EasyVibe lfo not working

[Dutchie]

Hi Gez....Thanks for your help

No luck still, but i measured round the rate pot, and coudnt get a good dc reading, so i thought hey lets look at the ac, so i put my multimeter in ac mode and depending on the rate knop position there was some ac movent of around 3,88 volt ( again around 3,9 )

So is the lfo working??? dont have a scope ( must buy one soon )

i thought lets see where the ac goes: it should get to the input of the leddriver. there there is only 0,4 ac volts left.....not enough to flash the leds.  at the output of the 1st lfo opamp ( 0,1u & 22k ) there is 0,8 V left

Is this normal?

[Dutchie]

Lonestar:

They r jumpstarted by the electrical noise that always there in a circuit.
Like the hiss in your pedals.

Only in some simulation packages where noise is not taken into calculation you need to manualy start it. in the real world, the thing we dont want in pdls does the trick hehe

[gez]

No luck still, but i measured round the rate pot, and coudnt get a good dc reading, so i thought hey lets look at the ac, so i put my multimeter in ac mode and depending on the rate knop position there was some ac movent of around 3,88 volt ( again around 3,9 )

So is the lfo working??? dont have a scope ( must buy one soon )

i thought lets see where the ac goes: it should get to the input of the leddriver. there there is only 0,4 ac volts left.....not enough to flash the leds.  at the output of the 1st lfo opamp ( 0,1u & 22k ) there is 0,8 V left

Is this normal?

OK, it's possible you've got the LFO working, this would explain some of the measurements.  

Do you have an old analog meter (with a dial)?  If you don't, digi will do though it's far from ideal.  Stick a larger value Non polarised cap in Parallel with the .1u cap and set the rate knob to slow.  Just use some leads with croc-clips on the end (if it's not too fiddly).  Take a measurement from the output of the first amp wired as the integrator (the one with the .1 in its feedback loop).  You should be able to see the thing ramp up and down with your meter.  This'll tell you for sure if the LFO's working.

If you've got the cap value wrong, or perhaps some of the resistor values, then it's possible the LFO is oscillating too fast and that's why you're not seeing any change in the LEDs.  

What's the voltage drop across the 4 LEDs wired in parallel pairs?

PS Apologies for being a grumpy old sod (bear with a sore head syndrome).

[Dutchie]

Gez,

Voltage drop is 1.7V per led , per pair 3,4V

Just for testing i inserted a 1u np C , thats when i noticed the lfo working
then i switched back to 0.1u and measured the ac voltages.

I'm totally puzzled now......not often i dont know where to look anymore

the Cap is free of solderbridges, i've checked it a hundred times.

Reheated all possible joints

Still nothing

NOT GIVING UP Though hehe

[gez]

I read somewhere long ago that some Oscillator's have to be strapped or jump started to get them to oscillate when first fireing up, is this something you have had to do or was i reading the info incorrectly ?

Thats true of some phase-shift oscillators.  I use a op-amp variation of a phase-shift oscillator that won't self oscillate, even though there's a T-network in the feedback loop, unless 'energised' by a signal fed back to it via a comparitor.

With things like relaxation oscillators, the output of the amp(s) will be at one or the other rail when firing up the circuit and it's this that enables oscillation to start.

[gez]

If your LFO is working then its either running too fast or the amplitude of the waveform is too small and isn't doing the required modulation.  Double check all your values - that 470k is just that and not 47k isn't it?  

If all values are definitely OK, stick another 22k (or smaller) resistor in parallel with that 22k resistor to develop some more output voltage across the depth pot.  I'm not suggesting you keep it there or change this value, just see what it does.  Are you sure you've got the right values for this resistor (and for the depth pot)?

[Lonestarjohnny]

Thank's Guy's, I've learned a lot just reading your thread, thank's for the answer's,
Johnny

[gez]

PS  Once you've tried all of the above, if there's still no joy then try temporarily disconnecting those four 1N914 diodes in parallel pairs at the junction they form with the 100k pot and 22k resistor.  It could be that they're shorting the LFO's signal and no voltage is developing across the pot (also look for bridges here).

[R.G.]

i put my multimeter in ac mode and depending on the rate knop position there was some ac movent of around 3,88 volt ( again around 3,9 )
...
Just for testing i inserted a 1u np C , thats when i noticed the lfo working
then i switched back to 0.1u and measured the ac voltages.

As Gez points out, the LFO is working, but either the cap value is wrong or the integrating resistor is wrong. Your LFO is oscillating so fast that the LDRs can't respond to it, and the LED light looks constant.

[Dutchie]

Thanks gez en RG,

The value's r as right as can be, tripple checked, replaced the intergrator C with another, same result.

Strange thing is when all opamps r removed except the ledriver the effect is the same, the leds stay on.

I checked the lfo with the oscilloscope freeware app. seems tot work , when rat is set to min, no oscilation takes place, when set to max there is osc. but not much voltage swing.

[gez]

I checked the lfo with the oscilloscope freeware app. seems tot work , when rat is set to min, no oscilation takes place, when set to max there is osc. but not much voltage swing.

OK, check the value of the 47k resistor from the integrators output to the Schmidtt's + input.  If you've made this 4k7 by mistake you'll have speeded up the LFO and made the amplitude smaller.

[gez]

PS  What was the amplitude (peak-to-peak) and what was the frequency with the rate pot set for max speed?