LSK pre - BAF 2013

[Samuel Jayaraj]

Thanks Jarkaa, I will now give the regulated supply a go.

 

[WalterW]

I have build one channel of this schematic from the Mezmerize thread, and I am testing it right now, but I noticed the offset is very temperature dependent.
If I wave some air over it with my hands, offset rises from 0 to + or - 60mV. Which is way too much in my all DC coupled setup.

I know I can use an output capacitor too solve it, but are there any other suggestions too make it more temperature independent ?

The 2sj74BL and 2sk170BL at IDss of 11.0 mA are thermal coupled. Rest of the transistors and J310's are not.
Thanks!

 

[Zen Mod]

couple them all ........ or use servo

 

[WalterW]

couple them all ........ or use servo

I was afraid you would say that..... Lots of work...starting over again....
Servo? Something with opamp controlling the offset? Do you have an example of that?

 

[Zen Mod]

better to clamp them all

take Froggie UGS as example

 

[AndrewT]

The Mez and the Hyp are based on the DCB1.
In all of these, the two jFETs in each channel are adjacent to each other.
An air stream across one device is virtually the same as an air stream across the adjacent device.
There is usually no problem with output offset varying even with the lid off.

I think you have a different problem.

 

[WalterW]

That's correct, and a different schematic, see post 442
My DCB1 is not drifting at all.

 

[CeeVee]

better to clamp them all

take Froggie UGS as example

...and your BJ2

 

[WalterW]

Ah, you seem to understand ZM
I always have to use Google translate and read Wikipedias before I do

Googled 'Froggie UGS' and did a forum search, found nothing.....

Walter

 

[Ryssen]

I have a problem with offset in my LSK,any advise how to implement a servo??

 

[pidesd]

first,

i d try to couple the ccs jfet only and the rest of transistors...simply close to each other(ideally face to face).

2 cents...

 

[prakit]

Coupled the devices as I did (shown in post#440), it didn't drift with time but still drifted with temp change. Five degree of ambient temp change easily caused a few tens of mV drift. Although this is not really dangerous but annoying so I used coupling caps.

 

[CeeVee]

Ah, you seem to understand ZM
I always have to use Google translate and read Wikipedias before I do

Googled 'Froggie UGS' and did a forum search, found nothing.....

Walter

...François Torres' UGS 3/4 ....better known as CheffDeGaar...there is a thread here on some of that.

Actually ZM is only half right....he is half French half Portuguese ( ...the Torres part )

 

[Zen Mod]

Yoda taught moi that Froggie is Froggie



(when you aren't Froggie , to know difference ; frankly , I'm purposefully ignorant about differences)

 

[CeeVee]

Yoda taught moi that Froggie is Froggie



(when you aren't Froggie , to know difference ; frankly , I'm purposefully ignorant about differences)

Yoda is always right....

 

[pidesd]

la petite broussaille de sous-jupe de ZEN MOD signifie qu'il a lui-même un peu de grenouille dans le sang...

 

[WalterW]

Ah, this work of art:

 

[CeeVee]

...what would you say about this then....

Martin's version of the preamp....leaves speachless.....

 

[WalterW]

Pffff, that's pure porn.

Sadly I will never reach that level of perfection

 

[CeeVee]

Look for Tiroler in this forum.....he has more....really refence stuff.