A question about Mark Hammers Chaos

Gilles C · June 05, 2006, 08:30:35 PM

I finished wiring the circuit today, and I just tested it with a signal generator to check if it was working well.

It does, but I found that while one LED is getting bright enough with a signal, the other one isn't getting very bright. Enough that it wouldn't look good as eyes.

So I was wondering if those who built it had the same result, or if the 2 LEDs are both getting equally bright enough.

For those with a fast internet connection, he is a video showing how it looks with a strong signal while I was varying the level of the input signal. I had to sature one of the LEDs to see the oher one light.

http://www.gtechblues.com/images/MVI_0965.AVI

Thanks,

Gilles

markm · June 05, 2006, 09:24:16 PM

That does look cool though!

Gilles C · June 05, 2006, 09:30:14 PM

I had to turn the light off for the video, but I agree that it looks cool. Enough that I really want to see those LEDs flash now...

That's why I was wondering how they normally light.

I may have to add a circuit just for the LEDs if they are not getting bright enough.

Gilles

Mark Hammer · June 06, 2006, 10:22:23 AM

That's because the first clipping section uses asymmetrical clipping, so the ceiling for one half cycle is higher than for the other. So, when you amplify and clip again, with LEDs, one LED is seeing a higher amplitude waveform than the other.

Here's an experiment. Turn the gain down for the first stage, and turn it up higher for the second stage. If there is no clipping for the first stage then there should be equivalent lighting of the two LEDs in the second stage.

That's one of the more interesting things about the circuit, is that it changes from more to less asymmetry as the gain is increased.

Gilles C · June 06, 2006, 12:19:10 PM

I had a flash about this detail after my post late last evening and shorted one of the 2 LEDs on that 2 LEDs side to see if it would change something. And the result was the same.The same LED was still brighter than the other one.

I will also try taking out the diodes on the first stage as you suggest.

The other thing I want to check is the DC level at the LEDs. I'll keep working on it this evening at work.

I could also try to put some LEDs from the output to ground as someone did.

Gilles

Mark Hammer · June 06, 2006, 02:53:03 PM

Well here is the $500 question: will any two red LEDs of the same "class" shine equally brightly with the same applied voltage? My meter lets me easily measure voltage drop in Ge and Si diodes, but with LEDs it gets tricky so I am flying blind here. Are they as variable as Si and Ge diodes? Are they uniform in how they translate voltage/current into light?

tungngruv · June 06, 2006, 03:09:18 PM

I built Marks "Chaos" using Paul Marrosy's layout. I perfed it with no part subs (If I remember right) and both LED's were shining about the same. I used 5mm Red LED's from Radio Shack. Maybe you could remove one of the 1N914's in the first stage, I don't think the tone change would be that different? Your pedal really does look great, using Marks Chaos for the circuit will make it sound as great as it looks!

Gilles C · June 06, 2006, 03:46:32 PM

Well Mark, the first thing I did was to change the weaker LED. It's the first thing that came to my mind. Now you make me wonder if I should change have the strong LED instead...

I also have a meter that checks the diodes voltage. I'll start with that to make sure of that detail.

Then I'll see what happens if I take the diodes of the first stage out. Then I'll go from there. I could connect 2 LEDs back-to-back in series with a resistance and plug that to a signal generator.

Tungngruv, thanks for the comments. And if yours shines equally, it means I have something not correct. I'll keep working on it.

I'm building it for the look more than for the sound (even if I still have to try it with a guitar..., who knows, I might even like it). So that's why the LEDs have to work well.

Gilles

tungngruv · June 06, 2006, 04:59:26 PM

Hey Gilles, first off, you can just remove 1 diode from the first stage, leaving two to clip. I doubt you'll hear much of a difference, if at all. Second, I actually like the way your eyes are lighting right now. They look more "alive". What a cool looking pedal!!!

Gilles C · June 06, 2006, 05:54:52 PM

LOL... When my wife saw the video, she named the skull "crosseyed"... She said it was a gentle skull

So at worst, I could leave it like that. You've got a good point. A positive one.

I'll work on it later today until I make up my mind. Btw, I just bought some new LEDs for another test. I'll see what comes out of that.

I already shorted one of the diodes in the first stage, so I know it's not because of that.

Gilles

goosonique · June 07, 2006, 05:52:54 AM

if it sounds good...what the heck...
my built

didn't have that crosseyed ...oh my goodness it's really starting to crack me up now...iam sorry but its so funny....oh my goodness this is the best laugh i have had for months....really ...thanks for that video....my tummy hurts...man i just cant stop....

tungngruv · June 07, 2006, 10:40:22 AM

Hey Gilles, after looking at my Chaos pic I posted on your first Chaos thread, both eyes are equally bright, but I notice in the pic I have the gain maxed out. Did you try that?

Gilles C · June 07, 2006, 03:51:33 PM

Quote from: goosonique on June 07, 2006, 05:52:54 AM
if it sounds good...what the heck...
my built didn't have that crosseyed ...oh my goodness it's really starting to crack me up now...iam sorry but its so funny....oh my goodness this is the best laugh i have had for months....really ...thanks for that video....my tummy hurts...man i just cant stop....

Glad you had a good laugh...

I was too busy "at work" yesterday to work on the Chaos board. But as you said, if it sounds good once I try a few things, I'll keep it that way.

tungngruv, I did tried that without success. The brighter one gets red while the other one changes.

Added: Ok, here is an update. I checked with my meter, and the brighter one had a different reading than the other ones. There was a 0.1V difference in their forward voltage. So I chose two that had the same forward voltage reading, and they are now equally bright. The brighter one being the one that was different, they are now both... dimmer.

My mistake is that I was so sure it was the weak one that was not correct that I didn't think of changing the brighter also. A mistake, and a deception...

Even after that, I am surprised that such a little variation made such a difference

Thanks for the support guys,

Gilles

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A question about Mark Hammers Chaos