Millenium Bypass Dim LED issue

[jophus]

Hi all,

made up a millenium bypass circuit (my first)  for my tubescreamer using a 2n3819- it works, after a fashion....

In the off position the led glows dimly- in the on position it is bright. Is this correct? I thought the led would go all the way out! Have I blown the 2n3819?

Help much appreciated!

Joe

[kurtlives]

I bet you one of your LED leads is touching the enclosure.

[jophus]

Nope!

Not even IN the enclosure yet!

But thanks for the suggestion

[kurtlives]

hahah damn

I have had the exact same problem before (wasnt useing that bypass system) and that was the issue.

[R.G.]

What is the range of Idss on the 2N3819? and what is the brightness spec of your led versus current?

[earthtonesaudio]

Yeah that sounds like something with the JFET.  I did some Millennium Bypass lights using J201's and I got a dim glow when I maxed the output volume of my heavily modded Fuzz Face.

[jophus]

Yeah that sounds like something with the JFET.  I did some Millennium Bypass lights using J201's and I got a dim glow when I maxed the output volume of my heavily modded Fuzz Face.

Earthtone- did you replace the jfet? did it sort the problem?

R.G. What is the IDSS? how do Ifind it? LED standard 5mm red

Cheers guys!

[R.G.]

A JFET has a maximum current it will pass under any conditions other than destruction. This is Idss: current (I) from drain (d) to source (s) with the gate and source shorted (s).

It's listed on the device datasheet.

A datasheet is a list of all the pertinent properties of the device that the manufacturer will guarantee so that designers have some clue about what it will do.

Datasheets are found on the internet by using a search engine.

The internet is a world wide network (net) of interconnected (inter) computers which share data more or less freely. A search engine is a web site that allows you to enter words and the search engine then tells you which web sites have the words in it that you listed to search for.

If the 3819 idss is smaller than the red led needs to glow brightly, it will glow dimly no matter what you do to the two of them.

If the 3819 has a Vgsoff (yep, datasheet) of more than 9V minus the forward voltage of the LED, the LED will glow dimly as there is not enough voltage left after the LED turns on to turn on the LED.

Then there is the whole panoply of ways to connect one diode, one JFET and one LED with one battery incorrectly.

[frank]

A JFET has a maximum current it will pass under any conditions other than destruction. This is Idss: current (I) from drain (d) to source (s) with the gate and source shorted (s).

Thanks RG, I have the same problem, now I understand more. Gonna look at that.

[earthtonesaudio]

Yeah that sounds like something with the JFET.  I did some Millennium Bypass lights using J201's and I got a dim glow when I maxed the output volume of my heavily modded Fuzz Face.

Earthtone- did you replace the jfet? did it sort the problem?

R.G. What is the IDSS? how do Ifind it? LED standard 5mm red

Cheers guys!

Nope, I left the J201 in there.  It was just a dim glow at MAX volume, and I never put the volume up that high, so it wasn't a big deal.

[jophus]

On reflection, a 3pdt switch just seems a whole lot less hassle! Thankyou for your contributions

[R.G.]

I guess it all depends on your hassle threshold.

[frank]

On reflection, a 3pdt switch just seems a whole lot less hassle! Thankyou for your contributions

Millenium is a good (and simple) circuit to understand and debug, I'd rather fix it instead of waiting two weeks for a 3 pole sw.  RG your explications were pertinent for me.