mismatched clipping diodes in series

[seedlings]

http://www.diystompboxes.com/smfforum/index.php?topic=107560.0

Regarding the above thread, and specifically this image



What happens when a 1N4148 and red LED are in series?  Would the knee look like the 1N4148 for the first few fractions of a volt, then the LED for the next few fractions, or would the result look like one or the other curve?

CHAD

[R.G.]

What happens when a 1N4148 and red LED are in series?  Would the knee look like the 1N4148 for the first few fractions of a volt, then the LED for the next few fractions, or would the result look like one or the other curve?

When things are in series, they conduct literally the same current at the same time. So the knee, and all other parts of a series diode curve look like the sum of the two voltages for every current value.

[seedlings]

Excellent.  Thanks!  I keep forgetting there are laws that govern electronics... but on a positive note, I'm also not in the running for any engineering positions. 

Now back to EQing.

CHAD

[GibsonGM]

It would be neat to see the comparison between 1/2 cycles for a 4148 vs. LED, in parallel, scaled and moved so you can see the traces at the same time! 

[digi2t]

It would be neat to see the comparison between 1/2 cycles for a 4148 vs. LED, in parallel, scaled and moved so you can see the traces at the same time! 

Being a visual creature myself, I concur.

I seem to be on a diode run right now, cramming my brain box with info about clipping, and clamping.

[GibsonGM]

If I get time this weekend, maybe I'll take a run at that.   Could put each diode on a scope channel and offset one enough to run them one over the other, a couple diff. frequencies, take a pic or 2.    Might be an interesting study (assymetrical clipping). 

LOL, my FIL is all about diodes now, too, since i showed him how to save his "snap switches" (train relays) by using a clamping diode across them.  He was burning them out, didn't know about that back voltage.  Diodes are wonderful things 

[karbomusic]

Might be an interesting study

It is, it's how I choose my diode switching options. In some switched configs I have it set so that one position is all odd harmonics and the other the even ones automagically pop in. 3 1N34As in series in parallel with two 1N914 that are already in parallel is a combo I found using the scope except I wasn't comparing individuals but different combinations. Point being I was using harmonic structure as my visual guide.

[seedlings]

Might be an interesting study

It is, it's how I choose my diode switching options. In some switched configs I have it set so that one position is all odd harmonics and the other the even ones automagically pop in. 3 1N34As in series in parallel with two 1N914 that are already in parallel is a combo I found using the scope except I wasn't comparing individuals but different combinations. Point being I was using harmonic structure as my visual guide.

Are the 1n914 back to back or same direction?

CHAD

[antonis]

It is, it's how I choose my diode switching options. In some switched configs I have it set so that one position is all odd harmonics and the other the even ones automagically pop in. 3 1N34As in series in parallel with two 1N914 that are already in parallel is a combo I found using the scope except I wasn't comparing individuals but different combinations. Point being I was using harmonic structure as my visual guide.

Are the 1n914 back to back or same direction?
CHAD
[/quote]

I think that same diodes in parallel with same direction shouldn't have any benefit...
(except of current sharing..)

[anotherjim]

Doesn't an LED have a relatively high capacitance though? So maybe the plain diode in series will act first, but only at high frequencies. Whether or not those high frequencies are within the 6Khz or so of the guitar bandwidth to notice is something I don't know.

[karbomusic]

Might be an interesting study

It is, it's how I choose my diode switching options. In some switched configs I have it set so that one position is all odd harmonics and the other the even ones automagically pop in. 3 1N34As in series in parallel with two 1N914 that are already in parallel is a combo I found using the scope except I wasn't comparing individuals but different combinations. Point being I was using harmonic structure as my visual guide.

Are the 1n914 back to back or same direction?

CHAD

Back to back so think of your normal diodes in a feedback loop (aka tube screamer) than strap 3 1N34as across that same loop. I hope that's the one if memory serves, if not I'll go back and confirm that that should be right. It brings the even harmonics back in at 50-60%, again via memory. Will post a pic later.

[GibsonGM]

Might be an interesting study

It is, it's how I choose my diode switching options. In some switched configs I have it set so that one position is all odd harmonics and the other the even ones automagically pop in. 3 1N34As in series in parallel with two 1N914 that are already in parallel is a combo I found using the scope except I wasn't comparing individuals but different combinations. Point being I was using harmonic structure as my visual guide.

Nice, that's one to look at!

[anotherjim]

I checked, an LED is only about 50pF, so it's not going to have much effect.

[karbomusic]

Apologies for the sloppy screenshots and alignment.... I'm sure it would be the same with a single extra diode but the germs required three to keep from losing too much gain (but in this case I wanted to lose just a tad) yada, yada, asymmetrical etc. The fun was the harmonic structure changes.

2*1N914



2*1N914 + 3*1n34A

[seedlings]

That is very impressive harmonics!  I'm about to assemble a 3-in-1 drive and this technique will be employed.

CHAD