Modified CE-2 Chorus Not Chorusing

[Zduck]

Hi all! First off, this is my personal build and not a PPCB project. If that is not allowed here let me know!

I am really stumped on this one. I designed my own layout and circuit board and it has been assembled with SMD components by JLC so I am confident that the component values are correct.

The audio passes fine though the top un-modulated section of the circuit. I audio traced the signal through the modulation section to the input (pin 3) of the V3207. It dies there. Nothing on the output pins 7 and 8. If I remove the V3207 and jumper from pin 3 to 7/8 the rest of the circuit works. So there is an issue with the BBD/clock/LFO section. I have swapped in a working V3207 pulled from a working chorus pedal so I know it's not the BBD as well. Also, I bought an oscilloscope to test the LFO and I get a nice triangle wave from the depth pot of the LFO and a modulated wave form on pin 7 of the clock when I adjust the rate and depth controls. I have checked my schematic at least 30 times, I can't see anything off from the CE-2 other than my vibrato/tone and master level mods which shouldn't affect the modulation section. All voltages seem good. Both VREF is around half supply voltage.

Thanks for any ideas to check!

My schematic attached.

Clip of wave form from pin 7 of the clock:

Video Unavailable

This video is unavailable.

streamable.com

Pic is of wave form on pin 2 and 6 of the V3207 from the clock (attached second pic).

Stock CE-2 schematic for reference:

https://docs.pedalpcb.com/project/Cepheid-PedalPCB.pdf

 

[Bio77]

You have verified all the components of a working chorus. I looked over the Porkbarrel schematic (link below). I could be confused by the different notations, but it seems like the clock isn't connected to the BBD the same. Might be worth a second look.

https://www.madbeanpedals.com/projects/_folders/FilterMod/schematics/PorkBarrel2019.gif

 

[jwin615]

Comparing to the PB as well, are there a couple components missing around R21?(Your schem)
Something leading to R17 Q2 node?

 

[Robert]

Just at a quick glance I don't see anything problematic in your schematic... are you sure the PCB layout is correct? No missing traces, pads/traces accidentally connected to a ground plane, etc?

... and it has been assembled with SMD components by JLC so I am confident that the component values are correct.

Don't make this assumption.

I have a friend who has had incorrect values / parts installed on more than one occasion. Make sure C13/D5/D6 are oriented correctly on your assembled board.

 

[Zduck]

Thanks for taking the time to review everything. I appreciate it. That's wild that JLC can install the incorrect values or wrong orientation - never thought to question it. In this case, I went through and checked C13/D5/D6 and they are oriented correctly. I went through all the LFO section and checked with my DMM and the values are correct and the paths are correct. I also don't see any missing traces or bad connections, and my software (EasyEDA) didn't bring up any errors.

Very frustrating. I've spent so much time on trouble shooting this. It's becoming not worth the time spent anymore. I think I have to wipe the board and re-lay everything out again in hopes that I inadvertently fix the error, whatever it is. I didn't really separate the LFO section from the rest when I designed the board, but have since learned that it is good practice for noise reduction to keep them separated and not cross traces from the LFO on the other layer. So it will be a good excuse to re-lay everything out again anyways. Thanks for the feedback as I continue to learn.

 

[Zduck]

So I redid the whole board layout and ordered another proto in and it has the same problem

I can hear the subtle swooshing of the LFO when I turn up the blend and the rate and depth, I think that section is working correctly.

I did another trace of the audio using my audio trace and found something interesting. On the RC4558 input and output stages I get no audio at the inverting input on both sections? But the audio comes out of the op amps fine? How is that possible for no signal to go in and signal to come out?

 

[PJS]

My understanding is that an op amp works by trying to make the 2 inputs the same. If one of them is tied to a voltage (ground or VB is usual), then it will try and make the other input a steady voltage as well. The output then will be whatever is required to cancel out the input, taking into account the feedback loop. You won't hear anything at the input, but will hear the output if it is working properly.