SOLVED Low Tide modulates only if i keep turning the depth control.

[eh là bas ma]

Hello,

I am currently building the Low Tide, from a musikding kit.

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

https://docs.pedalpcb.com/project/LowTide-Schematic-PedalPCB.pdf

First, i should mention that i have been confused with 2 unnamed smd transistors. probably the SK208 and the J201. No labels, i can't tell them apart.

I tried both at both locations, and chose the setting with the most noticeable volume boost, when toggling the internal DPDT.
The other smd transistor works too if i swap them, but the volume boost is a bit weak.
Edit 2 : I could read 62P on one of them, it's the J201, problem solved.

Everything looks fine so far, all controls are responding, but I can't keep the circuit's modulation on, unless i keep turning the depth control like a "manual" mode, or if Slew control is set in the first quarter of rotation. I do have a beautiful chorusing effect, when i do the manual mode, turning the depth control back and forth.

With Slew fully CCW, it sounds like the randomization thing is working, the modulation's curves are kind of irregular and weird.

On most settings, it sounds like a flanger stuck on "Filter Matrix", with a low-pass filter.

It's not very far from the utube demo though... but on my build, when Slew is near the middle of the rotation and above, the modulation disappears.

official demo from the original unit :
www.youtube.com/watch?v=sYWuTmgVU9k

On the other hand it doesn't behave like MichaelW's build, with all controls at 12' :

BBD trimmer is set near the end of the rotation, CW. at both ends there are distorted aeras. I notice a slight volume boost when turning the trimmer CW. I set it where it was the loudest, without being distorded.

Gate trimmer is also set somewhere towards the end of the rotation, CW. Around the middle of the rotation, increasing the lowpass i guess, i hear some sort of bass popping noises on the attack of the notes. I set it somehwere just before this happens.

In short, the modulation seems to be activated only when Slew is set in the first quarter of rotation. Other than that, i can get a nice enveloppe filter effect, once Gate trimmer and Gate control are set to do so.

It isn't chorusing, it isn't flanging, it does an enveloppe filter effect, and a weird and beautiful vibrato thing when Slew is fully CW.

I guess there's an issue somewhere...

What should I do ?

All suggestions and observations are welcome !

Edit : Hopefully, it's only a calibration matter.

Looks like I managed to get some sort of modulation with Slew at the middle of its rotation, by tweaking the trimmers. But nothing as beautiful as MichaelW's exemple yet.

I am using a loop station to send a signal into the circuit, while trying to calibrate it. It's a recorded loop with a few notes, played with a guitar equiped with active pick-ups, guitar's volume set at the middle of rotation. PAD switch is off, Boost is on.

Any tips about the calibration process ?

Edit 3 : I can't find the chorusing spot on the BBD trimmer. Here are some readings :

All controls at 12'.

IC 1 LM78L05

9.11V
0V
5.08V

IC2 randomizer

1= 4.75 8= 5.08
2= 4.00 7= 5.06
3= 5.06 6= 5.08
4=0V 5= oscillating from 1.00V to 4.00V

IC3 LM13700

1= 1.134 16= 1.134
2= 5.37 15= 5.37
3= 4.81 14= 4.80
4= 4.81 13= 4.81
5=5.73 12= 5.78
6= 0V 11= 9.11
7= 5.74 10= 5.78
8= 4.76 9= 4.69

IC4 LM258P

1= 1.222 8= 9.11
2= 2.5 7= 2.8
3= 2.5 6= 2.8
4= 0V 5= 2.8


IC5 MCP602

1= 4.0V 8= 5.08
2= 4.0 7= 3.9
3= 3.5 6= 3.9
4= 4.0 5= 4.4

IC6 CD4046

1= 7.7 mV 16= 5.08
2= 2.4 15= 1.2
3= 2.4 14= 5.8
4=2.4 13= 7.8mV
5= 0V 12= 2.7
6= 0.7V 11= 2.2
7= 0.7V 10=3.1
8=0V 9= 3.7

IC7 V3207

1=0V 8= 3.4
2= 2.4 7= 3.4
3= 2.8 6= 2.4
4= 4.75 5= 5.08

 

[Fama]

Here are the trimmer instructions I used https://forum.pedalpcb.com/threads/a-few-questions-and-trouble-shooting.8436/page-2#post-78794

Your gate sounds like it's fine, so just set depth to 100% and turn the BBD trimmer until you get the most modulation with least distortion. Not necessarily the most signal.

