Suggestions for Clipping Diode

[toddvirgil]

I'm putting together a PCB that will allow me to dial in various clipping options in a typical symmetrical or asymmetrical clipping path. Also thinking about offering this as a project for sale to the community when I get it done.

I'm hoping you guys can throw some diode suggestions out there... I'm thinking about having 10 different positions for each diode in the path.

1n34a, bat 41, bat 46, etc....

Thanks!

Todd

[GibsonGM]

How about different MOSFETs? Like 2N7000.....you can clip with BJT's, FETs....LEDs are awesome...

In my opinion, you won't find too many variations between diodes in the same family....less difference the harder you clip...Si vs. Ge you will notice, but less within each category. 

http://beavisaudio.com/bboard/projects/bbp_DiodeMods.pdf

[nate77]

+1. Diodes offer some clipping variance, but for up to 10 selections,  mosfets and fets would a great additions as you will get a lot of repetition unsung only diodes. LEDs, shottke, Ge, Si, etc have unique-ish characteristics, but even some of my first builds with the new standard of an on/off/on switch for clipping in OD and distortion circuits, there is not enough variation to make it terribly noticeable sometimes. This does sound interesting and something that would be received well. Good luck!!

[toddvirgil]

Thanks Fellas! Yeah, sorry if i didn't make it super clear -- didn't mean only diodes. I plan on having a couple positions for LEDs and transistors. Mainly I'm wondering what the favorites of everybody are... what are your "go-to"s?

T

[GibsonGM]

2N7000 mosfet is well-acclaimed.   I really like these odd green, flat LEDs I got in a pack at Rat Shack 15 years ago!  The Vf is 2.2v.   I also dig both red and yellow 5mm LEDs.

All you can really do is experiment, Todd.     Just out of practicality, you might get some '7000's, a few J201's, some 2N5457.....bunch of standard LEDs, some Schottky diodes.....try them out, and you win because you'll also use them to build other projects!  )
Might help to scan thru a bunch of project schematics at GGG and Runoffgroove or something, and see what parts are commonly in use....

[midwayfair]

Why's everyone suggesting FETs? When they're used as diodes, aren't they just a generic silicon diode? 

[amptramp]

Use an active clamp like the one on page 17, lower left corner of this app note:

http://www.ti.com/ww/en/bobpease/assets/AN-31.pdf

This uses the old LM301.  If you are using something more modern like a TL07X, omit the 30 pF capacitor and D2 but the output will slew to the opposite rail when it is not clamped.  Vref is the clamping voltage.  You can take the junction of the D1 anode and the inverting input and add resistance between it and the input resistor.  This effectively gives you a zener diode to ground that has a programmable voltage and you can add resistance as per the previous sentence to give a variable diode resistance.  Without this resistance, you go from effectively open circuit to clamped at the reference voltage within less than a millivolt, so you get very sharp clipping.  This works well with a diode to ground type of clipper like the ones in a DOD250.  It doesn't work in a Tube Screamer.  Use another op amp and diode with reversed polarity reference voltage and diode to get negative clamping.  You could design a clipping stage with independent positive and negative clipping voltages and resistances this way.  Four variable pots give you all possible combinations.

[GibsonGM]

Why's everyone suggesting FETs? When they're used as diodes, aren't they just a generic silicon diode? 

For the most part, yup, but you may find the forward voltages vary more than the typical .5V of a Si. I said "might".  You have to tell him SOMETHING to experiment with, lol!!

For me, I will either grab Ge, Si, or an LED for ALL clipping projects. I'm not very open-minded to 'how other things sound', having tried them a few times and found NO audible difference.   Only those three clippers to much for me by showing any difference between them. But that's just me, YMMV.

Internal capacitance differences don't do much for me, either.  We're talking dog freq's here, a matter of a few pF or 10's of pF - I can't hear anything vary when subbing different things in.  The differences ARE there, but can you hear them? I can't.   I'm more inclined to DIY the external capacitance, add 100's of pF and affect what is audible.   

Again, YMMV, I am more brute-force with clipping, I feel tone shaping pre and post clipping has MUCH more effect.    But the way one might determine that is by experimenting with lots of clippers, which is an awesome learning experience.

A good project might be switching in/out 10 different TONE caps pre AND post clipping, to see what sounds you can come up with...some simple circuits, even active mid boost/cut....that would be something.

[Gus]

Have you done a search? 
This has been posted about over the years
People often wire the diodes etc. to a rotary switch

asymmetrical DIODE or devices as diodes clipping never sounds that good to me.

There is a IMO better idea but you might need to search some threads

[nate77]

Guitar Mike has a good point. The caps on a switch has more of a noticeable and usable difference in my experience. Clipping diodes offer some variance but time caps will alter much more of the signal than the diodes. In most of my builds that I have slipping switches, I usually find what I like best and it stays there. Now combining these two ideas would be killer......and a bit of wire.

[GibsonGM]

Maybe something like: 
- no alteration
- some high cut (variable with a pot?)
- mid scoop
- mid boost

Just thinking out loud...like a "tone decade box" kind of thing! 

[DDD]

1N5817 Shottky (or SS12 SMD-version) produce very soft sound but with less output level and less overall gain.

[tca]

Instead of using different diodes you could do a diode function generator (look for analog computers schematics). I've played with DFG's and it can give good results.

[blackieNYC]

I came upon a few Ge transistors with gains in the single digits. I found them in a box with a curve tracer that had t been opened in 20 years or more so I'm sure they are someone's rejects from god knows what. Disappointing.   I was thinking they are probably only good for clipping diodes so I e started doing that. Single junction.  .2 volts or so. Probably sounds like a Ge diode, but inconveniently larger.  Maybe you've got a couple.  Maybe they're full of Mojo.