DeadEndFX Andamento & Meta-Morph Bypass LED Circuits

[Cybercow]

Just finished a pair of DeadEndFX builds . . .  the  "Andamento" and the "Meta Morph". And I have to admit I'm a bit confused by the reversed Zener diodes in line with the bypass LEDs.





I cannot get the LEDs to light up when engaged unless I short out the Zener diodes. I've tried a fresh +9V battery and a standard +9V DC (center negative) wall wart and no lighting. (Unless those Zeners are jumped.)

Can anyone explain why those Zeners are there?

[antonis]

Can anyone explain why those Zeners are there?

Extremelly bad design..

Make R7 muuuuch lower or delete Zeners

[amptramp]

I suspect the zeners were put in there to give a go / no-go indication of whether the battery voltage was sufficient to operate the circuit.  If the LED did not go on in the active position, you had a battery problem.  The last time I measured LED voltages, a red LED dropped 1.88 volts and a green LED dropped 2.05 volts.  A 7 volt zener as shown in the top schematic would barely allow a red to go on and would not let any other colour go on.  Drop the zener voltage and this would work, but do you really need a go / no-go voltage indication that is tied to on/off functionality?  I would just use a larger resistor and no zener.

[antonis]

Ron, as it is, LED is powered with only 25μA..
(for a healthy +9V source..)

[Govmnt_Lacky]

This topic has come up before and has been addressed. DEFX tries to stay true to original design. This includes the Zener diode. It can be eliminated if desired.

[Cybercow]

Thanks for all the responses folks. Now that "low battery indicator" has been suggested, it becomes clear. What's really odd is that even with a One Spot wall-wart, the LEDs do not light. So I tac'd a little jumper across the Zener on each build. All is good again.

[CheapPedalCollector]

Their designs are nice, but I really wish they would leave space for jacks instead of taking up the whole enclosure with useless PCB real estate, I have not purchased any due to that.

I too would just replace the zener with a jumper and put a trim pot to adjust the LED brightness as many these days are eye burning bright.

[amptramp]

Their designs are nice, but I really wish they would leave space for jacks instead of taking up the whole enclosure with useless PCB real estate, I have not purchased any due to that.

I too would just replace the zener with a jumper and put a trim pot to adjust the LED brightness as many these days are eye burning bright.

Better yet, drill another hole for a photoresistance sensor and connect it in series with the LED (with appropriate series and shunt resistors).  Then you have an LED that is bright in the daylight and dim under low-light conditions, just like you need it with no compromises.

[Govmnt_Lacky]

Their designs are nice, but I really wish they would leave space for jacks instead of taking up the whole enclosure with useless PCB real estate, I have not purchased any due to that.

So, essentially you are saying you wish they were smaller PCBs? I have built several DEFX designs and have never had one where I couldn't install the jacks