Triangle Wave LFO help request

[Ratbones]

 Hey everybody! I've got a problem that I need some help picking through...

I'm using an LFO driven vactrol in a circuit that was originally designed with a simple square wave LFO, and I'd like to sub in a triangle, or saw/ramp LFO in its place.

I selected this circuit:



"This LFO is made from 1/2 of a 4069. You can make a dual LFO by using the whole chip. This could be powered from 8 volts and ground on the FatMan. Actually, it can also be powered from ground and -12v. It can also be powered by a bipolar supply, but the data sheet says +/- 7.5 volts is recommended. However they also state that +/- 9 is the absolute max (you'll burn it out). I am going to experiment with +/- 8 volts. It will be alot easier to use these CMOS chips with a FatMan if it works."

Author's text in quote.

Looking at the datasheet for the 4069, I see that pin 7 is marked V_ss and pin 14 is marked V_dd.
It also states its operating voltage can be anywhere from 3 to 15 volts. If I understand the datasheet and the schematic designer's info correctly, I need to create a bipolar supply that outputs ~ +8v to pin 14 and ~ -8v to pin 7. 

I used this little circuit taken from another thread here to split the supply voltage into + and - :



I wouldn't be surprised if the +/-4.5 volts that it puts to those pins is not enough to get the thing going, but I seem to have no output at all at the wiper of the vol pot. Measured on a dmm, I should be seeing it climb and fall from 0 to 4.5 back to 0 right?

Questions:
* Did I just breadboard this wrong or is there a perceivable-to-the-experienced-eye problem with the schematic? (I suppose I should mention I've bb'd it three times now hoping to magically 'get it right')

* Is the +/- 4.5v the issue? If so, how can I go about getting a +/- 8v from a single 9 volt??
   Must I go bipolar here?

* Is there a better/more suitable LFO I can take a whack at?

Any help would be superb!

[smallbearelec]

The square/triangle LFO in my trem is fairly simple, use single-ended power and works well:

http://www.smallbearelec.com/Projects/TremBear/TremBear.html

[Ratbones]

Alrighty, I'll definitely take a whack at that. I had no idea that you could get a triangle wave out of a 555...

If I'm seeing this right, the LFO is pretty much the whole top half of that schematic right? I would just replace R13 and 14 with my vactrol and lop off the whole lower half of the schematic? Gosh, I'm having trouble separating the LFO from the rest of the circuit in my mind... I guess I'll see what I can manage! Thanks for the suggestion!

[CynicalMan]

That kind of LFO does work fine running on a 9v source (not bipolar). On your DMM you should see it oscillating around 4.5V. You can also get a square wave by connecting the pot to pin 4 instead of pin 6.
To give another example, the CMOS LFO here works fine on 9v, although the schematic shows 18V (+/-9V).

[Top Top]

You don't need a bipolar supply for that CMOS LFO in the original schem. Some people have done some parts subs to get more reliable results.



It works on 9V as well.

[Ratbones]

Alright, thanks guys for the input!

Top Top, on the edited 4069 LFO you posted, what is that just before the output going to ground? A resistor and capacitor?

[PRR]

> I selected this circuit

I say there is a typo. Two equal (100K) resistors won't Schmidt a CD4069. The input (here, right) resistor must be rather smaller than the other. See TipTop's plan: 20K and 10K. The exact values are not critical, but the 2:1 ratio may work a big heap better than 1:1.

> "This LFO ... ... could be powered from 8 volts and ground...

So why are you complicating it with bipolar? Don't get manic. The oscillator itself does not know or care where ground is. Use a simple 9V batt, pick one batt-wire (often black, but not critical) to call "ground", and see what happens.

> I wouldn't be surprised if the +/-4.5 volts that it puts to those pins is not enough

It should work (with right resistor ratios) fine at 6V, probably limp to 3V.

> I seem to have no output at all at the wiper of the vol pot.

What is "no output"? DMM blank? Zero? (Relative to what?) Dead-zero or steady 13mV?

Why stop with one reading? Check the pot-top. Why stop there? There's only 6 nodes. Read them all. Likely if pot-top is steady DC the others are stalled too, but some should be stalled negative and others stalled positive.... or some kinda clue.

> Did I just breadboard this wrong

That has happened. (IMHO, that's what usually happens.)

> is there a perceivable-to-the-experienced-eye problem with the schematic?

See above.

> I've bb'd it three times now hoping to magically 'get it right'

I've opened my wallet three times now hoping another $20 would magically appear.

Electronics may be magic on the inside. But part-connection is NOT magic, not even Rocket Science. More like nailing wood into a shed. This-connects-to-that. If you forget to put wall-studs between floor and roof, the shed won't work (no inside space). On a shed, you see such things; with electronics you have to check each connection like a pilot counting wings and peanut-bags before takeoff. Not just counting: one wing left, one on right? Firmly connected?

[Earthscum]

Hey, give this one a shot, maybe:

http://www.circuitstoday.com/category/signal-generators (bottom of the page)

I've boarded similar ones. You DO have to use a split power supply, though.