1 X 12AX7 killer stompbox schems needed

[Colas LeGrippa]

In fact, I have already built it, cool unit, clean overdrive, not noisy at all. The problem is that I crave heavy metal sound and this unit suffers from a lack of..nice distortion. I just can't understand how to chieve a GOOD distorted tone. I have been swapping cathode caps and resistors, from 820 to 15K and from .68 to 330uF  without good results. The max voltage I got at the plates is 120V.

Help.........!

Colas

[chocopower]

Can you post a schematic?

I have a vintage Guyatone TO-2 with a 12AX7 inside and REAL tube voltages with a nice "tubescreamer" sound.
that schematic is like mine, but without tonestack (mine have bass-treble controls)
http://www.freeinfosociety.com/electronics/schemview.php?id=985

[sluckey]

Do a google search for "The Real Mctube". Maybe that will work for you.

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

[terminalgs]

google 'matchless hotbox'  and look at those schematics.   If you are familiar with the fulltone OCD,  the matchless hotbox is that area of distortion. 

also,, if you are looking for a tube version of a 'fuzzface' or a 'boss metal zone' pedal,  its not going to happen with a single tube (or 2 for that matter).

[RicharD]

Notice in the schematic sluckey posted how frigid the bias is.  Hi gain, low current.  Traditional Fender values won't do what you want it to do.

[Colas LeGrippa]

Hi ! First, thanks for your replies.. I do not have any schems of the stompbox I have built  since it so simple to imagine and to build, I did not take the time to draw a so stupid thing...( stupid but hard to tweak..hey hey ). I looked at the real mctube and the plate resistors values seem very high ( maybe i should experiment with extra-ordinary values............). The other one, posted by Chocopower looks very interesting........one question, Mr Chocopower : what is the purpose of the 2 diodes ( 1n914 if I remember well) from the last coupling cap back to the first cathode ? They are fast switching diodes and I just can't figure out what they're doing there.

Best regards

Colas LeGrippa

[sluckey]

The diodes clip the positive and negative peaks on the signal, and that kinda squares up the signal. A square wave is full of harmonics and sounds very distorted/fuzzy. Many commercial distortion units use the back to back diodes.

[Colas LeGrippa]

cool ! I"ll do the mod with the diodes and get back later when it's done with the results !

thanks for the explanations

Colas

[terminalgs]

cool ! I"ll do the mod with the diodes and get back later when it's done with the results !

thanks for the explanations

Colas

for more reading on clipper circuits:

http://www.allaboutcircuits.com/vol_3/chpt_3/6.html

note that the DC voltage on the cathode of V1 plays a part in where the AC  signal is clipped.

[Ritchie200]

One that I've built several of is the PAIA Stack-in-a-Box.  It uses 1 12AX7 and starves the plates.  Lots more stuff going on in there with some really nice features.  Effects loop, filter switches, xlr out.  I think it sounds really nice, shimmer to grind.  Uses a couple of 5532 opamps to keep things quiet.  Nice rack mount too.  Probably cheaper to buy the kit than to piece it out.  I actually built one of these into a Firefly that I built for a guy, turned out really cool.

Kit
http://www.paia.com/proddetail.asp?prod=9210K
Schematic
http://www.paia.com/prodimages/siabsch.pdf

Jim

[Colas LeGrippa]

Thanks to all !

Colas LeGrippa