Tremulus Lune - Build Report and Troubleshooting

[studiostud]

Hey guys,

Just finished a Tremulus Lune from the tonepad layout and just trying to get the thing workin.  Here is my data.  Thanks in advance for any help.

Jeff


1. Name of the circuit = Tremulus Lune

2. What does it do, not do, and sound like? No sound.  Some noise depending on where the bias trimpot is set.  I can here some slight thumping when the speed pot is around max. 

3. Source of the circuit (URL of schematic or project) = tonepad.com

4. Any modifications to the circuit?  No

5. Any parts substitutions?
VTL5C2 for LDR with a 20K trim for bias pot

6. Positive ground to negative ground conversion? No

7. What is the out of circuit battery voltage? = 8.62

Voltage at the circuit board end of the red battery lead = 8.52
Voltage at the circuit board end of the black battery lead = 0


IC1 (JRC4558)

P1 – 3.60
P2 - 3.60
P3 – 2.90
P4 - 0
P5 – 2.90
P6 – 4.92
P7 – 3.70
P8 – 0

IC2 (TL072)

P1 – 4.19
P2 – 4.19
P3 – 4.00
P4 - 0
P5 – 4.00
P6 – 4.19
P7 – 4.19
P8 – 8.42

LDR:

+ Top (closest to pots) – 6.42
+Bottom – 3.21
- Top – 4.17
- Bottom – 4.18

LED:
A – 3.55-3.57
K – 1.89-1.91


OTHER NOTES & OBSERVATIONS:
All electrolytic caps tested ok with positive side always having a higher voltage than negative side. 

[blues_mang]

The first thing I would check is to make sure the LED/LDR is incorrect. Try flipping it. I had the same problem and that's all it turned out to be. It can be confusing to determine which was those things go in. Does the rate LED blink?

[studiostud]

The first thing I would check is to make sure the LED/LDR is incorrect. Try flipping it. I had the same problem and that's all it turned out to be. It can be confusing to determine which was those things go in. Does the rate LED blink?

Sorry I didn't include this in the report.  The rate LED does work fine.  It blinks and changes speed with the rate knob.

[frokost]

So the LFO is working. The problem is either in the audiopath or your VTL5C2 isn't oriented correctly. Use and audioprobe and see if the signal ever hits the LDR. Start from the input. By the way, the trimpot isn't a bias control, it's a gain control, to compensate for volume loss. I'm guessing there's something funky going on around IC1, maybe a solder bridge or something, but who knows. Try the probe.

[rubix cube]

Pin 8 of IC1 should be at the same voltage as pin 8 of IC2, roughly the 9V from the power supply. 

[studiostud]

So the LFO is working. The problem is either in the audiopath or your VTL5C2 isn't oriented correctly. Use and audioprobe and see if the signal ever hits the LDR. Start from the input. By the way, the trimpot isn't a bias control, it's a gain control, to compensate for volume loss. I'm guessing there's something funky going on around IC1, maybe a solder bridge or something, but who knows. Try the probe.

OK.  So I checked both ICs for solder bridges and didn't find anything.  I also check Pin 8 on both and they both registered at the same voltage as the 9V input source.  So here is something new, I used an audio probe and traced the signal to the LDR.  The signal is getting to the but on the other side, all I hear is a pulsing sound with no tone.  One thing I should mention too, I dunno if this make a huge difference but I just noticed that I have a 10K trimpot in there instead of a 25K.    Any ideas?

[frokost]

10K should work fine.

Are you 100% sure the VTL5C2 is oriented correctly? You could replace it with an LED and see if that works as it should.

[studiostud]

I think I'm pretty confident, but you gave me some doubts so I uploaded some photos of the front and back of the board.  In case you are wondering about the sockets with the component leads, I use those with a breakout box that I made to test circuits. 

[studiostud]

How would I replace the LDR with than LED since the LDR has for component legs?

[John Lyons]

The VTL5C2 is two things. An LED on one side and a LDR on the other side.
Light shines on the LDR and changes the resistance...hence "Light Dependant Resistor.
If you pull out the two LED legs and insert an LED you can tell if the LED portion is
working because the LED will light up. Then you know that that parts works at least.

john

[Fuzzy-Train]

I just built this bad boy, and you probably did the same thing I did. Wrong LDR orientation.

Just flip it around and it should work.

http://www.diystompboxes.com/smfforum/index.php?topic=65889.0

[frokost]

Yep, flip it around. Take a look at this page (http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ#DIODES) and cross-reference with the tonepad schematic and you'll see that it's the wrong way around.

EDIT2: By the way, you may want to move the other LED to the outside of your enclosure - it serves no other function than as a visual indicator for the user. It's the LED inside the VTL5C2 that does the actual work.

[studiostud]

OK.  I will try flipping the LDR and see what I come up with!

EDIT2: By the way, you may want to move the other LED to the outside of your enclosure - it serves no other function than as a visual indicator for the user. It's the LED inside the VTL5C2 that does the actual work.

I know.  I just put it in there temporarily as a visual indicator for testing.  Thanks for the head's up though!

[studiostud]

SUCCESS!!  The LDR was the problem.  I guess I just assumed that the writing needed to go on top. 

ONE QUICK QUESTION THOUGH...  The indicator LED won't stop flashing when I turn the pedal off.  Only when I disconnect the battery leads from the circuit.  I can't imagine that it would make any difference having the LED soldered directly to the board vs having wires going to it that are soldered to the board...  any ideas?

[hday]

The indicator light is always on, even when bypassed. It's a nice feature to see the speed before turning the pedal on. Someone else didn't like the indicator and put a switch on it. You can wire it to a 4PDT if you want, but for some reason I think there is some true bypassing issue. You could just scrap the "engaged switch" and use the speed indicator as your visual indicator that the pedal is on and just use a 3PDT.

[Fuzzy-Train]

^ That's what I did. I just wired the rate LED to the switch. It's kind of silly having 2 LED's with one constantly blinking.

Also IIRC, and just FYI, the LED lead going to lug 3 of the depth pot is positive.

[blues_mang]

Hmmm.. I recall my post, the second post in this thread, was to flip the LDR, but Noooo. No one listens to the new guy! 

Just kidding.  Glad you got it working. For what it's worth, I oriented mine the same exact way the first time as your pic shows and that's why I knew it would be the LDR. Enjoy the pedal. Definitely my favorite trem.

[tskullt]

same thing with me.   Had that thing flipped around.   One of my favorite builds EVER!
m.

[frokost]

Glad to hear you got it working, congrats! It's a nice circuit, isn't it? The moment my fired up mine I knew I would never build another tremolo again  .

About the assumption you made about the writing on top - it's always a good idea to know what the different parts are and what they do. You could easily had made this with an LED and an LDR, and then my guess is that you would have given the orientation a little more thought.

(Language barrier disclaimer: I'm not criticizing, just a little bit of friendly advice  )

[studiostud]

none taken.  thanks for the tip.  that's why I come here... to learn and help learn.