Figment voltages

[Morbidpale]

Would you be so kind as to tell me what my target voltages are for the figment 5457's? Thanks

 

[Robert]

JFET Parameters (PCB marked BF545A but 2N5457 installed)
Q1
Vgs(off)=-0.42V at Id=5.4µA
Vgs(on)=0.14V at Id=5.00mA
gfs=20.9mA/V at Id=3.0mA to 5.0mA
Idss=2.23mA at Vds=3.00V
Rds(on)=31.9Ω at Id=5.0mA and Vgs=0.0V

Q2
Vgs(off)=-0.31V at Id=5.2µA
Vgs(on)=0.24V at Id=5.00mA
gfs=21.9mA/V at Id=3.0mA to 5.0mA
Idss=0.90mA at Vds=3.01V
Rds(on)=37.2Ω at Id=5.0mA and Vgs=0.0V

Q3
Vgs(off)=-0.30V at Id=5.3µA
Vgs(on)=0.24V at Id=5.00mA
gfs=20.8mA/V at Id=3.0mA to 5.0mA
Idss=0.87mA at Vds=2.99V
Rds(on)=37.4Ω at Id=5.0mA and Vgs=0.0V

Source Resistors (fixed resistors in original)
Q1 - 22K
Q2 - 10K
Q3 - 10K

Voltages as measured
Q1
D 15.44V
S 0.328V
G 0V

Q2
D 16.27V
S 0.221V
G 0V

Q3
D 16.23V
S 0.224V
G 0V

 

[Morbidpale]

 

[maertz13]

I’ve only ever biased J201’s before, and I was just instructed to get them as close to 4.5v as possible. Do I bias 5457’s the same way?

edit: just remembered that this pedal runs on 15v with a charge pump. so should they be 7.5v?

 

[BrainDrain]

JFET Parameters (PCB marked BF545A but 2N5457 installed)
Q1
Vgs(off)=-0.42V at Id=5.4µA
Vgs(on)=0.14V at Id=5.00mA
gfs=20.9mA/V at Id=3.0mA to 5.0mA
Idss=2.23mA at Vds=3.00V
Rds(on)=31.9Ω at Id=5.0mA and Vgs=0.0V

Q2
Vgs(off)=-0.31V at Id=5.2µA
Vgs(on)=0.24V at Id=5.00mA
gfs=21.9mA/V at Id=3.0mA to 5.0mA
Idss=0.90mA at Vds=3.01V
Rds(on)=37.2Ω at Id=5.0mA and Vgs=0.0V

Q3
Vgs(off)=-0.30V at Id=5.3µA
Vgs(on)=0.24V at Id=5.00mA
gfs=20.8mA/V at Id=3.0mA to 5.0mA
Idss=0.87mA at Vds=2.99V
Rds(on)=37.4Ω at Id=5.0mA and Vgs=0.0V

Source Resistors (fixed resistors in original)
Q1 - 22K
Q2 - 10K
Q3 - 10K

Voltages as measured
Q1
D 15.44V
S 0.328V
G 0V

Q2
D 16.27V
S 0.221V
G 0V

Q3
D 16.23V
S 0.224V
G 0V

Are the drain voltages really that high? When I max out the trimmers I can only get around 13v. For now I adjusted each one to around 7.5v and it sounds pretty good. Just having a hard time doubting anything you post so figured I should just ask. lol. Thanks.

 

[Nostradoomus]

They’re hooked up to VCC of a voltage doubler with a bit of resistance attached, so yeah they should be that high. Your fets may be out of spec or your pots/trimmers may just be on the edge of 20% tolerance but if it sounds good don’t mess with it

 

[BrainDrain]

They’re hooked up to VCC of a voltage doubler with a bit of resistance attached, so yeah they should be that high. Your fets may be out of spec or your pots/trimmers may just be on the edge of 20% tolerance but if it sounds good don’t mess with it

Turns out the power supply I was using went bad


And that’s why I never doubt Robert. Ever.