Hello,
I've been trying to use a 555-based oscillator from this schematic: http://www.555-timer-circuits.com/up-down-fading-led.html ...
for the purpose of using the output as an LFO to modulate the filter and pitch of a synthesizer. I am using an NE555 and a 2N3904 transistor for Q1. Even though this circuit is intended to drive LEDs, I thought I would use it for this because it is so simple, and because I liked the shape of the waveform it outputs and the wide range of rates I could get by using a pot for R1.
When I first made the circuit, I could slow it down almost indefinitely by increasing R1. But it suddenly stopped working correctly for reasons that I don't understand. Now, the moment I turn up the resistance of the pot I am using for R1 past about 25K Ω, the oscillation will sort of "freeze" and the voltage at pin 3 will hold steady. If I turn the pot a tiny bit in either direction, the circuit will continue to progress through the cycle of the oscillator for a fraction of a second, and then freeze again.
I had made three more of this circuit a few months ago and had been powering them together on the same 9V adapter. I didn't realize it until just now but all three of those have the same problem, even though they started out working OK as well.
I tried switching out both the capacitor and the 555 chip on the one I just made, but to no avail. I haven't tried switching out the transistor yet, but before I do, I figured I would ask if anyone could explain why this would happen. Did I somehow destroy the transistor? Is there a problem with using the 2N3904 transistor specifically? I figured any general purpose NPN would be OK.
One thing I might mention: this may have started happening at the same time that I put in decoupling capacitors (100 uf and .1 uf in parallel across power and ground) so I could run the new 555 oscillator off the same power adapter as the synth. When I noticed the problem, the first thing I did was take the decoupling capacitors back out. Could they have irrevocably damaged something though?
Thanks in advance for your advice.
I've been trying to use a 555-based oscillator from this schematic: http://www.555-timer-circuits.com/up-down-fading-led.html ...
for the purpose of using the output as an LFO to modulate the filter and pitch of a synthesizer. I am using an NE555 and a 2N3904 transistor for Q1. Even though this circuit is intended to drive LEDs, I thought I would use it for this because it is so simple, and because I liked the shape of the waveform it outputs and the wide range of rates I could get by using a pot for R1.
When I first made the circuit, I could slow it down almost indefinitely by increasing R1. But it suddenly stopped working correctly for reasons that I don't understand. Now, the moment I turn up the resistance of the pot I am using for R1 past about 25K Ω, the oscillation will sort of "freeze" and the voltage at pin 3 will hold steady. If I turn the pot a tiny bit in either direction, the circuit will continue to progress through the cycle of the oscillator for a fraction of a second, and then freeze again.
I had made three more of this circuit a few months ago and had been powering them together on the same 9V adapter. I didn't realize it until just now but all three of those have the same problem, even though they started out working OK as well.
I tried switching out both the capacitor and the 555 chip on the one I just made, but to no avail. I haven't tried switching out the transistor yet, but before I do, I figured I would ask if anyone could explain why this would happen. Did I somehow destroy the transistor? Is there a problem with using the 2N3904 transistor specifically? I figured any general purpose NPN would be OK.
One thing I might mention: this may have started happening at the same time that I put in decoupling capacitors (100 uf and .1 uf in parallel across power and ground) so I could run the new 555 oscillator off the same power adapter as the synth. When I noticed the problem, the first thing I did was take the decoupling capacitors back out. Could they have irrevocably damaged something though?
Thanks in advance for your advice.