LED on dimly even when bypassed

[Toy Sun]

I'm sure this has been asked before, and I swear I searched...

FuzzDog Harmonic Percolator. Works great, bypasses great. But when using my switching power supply (multi out cheapo), even when bypassed the LED is on dimly. If I try it with a Boss standard PSU, no issue. Any ideas?

Schematic below.

Thanks
John

[FiveseveN]

There is no LED nor bypass in that schematic, so I'll have to assume what you built is 3PDT true bypass.

(multi out cheapo)

Those are not meant for audio and it looks like it's "leaky", making it potentially dangerous too. Use proper PSUs, problem solved.
If you want to go deeper into how modern LEDs can light up even disconnected, it's gonna take some RF wizardry:

[duck_arse]

There is no LED nor bypass in that schematic, so I'll have to assume what you built is 3PDT true bypass.

excellent.

[Phend]

And that, guys, is why you should not keep your phone in your pants.

[antonis]

Do cellphones turn a Si diode into a Zener, also..??

[Toy Sun]

doh!
Yes, 3pdt bypass board.
The PSU system is a cheap, but it is designed for guitar pedals. While not UL listed, I don't think it's totally dangerous (though it does have some questionable product design)
This is it: https://www.amazon.com/gp/product/B088R741JZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Would a photo of the 3pdt help?

[FiveseveN]

Oh I was thinking of far worse.    That actually looks like a deal if the outputs are indeed isolated. Have you checked?

Would a photo of the 3pdt help?

The fact that the issue is not apparent with the BOSS PSU suggests there's nothing wrong with your work but rather Hiree's. If it bothers you, try shorting the LED with a large value resistor (start from 1M and work your way down as needed). C11 and C9 in particular should take care of HF switching noise though. Maybe add a ferrite choke to the power cable?

[Toy Sun]

I didn't believe it was really isolated, at that price (it's pretty cheap plastic, but I don't  take my pedals out with it, it's just for home use)

The mfg is pretty honest that it's not isolated - I find this refreshing:
This power supply is not a true isolated power supply.Similar to the $30+ power supply in the market.It is an optimized 1 spot power supply.
This optimized 1 spot power supply can't compete with the real isolated power supply (such as voodoo) in eliminating noise. Because of this, we specially add four AC outlets to the power supply. We hope that customers can use AC outlets to power supply the noisy pedal when there is noise in pedal. In this way, customers can solve the power supply problem of pedal at a relatively low price.

[Elektrojänis]

If it bothers you, try shorting the LED with a large value resistor (start from 1M and work your way down as needed). C11 and C9 in particular should take care of HF switching noise though. Maybe add a ferrite choke to the power cable?

How about using the bypass switch to short the led to ground only when on bypass? Like connect the center terminal to the typical led/resistor -combination, the effect on side to the power and the bypass side to the ground.

I'd still be a bit curious where the leak comes from.

[anotherjim]

There is probably enough capacitance between open switch contacts to pass RF noise that an LED can detect. Enough capacitance in fact to cause hi-gain circuits to oscillate from positive feedback via the stompswitch input and output sides. If it can happen with audio frequency it can certainly happen with RF from a cheap switching supply.

All that said, the odd thing here is that the 9v pedal supply is properly filtered for RF by C9 in the circuit. The RF noise should prefer to pass through C9 and effectively get shorted out rather than the path via LED, CLR and switch contact capacitance.

Does the build have the same power filtering as the schematic?

[Elektrojänis]

All that said, the odd thing here is that the 9v pedal supply is properly filtered for RF by C9 in the circuit. The RF noise should prefer to pass through C9 and effectively get shorted out rather than the path via LED, CLR and switch contact capacitance.

Wouldn't that be heavily dependent on how the wiring is done? If the led powerwire is wired straight to power suply jack instead of the filter caps, the resistance of the wires could maybe be significant factor?

[anotherjim]

Slight, but some wire impedance for sure but it really needs to have things in the Mhz to be a real problem. If possible, moving C9 to the DC jack might help, or you can always fit a cap across the LED.
If this PSU is really horrible, this pedal won't be the only one with problems but they might manifest in different ways.