Pitch Witch LFO Not Working

[daveybee123]

I'm nearly done with my Pitch Witch build, but I'm stumped on getting the LFO up and running.

Here are the symptoms: Delay part works perfectly, but neither LFO or indicator LEDs are lighting up. I also think my dual op-amp chip is heating up a bit, and I switched chips to no avail. I used TL072 instead of 4558, which I think should be okay.

Here are the voltages on the chip:
1 - 6.7
2- 2.52
3- 4.33
4- 0
5- 5.2
6-4.33
7- 2.56
8- 8.72

Any help would be much appreciated, thanks!

 

[Nostradoomus]

Have you got some pictures? Voltages look off like you have an incorrect value somewhere

 

[daveybee123]

Here's what I got for now, I suspect I misplaced a resistor. Thanks!

 

[Nostradoomus]

Are the legs of your ldr/led touching each other? Separate them if they are, they could be shorting out on each other or that electro cap.

 

[Chuck D. Bones]

What a shitty LFO circuit. I'm surprised any of them work.
C16 should not be polarized because it sees voltage in both directions.
If you're going to use a TL072 for the LFO, then you need to get rid of C15 because it's probably making the TL072 oscillate at high freq, causing it to malfunction and heat up. Either that, of get a 4558.
No need to heat shrink the LED/LDR, you can mount them on the board next to each other. Once the box is closed, no stray light will get on the LDR.
Make sure your LED leads aren't shorting to the SPEED or WAVE pot leads.

 

[daveybee123]

Nostradoomus, the legs aren't shorting. I spread them out wide, and still no voltage on either.

Chuck, I will look into that! Other people have verified the circuit with C16 being polarized here, so I'll try keeping it for the time being. Sounds like I need to order some 4558 chips. How come a TL072 won't work? Would a NE5532 work?
Thanks!

 

[Chuck D. Bones]

There is no telling which opamps will tolerate having 47uF to ground on their outputs.

Loading the output of an opamp with such a ridiculously large capacitor degrades the opamp's phase margin to the point of oscillation. A more detailed explanation gets pretty involved, so I won't bore everyone with the math & feedback theory. Suffice it to say that putting a big cap on the output is a poorly executed, band-aid attempt to cure LFO tick.

 

[Mcknib]

I built this one on an etched board http://effectslayouts.blogspot.com/2015/04/mid-fi-deluxe-pitch-pirate.html and had the same problem delay and bugger all else, initially I had my vactrol LED in the wrong way round, you'll see in the comments my confusion (Billy that's me)

So I'd double check the LED polarity is correct

Another problem I had, although I don't think you'd have this problem on a fabricated pcb, with the one I built you had to have both ground and footswitch ground wired to the 3PDT which I didn't do because I usually wire indicator LEDs offboard

So the LFO wasn't switching on it's wired to go off in bypass mode to cut down on the pulsing noise through your amp, and on in effects mode by making and breaking the ground connection

You'll see my initial comment around April 15th 2018 asking for the LED orientation then if you scroll further down you'll see another guy with similar problems around June 25th (ElRuso82 username) might give you some insight your problem sounds similar