Mutron led and sweep

[twofootskunk]

I've been tinkering with a mutron iii build (madbean nautilus) recently, trying to get a sweep that sounds like recordings I've heard.
I made several of my own 1 led/2 ldr vactrols to test, matched ldrs, and the caps/resistors in the filter section.

When the pedal is set to LP and Up sweep, should I expect the LED to be completely off when no input signal is present?  Right now it's lit all the time and will just get somewhat brighter with the attack of the strumming.

I have Rx as a trimmer and there is a very specific spot where I get an ok sweep.  It just doesn't "womp" as much as I'd like.

[Mustachio]

Try one of these with a 8-10K resistor in RX

http://www.mouser.com/ProductDetail/Lumex/SSL-LX433GD/?qs=sGAEpiMZZMs4quMj8r4lmjaw8B5qKY8aX7D4mSD%252b5KI%3d

Or if your using a clear high bright or something similar try some where around 120K for RX. There's a ton of threads here discussing different options for the ldr/led set up in the mutron 3.

Good luck!

[twofootskunk]

Thanks for the link on the LED. I have a ton to try plus other LDRs also.

Currently I'm using a yellow water clear LED (2000-3000 mcd) The wavelength is really close to the peak wavelength of the LDRs.  Those are the waitrony ke-10720.  All epoxied in heat shrink with the ends capped with liquid electrical tape.

I've probably read every thread on this forum and the Internet about the ldr/led for the mutron!!

I guess I was just surprised that the led starts in a lit state and just gets brighter.
For some reason I had it in my head that it would be off and come on with the envelope. The down mode starts with the led  bright and sweeps to completely off.

I do get a decent sweep and it sounds ok. I'm just trying to make it better.

It's like the filter is sweeping up ok but just doesn't sweep back down as far or fast as i think it should. Which is why I was asking about the led being lit with no input.   I'll go back and re measure the max/min resistance of the ldr when it sweeps.  I wonder with the LED staying lit if the max dark resistance just isn't high enough.

[digi2t]

Here is thread on my clone of the Foxx Guitar Synth, which is an overblown Mutron III; http://www.diystompboxes.com/smfforum/index.php?topic=95016.0

I used a super bright white LED for my Vactrol. The build thread is here; http://www.diystompboxes.com/smfforum/index.php?topic=95269.0

Hope there's some info in there that might help you out.

Cheers,
Dino

[twofootskunk]

Ok let me approach this a different way.  Bear with me as I'm pretty much new to all this stuff. Please correct me if I misunderstand.

Assume we are in the up sweep mode.
If you look at the neutron schematic. U3A drives the LED. Correct?

1. If I wanted to get the LED to be completely off with no input signal, can I just increase R16 until it goes off?
2. What about R17? That's a feedback loop right? Does it act as a voltage divider with R16 for the - input of U3A?
3. Does anyone have a link that could help me understand how the basic op amp is controlled?


What I want to try is to get the LED actually off with no signal, then come on with the attack, and then go all the way back off with the end of the decay.  And then set Rx to limit the brightness/min ldr resistance.