Here's the deal, I designed a Tremolo, based on a PIC programmed mostly like ElectricDruid's Tap Tempo LFO and using a LM13700 VCA (Ray Wilson's Music From Outer Space VCA). I sync'ed an RGB led to the clock and apparently the led draws too much current and induces a ripple on the power lines. I thought this could be solved by using a larger capacitor, but even with 470uF it still affects, and on some settings (square wave), you can hear the 'click' when the LFO changes...
Any help? I am not at home, but I should be able to post the schematic soon.
LED blinking with LFO causes spikes on power lines
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frequencycentral
- Cap Cooler
RGB? Colour changing LED? Known to cause nasty spikes. Replace it with a red or green and you're good to go.
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PmCimini
- Breadboard Brother
It's not one of those ones that flash colors, is a 4-pin LED, mainly three LEDs in a single package. Are these also supposed to cause spikes?
Here's the schematic of the problematic part... The left line goes down to a switch, the two transistors and diode are a Millenium 2 bypass, and the section on the right is the CV (control voltage, 0~5V), and a simple inverter. The resistor values are for standard LED operation when input is 5V.
It may be also CV feedthrough on the LM13700 opamp, but I think this only started after I soldered the LED. Could bypass capacitors help in this case? Or are the frequencies too low?
Here's the schematic of the problematic part... The left line goes down to a switch, the two transistors and diode are a Millenium 2 bypass, and the section on the right is the CV (control voltage, 0~5V), and a simple inverter. The resistor values are for standard LED operation when input is 5V.
It may be also CV feedthrough on the LM13700 opamp, but I think this only started after I soldered the LED. Could bypass capacitors help in this case? Or are the frequencies too low?
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Information
- Posts: 9
- Joined: 10 Apr 2011, 20:35
- Completed builds: After 35 years of building, do we really have time for that?
- Location: Funkytown
Green, red or yellow LEDs usually have a forward voltage of around 2 volts. Blue has the highest forward voltage of around 4 volts. If the LED caused this, that is more than likely why. The imbalance between the red (which probably has a FV of 1.8-2.4 VDC) and the blue which will have a FW of around 3.8 is quite possibly the problem. For GPTS/Ss&Gs try the green and red and lose the blue. Green should be closer to the red's forward voltage. Blue LEDs have become incredibly popular, but I found that reverting back to basic red or green saves battery life, money, and gives more pedals per power supply on a large board. They had blue LEDs when I was a child of 10 blackening outlets in the house. They were very dim, and required a very dark room to be seen. Roughly 12 years ago the modern blue LED became commercially available and viable. They were >$6 each when they first came out. Red, green, blue? I could not give a crap. If I did give a crap I do have a crap list! It is currently full, and there is a waiting list. Maybe adding extra diodes, or a reistor on the blue LED might help. I think you have an imbalance in the LEDs. LFOs can really give people fits. I have a relaxation oscillator in an Estey Magnatone that starts motorboating the whole amp when things warm up. There are only 6 LFOs in that amp. A tremolo, and echo trem, and four for the panning stereo true vibrato using the SiC VDRs that shunt from low to high and right to left. Change one tiny aspect of the amp's power supply or output tubes/tranny and it is off to the races. (boat races) Preamp mods? Not so much. GPTS= General Purpose Trouble Shooting, and Ss&Gs are Sh**s and grins!