Flashing LED without altering effect?

[mr_sooty]

I have a Danelectro Cool Cat Vibe - fantastic sounding Univibe type pedal, covers all my phase/vibe needs for bugger all money.

I modded it as per these instructions:
www.diystompboxes.com/smfforum/index.php?topic=70874.20

I wanted the LED to reflect the intensity as well as the speed. I found I could acheive that by connecting the LED to pin 2 of the intensity conrtol instead of the speed one. I still get both speed and intensity adjustments reflected in the LED.

Only thing is, having the LED there reduces the intensity of the effect slightly. I also found that if you do it as per these instructions - connecting it to the speed knob - it reduces the top speed.

Is there something I can do to get the LED response I'm after without affecting the effect inensity? I'm imagining a diode or a resistor between the pot and the LED?

Cheers.

[newey]

Mr. Sooty-

Good to hear from you, it's been a while! Welcome back.

I don't have an answer to your question, unfortunately. We'll have to let someone more knowledgeable weigh in on this. But it is a cool mod nonetheless.

[ashcatlt]

Yeah sooty, you may get better answers faster over at diystompboxes. It's a bit over my head, and tough to say anything for sure without a schematic.

My gut says that any simple passive solution will be a compromise. I'm thinking you're gonna have to either tweak the LFO circuit to compensate for whatever the LED is doing, or maybe hack in a carefully designed buffer circuit.

[JohnH]

Hi sooty - I agree that a buffer is whats needed, so it has a high impedance input and does not load the point you connect to. Without a schematic, and the unit to test, its hard to know exactly what however.

If you want to persue that, the first thing that I would do if I was you, would be to disconnect from that pin 2 spot, and try to measure the voltage swings (relative to ground) at that point, up and down, as you adjust the controls. Then a buffer can be designed to make an LED react to those ranges.

John

[mr_sooty]

Yeah sorry I haven't been around. Has to do with the fact that A: I'm really happy with my rig so haven't needed to change much, and B: I'm getting much better at this electronics stuff, and don't need as much help as I used to.

Having said that, it sounds like I might be getting in over my head on this one. I don't have any idea how to make a buffer, and I'm not sure the problem is bad enough to warrant the effort.

[ashcatlt]

It would really only be a transistor and a couplefew resistors (maybe a cap?). JohnH will probably have to help you with that. I have some mental block when it comes to transistors. I just don't get it. I could probably help with an opamp based solution, but that'd be overkill.

[mr_sooty]

Yeah, seriously it's fine how it is to be honest. I just thought if I could overcome this incredibly minor issue very simply I would, but sounds like it's gonna be more hassle than it's worth - it's really not worth any hassle at all, the mods fix the things that were really bugging me about the pedal (mainly the long wait for effect to kick in after you hit the switch), so it's allllll goood. Thanks for your replies.

[sumgai]

sooty,

The LED is a load on an audio circuit. Yeah, you didn't hook it up to the signal path, but indeed, the LFO that causes the fluctuations is in the audio range. Like, Low Frequency Oscillator, ya dig. This is also why an external buffer won't help the situation any.

So anyways, the LFO is designed to run at a certain load, and adding the LED is upsetting the circuit's performance. Obviously not a lot, but equally obviously, enough to be noticed. What can be done? Not easy. Tweaking is the order of the day, but where to tweak, that's the $64 question. Tell ya what.... If you have a diagram, post the thing, and I'll take a gander at it and see if I can come up with something for ya.

HTH



sumgai