LUNE LFO, flashing but pots make no difference!!?

[craigmillard]

Hi guys,

I have built a Tremulous Lune off of the vero layout below but cannot get it to trem!

I have now spent about 4 hours (over a few days) fighting with this thing but cannot figure it out! So frustrating!

Right while debugging i have split it into two sections, lfo and output.

The output section is now working to a point (The tl072 needed reversing so that pin1 is nearest the electro caps, strange thou!)
The only problem is the trimmer doesn't seem to make a difference to the output level? Im using a 10k as suggested in the schematic but am using a NSL32 optical (http://uk.farnell.com/silonex/nsl-32/optocoupler-resistive-o-p/dp/3168773) would that make a difference?
Also cant tell that it trem's even thou i can prove the led is pulsing, is this due to the reversed IC?

The LFO Section is what i have been fighting with for the last couple of hours! The LFO is pulsing as i have removed the optocoupler and replaced it with a led and am getting a steady pulse, the only thing wrong is that none of the pots seem to make a blind bit of difference to it, allways ticks the same no matter what!
The IC is a RC4558P and has oscillating  voltages on it although they only seem to move up and down by .1  of a volt!

I have checked over and over for solder bridges and ran a craft knife between the traces but nothing, the only differences between mine and the vero is that i am using 1.5M resistors instead of 1M and an NSL32 optocopler!

I'm thinking this needs to go back to breadboard or attempt a new vero, but wanted to ask you guys and gals with infinite knowledge before i did anything that drastic

Vero Used: http://www.aronnelson.com/gallery/main.php/v/Gila_Crisis/Tremulus_Vero_NewRev.GIF.html?g2_imageViewsIndex=1

Any ideas would be great:)

Cheers
Craig

[JKowalski]

Hi guys,

I have built a Tremulous Lune off of the vero layout below but cannot get it to trem!

I have now spent about 4 hours (over a few days) fighting with this thing but cannot figure it out! So frustrating!

Right while debugging i have split it into two sections, lfo and output.

The output section is now working to a point (The tl072 needed reversing so that pin1 is nearest the electro caps, strange thou!)
The only problem is the trimmer doesn't seem to make a difference to the output level? Im using a 10k as suggested in the schematic but am using a NSL32 optical (http://uk.farnell.com/silonex/nsl-32/optocoupler-resistive-o-p/dp/3168773) would that make a difference?
Also cant tell that it trem's even thou i can prove the led is pulsing, is this due to the reversed IC?

The LFO Section is what i have been fighting with for the last couple of hours! The LFO is pulsing as i have removed the optocoupler and replaced it with a led and am getting a steady pulse, the only thing wrong is that none of the pots seem to make a blind bit of difference to it, allways ticks the same no matter what!
The IC is a RC4558P and has oscillating  voltages on it although they only seem to move up and down by .1  of a volt!

I have checked over and over for solder bridges and ran a craft knife between the traces but nothing, the only differences between mine and the vero is that i am using 1.5M resistors instead of 1M and an NSL32 optocopler!

I'm thinking this needs to go back to breadboard or attempt a new vero, but wanted to ask you guys and gals with infinite knowledge before i did anything that drastic

Vero Used: http://www.aronnelson.com/gallery/main.php/v/Gila_Crisis/Tremulus_Vero_NewRev.GIF.html?g2_imageViewsIndex=1

Any ideas would be great:)

Cheers
Craig

Are you sure you are aware of what pin pin 1 of the op amp is? If the op amp is put in the reverse way, it is likely that it will be destroyed or damaged. It should not work at all in the reverse direction. Make sure you are certain you know what pin "pin 1" is, and try putting a whole new op amp in.

It was a good move thinking of it in two sections, LFO and signal, it does help breaking it up like that.

I'm not so sure your signal path circuit is actually working right.

If you are attempting to pass a signal with it when the LFO is not oscillating, you will have a difficult time because when the LED is OFF completely, then the resistance of the LDR jumps extremely high and your gain is determined by the trimmer resistance/LDR. If the LDR resistance is way high compared to the trimmer, your signal will be heavily attenuated. To check if it is actually working without the LED on, put a 10k or so resistor in parallel with the LDR and adjust the trimmer back and forth. You should be getting a simple variable gain attenuator (depending on the trim position) that way, adjustable from x0 to x1.


Having a different LDR just means you might have to adjust the trimmer to match it, no big deal. For example, if you get an LDR that has more resistance for a given LED brightness, then you need to adjust the trimmer higher so that at the sweep of the LFO, highest point, you get unity. If the LDR has a lower resistance for a given LED brightness, you need to adjust it lower to get unity at the top of the sweep. Remember, gain is trimmer/LDR. So you see that you need to compensate for the LDR properties to get trimmer/LDR = 1 gain.

The 1.5Meg resistors should make no difference, they are components that are pretty much optional anyways.

I don't know what the deal is with the LFO section, perhaps some pics of the top and bottom of the board? And people here might want voltages for the various nodes in the circuit (under the sticky topic debugging) but I personally like to get around the obvious first before we go into technical data.


EDIT: Just had to add, you DID cut the traces underneath the OP amps and wherever else it was shown to cut the traces (red sqare with red dot), right? Alot of people unaccustomed to vero seem to forget to do this which is understandable given that it is usually not explicit on the layout diagram. Just had to ask.

[craigmillard]

hey JKowalski

Cheers for the quick response

Yer i have checked this, its the TL072 and have orientated it the correct way but get no signal through at all, the dot is pin one. If it is rotated though signal does pass (pin 1 bottom left) I have tried many dif opamps to too no success:(

I have also made all the cuts in the vero:) and tripple checked them!

The wierd thing is that the LFO does pulse, bout 2 a sec but cant hear it in the output, man this is baffeling!

The Voltages off of the TL072 are as follows (New chip + Inserted the correct way round, ie. no signal)

1. 7.55    5. 0
2. 6.40    6. 1.05
3. 6.51    7. 1.11
4. 1.05    8. 6.54

The Voltages off of the 4558 are:

1. 7.49             5. 0
2. 6.06 - 6.10    6. 3.45 - 3.48
3. 4.95             7. 3.46 - 3.48
4. 6.49 - 6.54    8. 3.18 - 3.19

Is there anything obvious indicating what it could be in those voltages? I havent got a camera at hand at the moment:(

On the verge of rebuilding it to PCB:( Thought it would be a good learning session to try and debug this on vero im used to using home made PCB's:(

Thanks for ya help!!

[JKowalski]

Those are some very wacky voltages.   

Your highest voltage is 7.5 volts, so I assume you are using a battery that is all but drained or a PSU thats too low voltage, for one. You need a fresh battery reading ~9.00 volts or a wall wart. I believe flipping the op amp around like you did will destroy the op amp and create a short condition, which will drain a battery very fast and noticably heat up the op amp. Did you notice your op amp turn into a hot plate?

This is what your voltages should look like.... I arranged the numbers in the way you count the pins on the op amp:

   __________________
  |    o       U               |   
--| 1. ~4.5     8. ~9     |--
--| 2. ~4.5     7. ~4.5  |--
--| 3. ~4.5     6. ~4.5  |--
--| 4. 0          5. ~4.5  |--
   __________________


Obviously there is some discrepancy....  Sorry to say it, but I think theres gotta be some construction mistakes. Double check part placement and make sure things go where they are supposed to (including off board wires!) Get a fresh power supply, and try it again.