Also remember that it won't chorus unless you set the mix to something lower than 100%, since chorus is a mix of the modulated and dry signal.

 

[eh là bas ma]

• 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”

Thanks for your reply !

12' = middle of rotation

I set Speed, Slew, Mix, Gate at 12', and Depth fully CW.

Turning the BBD trimmer slowly through the whole rotation, i do have distortion at two narrow spots, located at both ends of the rotation, but no chorusing.

I did set the Gate trimmer in order to be at the limit where the signal disappears when Gate knob is fully CCW.

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.

This works on my build, but i am not sure it means that the BBD is working correctly ?

There's probably something wrong with the build itself. I'll post some voltage readings.

 

[eh là bas ma]

All controls at 12'.

IC 1 LM78L05

9.11V
0V
5.08V

IC2 randomizer

1= 4.75 8= 5.08
2= 4.00 7= 5.06
3= 5.06 6= 5.08
4=0V 5= oscillating from 1.00V to 4.00V

IC3 LM13700

1= 1.134 16= 1.134
2= 5.37 15= 5.37
3= 4.81 14= 4.80
4= 4.81 13= 4.81
5=5.73 12= 5.78
6= 0V 11= 9.11
7= 5.74 10= 5.78
8= 4.76 9= 4.69

IC4 LM258P

1= 1.222 8= 9.11
2= 2.5 7= 2.8
3= 2.5 6= 2.8
4= 0V 5= 2.8


IC5 MCP602

1= 4.0V 8= 5.08
2= 4.0 7= 3.9
3= 3.5 6= 3.9
4= 4.0 5= 4.4

IC6 CD4046

1= 7.7 mV 16= 5.08
2= 2.4 15= 1.2
3= 2.4 14= 5.8
4=2.4 13= 7.8mV
5= 0V 12= 2.7
6= 0.7V 11= 2.2
7= 0.7V 10=3.1
8=0V 9= 3.7

IC7 V3207

1=0V 8= 3.4
2= 2.4 7= 3.4
3= 2.8 6= 2.4
4= 4.75 5= 5.08

Pin 3 of the V3207 can go up to 3.484V if BBD trimmer is set fully CCW. 1.725V if i set the trimmer fully CW.

I thought BBD ICs would need 3.5V to work correctly ?

 

[jesuscrisp]

Right now you have the pad on and the boost off (your switch is the wrong way round but that doesn't matter), try the other way round and adjust the trimmers accordingly. BBD for the loudest clean signal, the gate to taste but maybe start at half.

 

[eh là bas ma]

Right now you have the pad on and the boost off (your switch is the wrong way round but that doesn't matter), try the other way round and adjust the trimmers accordingly. BBD for the loudest clean signal, the gate to taste but maybe start at half.

Thanks, but I don't think so.

If i toggle PAD toward "ON", it's gets quieter. If I change the Boost position and move it toward the "1", it gets quieter.

Setting all controls at 12' and Depth fully CW, BBD trimmer on the loudest clean position : no chorusing.

 

[eh là bas ma]

I tried to reflow some pads, and check the board for shorts. No luck so far.

A few pics in case someone can spot something suspicious :

 

[jesuscrisp]

I mean I can just say that I built it recently and it worked with all the parts supplied by musikding but I needed a bit of time to get it modulating nicely. Boost on, PAD off did a lot after initial doubts as the modulation is controlled by the envelope and too little input signal means no modulation.

Honestly though, it's very high investment for rather little reward in my opinion.

