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Thread: Have schematic, help me smooth this Krank out

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    Have schematic, help me smooth this Krank out

    http://guitaramps.ru/Schematic/Krank...%20channel.gif

    It has a real bad buzzy distortion for a lead channel. I'd really like to keep the amp, because the clean is amazing. Anyone have any experience that could help me out here? Thanks in advance.

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    Old Timer Gtr_tech's Avatar
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    How do you mean "bad, buzzy"....too much high end? Try an EQ pedal in the fx loop. Its really just a jazzed up JCM800 front end. Mods here are real shaky ground because we don't know what sound you're going for, what guitar(s) you use, what p-ups, what spkrs, etc. I can't read some of the values on the schem you posted. Is there a larger version?
    The farmer takes a wife, the barber takes a pole....

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    Old Timer Gtr_tech's Avatar
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    I went to the site the schem was hosted at. There are 2 different versions there. One has the "envelope" control, which is just a gain control after the second stage. The other has no "envelope", but has the "sweep" control, which is a variable slope resistor for the tone stack. Which one do you have?
    The farmer takes a wife, the barber takes a pole....

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    I'm not so sure that schem is all there. The eq stack is legged off the cathode instead of the anode and it's missing the sweep pot. After an hour of rechecking this one looks to be more accurate, though the component numbering is off. I am comparing schems of some of my favorites, ENGL, Marshall, Peavey. Seems the cathode resistor and bypass cap are what's changing here. Is that gonna be sufficient? I'm for sure gonna have to change the caps in the tone stack. I like 47n bass, 47n mids, and 270p treble.

    I'd really like a way less obtrusive upper mid range. The gain character for this puppy is square-wave buzz. I'd like to hear something between ENGL, Mesa and a Peavey JSX.

    I know cathode resistors and bypass caps set the cut-off frequency, are they really that fundamental to the gain structure? I'm trying to wrap my head around tube amps for the first time, haha.

    A pattern I'm seeing is somewhere around 1.5K for the resistor and 22u for the bypass cap.

    Short version of desired tone: YouTube - SYLOSIS - After Lifeless Years

    Guitars:
    Jackson RR3: EMG 81-85
    Jackson RR1: SD Blackouts

    Speakers: G12T-75s always and forever(might grab some WGS versions just cuz later on)

    Oh, I tried my whole rack in the effects loop. Helps very very little. The base tone is just bad. Too many odd-order harmonics? I tried a tube swap(every single one) checked the bias. I even stuck my quad of 1976 GE 6L6s in it. Turd polishing. I gotta change it or eBay this animal. I can't believe it's sitting and I'm playing the Bugera 333XL instead. The trannies in the Krank are great, plus it has a Hammond choke. It has potential.
    Attached Thumbnails Attached Thumbnails krank-rev1-pre.gif  

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    Oh and I really enjoy this high-gain sound: YouTube - ELUVEITIE - Inis Mona

    I'm sorry that I like folk metal. I can't help it. It's the hurdy-gurdy that get me goin.

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    Old Timer J M Fahey's Avatar
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    As properly stated above, both channels mentioned are straight ripoffs of Marshalls, and should not be buzzier than the original ones ... if used as intended, driving a tubed power amp, preferably at high volume.
    Now, if you use them as pedals, getting into a typical guitar amp input, or even worse, going straight into a mixer or a PC sound board, yes, they will be buzzier than a wasp's nest.

  7. #7
    Old Timer Gtr_tech's Avatar
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    Every component has a say in the end result, not just cathode resistors. The resistor sets the gain of the stage, the bypass cap boosts gain above a certain freq (set by that cap). The std Fender 1.5k/22u combination is pretty much an even gain boost across the usable freq range. Thats fine for clean channels. Cascade 3 of those and its gonna be a mudslide. The reason designers use smaller value bypass caps is to cause a low end rolloff (yours uses .47u). Smaller value coupling caps also raise the pass freq going into the next stage. You don't want too much low end happenin' in a 3 stage or more front end because it gets muddy and unfocused in a hurry. Now that doesn't mean its gonna sound thin....the harmonics that get generated will still have plenty of low freq content once it hits the tone stack. You can remove high end there (think of it as rounding the corners off a square wave) and change the wave shape. The effect is more dramatic with active EQ. Same as in an analog synth. Dial an oscillator to a square wave.....sounds reedy and thin right? With the filter set to no resonance, bring down the cutoff freq. Now it sounds big and meaty....cause you're changing the shape....its not a square wave anymore.

    I hesitate to make any suggestions other than an EQ pedal in the loop with the highs brought down and a slight mid bump. Maybe a clean boost in front could be to your liking. For that generic metal tone in the youtube video...there's no shortage of pedals that can do that in front of just about any tube amp with a clean channel. What you have I wouldn't classify as a metal amp anyway.....
    The farmer takes a wife, the barber takes a pole....

