SOLVED Low Tide - LPG not working.

[selfctrl]

Hi everyone.

First post on your forum, so please be gentle.
I've been building for around 6-7 years, don't have a ton of actual electrical knowledge.
But I'm usually competent enough to figure things out in the end.

I've just completed my Low Tide build, all controls are behaving as expected, but alas the Low Pass Gate doesn't seem to be doing anything. I guess I'd describe it as permanently open, everything is very clear and turning the pot or adjusting the gate trim doesn't seem to be doing anything.

I've been testing voltages but honestly not 100% sure what to be looking for to start bug fixing it.
Looking at the schematic my understanding is IC4 should be sending out a control voltage [LPG Control] that gets passed to IC3 that does the filtering.
I might be totally wrong, corrections welcome!

I sort of expected that LPG Control voltage on the schematic would react based on instrument input.
But I'm not seeing anything like that.

One thing I am noticing is coming out of R29(2.2K) the LPG Control is 1.3V
Where it's coming in on the legs of IC3(LM13700N) legs: 5,7,12 it's 5.6V

Although I'm sure I'm probably barking up the wrong dog.
Any assistance/guidance and just general things I should be checking would be greatly appreciated.
Let me know if you need any further images or voltages posting.

Thanks in advance.

Stef

 

[bowanderror]

The envelope part of the LPG does indeed send a control signal to the LM13700. It's actually a control current, but I believe you should see a change in voltage if you probe after R29 (at Pin 1 & Pin 16 of the OTA). Both pins are connected, and the voltage should change as you play harder. I can't recall offhand what the voltage range is, so maybe someone else can chime in.

I know you said you played with the trimpots, but I'd go through the process below word-for-word as there is a lot of interaction between the front panel controls & the trimpots. Unfortunately, they both have quite narrow usable ranges (especially on the Gate trim), so make very, very small adjustments with a screwdriver. I see you've used multiturn trimpots, which will help with making small adjustments, but it might make it harder to find the halfway point to start the setup process. If anyone knows an easy method to find the end points/middle point of multiturns, let me know. You can always go to the end until it clicks, then count your turns to 1/2 the # of total turns (probably between 5-25 turns, with 5, 12 & 25 turns being most common).

I posted this on another thread, but here is info I've collected on setting the trimpots:

BBD/BIAS trim pot - Set for loudest, cleanest sound

1. Set your Slew control to 0%, Mix, Gate, & Depth to 100% and Rate to ~50%
2. Set both DIP switches to their OFF positions (to the left on your pic) - You can choose which DIP switch to use after setting up the Gate trimpot, but you should only be using either the Boost OR the Pad switch, not both at the same time.
3. Turn up the Level control to where it's loud enough to clearly hear the signal
4. Start with the trimmer at noon (50%) and gently adjust right & left to find the "sweet spot" where the signal is the loudest & has least amount of distortion. 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. Pretty obvious when set correctly, just set the trimmer for the least noise & fizz.

GATE trim pot - User preference - Controls the frequency of the low pass filter portion of the gate, and how much it's envelope is triggered by your input signal (interacts heavily with external Gate control)

1. The Boost & Pad DIP switches will change the sensitivity of the Gate to your guitar signal, so decide if you want to use either before setting the Gate trimpot. Otherwise, keep them both OFF - I keep the Boost switch ON at all times, because it has a more drastic effect on the Gate, and the preamp has a nice lofi sound.
2. Set Mix to 100% wet, Gate & Depth to 0%.
3. Set the Gate trimpot to 0% to start.
4. Slowly turn Gate trim clockwise, you should hear the filter "open up" as you turn the trimpot up.
5. After each Gate trimpot adjustment, try the external Gate control at settings of 0%/50%/100%. You want to set the Gate trim so the external Gate knob goes from completely off at 0% to completely open at 100%, with a good amount of different settings in between.

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 still don't have any envelope after setting both trimpots, I would take a closer photo of the text on your LM13700 chip. It has some earmarks of being sanded down, which can be a sign of a counterfeit IC.

 

[selfctrl]

Hi!

Thanks so much for your response. Been a busy weekend, I've only just had a chance to have a play around.

The envelope part of the LPG does indeed send a control signal to the LM13700. It's actually a control current, but I believe you should see a change in voltage if you probe after R29 (at Pin 1 & Pin 16 of the OTA). Both pins are connected, and the voltage should change as you play harder. I can't recall offhand what the voltage range is, so maybe someone else can chime in.

Damn, I am getting 1.3V on both those pins and absolutely no change when I play.

If you still don't have any envelope after setting both trimpots, I would take a closer photo of the text on your LM13700 chip. It has some earmarks of being sanded down, which can be a sign of a counterfeit IC.

I've ordered another from a different supplier, just in case. But if I am not seeing any change on that LPG Control voltage I guess that's not going to trigger the filter anyway?

Thanks

 

[Dan0h]

I will say my low tide mini had zero chorus or gate and it took me a lot of fiddling around and very tiny adjustments of the gate pot in order to find the magic sweet spot. You just need to spend some time with it and play around. The above instructions should come in very handy.
Beautiful build by the way. Let us know when you get it doing the thing it does. It’s pretty cool and worth the effort to dial it in. Good luck.

 

[selfctrl]

Thanks Danoh!

I've been tuning those trims following bowanderrors notes since I first finished the build last week.
I tuned the gate so many times I'm pretty sure I broke it! I've had to swap it out as it stopped clicking when it reached it's end point.

I think I might have just figured out the issue though!
Checking the values of things around LM258P I noticed R30 didn't look quite right.

When I pulled my bag of 1M resistors I realised that I'd managed to put a strip of 16K resistors in there with the 1M.
Looks like I grabbed 16k resistors when I was adding the 1Ms.

Hopefully that's it thankfully there are two 1M resistors in the circuit R30 and R49.
Since both of these are a part of the circuit around LM258P hopefully when I swap them out tomorrow it might get me closer to getting the filter working!

Lovely Jazzmaster! What's the amp?!

 

[selfctrl]

Need to spend some time fine tuning, but I now have the filter working!
Thanks for the support!

 

[Dan0h]

Lovely Jazzmaster! What's the amp?!

Thanks! Old WEST mini II. It’s amazing.

 

[dontstaylong]

Just want to say I finished my Low Tide build today (one of two! A buddy asked me to make him one), and it would've been wildly frustrating if it weren't for @bowanderror's post in this thread. Thank you! The pedal is really subtle, but it's a great texture to add some depth to sounds.