Hi,
I need to replace some fake BF245A that I bought from ebay. My local supplier have this:
2sk30a
j113
which one can I use for this build?
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus.html
Main Board:
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg1.pdf
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg2.pdf
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg3a.pdf
BBD Board:
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus_BBD_Board_sch_page1.pdf
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus_BBD_Board_sch_page2.pdf
Thanks.
From designer old forum:
"I haven't tried a BF245C, but I specified a BF245A for a reason: The threshold voltages are vastly different."
I need to replace some fake BF245A that I bought from ebay. My local supplier have this:
2sk30a
j113
which one can I use for this build?
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus.html
Main Board:
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg1.pdf
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg2.pdf
http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg3a.pdf
BBD Board:
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus_BBD_Board_sch_page1.pdf
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus_BBD_Board_sch_page2.pdf
Thanks.
From designer old forum:
"I haven't tried a BF245C, but I specified a BF245A for a reason: The threshold voltages are vastly different."
Last edited:
Yes. I agree. Add 2N3819, 2SK117, BF246, MPF102. All those JFET are very similar between them. Keep an eye at pinning. They may differ: VHF JFETs usually have their source between gate and drain to reduce coupling.
Sure, but the resistance is heavily correlated to Idss (which is itself heavily correlated to Vpo)
Its use is mainly around the zero crossing of Vgs and Id, both negative as well positive values allowed (under 0.6Vdc) just like their application in Wien-bridge oscillators controlling the amplitude, all ac related. It is a (rectified) 'dc voltage driven' variable resistor. It is obvious to keep a keen eye on the other specs (check), to stay in accord with the original circuit and the OP's request. C3 indicates no dc current, the 3819 suffices.
Attachments
Yes but the circuit resistances could be changed to suit another R(channel).
The VTO is important, not only as the other influence on R, but because it must be much larger than signal peaks or THD will be high.
Yes we could modify the gain and signal voltage but that will affect S/N, usually for the worse. And JFET compressors are typically better than FM but worse than CD, so we don't want any worse. (We do use JFET boxes for "CD-quality" because most compressed program does not need all 96 dB, because few listing space run 96dB dynamic range.)
Really we want a very large very low-'gain' JFET. And nobody makes that.
Is the J112 with -1 <> 5 V out of spec for the purpose ? seen that in lieu of the Philips of the #1 post
I've not examined the circuits in the links thouroughly enough to determine the exact control voltage for the 245's, so best prctise is to stay near the original specs as closely as possible. Given the OP's options locally, the choice has been made (#4).
