Valvecaster without tone pot

cnspedalbuilder · March 07, 2017, 07:21:10 PM

At the risk of being booed out of the forum, I have yet another question.

I've blown two LEDs that were on the switch for this circuit. I think maybe it's the 12V input. I have a 1.8k resistor for the LED which I thought would've been good enough. I'm not sure, maybe there was a short in both cases.

Any suggestions for resistor values for, say, a 3mm blue LED? I don't know the forward voltage or current otherwise I'd use a calculator. Values I popped in based on some google searches (3-4 volts, 25mA) gave pretty low resistor values (less than 1 k) so maybe that's not the problem?

bluebunny · March 08, 2017, 03:31:21 AM

The "pretty low" resistor value you get from these calculators is a minimum, below which your LED might be expected to fry. But that's not the same as saying you need this value of resistor for it to be visible. Far from it: you'll likely find such a value will zorch your retina and cause commercial aircraft to land in your back garden. Try a couple of (higher) values on a breadboard.

cnspedalbuilder · March 08, 2017, 01:20:27 PM

@bluebunny, true but in this case I don't mind blinding intensity because I'm putting the LED in the tube socket so that it will illuminate the tube. Also, it's a 3mm LED so the intensity isn't that bad. But for some reason I seem to have blown two so far. In both cases, the LEDs worked but then went out after a few days.

If a 1.8k resistor value isn't bad, then maybe it's a wiring issue?

GibsonGM · March 08, 2017, 01:38:08 PM

That is VERY odd. It should be ok with 1.8K. Are you SURE the resistor is the correct value? Can the legs of the LED short out against anything?

bluebunny · March 08, 2017, 03:02:19 PM

Where's your 12V coming from? A regulated supply, or somewhere a little more rock'n'roll?

cnspedalbuilder · March 09, 2017, 06:10:28 PM

Quote from: bluebunny on March 08, 2017, 03:02:19 PM
Where's your 12V coming from? A regulated supply, or somewhere a little more rock'n'roll?

I'm thinking of a million AC/DC lines right now...

It's coming from a regulated power supply.

Quote from: GibsonGM on March 08, 2017, 01:38:08 PM
That is VERY odd. It should be ok with 1.8K. Are you SURE the resistor is the correct value? Can the legs of the LED short out against anything?

That is my guess. I heat shrinked the last couple, but there were some exposed parts.

I'm using a 3pdt daughterboard and I wonder if another possibility is that the resistor isn't soldered in well. But I'm guessing if that happened then I would not get anything from the LED right?

GibsonGM · March 09, 2017, 06:19:31 PM

Yeah, you really shouldn't....anything bypassing the resistor would be considered a short. I haven't heard of an LED failing when it's getting the correct voltage and current for its operation. Shorting has to be the simple solution!

cnspedalbuilder · March 11, 2017, 01:53:11 PM

Well everyone has been so helpful, I thought I should share the finished product. Not nearly as neat as anyone on this forum, but it's the neatest I've been able to do, so that's something. Thanks for all the tips. Let's hope it holds up for the gig tonight!

cnspedalbuilder · March 11, 2017, 01:55:38 PM

By the way, it sounds great when driven by another pedal like a Rat. I will likely just keep it last in my distortion chain so that it's either just pushing the tube amp alone, or it's adding a massive gain stage when stacked with a Klone, Rat, or Harmonic Percolator.

rutabaga bob · March 11, 2017, 02:03:15 PM

Very nice - and it has that blue glow mojo!

GibsonGM · March 11, 2017, 02:57:57 PM

That came out really nice! Enjoy it! Have a good gig.

News:

Valvecaster without tone pot