Have schematic, help me smooth this Krank out

[cbarrow7625]

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.

[JacksonRR]

Why multiple small caps over the larger?

[cbarrow7625]

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.

[JacksonRR]

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?

[Gtr_tech]

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

[JacksonRR]

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. =)

[JacksonRR]

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.

[cbarrow7625]

Sure. Before and after clips would be great.

[JacksonRR]

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