A few questions and trouble shooting


New member

I'm Detrital, new here but not to building pedals.
If I've posted in the wrong spot - Sorry. Please bump me to where I should be...

I've got a few builds that are giving me trouble. Any help is appreciated.

ElectroVibe - No build docs yet, but the silkscreen is mostly complete. I need to know TO-92 what goes above the 47R and LT1054. Suspect it's a 78Lxx of some sort as the middle pin connects to ground. Also what LED is recommended for the opto. Looks like it could be a bi-colour from the orientation of the flat side?? or will a diffused 5mm red/orange/yellow work well here?

HAARP - Build works as it should but the wet output is very noisy. No noise when it's off or from the dry signal path. I'm testing on battery so there is no PSU noise. Have tried adding a few 104 MLCC caps to the rails and Vref and no improvement. Also a 100pF in parallel with the 2n2. Possibly a dodgy FV-1 ???

Low Tide Modulator - It just sounds a bit off. I mean all of the controls work but it doesn't sound like any of the demo's. I think I might have got a fake MN3207 as there is no real delay component to the sound. The modulation seems to only effect the filter (low pass gate). If I turn up the LPG it starts to distort too. I've got a V3207D on the way to test with and see if it sounds any better.

Cheers - Detrital
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Well-known member
HAARP - Looking at the schematic, if the noise is only present when the WET control is turned up, I think it must be coming from the FV-1, 3v3 or Vref. Any thoughts?

Low Tide - The silkscreen in the build doco doesn't match the PCB I have. It makes checking component values and build errors very difficult.
Does anyone know where I might find the schematic or an image of the latest component overlay? Or where I could request this?

I've completed the ElectroVibe. It's STUNNING !!! It's the kind of pedal that will probably trigger a pedalboard re-build so I can fit it on.
The Low Tide schematic was posted on a few previous threads: https://docs.pedalpcb.com/project/LowTide-Schematic-PedalPCB.pdf

Does your PCB layout match this build doc? There was an older build doc as well, but I can't seem to find it.

To hear the most intense modulation effect, set the Rate control relatively high and the Slew control to 0%. That will cause the delay to shift in pitch quite abruptly & randomly.

The amount of effect & it's response to your playing is somewhat limited by the internal trimpots. How did you set the BBD Bias & Gate trimpots? Here is the info:
  • BBD/BIAS trim pot - Similar to the pot on a CE-2 or Caesar. Adjust for the least amount of distortion with modulation. Pretty obvious when set correctly. Set the Depth to 100% and turn up the output loud enough to clearly hear the signal. There is a range on the trimmer where you will hear the chorus/delay effect. At either end of the range, there is quite a bit of fizz. Just set the trimmer for the least noise.
  • GATE trim pot - User preference, it controls the frequency of the low pass filter portion of the gate - Set MIX to 100% wet, LPG 0%, Depth 0%. Turn Gate Trim CW, you should hear the filter "open up" as you turn it up. You want to set the Gate Trim so the LPG knob goes from completely off at 0% to completely open at 100%, with a good amount of different settings in between - “I did have to fiddle with the external gate pot on mine to get a setting where I could hear the chorusing clearly, you may have to play around a little to get it completely tuned in”
GATE trim setup from Fairfield Shallow Water Manual:
  • LPG ADJUST (i.e., GATE TRIM) - The recovery filter’s lowest frequency can be adjusted, to fine tune the way it will react to incoming signals. Lowering this frequency emphasizes the action of the low pass filter, effectively raising the threshold of sensitivity. Adjustment should be made with the following settings: MIX full wet, LPG minimum, DEPTH minimum. While listening to a signal going through the pedal, you’ll hear the effect of the recovery filter at its resting state. Carefully turn the trimpot labelled LPG adjust (i.e., GATE TRIM), clockwise to raise the filter’s frequency, counter-clockwise to lower. Be very careful, adjustments should be minimal as the trimpot is very sensitive. After each adjustment, LPG should be turned up momentarily to listen at the envelope’s response to the incoming signal.
If you're still not getting any effect after that, I would use a DMM to check voltages at each of the IC pins & post them here.


New member
Thank you for the reply. I got it working last night thru trial and error adjustment of the trimpots.

Many thanks for the schematic link too, much appreciated.

My PCB does not match the layout in the build doc you posted, the trimmers are in a different position, the LM13700 has been flipped upright as well as a few other changes.


New member
I do have an audio probe. Inputs to the FV-1 are clean and perfect. There is no noise in the dry signal path either. Only noise on the FV-1 ouput and "wet" portion of the circuit.
I tried a 10k connected to the output filter as per the datasheet, and it did reduce the noise slightly, but it also made the signal very muddy and dull.