Easy Vibe debugging

[Renegadrian]

Schem is the modified one - I modified a vero layout I found with those mods, checked 12 times and it looks correct.


power board LEDs light on, the 4 LEDS driving the LDRs light on and pulse according to the rate and depth knobs.
Still I get no vibrato or chorus. one of the positions of the switch mute the ckt.
Tried to audio probe it, I got tremolo with a cable fron pin 9 to output.

Any clues?! thx
I'll check my wiring another hundred times in the meanwhile...

[JerS]

I am just taking a guess here - but, by disconnecting the (-) side of first opamp section after the input from vref, aren't you taking away the signal required to "phase" with? In other words - try getting rid of the 330n to ground connection, and connect the opamp (-) pin to vref instead and see if it will phase.

Jeremy

[JerS]

...of course, I mean connect to vref from the 100K resistor attached to the (-) pin of the opamp. Not from the pin directly.

[duck_arse]

this might sound rude, but do you have your ldr's isolated/insulated from the ambient light?

[Renegadrian]

The leds-ldrs combos are kept togheter with "paper" tape, some light leak from it but no light in the room apart the blink of the 4 I can clearly see...I have no shrink tube, anyway if I put a wire between pin 9 and output I got tremolo, tremolo is intended to come from the four or from the other chip driving the leds?!
Gotta try to tie that 100k the original way, found these mods in an italian site and guessed they were cool and wanted to try...
Also, the trimpot seems to do nothing...

EDIT
tried to tie that 100k res as the original, to vref and not to grd via that 330n cap. no differences to write about...only some ticking...

[JerS]

I probed my easyvibe - pin 9 on the "upper" opamp pulses similar to a tremolo, but the signal never fully shuts off as a trem would. I am wondering if you are hearing the same thing I am. Also, the trimpot is very subtle on mine too - so nothing out of the ordinary there. It is strange to get ticking when connecting the 100K resistor from pin 3 of the "upper" opamp to vref. Mine does not have this characteristic. Some more questions:

- do you get a strong clean signal when you probe at pin 1 of the upper opamp? Out of interest - the original design had a gain of approx 1.5 at pin 1, this version has a gain of ~5. Perhaps this is why there is a tick.
- when you probe pin 8 of the upper opamp, do you also hear the tremolo sound? If you do, does the same sound come through the output when the circuit is connected normally (without an audio probe)? I would expect that same sound to come through to the output.
- you say that when you use the switch it mutes the circuit in one of the positions. which switch poles are connected when the signal mutes? (dumb question - but are you sure it is an on-on switch?)
I am guessing that you get a strong clean signal when the switch connects SW2 and SW3, and then it mutes when SW2 and Sw1 are connected. My intuition says that you have an issue in the "phasing" section of the circuit (upper opamp - sections with LDRs connected). This would explain the muting.
Lastly - I would try clipping out the extra LED that is shown in the schematic (presumably it is a pulsing LED to show the rate...unfortunately I dont speak Italian!). At least you could rule it out as part of the problem. I have tried to add a pulsing LED indicator in the past and found the circuit is sensitive to the forward voltage of the LED and can screw things up.

I know you are very experienced around here, and have probably already thought of these things. Hopefully you sort it out. Please keep us posted with the outcome!

[duck_arse]

I have tried to add a pulsing LED indicator in the past and found the circuit is sensitive to the forward voltage of the LED and can screw things up.

the way to make the led type/colour not matter is to wire a 15k (or so) resistor between V+ and the transistor collector.

and renegadrian - it only takes a tiny bit'o light to swap ldr's. try it with the light off/something covering yr circuit board.

[Renegadrian]

I tried to play in the darkness all lights out but the 4 leds pulsing - no phasing.
I didn't incorporate the flashing led, that would be the final touch, but for now I got the main circuit not phasing.
Should I try to wrap these leds/ldrs combos in black tape?! I guess they should work this way too....

[deadastronaut]

hi adriano..get some heatshrink on the led/ldrs...isolate each one , otherwise they will interfere with each other

they really are quite sensitive....

[Renegadrian]

I am not in a hurry but I just got some heatshrink tube
now all four are shrinked, just a little pinpoint of light comes out but I guess it won't interfere with the ckt supposed effect.
still the same results...trying to swap to 074 (the leds don't pulse with it) noticed that I got a great tremolo effect with no chip on the top socket, putting the ic back in the ckt silences again. other position of the vibrato switch just gives a boosted sound, with or without IC on the top socket.

Maybe the voltage listings will help me!^?

battery 7.40V

TOP IC
1    3.73
2    3.73
3    3.49
4    7.40
5    3.49
6    3.73
7    3.73
8    3.73
9    3.73
10  3.49
11  0
12  3.49
13  3.73
14  3.73

BOTTOM IC
1    3.73
2    3.73
3    2.10 fluctuates
4    7.40
5    3.73
6    3.33
7    fluctuates
8    fluctuates
9    3.73
10  fluctuates
11  0
12  fluctuates
13  fluctuates
14  fluctuates

[Renegadrian]

For the records - It seems I managed to make it work
I took out the leds/ldrs combos from the main board, used black shrink tube ad made a secondary board just for them.
it now wails as it should, hendrix burning of the midnight lamp is mandatory with this pedal!!!
All the above modifications are to be considered verified.

[JerS]

Right on! - thanks for posting back to let us know.

Jer