the pdf attachment).

Francesco.

[woody]

Thanks I didn't read the tail end of the 6moons article. I might like 4 of those too if we
can get the cost low enough.

[Magura]

So, Semisouth offered a lead time of 6 weeks.

Could you guys please indicate how many you would like each?

Please quote and sum the amount up, with your name next to it.

The price a piece will end up somewhere around 50usd a piece, if we can get past 100pcs.


Magura