Millenium Bypass problem

[soggybag]

I built two millennium bypasses and recently and they both exhibit the problem. The circuit appears to be working. But. if in the off state over the course of a minute or so, the LED turns on! what am I missing?

[R.G.]

Divide and conquer. Remove the "control line" wire from the connection to the effect output, and temporarily connect/disconnect a 100K resistor to ground. Does the light still slowly come on? If so, the problem is in the Millenium Bypass  circuit. If not, something about the effect output is not holding it at DC ground, possibly lack of a resistance to ground.

[merlinb]

If so, the problem is in the Millenium Bypass  circuit.

Is there a reason you always spell it such?

[Mike Burgundy]

God, totally missed that
Must be a poetic license meets copyright thing.  ;P

[Joseeduardosn]

And if you try increasing the resistance. A doubt: the millenium bypass make a sound?

[soggybag]

I think R.G may be right. I think there may not be a path to ground from the effect output. I'll have to check when I get home. Thanks for the lightning fast answer R.G.

[R.G.]

Is there a reason you always spell it such?

Poetic license.

A doubt: the millenium bypass make a sound?

No, it does not, for the normal ways of operating it. It is possible to mis-operate it and have it make a slight noise. Correctly applied, it is silent, even on high gain distortion pedals. The math says it's good for resistances up to about 1-2M or more.

[soggybag]

That's good to know. I'm assuming if I don't have a resistance to ground, I can just add a 1M resistor to ground at the output. Which shouldn't even effect the volume.

I added the Millenium to an SHO clone which I had built with a Carling DPDT. I want to do another with Fuzz Face, that is also build with a Carling.

[R.G.]

Not having a resistance to ground is what I would have suspected from your description. The Millenium Bypass is a sensitive detector of resistance to ground. It distinguishes between resistances in the 1-10M range and lower and true open circuits, which are in the 100M and higher range. In between is a kind of indeterminate region. But putting a 1M resistor on the output is often done anyway, for other reasons.

If there is no resistance, the output cap charges up through the nano-amp charging current of the reverse biased high leakage diode. Like all good musical effects gear, it's done nearly all by the non-obvious side effects of the parts. 

[soggybag]

Thank R.Genius. That was exactly right. I threw a 1M resistor to ground in and it seems to be working correctly.

While we're on the subject. I've seen a few layouts for the millenium bypass that leave out the low leakage diode. I built one of these first and it seemed to work. Though, since I didn't have the path to ground this one had the same problem of lighting up over time.

[R.G.]

The low leakage diode is protection for the MOSFET, not strictly necessary for proper function.