Optical Tremolo build error - no sound

[wanchope]

Hi everybody, I create a new topic, as I tried to post in an old similar topic but seems like nobody has seen it. If it's a problem to duplicate the post just tell me and I'll erase it.

I am trying to make a tremolo w/rate variable on the fly, inside an old volume pedal case. So I built Das Tremolo kit from Musikding inside that case and everything looks ok (double checked all solders etc.), but when the pedal is activated doesn't play any sound. The led flashes right on time with the LFO, so i guess it should be something wrong with the IC1.
I try to report the values I measured on IC1, but as i'm a newbie I don't know which is to be called P1 rather than P2 P3 etc...so I simply report them as they appear (imagine you have the pcb in front of you):
P1 4,75       P5 9,54
P2 4,75       P6 4,75
P3 4,53       P7 4,75
P4 0           P8 4,53

when the fx is (should be) bypassed, still signal is not 100% dry, i feel just a touch of tremolo mixed in.
Anybody could help me? Any idea?

Thanks a lot in advance

[drolo]

It could be an error with the outboard bypass wiring. Verify that. You can also audio probe the signal path and check where the signal gets lost.

This page has some info on how to go about it:

http://www.diystompboxes.com/pedals/debug.html

[bluebunny]

Those voltages look OK to me.  BTW, you got the pin counting slightly wrong - it continues counter-clockwise.  So you got 1,2,3,4 in the right order, then it goes 5,6,7,8 from bottom to top on the right-hand side (see below).  Other than that, do what David suggests.  And welcome! 

   ______
1 [ o    ] 8
2 [      ] 7
3 [      ] 6
4 [______] 5

[wanchope]

Thank you Drolo and Bluebunny! I'll have another look at the bypass wiring, if the problem is there would be good news, but i've already double-checked it...I'm afraid that the IC1 could be dead because I didn't use the socket. 
I'll also try to make my audioprobe and follow the signal path, seems a very good idea!

[wanchope]

After some pointless attempts to re-solder somewhere, I finally made my audioprobe and tried to follow the signal path. It's really a great idea, thanks again for the suggestion.

So I have the signal ok up to the IC1, then again on AOl1, and that's it.
No more signal anywhere after the AOl1, just plenty of LFO noise.

Do you think the chip might have been overheated?

[drolo]

could you paste or link to a schematic ?

[wanchope]

Of course!
Here the dir where you find schematic, pcb and wiring layout
http://diy.musikding.de/?p=213&lang=en

and here is the schematic itself
http://diy.musikding.de/wp-content/uploads/2013/06/tremoloschalt.pdf

[drolo]

Ok, that you get signal after IC1 is a good sign. plus you mentioned the LFO is working. Can you check if you have the optocoupler oriented correctly ? The polarity of the led side and also if you have not by accident inverted the led side with the LDR side.

[wanchope]

Optocoupler is AOl1, isn't it?
If so, I don't know which is the LDR side , still I think the led side is oriented ok, as I've checked the picture in the wiring layout (genuine newbie here! ).

So, again, 


p.s. congrats for Belgium! 

[drolo]

Optocoupler is AOl1, isn't it?
If so, I don't know which is the LDR side , still I think the led side is oriented ok, as I've checked the picture in the wiring layout (genuine newbie here! ).

So, again, 


p.s. congrats for Belgium! 

Correct, AOl1 is the optocoupler. Depending on the kind of optocoupler you are using (are you using a VTL5C2 like on the schematic?) you will see a "+" sign on it. This needs to go to the "+" sign of the PCB.

[wanchope]

Yes, the + of the VTL502 is on the + of the PCB

[drolo]

Ok, not sure how your multimeter will handle this but it's worth a try.

Set the LFO rate to the minimum and measure the voltage at this "+" point.
See if you can measure a voltage that varies with the lfo rate. Try to note down what value that is.

Then try to measure the resistance on the LDR side of the optoisolator (the 2 connections opposite from the ones where you have the "+" and check if it is variying too with the LFO rate.

[wanchope]

The voltage at the + varies between 4,80v and 6v, when the rate is set to minimum.
When the rate is at the maximum, voltage is 0v. Don't know if this makes sense.

About resistance, I should first change my tester's battery....for now, seems kind of 1.4-1.6 Ohm, but not so stable. Now I'm in hurry, tomorrow I'll check it out better and let you know...
Thanks

[wanchope]

Ok, here we are:
with the rate set minimum, voltage at the + is between 4,80 and 6; as I fasten the rate, looks like voltage is more stable...at the maximum rate, is nearly stable at 5.35.

Resistance on the LDR side varies between 1 and 2, but doesn't seem trustable...continuously changing, maybe my multimeter is too much crappy. 

[wanchope]

Does it seem ok, or do you notice any trouble?

[drolo]

Ok, here we are:
with the rate set minimum, voltage at the + is between 4,80 and 6; as I fasten the rate, looks like voltage is more stable...at the maximum rate, is nearly stable at 5.35.

Resistance on the LDR side varies between 1 and 2, but doesn't seem trustable...continuously changing, maybe my multimeter is too much crappy. 

The voltage looks OK. But on the LDR side there seems to be something wrong.  and 2, you mean 1 and 2 Ohms ? That far too low. It should be varying between a couple of kiloohms to several hundred, depending on the particular optocoupler and the setting of the depth.

But measuring resistance in a circuit that is hooked to the power can be wrong. Try unsoldering the LDR side, at least one leg, and measure the resistance again, with maximum depth and a rate that is slow enough for your multimeter to track.

If you still get that strange reading, try to unsolder the optocoupler completely out of the circuit and test it outside. Try first if you get a voltage drop across the LED side when measuring with your multimeter. (should be something between 1.4 and 1.8 V) And then, hook the LED side to a 9 V power source in series with a 10k resistance. Measure the resistance on the LDR side. When the power is not connected, you should have a high resistance, when connected the resistance should be lower. Don't forget the resistance in series with the LED or you will fry your optocoupler :-)

[wanchope]

Ok, as soon as possible I'll try and post the results.
For now thanks again, I owe you some!