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    The gain knob on the drive channel does this: Clean, very excellent crunch, crap. What would you do differently than than guitar-->amp-->effects loop(mutli unit)-->power amp-->Marshall 1960a 4x12 cab

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    Tell that to Krank. They freakin market it as one. Andy Sneap kisses Krank ass all day. I bought it for $600 thinking I'd just fine-tune it at home. No sir. Sounds bad. Did try a clean boost pedal and a tube-screamer type circuit in front.

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    Old Timer Gtr_tech's Avatar
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    A 3 stage pre is only gonna get ya so far into metal territory....if your idea of metal is 80s Priest. ANd even if a "famous player" uses said model of amp...who knows what he puts in front of it or in the loop....or if its even stock. I'll make this one suggestion.....if yours is the model that has a 10k cathode resistor for the second stage (JCM800 value), try a 2.7k in place of it. That'll bump up the gain significantly. If its too bright still, add a 470p cap to gnd after the second stage coupling cap. A .001u will dump more highs/high mids to gnd if need be.
    The farmer takes a wife, the barber takes a pole....

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    Thanks man. I really appreciate the explanations. I'm gonna try some lower values in the cathode resistors starting with the second stage, as you suggested. Plenty of metal amp schematics are pointing at this as well, but I didn't know the interaction I was playing with. A lot of high-gain amps I really like are similar in design to the Krank. They rip heads off, but this one is ugly sounding at the moment. She does look sexy naked, though. All on the bench waiting for me.

    P.S. That "famous player" would be Michael Amott of Arch Enemy, who used SD JB and 59 pickups, into a SD pickup booster and a Wah, into a Krank Revolution, G-major in the loop for the best live tone I'd ever heard. I've been trying to get Krank to agree to a "Michael Amott Mod", but they're not in the mood to admit his wasn't stock. A sad truth for me.

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    WTF is up with the placement of R24 between the 4th stage cathode/grid? Either that is a mistake, intentionally wrong scheamtic drawing or just a really bad idea. If that is how it is actually wired, then the cathode and grid of the 4th stage will be at the same potential, i.e., biased at 0V. Yeah, that will sound like crap if you hit it hard. I will assume it was an intentional "mistake" and that resistor actually goes to ground. Can you verify in your amp if that is the case?

    I agree that this design should sound fine. I would prefer to see lower values of cathode caps on the first two stages (if it was my amp). 2.7k to 4.7 k on the early stages always sounds too crunchy to my likin. I would also suggest that you add a 100k-220k grid stopper resistor right before both the 2nd & 3rd grids. That will help smooth things out. Since there are HF bypass caps around the 470k series resistors before the 2nd and 3rd triodes, the preceding plate is effectively directly coupled (high AC frequencies only) to the following grid. I find that in hi gain designs that is usually not a good idea. When you get into heavily overdriving the grids funny things start to happen, like input impedance reducing. The preceding plates like to be decoupled from that mess by an isolating resistor. Those two simple resistors could make a world of difference when the gain knob is turned from around 8 up to 10.

  13. #13
    Old Timer J M Fahey's Avatar
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    Good suggestions, should be tried.
    That R24 drawing *might* be an error, certainly grounding its lower end would provide for a more "normal" gain stage, which would clip almost symmetrically, but as-is will work too, only distorting earlier and providing a very unsymmetrical wave.
    Anyway I feel closer to the mistaken drawing theory.

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    No doubt it would work. It would just sound U-G-L-Y. I'm sure they did it to protect their "original" design from all of us out here who are constantly ripping off all of their amp design ideas. Thank goodness Marshall didn't do the same thing; Krank may not have been able to "design" their other models.

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    Wow. I just got home. The resistor we refer to as R24 does indeed go to ground. I guess I'm gonna just hold off on this until the weekend, see if anyone else chimes in. Thank you for the advice so far.

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    I just listened to one of the YouTube clips you posted. To me that sounds a lot like a SLO/Dual Rectifier type amp rather than this one. It's a big thick sound but a little mushy. The schematic you have should produce something with a little more tightness, definition and upper harmonics. I actually modded a friends 1970's twin reverb to have almost this exact circuit about 10 years ago, right down to the sweep control on the tone stack (I preferred a more Fender-like tone stack though). The thing is a gain monster, but not anything like the clip I listened to. It has very fluid, singing distortion, not really what I would call crunchy (like the SYLOSIS clip). On that amp I had all 100k plate resistors and the cathodes, in order, were 1.5K, 2.2k, 3.3k, 3.3k (?). Not sure about the last one. I think I may have used a 1.5K there as well (maybe even bypassed) to help lower the output impedance of the tube so that it would work better with the tone controls. The first cathode was permanently bypasses and I had a "boost" switch through a relay switching in bypass caps for the 2nd & 3rd stages. Since the layout was not optimal, I had to use a good number of small pF caps all around the 2nd, 3rd & 4th stages to kill parasitics.

