SOLVED Low Tide (Full Size) Oscillator problem

[Jachiro]

Hi. I recently put my Low Tide modulator and I'm having some pretty nasty trouble with it. I'm unable to get a proper wet signal. I have set the bias point of the V3207 BBD to a healthy 2.5V (1/2 of the 5V going to the VDD terminal). At this bias point I should get something on the output but I don't get a wet signal.

My settings for trying to bias the bbd is 100% depth, 100% volume, 100% Mix, 50% rate, 0% Gate, 0% Slew. Here are my observations on troubleshooting so far.

No wet signal at all. But when I turn the gate trimmer past halfway, I get a nasty loud oscillation at the output. If I move the gate trimmer back closer to zero, it goes away.

I am definitely getting a good signal past Q1, Q2, and I am getting an input at the BBD on pin3. At the output, I am getting an extremely distorted output on pins 7 and 8.

Right now, I have disconnected the MCP602 IC to help isolate any trouble with the randomizer part of the circuit on though the CD4046 PLL chip. I still get the distorted output at the BBD and the oscillator.

I could really use some advice on how to go forward with troubleshooting. I put this circuit together carefully and I have had numerous successful builds in the past, including a mini low tide (which I sold last year). I've already spent quite a few hours in solving this problem on my own, but I could really use some advice. Thank you so much in advance for any expertise.

 

[inflatablerobot]

Double check the Q1, it kinda looks like your 2SK208 transistor is in backwards.

 

[Jachiro]

Hi. It does appear that it’s backwards. During my troubleshooting, I accidentally pulled my surface mounted Q1 and destroyed the pads. I ended up substituting another sk series transistor; I twisted the gate and source legs to go into the proper pads making it appear backwards. Q1 is actually working fine and amplifies and passes signal as it should.

As an update, I ended up causing damage to the board by desoldering and desoldering too many components; in particular, the IC’s. I decided to purchase a new pcb and starting over. I will build it slower and more carefully this time. Hopefully, I’ll not run into the same issues next time.

I’ll keep this thread open since this is a challenging build and I will no doubt have questions when it comes time to dial in the trimmers.

 

[Jachiro]

Ok, new update. I ordered a new pcb and started over. I was 100% sure all my values were correct per the documentation. I also made sure to use sockets instead of soldering IC's directly to the board in case I needed to replace one or more with no risk to damaging the PCB. I got very different results this time and everything worked out for me. Here are my notes on dialing in the trimpots:

1. Do the GATE adjustment first - Set the mix to 100%, Depth and Slew to zero and Volume all the way up. Start with the trimpot all the way turned to the left and slowly turn it up. Plug in a guitar and start playing. You'll hear a point where the gate "kicks in" and you'll start to hear the sort of "underwater" effect of the filter. From this point forward, make very small adjustments and turn the GATE knob all the way up and down after each adjustment. You should hear a good wide range. All the way clear (it can overdrive) when the gate is all the way up, to fully underwater and with a "woh" kind of quality to the sound with the gate all the way down. Once you feel like you have a nice range - it's done. Move on

2. BBD Bias adjustment: You'll need the GATE control to be set at a point where you can clearly hear the modulated signal. You can set the depth all the way up and the rate to wherever you like. I recommend at least halfway just so you can hear the sweeps more often. Volume and Mix up. Here you can just play and adjust the trimpot up and down until you hear a good modulated signal with no distortion. Just like other posts have said about this adjustment, it's pretty intuitive and easy to know when you have it set right. I like to use an oscilloscope at the output pin of the BBD and look for the largest wave with no clipping.

Additional notes: This wasn't my first rodeo building time-based effects pedals. The documentation for the Low Tide Modulator is pretty good, but it really needs to include a short paragraph or two about how to bias the trimpots. I've built pedals using Aion PCB's, Madbean, and LectricFX PCB's and documentation is excellent with a lot of information about bias adjustments. I think the forums are fantastic for getting great minds together and working through troubleshooting on pedals and amps, but in this build, I used the forum itself to find the bias procedure for this project based on troubleshooting posts. I think it was more difficult than it should have been.

With all that said, I really hope my post is helpful to the next person who decides to build this pedal. It's absolutely doable, but you have to tread very carefully to avoid donking it up.

 

[Erik S]

With all that said, I really hope my post is helpful to the next person who decides to build this pedal. It's absolutely doable, but you have to tread very carefully to avoid donking it up.

Congrats on getting it working!

Nice write up too - I bookmarked this post for when I get around to building mine.

 

[Jachiro]

Congrats on getting it working!

Nice write up too - I bookmarked this post for when I get around to building mine.

Feel free to reach out if you have any trouble.