Trimpot Adjustment - Son of Ben
- Thread starter Jovi Bon Kenobi
- Start date
I'm glad I never ordered from that guy. I was close on some GE transistors but I ended up just buying a DCA 55 and a bunch of transistors from Ukraine and Russia instead.
MichaelW
Well-known member
Well crap, I have some from him. The ones I used in my SOB were from GuitarPCB but I think I grabbed some from PedalHacker at one point. Unfortunately, I mixed them all in one bag so I don't which is from where. I guess I better go check them.
Chuck D. Bones
Circuit Wizard
How did you measure them and how far out of spec were they? Some pedal circuits will accommodate OOS parts and a few, like the Fairfield Unpleasant Surprise require OOS J201s.
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Better question is how should we all measure our less than ideal J201s...
Chuck D. Bones
Circuit Wizard
I believe the DCA measures Vp & Idss. The Cheap Chinese Transistor Testers do not measure Vp & Idss. A DMM & a 9V power supply wil measure Vp & Idss. Search these forums to see how.
They were all measured on my Greatly Improved JFET Tester back when I built the PAL M800 after I couldn't get it to work right, 1.2 to 1.3 from memory!
Some of the Voltages were at 2.5 to 3v or it would Fart out!, Used it for a bit but it never had the Sustain or Push.
Got hold of some Siliconix J201's and Tested them, All in Spec! .625 to .675 from memory!.
Replaced the Fairchild's ????? & dialed the trimmers to 4.5v & it was Bliss!!!!!!
I played it again Yesterday & I myself prefer it a tad better than the Golden Falk which is also a Great pedal, just different!
I'm sure Pedal Hacker sells some Legit components!!!
He just didn't do the right after sale service on this purchase!!!
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Chuck D. Bones
Circuit Wizard
Did I read that right? Are you reporting Vp in the 1.2 to 1.3V range?
I believe you told me up to 1.0 max!
These were 1.2 to 1.3, I told you they were out of spec!
Chuck D. Bones
Circuit Wizard
Vp spec is 0.3V to 1.5V
Idss spec is 0.2mA to 1.0mA
Idss spec is 0.2mA to 1.0mA
Yep, It was 1.2 to 1.3 Idss.
Chuck D. Bones
Circuit Wizard
you sure now? 
Those should be fine in 95% of the pedals that call for J201.
Those should be fine in 95% of the pedals that call for J201.
It sounded like SHIT in the Pal M800!!!you sure now?
Those should be fine in 95% of the pedals that call for J201.
Chuck D. Bones
Circuit Wizard
That would be one of the 5% then.
Idss a little on the higher than spec is not what made those J201's perform poorly in the PAL800. What made them perform poorly was the circuit needed JFETs with Vp near the low end of the spec range and yours had Vp at the high end of the range.
I've said it before, and I'll say it again: when it comes to JFETs, having the right part number is no guarantee that you'll get the right tone.
Idss a little on the higher than spec is not what made those J201's perform poorly in the PAL800. What made them perform poorly was the circuit needed JFETs with Vp near the low end of the spec range and yours had Vp at the high end of the range.
I've said it before, and I'll say it again: when it comes to JFETs, having the right part number is no guarantee that you'll get the right tone.
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DAJE
Well-known member
I'm not seeing any Vp on my Peak Atlas. I really don't understand what the figures mean, I'm much more of a music guy than a numbers guy, but here's one of my MMBFJ201s. I've compared this J201 to known good ones and I believe it's good, and the numbers seem pretty typical to me.
Vgs(off)=-0.56V at Id=5.0µA
Vgs(on)=0.43V at Id=1.18mA
gfs=1.9mA/V at Id=0.7mA to 1.2mA
Idss=0.43mA at Vds=3.00V
Rds(on)=607.6Ω at Id=1.2mA and Vgs=0.0V
Not seeing a Vp there, and the manual says nothing about it.
DAJE
Well-known member
I solder them to adapter boards then test them. Fig (of course) has some kind of SMD tester rig thing.
Chuck D. Bones
Circuit Wizard
Vp is the same as Vgs(off). With N-channel devices, Vgs(off) is always a negative number. Since that's understood, we frequently refer to Vp and leave off the minus sign.
Your Peak Atlas is not measuring/reporting Vgs(off) correctly. Vgs(off) is usually specified for Id << 1uA. In the datasheet above, it's specified at Id = 10nA.
