FirstWatt J2

[Phil Townsend]

Snowing in Santa Fe

Perfect day to setup the J2....

 

[Phil Townsend]

First Watt J2 is warm and cozy.

What if my 45 amp had balls?
That is a good description the J2.

Do I miss the 45's rich midrange... no...
but to be sure, it is not the same as the 45.

I have only a few hours on the J2...
Hey it sounds really wonderful.

Thank you Nelson !!

I like this sand amp. It has a new home and it will be very happy here.

I believe a have the makings of a good match for the Lowther Field Coil Drivers and the Altecs... 45 for the LFCD and the J2 for the Altecs...

Oh Boy!!!
Can't wait.

PS.
We have a passive solar heated house... The J2 is helping keep us warm as the first snow melts in Santa Fe.

Star Dust playing...Willie Nelson... Good stuff.

Won't take long to add some hours on this guy.

 

[Nelson Pass]

We aim to please.

 

[rickmcinnis]

I look forward to joining you

Decided having an amplifier tuned by its designer has to be better than trying to make it myself. Especially when I consider I am where Nelson Pass was, in my understanding of these things, when he was thirteen. And that might be an unreasonably rosy assessment of my abilities.

Sent my check last week and looking forward to listening to this affordable work of electrical art.

I have a couple of weeks to get everything prepared.

As appreciative as I am for all of the gifts of circuits and advice, an amplifier this good, for this amount of money, may be the greatest gift of all.

Thanks very much,

Rick McInnis

 

[fredlock]

I am just a poor boy that can't afford to buy this wonderful work of art amplifier. I'm longing to listen to it, as to what these guys have heard but nothing I can do, but to be patient untill the blessing will come.

 

[Tea-Bag]

I appreciate what I have, and what Nelson has given freely. We continue to feast on his designs.

 

[HVfanatic]

Lets continue with the guesses of the full j2 schematic:

I proposed to use a current source on top of the zehner for biasing it correctly. Giving this baby some thoughts, I would add another current source on the bottom. Reason for this: The current through both semisouth jfets should be equal, to allow better distortion cancellation...

Regs, Dirk

 

[Zen Mod]

Lets continue with the guesses of the full j2 schematic:

I proposed to use a current source on top of the zehner for biasing it correctly. Giving this baby some thoughts, I would add another current source on the bottom. Reason for this: The current through both semisouth jfets should be equal, to allow better distortion cancellation...

Regs, Dirk

I can't see how you can manage that - CCS on both sides of voltage reference ;

at least on one side you're short on voltage headroom

 

[HVfanatic]

you think, on the lower side??? well, then we may need a little helper supply...

 

[bobodioulasso]

Before trying to guess the schematic may be it should be nice to make some consensus about how it works.
What about my posts 276 & 277. Those resistors?

 

[labjr]

I wonder why I don't see any thermal compensation in the J2?

 

[Nelson Pass]

Doesn't need it - not much thermal drift.

 

[labjr]

Interesting. Is it because of the those semiconductors or the circuit ?

 

[Nelson Pass]

Well, they are both the same devices, and there is a fair bit
of degeneration, and there is a feedback loop.

 

[Nicola]

Dear Mr Pass
I read in a previous thread (shame i can't find it again) about the J2 and in the FirstWatt the following quote "There will be an effort to update the F2's that are out in the field to the particular power JFET used in the J2, as it brings a spectacular improvement there also. More on this at a later date when I have enough parts."

What does that hide ? Will users having purchased a F2 be able to change it for an J2 or will it be possible to perform a DIY update ?
Looking forward to read you,
Best regards

 

[Nelson Pass]

I am anticipating the replacement of the Mosfet gain device
in the F2 with the JFET. I have not decided on the particulars,
but I'll get around to it.

 

[Nicola]

F2 upgrade

I am anticipating the replacement of the Mosfet gain device in the F2 with the JFET. I have not decided on the particulars,
but I'll get around to it.

Would that mean the "upgrade" could by carried out by a non-expert (with some knowledge on parts etc) based on the specs you would provide (or even the spare parts) or would it mean shipping you back the F2 for upgrade ? I'm looking forward to read you.

As the F2 (unlike the F3) is dead silent (one of the most silent amps), hopefully this improvement will not make it noisier (a bit of a disadvantage when running with 100+db driver). I'm wondering if i would like to replace the F3 by a J2, but I'll wait to read more and seen what Mark suggest.

Anyway thanks it's allways very interesting to follow you work.
Regards

 

[Telstar]

As the F2 (unlike the F3) is dead silent (one of the most silent amps)

My F3 is dead silent.

 

[Nelson Pass]

Yes, so is mine.

 

[johnsonad]

I would like to be able to make my factory Aleph 30 as silent as the J2 was in my system. The J2 rejects all ground noise. It's scary how silent that thing is.