Nevertheless, it SHOULD work like in the demos when everything is built correctly and set up right. Check all components for correct values maybe.

 

[eh là bas ma]

Check all components for correct values maybe.

Fortunately, i measured every resistors before soldering them. The electro caps are quite simple, all 22uF except one 220uF.

C20 is 680p, musikding sent me a 470p. I guess it was a mistake and it's better to use a 680p from my stash, right ?

I also changed R55, supposed to be 4.7K, i use 10k, because i assumed it is the led resistor ?

too little input signal means no modulation.

Ok, so if the enveloppe filter is up and running, perfectly audible and sensitive to the playing dynamics, I should have some chorusing ?

I wonder if the sweet spot on the BBD trimmer is very narrow ? Like we can't hear it, even moving slowly, we have to do some ultra-micro-moves ?

From what i could read about it, it should be quite easy to find, right ?

On my build the loudest clean signal, in the BBD trimmer's rotation, is right before the distorting zone located at the end of the rotation, CW. At 3/4 of the rotation, precisely.

If i can get a chorusing effect by turning the Depth knob back and forth, doesn't it mean that the BBD IC is working ?

Right now the Depth pot doesn't do much on its own, unless i turn it. It behaves a bit like a Manual control on some Flanger : setting the frequency range on which the sweep will work : more bass, or more treble.

I don't have modulation, so it's mostly clean tones for now. changing the Depth knob position slightly changes the tone of the signal, like a filter.
It sounds like the Filter Matrix mode on some flangers : No sweep, but you can change the tone.

Why is there no sweep ? Where should i look to restore it ? Which parts are involved in the sweeping process ?

Edit : I found the schematics, every suggestions are welcome to understand what could stop the sweep :

https://docs.pedalpcb.com/project/LowTide-Schematic-PedalPCB.pdf

 

[Bio77]

"On my build the loudest clean signal, in the BBD trimmer's rotation, is right before the distorting zone located at the end of the rotation, CW. At 3/4 of the rotation, precisely.

If i can get a chorusing effect by turning the Depth knob back and forth, doesn't it mean that the BBD IC is working ?"

This sounds like your BBD is working. I'd guess that when you describe getting the "loudest clean signal" you are hearing the clean trace blended with the delay line (~2X signal). Sounds like your delay line is not getting modulated. Follow the oscillating signal coming from Pin 5 of the randomizer to the clock part of the circuit.

Also, can you post the schematic? It's not in the build docs.

 

[Bio77]

Sorry, just saw the schematic link. I think something is going on with the MCP602. If you look at the schematic there is a voltage divider after the 5V reference voltage that flows into pin 5. You have ~4V on pin 5, should be ~2V. Maybe pull the chip and measure the voltages. Anyway, my guess is that's the section you are looking for wrong or faulty parts.

 

[eh là bas ma]

Sorry, just saw the schematic link. I think something is going on with the MCP602. If you look at the schematic there is a voltage divider after the 5V reference voltage that flows into pin 5. You have ~4V on pin 5, should be ~2V. Maybe pull the chip and measure the voltages. Anyway, my guess is that's the section you are looking for wrong or faulty parts.

Thanks for your reply !

I took off IC5, I read oscilations between 0 and 10mV at pin 5.

There is 5.08V at one side or R41, and 2.172V on the other side.

2.172 on one side of R42, the other side is grounded.

With IC5 back in the circuit, i read 3.8V at pin 5.

Follow the oscillating signal coming from Pin 5 of the randomizer to the clock part of the circuit.

All controls at 12', Slew fully CCW. Audioprobe test :

Signal at IN and OUT are ok.

No signal on IC2 randomizer anywhere. Only some white noise with a cyclic popping noise at pin 5. No signal at CD4046 pin 9, or any other pin.

On the V3207, signal at pins 3, 7 and pin 8.

If i read the schematics correctly, i should have a signal at V3207 pin 2 and 6 ?

these are the points from where the signal should enter the randomizer/clock section, and then come back to the BBD, in order to reach the rest of the circuit ?

