Guitar tone craziness and new DIY amp-build

After days of re-amping through countless variations of tube types, knob tweaks, bias point fiddling, speaker models, mic types/position, recording methods and volumes… I have finally chosen what will be the basic rhythm tone for the final recording. Since virtually everything in the recording chain is unique to this recording (right down to building most of it from scratch just for this record), I am going to explain it all in lengthy and painfully-vivid detail for posterity.  This post is really for the benefit of any uber-geeked out DIY amp guys or home recording folks, so sorry if it is a bit wordy and dry. If you have any questions, hit me up on my/the band’s facebook page. I’ll break it down into categories. If you just want to hear the guitar and get out of here… scroll all the way to the bottom.

THE AMP:

I have mentioned before that I designed and built up an amp just for the purpose of recording this album. After the project is over, it will be going to an old friend Ben Peterson, who will be receiving it as a backer reward for his awesome donation to our kickstarter campaign.

The design is un-orthadox, but it worked out fantastically well for what I wanted… which was something that was different than any other amp in the world, would record well, had only 3 main gain stages to maintain the ‘impact’ of power chords without sounding compressed, with a nice upper-midrange presence to make the single notes stand out without being honkey, a bit of raunch in the low end response that could be dialed in and out as needed, and a smooth ‘chalky’ quality to the mids highs that had enough rasp to cut through the mix, but was smooth enough to let the bass guitar control the texture of the mix in parts.

After much tube-swapping and trying everything I had from vintage U.S. to modern Chinese tubes, the final tube compliment ended up being: V1 (input stage) JJ ecc803 long plate to provide a nice thick lower midrange and tame the high end rasp and junk coming in, V2 (overdrive stages) vintage Mullard standard plate 12ax7 for smooth highs and complex mids, Phase inverter is Electro Harmonix 12ax7 because it is even-tempered, noise-free and clear-sounding in that slot and I didn’t want it to color the post-preamp tone too much. I have had some of those that sounded a bit wooley in the past, but this one sounded nice and clear.

As for the design, all the plate loads are active current sources to milk the most gain as possible out of 3 stages and lower the noise as much as possible. There is a follower after the first stage to prevent loading/gain loss from the high-pass “tight” control. Tone stack has a sweepable slope for various midrange options, and there is a post-tone stack follower before the phase inverter labeled ‘saturation’ that can be dialed in to provide various amounts of compression and sludge if needed. It worked better on the breadboard than in actual use, so I just found a sweet-spot and mostly left it there.

Here is an unlabeled schematic of the general preamp topology. I don’t remember the exact component values, but I have them scribbled on a hand-drawn schematic somewhere. I can’t got the life of me find the poweramp schematic, so maybe I’ll reverse-engineer my own design and post it in the future. (Safety note, there is a decoupling capacitor before the tone stack in the final design that is not on the schematic to keep high-voltage DC off the controls… there is also a capacitor at the input to make a highpass filter, and there are probably some other changes as well):

Alex Kenis heretical Solamors preamp

The phase inverter has a current sink ‘tail’ to keep it evened out and clean sounding. The output stage is either el34’s biased at 70% or 6l6’s biased at 50% depending on the section. I used the EL34’s for the lead lines where the extra ‘honk’ and tighter lows help them stand out a bit better from the rhythms. (JJ 6l6GC’s. Generally their tubes are pretty rugged, but as a word of caution, their 6L6’s… not so much. I have a bunch of them and they frequently break. I cracked one in the course of working on this amp, and I did an amp for a friend of mine Chris Keeney a while back and 2 of the 4 tubes that he sent over to use literally crumbled in my hands after I unplugged them a few times… but thier EL34’s seem to last forever).

There is a decent amount of negative feedback in the power-amp section to give the presence and resonance controls a wide range. The feedback loop is switchable, so I can turn it off to loosen up the tone and let the mids run free for solos. I added a Vox-style ‘cut’ control across the plates of the phase inverter, voiced higher than the presence control to both tame the raspiness of the presence knob when the NFB loop is switched on, as well as to act as a ‘presence cut’ for solos when it is switched out.

