UGS with LSK170/LSJ74

[Oneminde]

Dear all.

I am planing a UGS preamp build and I want to explore the possibility for using JFet LSK170/LSJ74 instead the BJT ZTX450/ZTX550 found in this unit. I know that BJT are current controlled and JFet's are voltage controlled, so my question is:

Does the UGS remain the same and the only difference is JFets instead of BJT's and bias adjust ?

The BOM state that JFet's are compatible; Dropbox - UGS_Muse_ugs_BOM_1.0.pdf - Simplify your life

 

[Zen Mod]

as far as I remember , ztx part are used "just" as cascodes in UGS modules

-why changing them to parts worse in those positions?

being fancy is not most clever choice in all circumstances .........

 

[Oneminde]

Well, the UGS Muse edition use both the UGS Buffer (M1) and a JFet Output Buffer (M2) which I am guessing is the discrete OPAMP - (still learning). The JFet Output buffer (M2) which was developed by Flat, might now at closer inspection be the one referred to in the BOM I attached. Meaning the N.Pass UGS (M1) could stay intact and the only stage getting the LSK170/LSJ74 is the OPAMP (M2).

Not easy when certain things are called almost the same.. lol

Oneminde

 

[Oneminde]

Perhaps the JFet output Buffer is a Common Source JFET Amplifier.

 

[Zen Mod]

post #3 , ztx again "just" cascodes

 

[Oneminde]

post #3 , ztx again "just" cascodes

I see now. The UGS Buffer use the 2SK389BL and 2SJ109BL Jfet's. These might need to be replaced. Obsolete perhaps.

Replacement for 2SK389BL?

Anyway - thanks for the input. I'm quite pleased.

 

[Zen Mod]

2sk389BL is practically pair of 2SK170BL on same die and in one 7-pin case ; 2SK170BL you can replace with LSK170B

2SJ109BL is practically pair of 2SJ74BL on same die and in one 7-pin case; 2SJ74BL you can replace with LSJ74B

 

[Oneminde]

Thank you Zen Mod - greatly appreciated 🙂