Tonepad Version of 4ms Tremulus Lune - no effect sound - details inside

[$uperpuma]

I built this cool trem pedal and went to play it...doesn't look like it will be today  .
What it does:
plays on bypass (but I took the switch out to rule out bypass switch soldering error)
Speed indicating LED pulses correctly
Potentiometers change the speed of the speed indicating LED - so I can assume they are having an effect.
What its not doing:
Making sound when turned on
here is the PCB layout and schematic for it. http://www.tonepad.com/getFile.asp?id=84
There are 2 IC's in this circuit.. and a vtl5c2 photocell...  I took some measurements POTS ALL THE WAY OPEN hopefully someone can make sense of them...
Heres what the pins are indicating...
battery- on 9v terminal of board and input pad - 9.4v
after 1st cap 4.65
IC 1 - TL072
1. 4.68v
2. 4.68v
3. 4.68v
4. 0v
5. 4.68v
6. 4.68v
7. 4.68v
8. 9.4
IC 2 - 4558
1. 6.1v
2. 6.1v
3. 6.1v
4. 0.0v
5. 6.1v
6. 6.1v
7. 6.1v
8. 9.37v
the photocell is oriented just as shown and voltages at its pins are:
1. 3v                                       2. 4.6v

3. 6v                                       4. 4.6v

Hopefully someone can help me out with this... I am new to pedal building so this can be a stumper. I have a DMM if further measurements would help.

Thanks in advance to anyone who can help! 

Nathan

[johngreene]

The data sheet for the VTL5C2 shows the diode the other way around. Reverse the connections on the left side. Or just flipping it horizontally.
http://optoelectronics.perkinelmer.com/content/Datasheets/vtl5c1_c2.pdf

--john

[$uperpuma]

ok... photocell flipped... still the same problem...thank you for pointing that out by the way... (I've never used one of these before)... I've gone through and tested the caps too... they all show good as far as + leads being much more +V than the other... Any other ideas?

[johngreene]

At this point I would recommend a divide a conquer approach. Remove the VTL5C2 and replace the right-side connection with something like a 10K resistor. Anything less than 25K should work but don't use a short. Now all you have is 2 inverting amps, the first with unity gain, the second with gain more than 2 if you used the 10K. If you don't have sound at this point, there is something up with either the first or second opamp. You voltages all look good so trace the signal path using either an audio probe, or as I like to do, with it plugged into your amp, touch the signal path from the output back towards the input. You should hear hum everytime you touch something in the signal path. If you hit a point and there is no hum, you found the area of the problem.

--john

[$uperpuma]

Ok... so I put the 10k across the right side (the wide side) ..OH BY THE WAY...you help is REALLY appreciated... I would not have known where to go on this one... anyways... I have sound and that opamp the TL072 gives me a hum, the 4558 does not... I swapped the opamp out for two others... so unless I had 3 bad ones right out of the package...then it needs to be something else...if my voltages were ok.. then what else can I check?

[johngreene]

The 4558 is the LFO so that wouldn't cause any hum. But are you saying that with the 10K in place you get signal from input to output?

If so, then everything is working except for the VTL5C2. Since from you diagram it appears you had it in backwards when you took the first voltage readings, can you measure the voltages again with it installed the right way around? There maybe just not enough current flowing through it to get it to a low resistance value.

And now that I look into it....... 

The data sheet says that the LED has a forward voltage drop of at least 1.5v. So, before the LED will light at all, you would have to see 1.5V on the 1K resistor to ground (because the LED has 1k in parallel). Your measurement shows 1.3V which means the LED would have been dark.

You also show 3.6V on the other terminal and this should be 6.1V minimum (same as pin 1 of the 4558). If the depth pot was at the other extreme it would be closer to 9V. I suspect your problem is in this area. Maybe the 330 ohm resistor isn't connected to +9V?

Sorry I didn't notice that earlier.

--john

[$uperpuma]

ok.. well I'll check those things out.... I really appreciate all the help... I'm sure I'll be back  

[$uperpuma]

So i retry to ldr/led, I strum the guitar...hold it on there to see if it works... I get the sound!   

a lead breaks off the photocell 

now I have to wait however long it takes to get one for this silly pedal to work! AAAARRRRGGGHHHH!

John, thank you so much for your input. anyone in tulsa have an extra vtl5c2 lying around? 

[hank reynolds 3rd]

 Try a green led and an LDR if you've any lying around

[$uperpuma]

yeah... I'll have to get down to Rat Shack and see if they've got any LDRs.... or I may just wait for small bear...*SIGH* well at least it worked for a second...

[johngreene]

How bad is the broken lead? Can you cut back some of the body and reconnect? Or did it come apart from inside?

--john

[$uperpuma]

its way in there... I tried to shave some off to reconnect it... but the way it was oriented on the board the leads had to be tweaked a little and they just couldn't hold up to being reversed... I have enough of everything else to completely build another one... EXCEPT I only got one vtl5c2    Oh well... I knew better... BRIGHT SIDE...IT WORKS!!!