Obsidian X Vulcan = Hybrid Vigor?

[WGTP]

Joe Davidson is the MAN.  Thanks Again for the great circuits  

I'm sitting here with one of each breadboarded and sitting on my SS PV practice amp thinking it doesn't get much better than this (playing my new Gibson Les Paul Melody Maker that I bought 1/2 price at Guitar Center)  

I noticed when Joe came back with his new site that it wouldn't take much to make an Obsidian into a Mosfet Vulcan.  So like the neo-mad scientist I aspire to be I mixed them.  The Vulcan sounds great and the Obsidian sounded a little mild by comparison (imagine that).  It seems to want 5.1K resistors rather than the 3.9K in the scheme to bias around 4.5V but all I had was 4.7K which got into the low 5V range with the batch of BS250's that Vishay kindly sent me.  I also took out the 10K resistors between stages and just used the coupling caps (forgive me Joe).   :twisted:

When I inserted the diodes into the Obsidian (with the 4.7K bias resistors) it dropped the bias voltage right around 4.5V and got that nice Vulcan sort of squishy distortion sound.

The cool part is you could use a 3 pole switch and by-pass the diodes and have a plain Obsidian.  With the BS250's instead of 2N5089 though the Vulcanized version doesn't sound a WHOLE lot different than the plan Obsidian, since they both sound good.  I haven't had a chance to compare the BJT and Mosfet Vulcan yet, but they both sound great, as in one of my top 3.  

[Lonestarjohnny]

WG, what pickup's do the new Melody Maker's come with ?, I got 2- 60's model's, one with single coils, the other has been modded for P-100's and it has great Rock or Slide tone,
I'll have to do build on Joe's pedal in the Fuiture, Sound's very interesting,
JD

[WGTP]

Mine has a P-90 in it with the standard tune-o-matic bridge.  I got the vintage yellow one.  Plays nice.  I have a '60's model I hacked up that has a Seymour Duncan Full Shred and Badd Ass bridge.  I guess t's my favorite guitar.  Nice fat neck.

I highly recommend Joe's pedals.  I usually have to mod the by-pass caps to something lower.  I think Joe uses a single coil for his "voicing" and usually use something Fatter.  If you like distortion, you need to try a Vulcan.    :twisted:

[Gringo]

How low do you go when lowering the coupling caps? i have built some of joe's designs and they are always too bassy for my rig too. I'm still tweaking them and i'd like to know your experiences.

[Lonestarjohnny]

I was just playin my M/Maker last night with the Thunderchief and my Ol PV, talkin bout some HonkyTonk Women, with a light wieght slide and cranked on about 4 I was shakin the tree's outside, LOL !
My P-100's were on the money for that kind a stuff.
I gotta try a build on the Vulcan from hearing all the compliment's Joe get's from all the guy's that have built it. maybe next week I'll get time, I just got in a new batch of tranny's and diode's so I won't be put'in it off much longer, and I'll keep in mind what you said about the EQ
JD

[WGTP]

For the Vulcan I'm using a 1uf or 2.2uf for stage 1 and 10uf's for the 2nd and 3rd stage.  I also didn't use the cap between stage 1 and 2 that is parallel with the resistor

For the Obsidian, I'm using 2.2uf, 4.7uf and 10uf.

I like the first stage with the least bass.  It seems to smooth things out.  

The less bass the smoother they get, but then you have less bass, so it is a compromise.  That's why some of the guys are using a bass boost after the distortion.  

Comments Joe???

 :twisted:

[WGTP]

Got a lesson in bias and battery voltage.  I was using an old battery that was down to 8v. but the voltage at the drain was higher than the voltage with a new 10v.  Must have something to do with the resistance in the battery.

With the low voltage, I like the regular Obsidian better than the Vulcanized one.  It is tighter and crisper.  With the new high voltage battery, it was the other way around.  The Obsidian was brighter and harder.  Vulcanizing softens the distortion sort of like a low batter does.

I keep thinking someone is goint to say the Vulcanizing doesn't work on the Obsidian and I'm imagining the whole thing.  Sort of like the op amp debates.  Still haven't compared the mosfet Vulcan to the BJT, but the BJT had butt loads of gain and had more noise.  The Obsidian is very quiet.  I don't want to build 3 new pedals.  Just the one I like bestest.

:twisted:  

[Joe Davisson]

My whole system is dark sounding, with HS3's in the guitar and a pretty bassy Fender combo. So maybe I don't notice as much difference with input caps as I should. I do notice a lot with bypass caps, but usually keep them all the same value, for no real reason though.

Noise in the Vulcan comes from the diodes, which act as RF detectors. Gadgets like space heaters, etc, really screw with it. Shielding the diodes reduces the noise significantly. Perhaps some special low-noise diodes would help?

R.G. Keen has also pointed out many times that reverse-biasing a transistor even once screws up the noise performance. I've tested this myself and the difference is startling.  It's easy to do this when tinkering around, so you listen to your uncle R.G. and don't reverse-bias them transistors!

-Joe

[WGTP]

Well, now I have gone over the edge.  I modded my Obsidian thusly:

First stage stock with 4.5uf bypass cap

Second stage Vulcanized with 10uf bypass cap

Third stage Black Fire with 10uf bypass cap

All mosfet.  Had to work on the BF stage to get it to bias correctly.  Using 47k resistor instead of 15K.  

What can I say???   :twisted:   Added a .0047uf to ground at the end to reduce the treble and smooth it out, but it doesn't need much.  Great grind, sustain, detail, clarity, Magnificant.  Grace bestowed on a tone seeking guitarist.  "Sitting on a Rainbow high above the world."  

Breadboards are wonderfull.  I can mix up whatever I can dream up.

Next up Obsidian stage, BJT Vulcan stage (either mirror image or 2N5087)
Black Fire or whatever sequence.    Joe was talking about a Jfet Vulcan???

Turn my guitar into a newage device.  Who needs tubes??? Maybe Live.

The laundry closed it emitting the tones of the Godz. :shock:

[WGTP]

Now I have Vulcanized a Black Fire Stage.  Next a Fuzz Face.  Hmmm a BMP might work.  Joe, this is all your doing.  Thanks.

Live Long and (Rock) Prosper   :twisted:

[David]

You're going to "Vulcanize" a Fuzz Face?

That is not logical...   :lol:  :lol:

...  but I want to see it!!   :mrgreen:

[WGTP]

Hey Joe, I finally listened to the individual stages of the BS250 obsidian/vulcan/black fire hybrid and I'm not sure the diode compression mod does a whole lot.  It seems to reduce the gain a little, but the resulting distortion isn't that much different.  I'm thinking either it doesn't work with mosfets, or the the mosfets already sound that way.  I would think that might be true for jfets as well.  It still seemed to soften and smooth the distortion as a whole, but maybe I imagined it.  

[Joe Davisson]

The diode trick doesn't really work on P-channel (or PNP) transistors. The MOSFETs already operate at a slower speed so the diode won't do much anyhow. I would say just use it on Bipolars and JFETs. A J201 Vulcan setup goes something like this:

100k drain
33k source/1uF bypass
10M/1M biasing, with diode between as in Vulcan

The larger values increase the gain to more usable levels, so three should still be enough. Might need a small .1uF cap across power supply in places to curb the JFETs desire to freak out. Have fun...

-Joe