Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on November 23, 2011, 05:28:23 pm
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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
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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 (http://www.freeinfosociety.com/electronics/schemview.php?id=985)
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Do a google search for "The Real Mctube". Maybe that will work for you.
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm (http://www.dogstar.dantimax.dk/tubestuf/mctube.htm)
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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).
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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.
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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
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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.
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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
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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 (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.
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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 (http://www.paia.com/proddetail.asp?prod=9210K)
Schematic
http://www.paia.com/prodimages/siabsch.pdf (http://www.paia.com/prodimages/siabsch.pdf)
Jim
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Thanks to all !
Colas LeGrippa