FirstWatt J2

Official Court Jester
Joined 2003
Paid Member
Try reading this thread. It's not that many pages, and it will answer your questions.


Magura :)

I already polluted your GB thread ..... :rofl:

assuming that amp is nothing else than augmented Aleph J input stage , with SRPP output stage - matching of output jfets between channels isn't necessary , and even matching of two output jfets in one channel isn't so critical

but - as I wrote there - ask Papa directly ;

his answer will save you at least 50% of matching efforts ( considering that spoiled kids are already talkin' about matched quads )

:spin:
 
his answer will save you at least 50% of matching efforts ( considering that spoiled kids are already talkin' about matched quads )

:spin:

Well, let's see, I doubt that it will save me much effort....I also don't have a problem with a bit of matching, as I would be surprised if this hits 300 pcs.

Matching 300 fets is no big deal. It takes a couple of afternoons, and a few cups of coffee, which Mrs. Magura will happily supply to the cause:D



Magura :)
 
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:D my first thread in years and just over a weekend and it's already 5 pages...

Morten, I'm interested in your GB the jfets being TO-247s...

Mr. Pass, are the Lovoltechs even an option for the "other" output jfet (CCS)? Might be useful to some who have a stash of those...and cheaper;).
 
Official Court Jester
Joined 2003
Paid Member
.......

Mr. Pass, are the Lovoltechs even an option for the "other" output jfet (CCS)? Might be useful to some who have a stash of those...and cheaper;).

let me chip in ..... even if my hair still isn't Papa Gandalf like .......

being SRPP output stage - that means Shunt Regulated Push Pull , where CCS part of totem pole is modulated ..... sort of ....

that means - there isn't exactly needed to have identical lower and upper half , but it's certainly more practical to have them identical

:clown:

just think about xconductance .....

edit :

pic just for you :
 

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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.

That's not o bad compared to old Sony VFETs on ebay? Even though those might be n-channel and p-channel. :D

Rolv-Karsten
 
That's not o bad compared to old Sony VFETs on ebay? Even though those might be n-channel and p-channel. :D

Rolv-Karsten

Yes, at the last, but Nos Vfet are as a meteor today.
Also i have received vfet from ebayer one week ago and will try its next days in two stage single ended amp (first stage with 2sk79 :D).
I like to find any devices that i think should have a good sound quality.
However i think V-fets are a quite different from these sic-jfets.
So i would value their global impact and sonic signature above all.

Francesco.
 
If these are going to be matched, I would like 8 (ie 4 per channel).
It would be nice if you labelled them with the values. A bit of masking tape will do.

I just need the matching for equal heat dissipation, so they just need to be matched in pairs.
 
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If these are going to be matched, I would like 8 (ie 4 per channel).
It would be nice if you labelled them with the values. A bit of masking tape will do.

I just need the matching for equal heat dissipation, so they just need to be matched in pairs.

At this moment, please you must follow the thread opened by Magura in Group Buy. ;)

Best regards, Francesco
 
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:D my first thread in years and just over a weekend and it's already 5 pages...

Morten, I'm interested in your GB the jfets being TO-247s...

Mr. Pass, are the Lovoltechs even an option for the "other" output jfet (CCS)? Might be useful to some who have a stash of those...and cheaper;).

The upper FET would appear to have to dissipate as much power as the lower FET, so no dice with the tiny Lovoltech. Using a MOSFET as a cost saving option up there is more realistic.
 
Mr. Pass, are the Lovoltechs even an option for the "other" output jfet (CCS)? Might be useful to some who have a stash of those...and cheaper

I was thinking along the same lines. The Lovoltechs are depletion mode devices and the Semisouth are enhancement devices, so just with a bipolar supply there is no headroom for biasing the Lovoltechs. However, an extra voltage source for the input stage of a few Volts and cascaded under the negative supply voltage should work?

The upper FET would appear to have to dissipate as much power as the lower FET, so no dice with the tiny Lovoltech. Using a MOSFET as a cost saving option up there is more realistic.

The Lovoltech need to be cascoded, same as in the F3 so that takes care of dissipation. Since the Mu follower should be there to cancel distortion, I presume upper and lower device should be the same. The one caveat is that the (Lovoltech + Mosfet) cascode already removes a lot of distortion so it is not clear what effect the mu follower would still have.

My two cents ...
 
Power Supply

Quote from the owner's manual:

"On the front panel there are two blue LED lights, one for each channel, indicating regulated power to the channel."

Does this mean that the J2 will be getting a regulated power supply instead of the unregulated First Watt power supplies in the previous offerings?

Steve