EasyVibe lfo not working

[Dutchie]

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

[Dutchie]

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

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

[David]

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.

[Dutchie]

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......................

[gez]

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?

[Dutchie]

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.

[Torchy]

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  

[Hal]

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.

[gez]

The 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)...

[Dutchie]

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

[Dutchie]

BTW:

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

This kinda rules out the fast blinking doesnt it.

[gez]

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.

[gez]

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.

[Dutchie]

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

[Dutchie]

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??

[gez]

Voltages 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.

[gez]

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.

[Dutchie]

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

[gez]

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.

[Lonestarjohnny]

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