The power supply uses solid-state diodes and is completely regulated for low noise and consistency… but that is boring so I won’t go into details.

Here is an obligatory gut-shot. Not my cleanest build, but it works well. I don’t usually build on perfboard, but I was in a hurry and was short on lug strips. I probably won’t do it again since it leaves little room for mods and tweaking (I had breadboarded the whole thing ahead of time and tested it quite a bit so I was not so worried about that):

solamors amp gut shot

I also used a DIY solid state chip-amp poweramp (lm3886) for a few of the layered rhythms with a more midrange and low-end tone that I mix in at times to thicken up parts. The solid state amp has much higher damping than the tube amp, and much more chisled and defined low end, so that is nice to be able to bring in more thickness in the lows without the speaker farting out.

Here is a picture of the amp settings, the transformer-isolation box I built to make the ground loops behave (the thing in the Hammond box in the front right corner with the cables plugged into it), and the solid state chipamp used for some of the passes (back right corner… the chrome box with the heatsink on it):

amp settings

THE CABINET:

The cabinet is the prototype of a cabinet that I designed back in 2005 or so for ax84.com. It is just built of home depot pine and MDF mostly. I originally tuned the design to emulate more or less the response of a 4×12″ cabinet by taking T/S measurements of common speakers and using them to mess around with the internal volume and dimensions of the cabinet to get the modal reinforcement and cancellations as well as speaker excursion damping that you would typically see in a 4×12″ cabinet …but in a 1×12″ package so that you can get the speaker cone moving a bit more at a lower volume than a 4×12″ with the same amount of speaker excursion and cabinet resonance without having 3 unneeded speakers blaring away. It was a lot of experimentation, followed by a lot of math and computer modeling.

I used that as the basis for the dimensions and then did a metric crapload of trial-and-error and tweaking-by-ear. I deviated from the “sound like a 4×12” idea a bit in the end phase, and just tweaked it until it sounded best (to me) with a nod toward recording well rather than just sounding good in the room (what sounds good to your ears doesn’t always sound good to the mic). It is great for bedroom recording because I can dial in the volume that works best, mic it up, cover it in blankets, and the neighbors never hear a peep.

Here is a pic of the cabinet with the mics in place (the tape is to keep the mics from falling into the speaker if anything bad happens):

mic position

SPEAKER:

The speaker is an Earcandy Cabs ‘Green Machine’, which is a nice even-toned speaker that has a nice low end whack that doesn’t get floppy, and no honk or cone cry issues higher up if you crank them louder. It seems to have some of the charactaristics of a Celestion V30 mixed with a G12T while avoiding both the icepick-in-the-ears treble zippiness/fizziness you can get near the center of a V30, and also avoids the kind of flat mids and honk of the G12T that can sometimes be hard to deal with when mic’d up close and layered in a mix… so it has the whallop and thrust of a G12T and the warmer/thicker mids of the V30. It seems to have a bit of fuzziness on the top, which I like as a matter of taste because it smooths out the top-end, but might require a little attention on some sections to keep them from getting vague. I have some other speakers here that I tried out, including the usual Celestion suspects, but they didn’t work as well for what I was going for.

MICROPHONES:

The mic setup was the one I usually use… an on-axis mic near the center with an off-axis mic mixed in lower. That thickens up the mids and mellows out the highs, but can be tweaked in the mix as needed (as in… on-axis mic brought up for chisled fast palm mutes to give them definition and tightness OR the off-axis mic brought up on single-note phrases to give them thickness and mellow out the pick attack/scrape). I used an Audix i5 in the center and a stock Shure SM57 off-axis. The off-axis mic was positioned over the edge of the dust cap at a 45 degree angle toward the center of the speaker, close up (where the grille cloth would be). Having that mic off-axis seems to trip out the proximity effect of the mic a bit so you can get it close for more presence without making the bass tubby when you mix it with the on-axis mic in addition to rolling off the highs and changing the contour of the response. I had to screw around with distance from the speaker to get the right amount of proximity effect to get it thick without being tubby and get the right midrange dips without losing too much high end. The on-axis mic was right next to that mic (the side closest to the center of the speaker) with the edges of the mics’ grilles touching (which puts the sm57 back about 1/2″ to 1″ from the ‘grille cloth’… which is about 2-1/2″ from the highest point of the speaker’s dust cap).

