Hi,
I'm trying to add some funky 4 color LEDs (auto change colors every second or so) to a small guitar amlifier that I built. The problem is that when I connect the LEDs (and required resistor) to my amp circuit the LEDs make a really nasty humming sound, even when the volume is all the way down. The humming increases and decreases when the color changes occur. Is there any way I could attach these LEDs and eliminate the noise?
Any help would be greatly appreciated!
Many thanks!
N
I'm trying to add some funky 4 color LEDs (auto change colors every second or so) to a small guitar amlifier that I built. The problem is that when I connect the LEDs (and required resistor) to my amp circuit the LEDs make a really nasty humming sound, even when the volume is all the way down. The humming increases and decreases when the color changes occur. Is there any way I could attach these LEDs and eliminate the noise?
Any help would be greatly appreciated!
Many thanks!
N
what kind of amp have u got? a solid state or a tube-amp?
and to wich voltage supply have u connected the LED and R?
and to wich voltage supply have u connected the LED and R?
The amp I have is a 20W portable solid state amp with a rechargeable battery. The volume control is also the on/off switch which carries 12V DC to the circuit. I have tried connecting the LEDs and R to everywhere I can think of, but the bottom line is that I have to use the switching circuit to turn them on and off along with the amp.
Do not put LEDs in your signal path!
Do you want the LEDs to blink in time with the music? Use a capacitor (to select frequency response) and a transistor. We used to build these "color organs" all the time in high school, except we used SCRs and 120VAC lights.
Wes
Do you want the LEDs to blink in time with the music? Use a capacitor (to select frequency response) and a transistor. We used to build these "color organs" all the time in high school, except we used SCRs and 120VAC lights.
Wes
There's a strong possibility that the noise is from ambient light- LEDs make lousy photodetectors. Try shielding them from light (black tape or whatever) an see if the hum goes away. if it does, you may not have a fix, but at least you know the cause.
First off, I'm not putting the LEDs in the signal path. The volume control has a built in switch that has nothing to do with the signal. The switch is seperate from the connections for volume. The connections that I am using are solely for power to the circuit and have nothing to do with the signal path.
Secondly, I have tried blocking ambient light, and..... no dice. The hum is still there, and, as I said, it comes and goes with the fade in and out of the color changes. The LEDs switch from red-green-blue-yellow. This makes a very cool effect behind the clear control panel..... if I can get it to work.
Thanks,
N
Secondly, I have tried blocking ambient light, and..... no dice. The hum is still there, and, as I said, it comes and goes with the fade in and out of the color changes. The LEDs switch from red-green-blue-yellow. This makes a very cool effect behind the clear control panel..... if I can get it to work.
Thanks,
N
try running the LED, in it's intended physical location, but off of a seperate supply/battery with no connection to the guitar amp circuit and then see if it makes noise.
Can you draw a quick sketch of what you've done here? It's possible that the LEDs are in the signal path but not in an obvious way (e.g., grounding).
Using a seperate battery to power the LEDs eliminates the noise completely, but this does not help me because I wanted to use the internal battery that also powers the amp to power the LEDs. Adding a seperate battery just for the LEDs would be way too much of a hassle just to get it to light up.
I've attached a very basic drawing of what I am doing to give you a better idea of what is going on here. The grounds are all tied together and terminate at the battery.
Thanks,
N
I've attached a very basic drawing of what I am doing to give you a better idea of what is going on here. The grounds are all tied together and terminate at the battery.
Thanks,
N
Attachments
The diagram does not show where the grounds go. You might be injecting noise from the LED (the mulicolor LEDs, the blinking ones, and the kind that don't need resistors (current source LEDs) have electronics inside them which might make noise, espeically when they "fade" from one color to annother, since LEDs work more efficiently when you pulse them on and off at full power rather than reducing the power level) into the ground. Try moving the ground of the LED to somewhere else, prefereably as far away from the input jack and preamp grounding circuitry as possible. Try to connect it to somewhere around the battery.
Are you using a PWM circuit to achieve the fade-in/fade-out of the LEDs? (I'll bet you are) This can cause lots of noise on your supply rails. Since you don't have an AC power source, the easy/obvious answer is gone.
Have you tried snubbing the circuit leg that the LEDs are on? A small film cap (100pf) and an electrolytic (220uF) in parallel across your supply leads, right before the LED circuit might reduce the noise. And maybe a resistor (1K?) in series with the caps.
BTW, I'm just pulling those values out of thin air. But I think it's worth a shot.
Wes
Have you tried snubbing the circuit leg that the LEDs are on? A small film cap (100pf) and an electrolytic (220uF) in parallel across your supply leads, right before the LED circuit might reduce the noise. And maybe a resistor (1K?) in series with the caps.
BTW, I'm just pulling those values out of thin air. But I think it's worth a shot.
Wes
PS -- if your LED circuit *IS* PWM, maybe the Class D guys have a ready solution.. They would encounter that problem with their switching transistors.
Wes
Wes
All the grounds go straight to the battery. I think you hit it on the head when you mentioned the problem with multi-color LEDs. The electronics within the LEDs is definately what is causing the noise.
I have moved the LED ground to everywhere I can think, including straight to the battery, and still no luck. What I need is some sort of filtering circuit that I can use in order to isolate the noise (if possible). I have gone as far as connecting the LEDs & R directly to the battery and still no luck.
I have tried the caps, but the only success I have had was when I increased the value of the cap across the supply leads to upwards of 2200uF. The small film cap and resistor did not do anything so I gave up on that idea.
What is causing the color changes? Some type of circuit inside the led? Maybe it overcomes the rev brkdn of the led? Try adding a regular non led diode in series behind the led and maybe in front of it to see if the noise goes away. That is if you have not tried this already.
Yes, the LEDs have some circuitry built in that makes them blink.
But, you guys have come through yet again! I have combined the things I have tried together with your suggestions, and have finally eliminated the noise.
Although I had previously tried adding diodes before and after the LEDs, with no success, adding the larger 2200uF cap across the source, combined with the diodes before/aft did the trick. The noise has been completely eliminated. If I remove any of these components, the noise returns.
Thanks again to all of you! You have saved me a lot of aggravation and hair pulling! You guys ROCK!!!
Thanks,
N
I know exactly what kind of LED he's talking about. It's looks like a normal clear or a large clear LED, and you connect it to some voltage between X and Y volts (decent range) without a resistor and it does the rest. If you look inside, you'll see three LED dies, red, green, and blue, all connected to a 4th die which is a controller IC that's implanted into the LED. They cycle through some kind of program of flashing/fading. They use PWM to dim the LEDs for fades (you can see it if you try hard enough).
If you have a cheap blinking pen or Rave wand or something, it's just one of those LEDs with some batteries. They're pretty neat and easy to use.
If you have a cheap blinking pen or Rave wand or something, it's just one of those LEDs with some batteries. They're pretty neat and easy to use.
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