Joe's Vulcan diode compression

[will]

Hi,

I’m quite intrigued with the Vulcan diode compression idea. I was wondering if an ideal candidate would to use it in front of a Mosfet booster as it can provide lots of clean gain and use virtually no bias current.  I also wonder if a germanium or schottky diode would give greater compression in a Vulcan type circuit with less gain loss.

I have lots of questions:
Would stacking diodes increase compression?
Is this providing asymmetrical compression?
When will the circuit start rectifying ½ of the waveform?
What is the ideal load the diodes need to work in this fashion?
Can you dial in the ideal compression by changing the load with a pot?

I wonder if one can build an orange squeezer type clone with say 10 parts. I'm thinking I could probably retrofit some current effects.

Comments?

Regards,
Will

[Gary]

Will,

Don't worry about gain loss.  There is plenty in the Vulcan.

[WGTP]

Gary, don't stop there, what else.  

[will]

Will,

Don't worry about gain loss.  There is plenty in the Vulcan.

Hi Gary,

I was not really concerned about the gain loss in the Vulcan. I was more thinking out loud about alternate configurations. What came to mind was vulcanizing the AMZ Mosfet booster and the Peppermill circuits. The Vulcan mod can be simply bypassed with a switch.

Based on Marco's review I want to give it a try.

Regards,
Will

[Marcos - Munky]

Yeah, try it. Maybe a cool distortion (like the Obsidian . Joe's effects rocks!!!) will sound very good with this mod, and with a switch you can turn the mod off. Yeah, sounds interesting.

[Joe Davisson]

Some remarks about the diode compression:

-Diode must be forward-biased at a tiny current level. Therefore, two-resistor biasing must be used.
-Diode can be anything: Si, Ge, or BJT/JFET/MOSFET configured as a diode.
-Circuit must be NPN when using discrete diodes. PNP devices configured as diodes may work, but I haven't tested it.
-Compression is on positive input peaks, but I have no test equipment to work with besides the "oscilliscope in my head".
-A signal can go directly to the transistor input, or the diode input, without switching out the diode. So switching the effect in/out is a snap. Both could also be used simultaneously.

I have not tested any of Will's ideas, but I think they are interesting. The whole thing is a bit of a hack, which I'll try to explain.

When a diode is reversed-biased, the P-N depletion zone is "thick", which blocks electricity. When it's forward-biased, it's "thin". So the trick is to forward-bias the diode with as little current as possible, and then let the input signal reverse-bias the diode slightly with each input peak. This is how stronger peaks are resisted by the diode.

The drawback is gain loss, which is why I think it works best with high-gain BJTs. MOSFETs should work, but the difference in sound may not be as apparent as with the BJT, in which case the difference is dramatic.

It "should" work with opamps, or even tubes, but I haven't tested that either. Something to try, for sure...

[Kleber AG]

What about using it on Silicon Fuzz Face circuit? To lower down the gain and maybe smoth/compress the tone???
That would be cool!

Thanks for sharing Joe!!!
Kleber AG

[jrc4558]

Wow-how-how...
That IS a very interesting research field!

[WGTP]

Hmmmmm.  I'm thinking the mosfet Obsidian with the BS250's looks primed for diode insertion.