FirstWatt J2

[luvdunhill]

Last time I looked it was stable to unity, so you can generally adjust it

without fear of instability.

Hm. Bi-amping with F4 and J2 unity gain? Oooh, la, la! And here I thought this was a family friendly forum

I will see what I can figure out.

 

[Nelson Pass]

Bi-amping with F4 and J2 unity gain? Oooh, la, la! And here I thought this was a family friendly forum

I don't actually recommend it - the front end can't see the full voltage output
swing as an input without issues.

 

[Zen Mod]

if unity gain , then either F4 or M2 sans xformer

wasting so much OLG in J2 is both sacrilege and few steps backwards in sound quality

 

[luvdunhill]

Ok, with gain around 5.5 (90.9K + 20K), reduced CCS current on the front end (now 8mA) and a lower bias through the output stage (from 1A to 0.8A at 24V rails), I think it will all work just fine. Adjusting the diode current in the CNY didn’t do much to reduce the bias, so I added a resistor across the transistor side of the opto to adjust the voltage.

All this meddling allows me to not externally cut the gain at my active crossover, which was my goal.

So, still have some gain so hopefully back in “recommended” territory.

I suppose that raises the question of why not a F4J - despite the fact I don’t have enough devices...

 

[6L6]

The reason for no F4J is because being a follower, the sonic signature of the outputs devices is minor at best.

 

[Zen Mod]

there is ......... Beast with Thousand (and few more) JFets

 

[6L6]

Does that count? It's a one-off amp made by a kindly and wise old Elf, made from parts as rare as pure unicorn horn and Phoenix feather...

 

[Zen Mod]

I had same thinking ....... then Mithrandir decided to make Sony VFet source follower stage .....



regarding The Beast ...... , here it is , collecting dust in OPLDF , waiting for crash weight quota

(biz going slow during Holidays)

 

[WBS]

OPLDF???

 

[6L6]

Old
Pass
Labs
Disposal
Facility

 

[Zen Mod]

well , almost .......

Official Pass Labs Disposal Facility

 

[mach.88]

...anyone willing to part with a set of four Semisouth R125 to complete a J2???

 

[Zen Mod]

park an eye on trade posts

 

[mach.88]

Problem solved...thank you!

 

[Zen Mod]

and how much for 2 pairs , these days?

 

[Russellc]

I cant find at any price, or I might snap up another set as back up. The ones I have came from Semisouth...the member not the company,,,,well, both I guess.


Russellc

 

[ernesternest]

I cant find at any price, or I might snap up another set as back up. The ones I have came from Semisouth...the member not the company,,,,well, both I guess.


Russellc

Ebay is listing a pair with an amp around them : First Watt J2 Stereo Power Amplifier - Nelson Pass - Audiophile - Made in USA | eBay

 

[Zen Mod]

 

[mach.88]

Yes and it seems to be one out of Nelson‘s garage/ kitchentable...don‘t expect it to be changing owners for anything less than €2.000/US$2.360...

 

[Nelson Pass]

I still have inventory of R100's, and I will plan some sort of DIY offering
through the store for later this year.