Hey All,

I put together this simple LFO with a frequency range of 3 mHz to 3 Hz. The problem I'm experiencing is that when I turn the 500k potentiometer to go near 2Hz and above, it will oscillate for about a minute then stop. I believe this is what electrical engineers call "latching up," I could be wrong. I'm looking to keep the same frequency range, 3mHz to 3 Hz, but would like it to fully function without it locking up. The schematic is attached to this thread. Can you help?

Thanks.

The Damage Dealing Meat Shield

 

Hi,

There is an error in the schematic. The 10M resistor should read as 1M resistor. I was experimenting with even lower frequencies and forgot to update my resistor in the schematic.

TDDMS

 

Hello,

I assume that the gain of the second stage is not enough.
Try to reduce R6 to 10K and see how that works.

Here is a schematic from the website of "music from outer space" with a voltage controlled LFO:
http://www.musicfromouterspace.com/analogsynth_new/VCLFO200607/VCLFO200607.php

Bertus

 

You are using an LF347 quad opamp that does not have single supply opamps.
Its inputs DO NOT WORK and might casuse the output voltage to go high (opamp phase inversion) when they are within 3V to 4V from its negative power supply pin. The circuit needs a negative supply in addition to its positive supply, or it needs a virtual ground at about half the supply voltage.

 

You are using an LF347 quad opamp that does not have single supply opamps.
Its inputs DO NOT WORK and might casuse the output voltage to go high (opamp phase inversion) when they are within 3V to 4V from its negative power supply pin. The circuit needs a negative supply in addition to its positive supply, or it needs a virtual ground at about half the supply voltage.

It has a virtual ground (R1 and R3), but that puts his supplies at ±4.5V or less, relative to the virtual ground. I suspect you are correct about the phase inversion.
A dual rail-to-rail op amp would work nicely here.