SemiSouth power Jfets .......... FW J2

[Zen Mod]

there is no dynamically matched pair of jfets , even on same dye - so yes - with little degeneration - they're closer matched ;

using Idss matched J74s is still a must

anyway - you know that Papa is no loosing sleep about that issue ( degeneration) , and I'm putting them there just for - say - engineering reasons

[generg]

o.k. thanks Zen Mod! is it necessary that the IDSS of the J-Fets must be in the region of the current planned to go through them? may be a silly question to make it clearer.... Babel J2 wants in the input stage a current of 10mA going through one half of the coupled J74s. Must every J-Fet have at least an Idss of 10mA or better higher?Is less also allowed, when they are matched?THX

[Zen Mod]

current through each input Jfet is 5mA , as prescribed :rofl:usual BL suspects are good enough ;do not worry .........

[generg]

I do not worry, it is only for engineering reasons......

[sp300b]

The message from "Unknown soldier"

Hi Slobodan,

You had the right feeling - the highest value in the middle sounds best....Congratulations!

p.s. I put it here only for Engineering reasons

[Zen Mod]

OK - just from engineering reasons , find them enclosed here :FW J2 rev. 0 and rev.1:Viannen_loungelizard:

[sp300b]

Just for engineering reasons...

Some brain food - Optocoupler's base connections

[Zen Mod]

naah ....that's just for engineers amongst us .......

[Zen Mod]

.............R29 = 0,33 OhmR30 = 0,5 OhmR31 = 0,33 Ohm already sounded the best among the tested combination. OK, I have replaced all the resistors with this last change, but I don't think the resistors type made difference itselfAgree with ZM, most probably it's only a matter of taste (pardon, ears)

[sp300b]

Current (last setup so far) is actuallyR29 = 0,33 OhmR30 = 0,68 OhmR31 = 0,33 OhmCan we make it better ?

[Zen Mod]

let ears decideI'll order 0R47 and 0R68 MOX's , besides already arrived 1R's ;

[sp300b]

let ears decideI'll order 0R47 and 0R68 MOX's , besides already arrived 1R's ;

Order for me bunch of 1/0,68/ 0,47, too, please.

[Zen Mod]

as I said - we already have bunch of 1Rwhen I get two other bunches , then you have them , too

[generg]

Things go on.... audio nirvana is near

[Zen Mod]

naah .........beter learn how to live in Nirvana all the time ........ ( I reckon you are just not aware )

[Tea-Bag]

ChangesR2, R21, R24 4.7kR25 500R PotR26 390R22 .47RR29 1RR36 1RR30 2RR37 .47RR31 1RThe new values are below the orange higlights if they changed. The last swap was only on R25,R26.current offset in the channel .5v runs steady at least. Other channel is .01v and is stready.Listening right now. The above channel runs at ~ .6v bias, the good offset channel .520v. The higher bias and offset channel sounding a touch warmer sonically.Let me know if you need anything else.

Zen Mod, Did you take a look at the measurements I sent to your geemail account?I too find the source resistor changes a thing for the better. Less aggressive sounding, a bit more relaxed.Not that some will believe it, but it sounded better after about 20 hours of listening. More champagne sound and smoothness.Not in a rush on this. But if I want to take cap off fullranger I want to get the offset lower.

[Tea-Bag]

Okay, got the offset problem under control - I think. Looks like the bf245 may have been shorted with the leads touching under the pcb.

I am further exploring source resistance mods.

R22 .47R

R29 1R .620v

R36 1R 1.0v

R30 1R

R37 .47R .500v

R31 .47R

The amp now runs quite hot, with sinks at 52c.

Once warmed up, the sound gets more relaxed and softer, but still has a dynamic punch to it. The soundstage now seems well focused now.

[sp300b]

:Viannen_loungelizard:I would stop here

[Tea-Bag]

Why? - you thinks it's as good as it can get?A bit back, someone suggested biasing down a bit.I will give it a good listening session this wednesday.My F2J is up and running , so some comparisons will be done.

[sp300b]

Why? - you thinks it's as good as it can get?A bit back, someone suggested biasing down a bit.I will give it a good listening session this wednesday.My F2J is up and running , so some comparisons will be done.

1) Bigger Bias is always better2) Big Resistors combination seems to be the best possible

[Tea-Bag]

sp300,How would you describe the sound of your setup?Do you get similiar results?

[sp300b]

sp300,How would you describe the sound of your setup?Do you get similiar results?

I got the same result - Bold music with lot of details. Like a Shark - It's (music) everywhere