    If you want a more crunchy sound out of this thing then you might want to get rid of some of the high end. Get rid of the 470pF bypass cap between stages 2 & 3. Try different values of caps around the 2nd & 3rd stage to reduce some of the upper distortion harmonics. To me, they tend to add a "fluidness" to the sound (that I like) but they really take away from the fundamental "grunt". You could bypass the plate resistor, put a cap form plate to cathode, grid to cathode, grid to ground, plate to ground, plate to grid, even plate to plate. Try anything for 100pF up to about .0047 uF. It's really a "season to taste" kind of mod. I would suggest using multiple small caps rather than just one or two larger caps.

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    Why multiple small caps over the larger?

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    Personal preference really. My experience has been that one large cap can "solve" tone or oscillation issues fine but to me it impacts the tone in a way that I don't care for. I think it tends to take away from the inherent character of the channel. In other words, one large cap can solve the hi gain issues but affects the tone negatively at lower gain settings. Adding smaller caps in multiple places typically keeps the knee of the low pass filter at a higher frequency. To my ears, that allows the channel to "breathe" better (do you like all of these finite scientific terms I'm using?).

    To use an analogy, you can take a dent out of metal with a large hammer and a flat surface but you will likely cause other problems. If you use a small hammer and metal block (what are those called, I can't remember?) you can remove the dent in far better detail and get it closer to the original shape.

    I know it has been done thousands of times with one or two large caps but when I'm building a hi gain amp for myself I never can get the tone I'm after taking that approach. Some folks may like it just fine.

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    Well that makes sense. I typically apply a high-pass filter in the loop. 40 hz and down gets deleted. I feel palm mutes are much more effective without those frequencies. I like a lot of upper harmonics, so I think I'm gonna leave that bit alone. I just wanted to get that theory of yours understood. =)

    So I still have some work ahead of me getting that schematic relabeled. I've located and renumbered the 1st and 2nd stage cathode resistors and bypass caps. I have traced a bit more on the grid side of things, but the rest is yet to come. It's a 3 layer board, so I have the flashlight out making use of the transparency available, haha. The clean channel on the schematic is all 100%. The overdrive schem, from what I've mad out so far, has all the correct component values, but the reference numbers are all way off. I really need to get this traced and labeled correctly so I can do this mod correctly. That is, learn everything I can instead of swapping parts based on suggestions where I don't even know the whole reasoning. I love the info you guys are putting out.

    So to recap what I've learned here:

    The circuitry into the grid affects how the triode is being hit.
    The cathode resistor sets the gain for that triode.
    The cathode bypass capacitor is an EQ filter for that triode.

    Correct me if I'm absorbing this wrong.
    What is happening plate-side of things?

  20. #20
    Old Timer Gtr_tech's Avatar
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    Quote Originally Posted by JacksonRR View Post
    So to recap what I've learned here:

    The circuitry into the grid affects how the triode is being hit.
    The cathode resistor sets the gain for that triode.
    The cathode bypass capacitor is an EQ filter for that triode.

    Correct me if I'm absorbing this wrong.
    What is happening plate-side of things?
    All but the bypass cap. Its not acting as a filter per se. When you use a bypass cap on a K circuit, it boosts gain. How far down the freq range that boost gets applied to is determined by the value of the cap. Higher value, boost down to a lower range. Thats why your has the lower values....to *not* boost gain at freq's that will cause flubby low end response by trying to push too much low end thru the cascaded gain stages.

    Read all about it here:
    http://www.freewebs.com/valvewizard1...Gain_Stage.pdf
    The farmer takes a wife, the barber takes a pole....

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    That's good stuff. I've read that before once. It makes more sense this pass through. A lot of what was mentioned was applying to my current problem. I'm gonna bookmark it and give it another read in a week. I think I can handle this hobby. =)

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    Well I replaced the first two cathode resistors with 1.5K and 2.2K. Took out the 470pf bypass cap on the second stage. Replaced with a 22u. I'm gonna play it out a few days and see what this configuration is made of and then maybe move onto that grid stopper resistor mentioned earlier. I have noticed an increase in distortion earlier and the flavor is more to my liking. Thanks guys. You guys want before/after/and after that clips? I did do a small recording of it stock so I can knock a few little riffs for each change to the circuit.

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    Sure. Before and after clips would be great.

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    Traded for a 5150 today. Headache's gone. Screw it. Returned to stock and Craigslisted it. Ultimate Krank Mod: trade it

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