Millenium 2 bypass led not working

[Perrow]

Drain to positive, gate to switch, source to LED.

Are we talking about M1? Or did you mean D to led and S to ground?

[frank_p]

Drain to positive, gate to switch, source to LED.

Are we talking about M1?

Yes, like in R.G.'s schematic.  Millenium 1 is with a JFET.
I don't know if what Deadmax uses is working.  No idea.

[merlinb]

I thought S was supposed to be on the positive side and D closer to ground

JFETs are bidirectional, so it doesn't matter which way round you put D and S. As long as you get the gate right, the circuit will work. Only the diagram will look funny.

[Perrow]

Drain to positive, gate to switch, source to LED.

Are we talking about M1?

Yes, like in R.G.'s schematic.  Millenium 1 is with a JFET.
I don't know if what Deadmax uses is working.  No idea.

Ok, this was supposed to become M2

I'll breadboard this some tonight and see what happens.

[Earthscum]

JFETs are bidirectional, so it doesn't matter which way round you put D and S. As long as you get the gate right, the circuit will work. Only the diagram will look funny.

I thought that was mainly with symmetrical channel jfets, like MPF102, and that the asymmetrical channel fets had a harder time working that way?

[frank_p]

-I'll breadboard this some tonight and see what happens.

The problem is that the LED does not get as bright as it should in the M1.
If you breadboard, keep in mind that there might be capacitive effects at the gate.  So if it does not get to switch or the LED sits in between, do a small perfboard.

[merlinb]

JFETs are bidirectional, so it doesn't matter which way round you put D and S. As long as you get the gate right, the circuit will work. Only the diagram will look funny.

I thought that was mainly with symmetrical channel jfets, like MPF102, and that the asymmetrical channel fets had a harder time working that way?

I didn't know there were any asymmetrical small signal JFETs. Never noticed it on a data sheet...?

[R.G.]

I didn't know there were any asymmetrical small signal JFETs. Never noticed it on a data sheet...?

There are asymmetrical small signal JFETs, but they're not all that common. Most are symmetrical, but may or may not state it on the data sheets. Problem is, the asymmetrical ones don't state explicitly "not symmetrical", the presumption being that if it doesn't say symmetrical it's not. This leaves you in the lurch with the symmetrical but non-professing ones.

As a suspicious datasheet reader, I would not trust a JFET whose datasheet doesn't explicitly state that source and drain are interchangeable, even if I found by experiment that they were. The maker could change the process and not tell you.

[kaycee]

If I remember well I had trouble with a millenium II:  Not all mosfets will work optimally in the circuit.  I had to get back to the 2n7000 in my case.

I find the 2N7000 the most consistent device for this as well, others tend to have occasional problems, not turning off, not turning off fully etc. You might want to wire it up to a circuit to test properly as well, I also find that for some high gain circuits that I get bleed through on bypass with the MBP, on those I go back to the old 3PDT and ground the circuit input on bypass.