Dead End Fx Lola Phase - CV pedal fries resistor!

[spacekid71]

Hi everyone,

I was calibrating the Dead End Fx Lola Phase that I built some time ago. It was going well and I was advancing really nicely until I got to the CV pedal calibration...

After I plugged a cable from the CV pedal socket to the expression pedal with a B1M pot in it, smoke started to come from the pedal!

I quickly disconnected the cable and the smoke stopped right away. I checked that the wires for ground, CV, and +15V were correctly attached, and nothing seemed out of sorts. When I inspected both PCBs for any fried parts, I saw that the R11 (12R value resistor) had gotten fried.

I remember from a previous issue that someone had mentioned that both R11 and R12 are used as fuses for the control pcb power supply section. It seems that plugging in the CV pedal cable to the expression pedal shorted out the fuse resistor R11.

I am not sure what is going here, it would be good to get some help. I can supply more diagnostics information if necessary. Below I have added some images from the schematic and a link to the build documentation from Dead End Fx.








Build documentation for the Dead End Fx Lola Phase

[ElectricDruid]

It seems fairly clear that too much current is being drawn from the +15V supply when the CV pedal is plugged in. Since there's supposed to be only a 1 Meg pot across it in the CV pedal (and 15uA just won't make things smoke like that!), something must be wrong. Either bad pot, wrong pot value, badly wired, shorted to the enclosure, etc etc. First test would be to put a multimeter on the CV jack end of the expression pedal, and check that you're seeing the resistances you expect (looks like 1Meg from sleeve to ring, variable value from sleeve or ring to tip). Since bad stuff is happening, I expect that's *not* what you'll see.

Good luck!

[spacekid71]

It seems fairly clear that too much current is being drawn from the +15V supply when the CV pedal is plugged in. Since there's supposed to be only a 1 Meg pot across it in the CV pedal (and 15uA just won't make things smoke like that!), something must be wrong. Either bad pot, wrong pot value, badly wired, shorted to the enclosure, etc etc. First test would be to put a multimeter on the CV jack end of the expression pedal, and check that you're seeing the resistances you expect (looks like 1Meg from sleeve to ring, variable value from sleeve or ring to tip). Since bad stuff is happening, I expect that's *not* what you'll see.

Good luck!

I understand a bit better now what happened from your comment. I just replaced the 12R resistor and I have been looking into the resistances.

From your description I am understanding that the expression pedal pot should have the +15V tip wired to pin 2 so that ring to sleeve (pin 1 and pin 3 on the pot) would measure 1Meg and tip to ring or sleeve would be variable.

Currently, I have the pot wired as follows as indicated in the documentation:

1. TIP (+15V)
2. RING (CV input)
3. SLEEVE (GND)



Thanks for your help,

Mart

[idy]

so that ring to sleeve (pin 1 and pin 3 on the pot) would measure 1Meg and tip to ring or sleeve would be variable.

Almost: Tip to sleeve 1M, ring to either tip or sleeve is variable.

[spacekid71]

so that ring to sleeve (pin 1 and pin 3 on the pot) would measure 1Meg and tip to ring or sleeve would be variable.

Almost: Tip to sleeve 1M, ring to either tip or sleeve is variable.

Tip to sleeve 1M is how it is currently wired and it fried the R11 fuse resistor.

The only explanation I have is that I used a mono cable instead of a stereo/TRS cable to connect the expression pedal to the Lola Phase. Does it make sense that a mono cable would connect things so that it would short circuit?

Thanks,

Mart

[idy]

does it make sense that a mono cable would connect things so that it would short circuit?

yes! That surely will! Mono means ring and sleeve shorted!