Low Tide (help to solve power supply noise)

[Pietro]

So finally I decided to build this wonderful pedal. I adjusted the trim pots for the BBD and the LPG, I also enclosed everything in its Hammond box. If I connect the pedal to a 9V battery, it works perfectly fine, actually it works better than the original, with less noise as well! Every control knob does what it is supposed to do (I had an original Shallow Water pedal). The input signal is undistorted and clear, the filter opens and close as it should.
Now the problem, as soon as I connect a 9V power supply the trouble start, I can hear a constant high pitch noise, like a sine wave at 2-3 kHz, it seems to change according to the power supply I use, that's why I believe it's caused by the ripple of the power supply. The noise has the following characteristics:

• The intensity of the high pitch noise is constant and independent of the pedal Volume, I can turn the volume fully anticlockwise and it's still there with the same intensity.
• With the switch in bypass mode it disappears.
• The noise seems to be modulated by the LPG circuit. For example, if I turn the Depth all the way anticlockwise, it becomes constant without fluctuations in pitch and intensity, if I increase the Depth, then it starts to follow the modulation.
• The noise is still there if I turn the Mix knob fully dry or fully wet. Like the Volume knob the Mix doesn't seem to affect the noise at all.
• Everything still working perfectly fine, I just hear that annoying and constant little squealing sound.
• As I said before with a 9V battery the noise completely disappears and the pedal works perfectly fine.
• I noticed that when I connect a power supply or a 9V battery to the pedal after it has been disconnected for a while, the LED lights up for a fraction of a second, in spite of the pedal being in bypass mode. After I connect it, this doesn't happen anymore and the LED works as it should. Probably this is not related to the noise, but it seems a strange behaviour.

Before I start to take everything apart and examine every single part of the circuit, is there anyone that experienced this before and can point me to the right direction to solve the problem? I would really appreciate any help or suggestions.

Please note that I covered the usual suspects already, it's not a mains socket problem, or an amp problem, or a ground loop problem, I tried different setups and the noise is always there no matter what, literally every single pedal I have, from simple analog ones to more complicated digital ones work perfectly fine without any noise. Also I tried several different powers supplies.

Thanks!

 

[JamieJ]

Do you have any cold solder joints to the power filtering caps? C16 and 32. Can you upload pictures of the solder side and top side of the board.

 

[Robert]

• I noticed that when I connect a power supply or a 9V battery to the pedal after it has been disconnected for a while, the LED lights up for a fraction of a second, in spite of the pedal being in bypass mode. After I connect it, this doesn't happen anymore and the LED works as it should. Probably this is not related to the noise, but it seems a strange behaviour.

This is due to how the anti-pop LED switching circuit works and is normal.

 

[Pietro]

I checked and it seems to be fine, I also replaced C32 since this should be the main filter for the power supply? I admit it I could solder better, but I am improving...damn it would be so perfect if it wasn't for the sneaky squealy sound! Thanks for the help, please see pictures below

 

[Pietro]

This is due to how the anti-pop LED switching circuit works and is normal.

ah nice, at least this is out of the way

 

[Robert]

If the filter capacitor is good and you're only having noise issues when powering from a power supply then the issue is likely the power supplies.

You could have clock / BBD noise bleeding into the audio path but that would happen on battery power as well, unless it's heterodyning with the switching frequency of your power supply.

 

[Pietro]

I tried all the power supplies I had, 7 to be precise, connected in different sockets, also tried with a power supply and a battery powered preamp and headphones, still the same problem, also a few of these power supplies were perfectly fine with the original Shallow Water I had. It is frustrating

 

[Pietro]

On battery works so well, I can barely hear the classic BBD noise when the filter fully opens up, on the previous original Shallow Water I had, the noise was massive, I returned the unit for that reason.

 

[pricklyrobot]

I know you said you already ruled out the wall mains being the issue, but are you able to plug it in at a friend’s house or somewhere else, just to see if it behaves any differently?

 

[Pietro]

mmmh no I didn't try in another house, but I tried in different plugs and also with an battery powered amp to rule out any ground loop, also any other pedal I have works fine. This is not the usual ground loop problem it's a pretty clear sine waveish high pitch sound, I've heard it before in faulty pedals.

 

[Robert]

Try this one at a time, in this order, and see if the noise stops... do not reinstall each IC as you progress forward.

Remove the microcontroller (ATTINY IC), check for noise.
Remove the V3207D, check for noise.
Remove the CD4046, check for noise.

 

[Pietro]

Try this one at a time, in this order, and see if the noise stops... do not reinstall each IC as you progress forward.

Remove the microcontroller (ATTINY IC), check for noise.
Remove the V3207D, check for noise.
Remove the CD4046, check for noise.

No difference, the noise is still there loud and clear...thanks for the suggestion, does this points toward another direction?

 

[Robert]

It rules out everything with an internal oscillator, and the BBD itself.

If you're hearing a clear sine wave it's coming from something outside of the pedal.

 

[Pietro]

It rules out everything with an internal oscillator, and the BBD itself.

If you're hearing a clear sine wave it's coming from something outside of the pedal.

yep that's what I thought, it must come from the power supply