Can guru's help?? Looking for a tube-like clip diode.

[GrantsV]

Hello thanks for reading,

I have found the impressive looking diode which has a "Forward current vs. recovery time" response just like a tube!

http://www.fairchildsemi.com/ds/IS/ISL9R8120P2.pdf

Unfortunately this diode is rated for high current amps (like 8 amps). I require a diode with these characteristics as a replacement for 1N4001/Germanium 1N34A or standard 3mm LED (used as diode).

Does anyone know of a diode that has these same charactistics that are suitable for my low current requirements?

I am looking for a new type of diode (smooth transition/soft recovery) for the valve like clipping.

Thank you for your help,
GrantsV

 

[ilimzn]

Probably one of the small shottky diodes, BAT 42?

 

[GrantsV]

Thank you! I have looked at the spec sheet and this does look promising:

http://www.farnell.com/datasheets/45257.pdf

Forgive my ignorance, but these shottky diodes are all new to me coming from the land of traditional SI, GE and LED's as clipping diodes!

Are these a cousin of silicon diodes?

 

[darkfenriz]

Building guitar distortion?

 

[ilimzn]

Forgive my ignorance, but these shottky diodes are all new to me... Are these a cousin of silicon diodes?

Yes and no. Unlike 'regular' semiconductor diodes, where the junction is formed between P and N doped semiconductor, in Schottky diodes, it is formed between semiconductor (usually silicon) and metal. Because the metal region has negligible minority carriers in comparison with majority, these diodes have lower threshold voltages (close to Ge), but do not have a recovery time in the same sense regular PN diodes do, so they are very fast.

 

[GrantsV]

Thank you for the explanation.

Yes I am building guitar distortion but am unhappy with GE diodes (they have a nice soft recovery, but are too distorted being only 0.3v). LED's have a much better crunchy breakup at their clip range of 1v+, but they have a horrible harsh un-tubelike recovery. This means that with LED's I get solidstate fizz when the note dies off to clean.

I am looking for a non-guitar mainstream diode for a tube like breakup.

Thank you again for your help,
GrantsV

 

[darkfenriz]

So why not put GE and LED/SI in series?

 

[GrantsV]

Hello,

Could you please explain how chaining a GE and LED in series would work?

I understand that the forward voltages are added together, this results in a forward voltage of diode1+diode2 required to clip so chaining GE and LED would reduce my distortion and increase headroom.

But which diode would clip when that clip voltage is reached? Both together, or the lowest voltage diode first?

Thanks for your help,
GrantsV

PS. I like the compression and soft "turn on" characteristics of GE when gain is low, but I want to then have the crunch of LED's when the gain is raised up past just a subtle breakup point.

 

[wes-ninja250]

Any chance you could re-work the circuit to use an LED + phototransistor instead?

I don't know what it would sound like, but it would at least be a neat experiment.

Wes

 

[darkfenriz]

Hi
LED with GE in series will have GE-like soft turn-on. When they both clip their on-resistances add on. LED's on resistance is low, GE on-resistance dominates.

I like the compression and soft "turn on" characteristics of GE when gain is low, but I want to then have the crunch of LED's when the gain is raised up past just a subtle breakup point.

Everything depends on the circuit you use them in. Is it simple resistor-diode voltage divider?
If so, you could give four or five GE diodes (1n34?) in series to have soft cliping at 1.2-1.7V and this chain parallel with one LED (1.8-2.2V hard clipping).
Anyway this can be lots of experiment and fun.
Resistor-diode ladders may also play nice. This way you could tailor virtually any usable distortion curve, symetric or asymetric by changing values of resistors.

 

[GrantsV]

Wow! Thank you for your response. That is a real eye opener. The soldering iron is going to be busy this weekend!

Just a query though, I thought that when you parallel diodes the one with the lower threshold is the only one that will turn on. Therefore if I parallel a LED with a chain of GE's, if the GE's have lower clip voltage then the LED, the LED will never turn on anyway?

Best regards,
GrantsV

 

[darkfenriz]

Hi

I thought that when you parallel diodes the one with the lower threshold is the only one that will turn on. Therefore if I parallel a LED with a chain of GE's, if the GE's have lower clip voltage then the LED, the LED will never turn on anyway?

Basically you are right, but I think GE's have high enough on-resistance (soft clip) to raise voltage drop on them (english??) so that a LED can turn on.

regards

 

[rodriki]

Hi

I have the same question as you.
Led and diodes give the harsh sound when notes are fading.

One solution i found was having more HEADROOM.

Using zener in series (one inverted in relation with other -|<-->|- ) in the feedback of inverter op amp input i got the best distortion for op amp.

Using 18v source and 4.7v zener. One of the zeners can be diferent voltage to get even harmonics.

The idea was used by some patents and stephan moeller vox ac30 sim not anymore available.

Some boost in front of circuit may be necessary.

Look for ideas at soft clipping at google.

Aron forum and site has a lot of solutions.

But the site is unavailable for the moment.

Lets keep studying.

Rodrigo

 

[Alex Frias]

I saw part of this kind of clipping with zeners and it's really interesting soundwise.

A combination of 4.7 and 5.6 zeners in anti-series through the negative loop at the OpAmp is pretty usable. I will try it in my Vox Pathfinder. I added a pair of 1N34A to the clipping LED's at the output of the gain stage and it worked fine. But not that great yet...

 

[Tekko]

Tube like chip diode, sounds like you mean the MELF package.