Here is a closeup of the mic positions:

mic position closeup

MIX:

I didn’t do very much to the main guitars in the mix. There is no post-mic EQ in the ‘musical’ part of the guitars (I DID EQ the raw guitar tracks before sending them to the amp but for response not tone… just cut out some lows and highs to keep that crap out of the preamp). I wanted the guitars to sound fairly natural while being as thick as I felt comfortable with, while leaving plenty of room for the other instruments/vocals. That is the tricky part…. it is much easier to scoop out  the mids, boost the high-end and call it a day, but even though that tone is popular these days it sounds unnatural to me.  So instead of using post-EQ, what I did was re-amp the guitars over and over and over, looking at an FFT plot of their frequency response while tweaking the knob settings and mic positions until the natural guitar sound had dips in the frequency response in the right places to be complimentary to the peaks in the vocals and snare so that the guitars were not stomping on them.

There is a bit of a saturation plugin on the main bus to deal with the hard-sounding digital in-the-box mix, and I used a multi-band compressor on the lower-mids (bell curve, centered at the snare peak… around 215Hz or so) and lows (shelf, starting at the beef of the bass guitar) to keep them from dancing around from part to part so that space is nice and even to leave consistent room for the bass guitar, snare and vocals. On the main guitar bus, I high-passed at 70-80 hz to keep the non-musical portion of the lows from tripping out the compressor and to make sure that everything under cabinet resonance was solely the domain of the bass guitar and kick drum, and I low-passed at 12-13kHz or so to keep the ultra-high-end hash out of the cymbal/keyboard/clean-vocal air reverb tail territory.

I ended up using 3 different passes of re-amping with different settings, blended together so I can bring them up and down in the mix when I need to… #1 a wide, warm tone, slightly mid-sucked for the main voice, #2 a thicker, bass-ier tone to blend in for sections where there are no vocals so the mix doesn’t sound suddenly thinner, and #3 a third pass with subdued lows and mids and more high-end to mix in for scrape/rasp when I need the guitars to stand out a bit more or have more definition or presence in the mix without having to cut frequencies in other instruments. I also did a separate raunchier pass for the lead lines (not the solos… those were completely different) with more mids, less bass and EL34 output tubes to give them a bit more ‘honk’ and presence in the mix so that they stand out from the rhythm guitars when they come in. I could just as easily have gone for a tighter, brighter, more compressed tone for the lead lines instead, but I wanted to being in a little raunchy organic-ness occasionally to keep the guitars from sounding too robotic.

The strip in the master mix bus was bandpass EQ from 40Hz-18k to keep the crap away from the compressor, some light mix glue compression (-2dB), tape-emulation, slight smiley-face EQ for to bring up the kick thump and cymbal/vocal air, stereo widener (just a few dB to push the guitars away from the vocals a bit), clipping/saturation, and finally a brickwall limiter with makeup gain. I might add a psychoacoustic bass enhancer so that people listen on crap speakers or earbuds can still get a sense of the bass… but maybe not if it clutters the mix on good speakers.

So yeah, that was a whole lot of work. It was about a week of tweaking, which would have been impossible (or impossibly expensive) if I were not doing it at home, but I am finally happy with everything, and in the end… that is what counts. Whether everyone in the world likes the tones on the album or not: at least they are exactly what I was going for.

Here is a short, full-mix clip (minus the vocals) of a simple chuggy section to show the end result (the tone is likely to change as the mix dictates, but here is the basic raw tracks):

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About alexkenis

Guitarist, philosopher, tinkerer
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