LFO Locking Up

Thread Starter

DamageDealingMeatShield

Joined Jul 18, 2012
5
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
 

Attachments

Last edited by a moderator:

Thread Starter

DamageDealingMeatShield

Joined Jul 18, 2012
5
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
 

Audioguru

Joined Dec 20, 2007
11,251
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.
 

Attachments

Ron H

Joined Apr 14, 2005
7,012
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.
 
Top