Hello Juma,regarding the small preamp i attach,you specified Q1 as BF245C and R8 as 150Ohm in order to have a drain current of about 9.7mA. I dont have BF245C but i have 2 pieces BF245B that have a matched idss of 8.8mA.Can i use these instead of BF245C and what changes do i have to make?Thank you!
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Maouna, I would not recommend that schematic. There is a better one. I attach the schematic, layout (100 x 32 mm, copper side view) and picture of the test module.
It's about 6 dB gain. For 12 dB gain change R5,R25 to 10k. The value of R3,R20 will set the MOSFETs' Id to 12-15ma (that's what we want) - you measure it as a voltage drop over R11,R18.
It's about 6 dB gain. For 12 dB gain change R5,R25 to 10k. The value of R3,R20 will set the MOSFETs' Id to 12-15ma (that's what we want) - you measure it as a voltage drop over R11,R18.
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Because the other one is better. The one from post #209 will work OK - use those BF245B that you have (Idss=8.8mA) without source resistor (R8,R17) or a very small one (10R) and adjust the value of R3,R21 so that you get half of the regulated power supply voltage at the MOSFET's drains (Q2,Q3).
Is the BF861B a suitable replacement for the BF862? What about any of these other jfets at Mouser?
JFET N-Channel SMD/SMT RF JFET Transistors | Mouser
What's the ideal jfet Idss for the circuit in post #1?
I would like to build it like the original circuit.
Are there any changes to the circuit in post #1?
I want to drive an F4 and MoFo power followers.
Thanks,
Vince
JFET N-Channel SMD/SMT RF JFET Transistors | Mouser
What's the ideal jfet Idss for the circuit in post #1?
I would like to build it like the original circuit.
Are there any changes to the circuit in post #1?
I want to drive an F4 and MoFo power followers.
Thanks,
Vince
It's a gate stopper. It doesn't make a difference here because R3 (22k) does that job already.
2sk170 or 2sk246 (any grade will do).
BF861B with Idss >= 12mA will do OK.
Got no time to browse through all those datasheets but you should look for parts with high gm and linear transfer curve. Although, with some effort, many will work OK.
12-15mA
I don't remember - did many different stuff since then. Maybe you should search/browse through thread(s).
12-15mA
If i want to put a coupling capacitor between input volume pot and R3,where should i connect the + of the 10u electrolytic capacitor?(i only have 10uF/50V electrolytic nichicon FW series)
Regarding the 470ohm gate stopper resistor,should i ommit it ithis case? i have already made space for the resistor in my small pcb.
Regarding the 470ohm gate stopper resistor,should i ommit it ithis case? i have already made space for the resistor in my small pcb.
