Indicator LED current draw

macumbista · Posted: Sun Oct 04, 2009 3:17 am Post subject: Indicator LED current draw

Is there any rule of thumb or estimates of how much current draw it takes to audibly change a VCO frequency in a system? I put some UltraBright LEDs in my SuperPsycho LFO and you can definitely hear them in the VCOs!!!!

The current draw for each UltraBright is approx 20 mA, and Tom Bugs recommends using a 4k7 limiting resistor with the low current ones he has for 2.5 mA draw. That's a big difference. But if you add up 10 low current ones, will I still hear them in the VCOs?

I guess it depends on the PSU and what else is in the rack I suppose, but I'd like to know how many LEDs you can get away with. Most EuroRack systems seem to have dozens running off the same PSU, while other systems (like Buchla) have dedicated power lines for digital stuff and LEDs.

Besides reducing current (or putting as separate power rail for the LEDs), what else can you do? Put some big caps on the power rails?

best!
D.

slacker · Posted: Sun Oct 04, 2009 5:49 am Post subject:

I haven't got any experience of this in synths but you get similar issues with guitar effects pedals. What I do is use super bright or ultrabright LEDs , if you run these at 20 - 30 milliamps you could use them as a torch they're so bright Smile

For indicators in pedals and in my Lunetta I run them with anything up to about a 50k resistor this gets the current draw down to somewhere between a 10th and 100th of a milliamp.
Depending on your voltages you could probably go up to 100k or so and they would still be bright enough.