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Hi Guys,

I built an EasyVibe, but cant get the lfo working,
i connected both pots, and the toggle-switch. not yet the jacks and foot- switch.

Now here's the problem, the lfo wont oscilate. all 4 leds are on and stay on nomatter wich setting of the pots i dail in. I used RG's layout.

All the opamp voltages seem fine, 0V on all pin4's 9,11V on all pin8's
The rest of the pins around 3,9V and they stay there. Except for pin3 of U1 wich is around 1,9V ( strange?? )

The 2 "Vref"leds are on constantly and make the Vref of 3,9V.

What am i missing here , why wont it oscilate????
Anybody??

Greetzz

I forgot to tell that only the trimmes seems to fade the 4 leds, depth does nothing as does rate

GRRRRr.......Help!!! :?

Are you testing this on a breadboard?  If so, are your LDRs and LEDs exposed?  Even ambient light will probably screw up circuit operation.  One thing you could try is repeating your tests with the lights off.

Thanks david, but its just the lfo leds not blinking, not the sounds that's not working.

I added the jacks to see if sound is comming through, and it is.
when i put my hand over the pcd to block daylight i can hear the phasing sound, or when in chorus mode, the detune.

So the signal path seems to be ok.

Now For the LFO......................

Post a link to the schematic, it helps.

Can't remember what the LFO arrangement is, is it a two op-amp affair or a single?

The schematic is on john hollis's site.
http://www.hollis.co.uk/john/

The LFO uses 3 opamps, i used RG's layout, with dual TL062's

Like i said, signal path seems fine. The 4 leds that should be blinking are on all the time with not even a hint of blinking. Depth pot doesn't do a thing, wich i find strange cause that pot with the wiper to gnd should dim the leds right?

All opamp voltages seem fine ( see 1st post ) with 1 odd one, but thats a signal opamp, and seems to work fine.

dimming external light by hand makes te desired fx , but I need both hands to play, so thats not an option  lol.

Ive built (and modded) half a dozen of these now but the lfo always fired up first time.

The most important aspect of the EZvibe is that all the LEDs must be the same - 3mm red lo-current. I bought 50 off ebay just for EZvibe building. I had serious problems when I used green & yellow LEDs while experimenting.

Make sure the 4 diodes in the lfo have the correct polarity in the board.

Make sure the lfo LEDs go to 0V and not the bias rail.

Check the cap value on the first lfo opamp. I fitted a 1nf by mistake once.

On every pcb I have made using RGs excellent layout, I have had to use a dremel on the pad for R18 shorting out to C9 -ve. This is the lfo output resistor from the drive pot.

Best of luck, the EZvibe has to be my all-time favourite diy pedal  8)

I've learned the hard way, once, that "not blinking" is the same as blinking really fast.  Check the connection with the rate pot - if its maxed out, you might not be able to see the blink.  Also, check all resistor and capacitor values in the LFO.

Quote from: DutchieThe rest of the pins around 3,9V and they stay there. Except for pin3 of U1 wich is around 1,9V ( strange?? )

On this schematic:

http://www.hollis.co.uk/john/easyvibe.jpg

which IC is U1?

Edit:  Ahh, it's probably the first amp connected to the huge 10M right (voltage drop across this resistor accounts for the lower reading and the feedback resistors compensate for the offset)?

Follow Torchy's advice and use matched LEDs (use the same for the ones setting the bias too)...

Thanks for all the advice.

As for using the same 3mm low current leds, done that.
also in the biasing.

they are all on, same light intensity so nothing seems vrong with that.

diode polarity is like shown on the RG layout pdf, black line on diode corresponding with blackj line on the layout, seems foolproof hehe

Did the the dremel-trick on de pad also, noticed that before even soldering..........i must be overlooking something very trivial...but that kind of mistake always seem the hardest to find

I'll go and check the colorcodes for the resistors again. and dbl check the C's

Wish me luck

BTW:

Isnt it strange that the depth control does nothing at all????

This kinda rules out the fast blinking doesnt it.

Turn the depth pot all the way down so that the wiper, effectively, connects to the bias point without any resistance in its path.  Measure the voltage at the output of the op-amp used to drive the LEDs (it connects to the 1k 'drive' trimpot).  It should be at the same voltage as V bias (junction of the 10k and 1N914 diode) - I think you said this was 3.9V.

If there's no problem there then check all your joints/connections around the LFO.

Post some voltage measurements for the two op-amps used for the LFO (one amp has the 0.1ucap in its feedback loop, the other is connected to this amp via a 47k resistor).  Post +ve/-ve inputs and outputs.

Hi, no matter if the depth is fulle CW or full CCW the output of the led-driving op amp is always 3,9V

Does it mean the flaw is in that small part of the whole circuit, just the led driving part?

Voltages i posted in my first post, still the same

Just figured out that the led driving part must be ok. and why the depth isnt workin, one lug  goes to 3,9V the other to just under 3,9 , not much voltage to divide, so no visible working of the depth pot

so must be a problem with the other 2 opamps, but what?

What can be wrong if the voltages seem to be what the should be, what other options do i have.

Replace parts maybe? wich first , the 0.1u? the 470K ???? wich is ( more )essential in the feedback loop??

Quote from: DutchieVoltages i posted in my first post, still the same

No you didn't.  For example, the output of the amp wired as a Schmidtt will not be (or shouldn't be) 3.9V, it'll probably be a volt or so above ground/short of V+ (don't have the data sheet in front of me for this amp so I can't be more exact).

Please do as I say, measure both inputs and output for each amp and post voltages for each amp.

As you rightly say, there's something up with the LFO, but if you don't post the voltages you're not giving us much to go on.

Measure either end of that 100k rate pot and post voltages.  Check the connection of its outer lug to the output of the second amp (Schmidtt trigger).  If it's not connected properly (poor joint/trace etc) then that might explain a few things.

Also check that you don't have a solder bridge where the .1u cap is.  If the LFO is locked up then this cap will eventually charge up so that the output of this amp is at one of the rails.  The fact that you're measuring 3.9V here suggests a bridge/dodgy cap.

kee here they r.

This is for U2 in RG's layout, wich contains the 2 lfo opamp
Vcc. 9.33

p1 3,57  (out  1)
p2 3,9
p3 3,9
p4 0,0    ( gnd )
p5 3,9
p6 3,9
p7 3,9   (out 2 )
p8 Vcc

The outputs of both amps are biased at V bias so somehow you've biased both amps as followers.  Either that or the amp is dodgy.  

Check that the 100k resistor from the output of the Schmidtt to the +ve input is connected properly.  If it isn't then this might explain a few things.  

Be sure to check things around that .1u cap as I mentioned in my previous post.

Gez, You seem to have a good base of knowledge on the timmer's and Lfo's, My question is, 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 ?
Johnny

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?

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

Quote from: DutchieNo 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).

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

Quote from: LonestarjohnnyI 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.

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)?

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

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).

Quotei 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.

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.

Quote from: DutchieI 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.

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