SOLVED Trembling Loon depth issue

[keevohn]

Just finished a Trembling Loon. It does the tremolo thing just fine, but the Depth knob isn't functioning properly:

- There's no tremolo effect until about 10:00. It just sounds like a clean boost.

- The usable range of the Depth knob is limited to 10:00-2:00. It's really sensitive in this range.

- Past 2:00, the overall volume tapers off quickly until it's silent from 3:00 on. Cranking the Gain knob does nothing to bring it back.

Pics of my build are attached. I double checked that I have the right pot for Depth, but I haven't tested it with my DMM yet. Can this be tested in the circuit?

The only substitution is a Tayda KE-10720 for the LDR. I'm planning to get a GL-5516 from PPCB to replace it.

Besides the pot and the LDR, is there anything I'm missing?

Thanks!
Kevan

 

[Chuck D. Bones]

Are you testing it with the box closed up tight?

Have you measured the light & dark resistance of the LDR?

 

[DailyDovetails]

It looks like LED1 might not be soldered in. I’m not sure but it’s close to the LED that feeds the LDR in this circuit and may be needed.

 

[Chuck D. Bones]

LED1 is purely an indicator and does not affect the circuit operation.

Good catch though...

 

[Nic]

Not sure where all your switch wires are going. The IN ???

Forget that ... if it works then no problem there. Sorry about that.

 

[keevohn]

Thanks all. To answer Chuck's questions, I'm getting this behavior with the boxed closed up tight. When I take the lid off, I can see that the intensity of LED2 varies through the whole range of the Depth pot, as it should. This pot also measures correctly, so I think the issue is with the LDR.

I haven't measured the KE-10720 LDR yet, but will post results when I do so. I'm thinking about going the DIY Vactrol route once my GL5516's show up.

For what it's worth, it looks like another member built this pedal with KE-10720's as well: https://forum.pedalpcb.com/threads/trembling-loon-tremolo-build.10522/ The orientation of LED2 and the LDR is slightly different than how I configured it... not sure if that makes a difference?

Good catch on the LED wiring. I have it wired so the Rate LED goes on and off with the footswitch. I just ran a wire from the "A" pad of LED1 to the LED anode, and ran the LED cathode to the footswitch. I left the pads for the regular on/off LED empty, although I went ahead and soldered a 4K7 in for it anyway.

Finally, a little digging on the Tremulus Lune turned up a thread on DIY Stompboxes that talks about changing resistor values to tweak LED2's behavior: https://www.diystompboxes.com/smfforum/index.php?topic=121067.0 I may explore this more if the GL5516's don't fix the issue.

 

[Erik S]

I haven't built this one, but I did a couple Sproing Deluxe which I think is a similar tremolo circuit.

I found those to be pretty sensitive to the amount of light hitting the LDR to the point where adjusting the gap made a noticeable difference.

You could try increasing the gap or adding a little tab of scotch tape to the ldr for some more diffusion. If that moves things in the right direction you could try dimming the LED by bumping up it's resistor. If those things made it worse, you could go down on the resistor to brighten it up.

 

[Locrian99]

The 10720 and 5516 are rather dofferent. 10-20 vs 5-10, 200k vs 500k.

 

[Locrian99]

For what it's worth, it looks like another member built this pedal with KE-10720's as well: https://forum.pedalpcb.com/threads/trembling-loon-tremolo-build.10522/ The orientation of LED2 and the LDR is slightly different than how I configured it... not sure if that makes a difference?

The ldr being right up against the led can make some differences. I would certainly try it, see if it makes any difference.

 

[keevohn]

UPDATE: Swapped in the GL5516 today, but still had the same issue. Turning the Depth pot clockwise past 3:00 caused the volume to quickly drop off. Interestingly, turning it CCW gave a volume boost around 9:00.

As it turns out, this was the problem:

I have it wired so the Rate LED goes on and off with the footswitch. I just ran a wire from the "A" pad of LED1 to the LED anode, and ran the LED cathode to the footswitch. I left the pads for the regular on/off LED empty, although I went ahead and soldered a 4K7 in for it anyway.

I reconnected the Rate LED to the LED1 pads and added a separate on/off LED - just like the PCB was designed. Lo and behold, it works perfectly now.

I don't understand it, but it seems like tying the Rate LED to the foot switch caused the problem. Which is strange, since that's how I have my Caesar wired... Oh well.

Thanks all for the input!