LED not working on Arachnid V2 pedal.

[Walter]

Hey everyone,

I have assembled an Arachnid V2 guitar pedal but the LED isn't lighting up. This is because the LED is receiving the supply voltage (8-9 volts) instead of the rated 3.3v. I'm unsure of why this is happening, I haven't found any shorts and everything looks like it's correctly wired.
Anyone have any ideas as to what could be happening?

Thanks,
Walter

 

[benny_profane]

This is because the LED is receiving the supply voltage (8-9 volts) instead of the rated 3.3v.

Where are you getting those numbers? Did you measure the voltage at the anode of the LED?

I'm not familiar with that DC jack. Guitar pedals expect center-negative supplies. That seems to be a center-positive jack as it is not insulated and will short the barrel to the enclosure, which is connected to ground via the sleeve(s) of the audio jack(s). (EDIT: Are the jack sleeves connected to circuit ground? The sleeves are connected, but I can't see how they're connected to the board ground pad.)

The LED is powered via the supply voltage and the series current limiting resister. Is the LED installed correctly?

 

[jimilee]

If your LED is getting that much voltage, it’s toast. You’ll need to figure out why it’s getting that much and then replace it.

 

[Robert]

When the switch is open you will measure 9V on both sides of the LED.

 

[jimilee]

When the switch is open you will measure 9V on both sides of the LED.

Good point.

 

[Walter]

I was able to fix the LED, it was burnt out.

However, i'm only getting bypass sound when I try to use the pedal.
Any specific points that I should look at? I've had this issue before but I don't know what I did to fix it.

Thanks for your help,
Walter

 

[PJS]

A few things to double check first.

I know it sounds basic, but double check and make sure you haven't plugged the guitar into the output and the amp into the input. Most (all?) of us have done that.

Check that the board is getting voltage with a multimeter.

The arachnid has a mix pot to blend the effect and clean sounds. Check at both ends of that mix pot with the pedal engaged (and the volume up). If you can't get any sound at either end of the mix pot with volume up, then it is 90% likely to be the switch - either wired incorrectly or damaged by too much heat. Check continuity on the switch and make that what is supposed to be connected is, what is supposed to not be connected isn't, and in both positions.

 

[Walter]

Wanted to update this thread.

I checked both ends of the mix port but it doesn't have any effect on the volume. I ended up replacing the switch but that didn't fix the problem either. I did realize that the potentiometers I used have the wrong resistance value (10k instead of 100k). I'll try replacing those next.

 

[PJS]

OK. The dry sound in the arachnid bypasses the FV-1 chip. If you are not getting dry sound through the mix pot then you will not be getting any signal into the FV-1 either, which means that even if the FV-1 is working, you won't get wet sound out of it. You need to audio probe from the input to see where the signal is being lost.

 

[Walter]

OK. The dry sound in the arachnid bypasses the FV-1 chip. If you are not getting dry sound through the mix pot then you will not be getting any signal into the FV-1 either, which means that even if the FV-1 is working, you won't get wet sound out of it. You need to audio probe from the input to see where the signal is being lost.

Sorry, I misunderstood what you meant.

I get dry sound on one end of the mix pot, the other end doesn't give any sound at all.
Correct me if i'm wrong but i'm pretty sure it's the potentiometers having the wrong resistance.

Thanks,
Walter

 

[PJS]

I haven't tried with the wrong value pots but I am reasonably certain it will still work OK. By all means change them but I don't think that is the problem. Do you get audio going in to pin 1 of the FV-1, and it it coming out at pin 28?

 

[Walter]

I just probed pin 1 and 28. No sound on either. Pin 28 is silent, pin 1 pops the amp frequently.

Thanks for your help,
Walter

 

[PJS]

OK, so probe pin 7 of the TL074. If you are getting dry sound at the mix pot then you should have sound at pin 7 of the op amp. Then probe both sides of C3 and both sides of R3. If you have audio at the op amp, but nothing at the input of the FV-1, then it has to be getting lost at C3 or R3.