Low Tide Modulation Behavior Troubleshooting/Tuning Questions

Depattern

Member
I've been a fan of the Shallow Water for a long time but never tried it. So i think i know what the expected sound should be,but Im having some major issues here with mine:


1. I hear pretty much 0 modulation unless I manually modulate the amplitude of the incoming signal (outside of the pedal). So here im sending in triangle waves from the sh-101 clone, and the only time i hear modulation, is when i tweak the volume on the synth going into the pedal. when i do that, its pretty extreme, but I cant get that effect otherwise.

when i dial the BBD BIAS pot, it goes from very noisy buzzy fuzz to nothing, then an extremely short range where i almost hear a pitch warble when turning it at a certain point, but nothing obvious. like i can hear the slight pitch drift as i turn from one increment to another very small increment, but its only audible int hat specific range and ONLY when im turning the trimpot.

i can see where the behavior might be sort of intended where the pitch modulation reacts ONLY to your playing dynamics, and i guess there isnt a wide dynamic range coming from the synth notes, but you'd think i would hear a difference in depth and rate from the lfo either way

2. the MIX effected sound is only within the VERY last like 5% of the MIX knob range. I only hear effected signal at the extreme clockwise end of that knob. I dont know if this correlates with the gate tuning or what, but i've experimented with that pretty extensively I feel like

3. The DEPTH, RATE, SLEW dont seem to have any effect. I am hoping that these modulation issue can be solved if i keep working away at tweaking the BBD trimpot, but it just doesnt feel like thats going to work

4. The gate itself is not as easy to figure out whats going on. I hear when it kicks in if i set it a certain way on the trim, but its not exactly "low pass filtered"/watery to completely open, although i do hear the lo pass effect and when the BOOST switch is set, it does behave like a low pass vcf envelope, or a real lpg sort of, but its a little tricky to determine what the actual range should be. not too worried about this one, but im just not sure whether or not this is tied to the problem im experiencing with the lfo modulation

I have probably not read through every troubleshooting thread about the Low Tide here but Im working my way through them and I have read a decent amount so far, including @Jachiro's extremely helpful post about tuning the trimpots

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I believe this could be a fault in the randomizer IC. I don't think I can order them individually from PedalPCB though. Is there a recommended source for additional LM258P's?

I worked through the entire signal chain with a multimeter to isolate the fault:

1. IC6 (CD4046BE) pin 16: 5.05V - correct, chip is on the regulated 5V rail as expected
2. IC6 pin 4 (VCO output): 2.46V - clock is running
3. IC7 (V3207D) pin 3 (clock input): 1.703V - clock is arriving at the BBD
4. IC7 pin 4 (Vgg bias): 4.72V - BBD bias is correct
5. IC4 (LM258P) pin 7 (op-amp output to IC6): 1.782V fixed - does not change with RATE or DEPTH
6. IC4 pin 3 (non-inverting input, RANDOMIZER signal in): 2.36V fixed - does not change with RATE or DEPTH
 
I would recommend getting most if not all chips whenever possible from Mouser or Digikey. LM258P chips are made by Texas Instruments and are currently in production if I’m not mistaken. It’s the older discontinued chips that are at higher risk of getting bad chips or fake ones if you get them from eBay.
 
Is it likely at all that this randomizer is bad? It seems to be the issue from what I can tell
You can test the randomizer (IC2). Multimeter set to DC, measure pin 5 to ground, it should ramp up and dwon somewhere arounds 1 to 3 Vdc, faster and slower by changing the rate pot.

If it works, measure the BBD pin 2 or 6 AC to ground, should see around 10 maybe 100 millivolts ramping up and down.
If nothing there, IC6 pin4 same thing. If nothing there, do back to IC5 pin 7, look for either ac or dc volts ( I can't remember) going up and down.
 
Thank you for that, thats extremely helpful

i am getting 1-3 on ic5 pin 7 and ic2 pin 5. but the A1m dual gang SLEW pot bottom outer legs are only sweeping from 0 to 324v. while the top outer legs sweep from 0 to 1m.

i dont know if this is a fault with the dual gang a1m pot from pedalpcb OR something to do with r39. i dont want to pull out r39 if i dont have to, so i wanted to ask for advice here first, to make sure im even looking in the right place. should i try pulling out the A1m, ordering a replacement and testing that? should i rip out/clip r39 and replace that? i checked the stripe pattern and its the proper markings for a 470k resistor for R39. is there somewhere else i should be testing?

If i go through this circuit with my audio probe, what am i looking for?

there shouldnt be any cold joints or anything like that. ive been very careful about that any hadnt had any such issues in my last 6 or so builds.

TO RECAP:
  • DEPTH, RATE, SLEW have no effect on modulation
  • MIX wet signal only present at extreme CW end of knob
  • LPG responds correctly to input amplitude changes
  • No continuous pitch drift/LFO behavior

What I've confirmed working:

  • RANDOMIZER (IC2) pin 5: ramping 1–3.33V continuously, speed changes with RATE
  • IC5 (MCP602) pin 7: oscillating between 1–3V on its own
  • IC6 (CD4046BE) pin 16: 5.05V (correct, on 5V rail)
  • IC6 pin 4 (VCO out): 2.46V
  • IC7 (V3207D) pin 3 (clock in): 1.703V
  • IC7 pin 4 (Vgg bias): 4.72V

Where the signal dies:

  • IC4 (LM258P) pin 3: stuck at 2.36V regardless of RATE, DEPTH, or SLEW position
  • IC4 pin 7: stuck at 1.782V, does not vary

The modulation signal is confirmed alive at IC5 pin 7 but is not reaching IC4 pin 3. Between those two points per the schematic I have SLEW 2 (second gang of the A1M dual-gang) and R39 (470K).


What I've checked in that section:

  • Reflowed all solder joints on the SLEW pot - no change
  • R39 color bands read correctly as 470K (yellow-violet-black-orange-brown)
  • In-circuit resistance between SLEW 2 output leg and IC4 pin 3 reads ~490Ω unpowered - suspiciously low but may be circuit loading
  • In-circuit resistance across SLEW 2 outer pins reads 26K–324K sweeping CCW to CW - also suspicious but again may be loading from surrounding circuit
  • No visible solder bridges anywhere in that area under magnification

    I also swapped out the ic 2, ic4, and ic7 just to be sure, before i got these final results. all ic's are socketed.

I'm hesitant to start lifting component legs without being more certain of the fault location. My audio probe wont be helpful for modulation signals, i imagine. Has anyone seen this exact symptom: signal alive at IC5 pin 7 but dead at IC4 pin 3, and can point me to what to check next?
 
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