Am I right to think that I should try to restore the signal at V3207 pins 2 and 6 ?

Edit : I did a continuity test between R41, R42 and IC5 pin 5 : no continuity. I guess i need to fix this too...

IC5 soldering pads are under the stereo pot... Some luck would have been nice for a change.

Edit 2 : Two soldering pads on IC5 were left empty, without solder. No wonder it wouldn't work.

Let's smile and shrug.

 

[Bio77]

Okay, I'm getting a little past my knowledge here, so, I won't feel offended if someone says I'm all backwards on this. But, you shouldn't read 3.8V at pin 5 of the 602. It's on the same trace as R41 and R42, where you measure 2.17V, it should be the same. Is there a solder bridge that you can see under the mount for IC5? When you take the chip out try testing for continuity between adjacent pins. Also test for continuity between pin 5 and R41 and R42 to make sure that trace is there.

Your audio probe is only good for tracing signal along the audio path. Pins 7 and 8 of the 3207 are the delay audio outputs, so, if you are getting sound there, that means the delay chip and the clock are working. BBD delay chips only work if they are getting a clock signal to turn the buckets on and off. To measure the clock signal at pins 2 and 6 of the 3207 you use the frequency setting on your DMM, you can also see the signal if you have a scope (should be a square wave). The LFO (randomizer in this case), feeds into the clock and changes its frequency at the LFO rate. The randomizer signal you can see as a varied voltage on your DMM, you should be able to see varied voltage along the path from the LFO to the clock, unless something is faulty. But I'd put my money on the something connected to the 602.

 

[eh là bas ma]

Okay, I'm getting a little past my knowledge here, so, I won't feel offended if someone says I'm all backwards on this. But, you shouldn't read 3.8V at pin 5 of the 602. It's on the same trace as R41 and R42, where you measure 2.17V, it should be the same. Is there a solder bridge that you can see under the mount for IC5? When you take the chip out try testing for continuity between adjacent pins. Also test for continuity between pin 5 and R41 and R42 to make sure that trace is there.

Your audio probe is only good for tracing signal along the audio path. Pins 7 and 8 of the 3207 are the delay audio outputs, so, if you are getting sound there, that means the delay chip and the clock are working. BBD delay chips only work if they are getting a clock signal to turn the buckets on and off. To measure the clock signal at pins 2 and 6 of the 3207 you use the frequency setting on your DMM, you can also see the signal if you have a scope (should be a square wave). The LFO (randomizer in this case), feeds into the clock and changes its frequency at the LFO rate. The randomizer signal you can see as a varied voltage on your DMM, you should be able to see varied voltage along the path from the LFO to the clock, unless something is faulty. But I'd put my money on the something connected to the 602.

Soldering the empty pads on IC5 allowed to restore continuity between R41/42 and IC5 pin 5.

Now it reads 2.172V at IC5 pin 5, with the IC back in its socket.

Hoping this was the only problem, i'll try the circuit once more. Fingers crossed...

 

[eh là bas ma]

Yeeeehaaaaaa ! Woooohooo ! Gloire ! ô joie !

It's working.

Is it the most beautiful modulation I've ever heard, or just the relief talking ?

Be that as it may, it does look like I just forgot to solder two pads at IC5, hidden under the stereo pot...

I often trick myself into thinking that i am a shrewd and crafty young man.

Low Tide Modulator building experience taught me, once again, that I'm just a vain clown.

Surely there's a deep diy lesson to be remembered in this story, i'll have to reflect on all this for a while, see if i can grasp it.

At least i managed to get things done with the help of Fama, Jesuscrisp, and Bio77.

All my thanks, and my everlasting gratitude to you guys !

If you ever come to France, let me know. We'll drink wine and play some music ?

Now i'll get back to the fine tuning of the BBD trimmer, but it should be much easier from here.

Nevertheless, i'll mark it [Solved] once everything will be calibrated and ready, just in case...