Terry, I ran all required simulations - here are the amendments for JFET input version.
Basically, three values need to be corrected - R5, R10 and C9.
Please test IPS standalone first, as usual.
Cheers,
Valery
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Hi Thimios,
2SK146 is an "ancient" Toshiba dual-fet with slightly higher noise and higher reverse transfer capacitance (G-D). Vgds is also 10V lower, comparing to 2SK117.
So... possible, but not so good 🙂
2SK389 dual-fet is much closer match.
Cheers,
Valery
Where can the 2SK389 be purchased? That is the jfet that Dado required for the TT amp I just built but I couldn't find them anywhere. I had to use 2SK170s as replacements. I had to twist the legs to make them work.
Thanks Valery but all these are difficult to find & very expensive 🙁
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There are many offers on e-bay - from China, Hong-Kong and Taiwan - but I'm absolutely not sure how they are manufactured (looks like Toshiba has stopped producing them some time ago).
In the modern product line, they've got only two dual-fets (2SK2145 and 2SK3320, SMD-packaged), both are very good for audio applications, but in both packages they've got sources connected internally - no way to use degeneration in differential pair:
>Modern Toshiba JFETs<
The world is not perfect 😀
Thimios, I will send you some 2Sk117 ones together with CFA-CFPx2 PCBs as soon as they arrive - easy to buy here 😉
In the modern product line, they've got only two dual-fets (2SK2145 and 2SK3320, SMD-packaged), both are very good for audio applications, but in both packages they've got sources connected internally - no way to use degeneration in differential pair:
>Modern Toshiba JFETs<
The world is not perfect 😀
Thimios, I will send you some 2Sk117 ones together with CFA-CFPx2 PCBs as soon as they arrive - easy to buy here 😉
Terry, my TT amp does not use 2SK389BL, this is Toshiba plastic case, but LSK389B from Linear Systems in TO71 metal case and Google shoved this link where to buy: Trendsetter Electronics Online Store - Parts, Components and Electronics and I think it's worth the price.
BRDamir
I remember seeing recommended changes for BJT inputs but I've reread the whole thread a couple times and can't seem to find them. Will values in the first post work?
Jeff, I have checked the same way as for JFET inputs - better use the following values:
R5, R10 = 430R
C9 = 220pF (same as for JFETs)
Transistors, used in simulations, were BC550B.
Cheers,
Valery
Thanks. I might populate some boards with bc550s until my 2sk117s arrive. I'd like to compare to my tube inputs for troubleshooting.
It will work, but 2SK117 is better in terms of noise level and input capacitance - it's quieter and faster device.
Too bad, that the K170 is not optimal; I have a stash that I could use well.
What about cascoded BF862s, considering their lower operating voltages but other characteristics being better than 170?
Thanks.
K170 has lower noise and higher transconductance then k117, only lower max voltage.
This one should be excellent choice specially BL type.
I have re-checked the original datasheets - Damir, you are actually right, thank you for clarification. K170 may typically have slightly lower noise. However, capacitances (Ciss, Crss) are twice as much, although it's not really a problem here.
Well, must be ok. Sam - try it, it's really very close.
Well, must be ok. Sam - try it, it's really very close.