Vulcan Mod

[WGTP]

If your using this, or one of Joe Davidson's other 2 or 3 stage distortions, replace the resistor, 220K in the Vulcan, before the last stage with a pair of inverted GE diodes and tell me what you think.  

[pyrotek]

WGTP,

Can you post an illustration of it, i'm not sure if i got it you right. Is it a pair of inverted GE diodes is the same as a pair of GE clipping diodes? It is just before the diode connected on the base of 2N5089?

[WGTP]

I think they are called in line diodes and they replace the resistor in the signal path arranged opposite each other for clipping purposes.  Previous discussions indicated that it creates "crossover" distortion similar to that of a push pull tube output stage IIRC.  I think it works inside out compared to the other diode clipping methods, clipping the smallest signals the most???  Please correct me if I'm mistaken.

The Boss Heavy Metal, as well as clones, use this arrangement, in addition to the loop and grounding method.  

[pyrotek]

Ok, got it, now i know... :idea: I'll try it on my Vulcan. Be back with the result. Thanks WGTP

[pyrotek]

WGTP,

I've tried it and it kick ass!!! High Gain Heavy Metal Distortion!!! I can easily produce pick harmonics almost anywhere on the fretboard. Vulcan with a little bit of BOSS Heavy Metal distortion character.

[WGTP]

I'm glad you tried it and that is exactly the conclusion I came too.  Seems to add to the compression and grind, plus reduce the mids some.  

It could easily be made switchable with the 220k resistor.  

Now I will have to try it with a BlackFire and Obsidian.  

[ragtime8922]

I don't see a 220k resistor on the Vulcan. Since this can be done for all of Joe's works of art can you explain which resistor this is exactly?

[Samuel]

the inline resistor before the last stage is a 470k, is this the one you mean?

[WGTP]

Whoops, looks like the newest one posted has a 470K between stages instead of the 220K.

It's at the connection between stage 2 and 3.  A 470K would probably be even better for switching with the diodes (greater variation).  

I think they let more signal thru than the 220K resistor does, but it may just sound that way because of the extra distortion.  

I have a Jfet stage1 and then 2 regular stages.   :twisted:

[ragtime8922]

WGTP, I feel stupid because I have to ask for clarification on this because the words "in-line" and "clipping diodes" are conflicting in my brain. Are these two diodes in parallel facing opposite directions like the traditional "diodes to ground shunt" (but not to gnd in this case) or something else?

[ragtime8922]

WGTP said: [/quote]I have a Jfet stage1 and then 2 regular stages.

Where did you get that schematic? Where can I get it? Does your mod sound a lot different with that schematic?

[ragtime8922]

Sorry WGTP, I messed up the above post but you know who said what, right?...lol.

[WGTP]

Yes it is the 470K in the signal path between stage 2 and 3.  The "in-line" diodes are as you said, directly in the signal path, not in the feedback loop, or going to ground.  This is like a 3rd way to use diodes to clip the signal.  It is not used much, but has been discussed at times around here.   :wink:

The Boss Heavy Metal Petal and some of it's clones use it in addition to the 2 standard diode clipping methods.   :twisted:

This sounds silly, but the first time I tried it with a distortion, I thought I smelled that hot tubes and vinyl smell that Fender amps put off. :shock:

R.G. explained that it was called "crossover" distortion and worked differently than the other 2 methods.  Might do a search for In-Line Diodes.

The Jfet Vulcan is on Joe's site and what I essentially did was use that for the first stage.  I used a 47K resistor instead of 33K.    It probably has higher input impedance and acts more tubular.   :roll:

[pyrotek]

I'll build the JFET version of VULCAN and try adding the in-line diodes.

I noticed that your version of the JFET Vulcan doesn't have a (470k) resistor before the last stage and Joe used a combination of 100pF/2.2M instead of 470pF/470k.

Maybe i'll try using 33k and 47k resistor or even a trimpot and try your suggestion instead of J201 i'll use J202, it is easier for me to get J202s than J201s.

[WGTP]

I haven't looked thru Joe's latest posted schematics, but it appears their are some changes.  Looks like the Jfet version may be "smoothed" some.

I'm also using J202's, but J201's work as well.  

[bwanasonic]

R.G. explained that it was called "crossover" distortion and worked differently than the other 2 methods.:

It's interesting that you like this sound if it is indeed crossover distortion. IINM - Crossover is widely considered an unwanted form of distortion in tube amps. It's normally something you are trying to minimize when you bias an AB tube amp. Not sure this is the same thing. Don't think I've ever heard of someone liking crossover distortion in an amp. Interesting.

Kerry M

[WGTP]

IIRC most class AB amps have this type of distortion, so it is present in some of the most famous of tube output stages.

I'm not sure it would sound good on it's own, but mixing it in with the other distortions seems to have some desirable characteristics.

When I have tried it at the end of the distortion chain, I haven't cared for it as much.  

In this application, as we said, it seems to add more compression and grind to a circuit that is already pretty compressed, but smooth.  

Some may not care for it, but I have wondered how much of the sound the Boss Pedal gets comes from this.    

[GVC]

Hello,

I know I am bringing up an old topic , but I have a stupid question.  using Marty's layout are we talking about R11?

http://aronnelson.com/gallery/Martys-layouts-and-photos/Vulcan3?full=1

[MartyMart]

Yes, that looks like the right resistor.
Tell me what you think of the circuit/layout
MM.

[GVC]

I will try to Perf Board it this weekend!