FirstWatt J2

[Zen Mod]

Zen Mod, we may not get these schematics early. If you look back at post #20
Nelson says " the schematics of the J2 will be released when production ceases"

And I believe in another post nelson says the J2 not stop at 100.

I was teasing ......

anyway - considering that I'll not build (at least not ) Papa's J2 , I'm not so interested in schematic ; all I'm interested in this very moment (considering fact that Papa revealed more than enough details of rest of schematic ) is that 6-legged ("soon to be 8 legged" as Papa sez ) thingie explanation.

devil is in details ....... , so I'm waiting for that detail to learn something new ...


one can bias these little output thingies in several ways , and I'm curious in Papa's solution .

front end is beefed Aleph J ; output is -say- good ole toob-like SRPP (totem pole ,if I understood usage of that term) ...... if I want to - I can build diminutive one with 2SJ74 & 2SK170 on output - for fun and analysis ......


but not this time .... just because I already have too many things on schedule sheet

 

[labjr]

Zen Mod, we may not get these schematics early. If you look back at post #20
Nelson says " the schematics of the J2 will be released when production ceases"

And I believe in another post nelson says the J2 not stop at 100.

Yeah, that's what I thought I read. And there'll probably be something even better after the J2.

 

[bobodioulasso]

I respect your feeling, Zen.
But hasn't Nelson himself invited us:
"In the meantime, you should have enough smarts to cobble
together your own versions based on the simplified
schematics. Much more fun that way." (post 20)

 

[labjr]

I'm curious about his Big Open Baffle project. I have some nice 300B amplifiers to listen to for now.

 

[DQ]

Someone asked what the J2 replaced in my system. Most recently the F5 and a 2A3 SET. Both very nice amplifiers. I have heard all of the First Watt amps in my system. The F1 is perhaps a little more accurate, the J2 has just a touch of that sweetness (like an SET) that makes it better to my ears.

Could you also compare it to the F2? Excuse my great ignorance, the J2 is not a transconductance amp anymore like the F1 & F2, right? How does it compare in the bass with these two siblings?

Many thanks.

 

[HVfanatic]

I think, we don't need the npn transistor. Just put a good capacitor across the 6 critter. And if someone would see the need of an npn: build a current source to have constant current through the 6 cretter, because he loves it...

 

[Zen Mod]

I respect your feeling, Zen.
But hasn't Nelson himself invited us:
"In the meantime, you should have enough smarts to cobble
together your own versions based on the simplified
schematics. Much more fun that way." (post 20)

I just explained why I am not all over it .....

Papa already gave answer to riddle ......

 

[bobodioulasso]

I think, we don't need the npn transistor. Just put a good capacitor across the 6 critter. And if someone would see the need of an npn: build a current source to have constant current through the 6 cretter, because he loves it...

Do you mean this.

 

[HVfanatic]

No exactly. No bootstrapping, ony one resistor to positive voltage (from Zehner) or alternatively, I could imagine a current source connected to the zehner, no resistor. In this case we may get better results.

 

[bobodioulasso]

Isn't a bootstraping a kind of current source? Or can'tit work there?

 

[HVfanatic]

I wouldn't do any bootstrapping - what should be the benefit. Bootstrapping creates a higher voltage for the driver. A simple current source would keep the current through the 6-critter constant. Therefore, voltage is stabilized.

I think, replacing the 6-critter by selected leds could be cool....

 

[HVfanatic]

A current source would also insulate against voltage variations... ;-)

 

[Jon Ver Halen]

J2 v F2

Could you also compare it to the F2? Excuse my great ignorance, the J2 is not a transconductance amp anymore like the F1 & F2, right? How does it compare in the bass with these two siblings?

Many thanks.

The biggest potential weakness of the current source amp (F1 or F2) is its bass. With no real damping factor, you had to rely on the speaker and cabinet to provide and damping. The J2, with its lower output impedance, does a much better job of controlling the bass for most speakers. (Yes, the J2 is a voltage source amp, not a current source amp).

Perhaps the ideal speaker for a current source amp is a back loaded horn. It has plenty of internal damping, and the increased impedance at resonance created a situation where the current source could better drive it. Under these conditions, the current source is the better amp for bass.

So, as always in this sport, you have to balance your system.

 

[fff0]

Goosebumps? Not a problem. Assuming the rest of the system is up to it. ......The F1 is perhaps a little more accurate, the J2 has just a touch of that sweetness (like an SET) that makes it better to my ears.

Hi Jon,

Many thanks for your input. Appreciate it.

 

[DQ]

The biggest potential weakness of the current source amp (F1 or F2) is its bass. With no real damping factor, you had to rely on the speaker and cabinet to provide and damping. The J2, with its lower output impedance, does a much better job of controlling the bass for most speakers. (Yes, the J2 is a voltage source amp, not a current source amp).

Perhaps the ideal speaker for a current source amp is a back loaded horn. It has plenty of internal damping, and the increased impedance at resonance created a situation where the current source could better drive it. Under these conditions, the current source is the better amp for bass.

So, as always in this sport, you have to balance your system.

Thanks a lot. What about the rest of the audio performance (mids, highs, dynamics...)? You called the F1 "more accurate", but the F2 has much higher distortion figures than both F1 and J2. I'm not asking for a very detailed comparison, I guess I would just like to hear that the F2 is not overshadowed by this new star from a sound quality point of view, that they are at least comparable.

 

[bobodioulasso]

A current source would also insulate against voltage variations... ;-)

Something like:

 

[HVfanatic]

I guess, that's it. Now there are only a few open points: Do we need compensation against thermal runaway? Temperature behaviour of the J-Fets??? Values for R1, R2...

Looking forward to hear Nelsons comments... We all have to buy J2 amps to suck out the secret...

Maybe we should have a current limiter to protect the most expensive silicons ever... ;-)

 

[labjr]

I guess, that's it. Now there are only a few open points: Do we need compensation against thermal runaway? Temperature behaviour of the J-Fets??? Values for R1, R2...

Looking forward to hear Nelsons comments... We all have to buy J2 amps to suck out the secret...

Maybe we should have a current limiter to protect the most expensive silicons ever... ;-)

I wonder if tweaking for the sweet spot will buy more than eliminating the current limiting circuitry. After all, First Watt doesn't seem to have a hard time selling their amps despite having the circuitry built in.

 

[bobodioulasso]

I think, we don't need the npn transistor....

I fear the zenner current to be perturbated by the output gate one.

 

[Zen Mod]

I fear the zenner current to be perturbated by the output gate one.

nope ;
that's jfet , remember

put 5mA through bias string and you're good for several gates