lfo on a breadboard

[jambers]

Hello,

I've got a question/problem with triangle wave lfo's with op amps on a breadboard.

I've tried several circuits that I've found on several sites and in many schematics (e.g. [mac]'s lfo for the bjt phaser, dual op amps lfo's, etc...), but the only lfo that's been working on a breadboard so far is a square wave lfo with a cd40106. With op amps, the only thing I get is a led that gets dimmed when turning the rate/speed pot. But it doesn't blink.

Is it that hard to get that kind of lfo working (blinking a led) on a breadboard? Has anybody else had this kind of problem? Is it because of the nature of a breadboard? Or am I doing something very wrong? For instance, last night I've used the circuit of [mac] for the fet phaser.

It would be a pity to just build an oscillator on PCB and than to find out that it doesn't work. 

[JKowalski]

No, it should work fine on a breadboard. There's just some small mistake you made, it always happens. Go over it a couple times after you put it together.

An oscilloscope is verrry handy with oscillators! 

[frequencycentral]

(e.g. [mac]'s lfo for the bjt phaser, dual op amps lfo's, etc...),

I've breadboarded that LFO a couple of times, it's very flexible. You can do a lot with it re. varying the range of speed and amplitude by changing some component values. Instinct tells me that if you've had success with a 40106 but not with opamps the fault may lie with the vref. That's the voltage divider formed by two equal value resistors between +ve and ground. Give it another go!

[jonfoote]

ive had the same problem with LFOs

always got this one working though, nice simple square and triangle oscillator

http://experimentalistsanonymous.com/diy/Schematics/Oscillators%20LFOs%20and%20Signal%20Generators/Simple%20Dual%20LFO.gif

[Top Top]

I just built a dual opamp LFO and had the same problem. It ended up being a broken solder trace to one of the pins on the IC, so I would just check your connections.

[JKowalski]

I personally like using the schmitt trigger type:



The left one's big chunk of diodes/jfet/resistor is a bipolarity current source - it provides a much better linearity for the triangle wave then your standard resistor, as is shown on the right schematic (and you can use a bridge rectifier package for the diodes, too! so you dont have to mess with four components, just one!). In each case the resistor in the path from the inverting input to the output is the frequency control.

The right one has decent linearity, but is less consistant then the left one at different frequencies. If you set up the left one correctly you get a wide range LFO with a pretty precise traingle wave that is amplitude stable over the frequency range.

If you add a tubescreamer-stlye clipping stage to the output of the triangle wave (op amp inverting gain stage with antiparallel diodes in feedback path), you can adjust it to get a nice sine wave fairly easily.

You need a buffer for the outputs of this one, definitely.


EDIT: I forgot to mention, I believe you can get bridge rectifier packages that are basically a four lead (but six lead spacing) DIP. So you can get a 7 pin socket for your op amp and your rectifier)

[jambers]

Well,

yesterday I breadboarded the [mac]'s lfo again... and now it worked
Seems that it was indeed a question of not making a mistake with the connections.

http://experimentalistsanonymous.com/diy/Schematics/Oscillators%20LFOs%20and%20Signal%20Generators/Simple%20Dual%20LFO.gif

I've tried that one as well... but with no success.

Although... I'm still not quite convinced that in my earlier attempts, mistakes were the problem.

I've breadboarded a SHO kind of circuit the other day, and i had to wiggle about the mosfet a bit to get the thing going.

So maybe there is an issue with a breadboard (or at least my breadboard) that it is sensitive regarding to some connections?

Anywho... your circuit look interesting as well Jkowalski. I'll give that one a go, and see if I can get it working.

[solderman]

As stated above, bred board should not be a problem. But I always screw up and put things in wrong wholes etc. and hav to trouble shoot before getting it to work.
This is my favorite LFO from the Tremulus Lune
http://fuzzcentral.ssguitar.com/tremulus.php