Simple LFO schematic, opinions?

JingleJoe · Posted: Fri Dec 07, 2012 2:46 am Post subject:

I don't know about RF (radio frequency) noise but there's allways the problem of induction- any two wires or pcb track running near one another can induce a current in one another so if you have any high currents flowing through wires, the larger current will create a greater electromagnetic field around the wire thus inducing a signal in nearby wires.
Reduce the current flowing to solve this.
Also that 100 ohm resistor sounds like a bad idea to me, I've never seen that done before, maybe a 10 ohm resistor to prevent direct shorts but 100 ohm in line with the chip? That'll just power starve the IC.

Try putting a nice big cap, something like 470u or 1000u accross the power supply Smile

I have done that in the past to remove interference caused by 555 timers and other oscillators in high gain amplifiers (gain>1000) which were all on the same power supply.

Rolbista · Joined: Nov 17, 2012 Posts: 23 Location: Poland

ok, i'll try that, one more thing, I'm currently using a switching transistor with an LED for a rate indicator, but could i just put an LED in parallel with whatever i'm modulating with the LFO? stick it on the output?

*EDIT* would it be a good idea to ground all the unused pins?

hedefalk · Joined: Aug 29, 2017 Posts: 51 Location: Stockholm, Sweden

I just built this on a breadboard with a 074 and was going to move it over to something more permanent. I noticed that I have

Sine Vpp: 11.8
Square Vpp: 22
Triangle Vpp: 7

1) Do you think there's anything wrong in my build with those numbers?

2) If not, I'm thinking I could probably use my last opamp from the quad package… What's your recommendation as far as usability goes? My intuition would be to maybe double up the triangle since this is the lowest Vpp now? But maybe it's more important to have a strong sine? I'm super noob at actually trying to y doing anything with the synth so haven't got a clue on what is important yet Smile

hedefalk · Joined: Aug 29, 2017 Posts: 51 Location: Stockholm, Sweden

One more thing, the schematic has a 100nF timing cap. I'm thinking I'll use a STDP switch with two caps for range selection for kicks. I'm thinking 104 and 103, is that reasonable? Tried the 103 and got a little bit higher in the audio range which might be useful. Or should I rather extend range in low end with a electrolyte?