Should an arrangement like this (with the diode in place of the resistor, of course) work for tracing the curve? I'm not sure if it'd be precise enough, though, with my multimeters
JFET Shootout
- Thread starter Chuck D. Bones
- Start date
Should an arrangement like this (with the diode in place of the resistor, of course) work for tracing the curve? I'm not sure if it'd be precise enough, though, with my multimeters
Chuck D. Bones
Circuit Wizard
That will work. Put your voltage DMM on the other side of the current DMM because otherwise the voltage drop in the current DMM will affect the voltage reading. You also need a resistor in series with the power source to limit the diode current to a safe value.
Your DMMs need to resolve better than 100μA and 10mV. 20μA and 20mV is better. We want to make multiple measurements between 100μA and 10mA. Most pedals run the diodes at 1mA max for soft clippers, 4mA max for hard clippers. Doing it manually takes a lot of time.
Your DMMs need to resolve better than 100μA and 10mV. 20μA and 20mV is better. We want to make multiple measurements between 100μA and 10mA. Most pedals run the diodes at 1mA max for soft clippers, 4mA max for hard clippers. Doing it manually takes a lot of time.
I'm not sure I understand what you mean by that. Shouldn't the voltage DMM be parallel to the diode?
Chuck D. Bones
Circuit Wizard
Yes, it should be directly across the diode, not the diode + the ammeter. Just like real world voltmeters do not have infinite input impedance, real world ammeters do not have zero voltage drop.
Ok, I see what you mean. I'm not sure I'll do it, but if I do, I'll report back here
Chuck D. Bones
Circuit Wizard
If you do make measurements, try this to get the most useful data from the least number of measurements. Measure Vf at 5 currents:
100uA 300uA 1mA 2mA 4mA
That should give a pretty good indication as to which diodes & JFETs are similar.
It is so much easier with a curve tracer. Here's some data I collected. The squiggles are caused by the resolution limit of the scope. JFETs were measured with D & S shorted together.
100uA 300uA 1mA 2mA 4mA
That should give a pretty good indication as to which diodes & JFETs are similar.
It is so much easier with a curve tracer. Here's some data I collected. The squiggles are caused by the resolution limit of the scope. JFETs were measured with D & S shorted together.
Could you identify the fake 2n3819? Are they jfets, at least?
Chuck D. Bones
Circuit Wizard
That one MMBF5457 (green trace) is strange.
temol
Well-known member
I realized it is a fake 2n3819 after measuring Vp and Idss. They're jfets. Anyway... when I bought them on Aliexpress, I didn't expect anything else. I bought them rather as an experiment.
Here's a comparison. Can you guess which is which?
temol
Well-known member
I agree. I'm going to test some more of them.
Chuck D. Bones
Circuit Wizard
I'm guessing left one is Fugazi.
Mine look exactly like the left one, and they have all been in-spec for a 2n3819, which is not a super hard task, considering the parameter spread
Feral Feline
Well-known member
I guessed left was bogus simply because I've never seen a fake whatever split up the lettering/numbering as per the one on the right.
I'm not saying there aren't fakes with the letter-number pattern:
xxx
#x#
###
...just that I've never seen them.
I'm not saying there aren't fakes with the letter-number pattern:
xxx
#x#
###
...just that I've never seen them.
temol
Well-known member
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