Fattening up a classic rock tone

[daz]

I have a build thats basically a 3 stage marshall preamp with fairly lower gain stages into a cathode follower and typical marshall tone stack and 2x6V6 output with a 30 watt OT. This amp absolutely nails the tom campbell/petty thing even tho it;s not a vox circuit, tho i believe they used a lot of fenders too. Anyways, i absolutely love the tone but it;s a 1x12 combo and the circuit is pretty bright in a good way and i don't wanna lose that jangle. But there is not much at all in the way of low mids which i think it will sorely miss in a band mix. The mid knob is mainly high mids so that doesn't fatten things a lot and the bass is pretty anemic too tho not to a fault. If you have spent a lot of time tweaking tube circuits you know the dilemma i am facing....you try and add or subtract something from the tone and it loses what u love in that tone. But you also know that there IS a way to do it w/o losing the tone but it can be a bitch to find that solution that gets u what u want w/o ruining everything you like. I love the tone but for that bit of needed fatness and everything i have tried that adds any beef causes it to lose that beautiful jangle. I've tried adding a crossline cut control, adding bigger caps to the coupling caps and the tone stack mid and bass. Tried bigger cathode bypass caps in the preamp but most of what i try muddies things up to where the tone i love is gone. Anyone whos been there, have you found something that worked to fatten it up w/o ruining what u love about the amp?

[The Dude]

Sounds like you tried most of the things I'd try. I agree, that's a tricky thing. The only other thing I might suggest is playing with the amount of NFB, though I'm not sure what you have in front of you without a schematic. I have found that running a little less NFB can open up the bottom end of an amp. I also suggest you try the amp as is in a band situation first. If you listen to a lot of the solo guitar tracks of songs on YouTube, you'll often notice that the guitar tracks sound pretty thin out of the mix, but work just fine in context.

[daz]

Thanks, but i have a variable NFB pot on it that goes from full on typical amount of NFB to none with a no load pot. Losing more then a little FB just makes the amp brighter which is the last thing it needs. I've also tried various preamp tubes and biasing the 6V6's different. I had it biased pretty high i think (tho it has JJs) and bringing that down really helped soften some stiffness n the highs but it still needs that little bit of beef. The band is 3 piece so while i know what u mean about it may sound right in the mix, in a 3 piece its not the same and thin is thin. The problem with trying it in the band first is we play only every couple months and if something doesn't work it;s a couple more months before i can try something else. Anything i can try that can be switchable i always do that so i can try it in the band and switch back and try it w/o.

[Chuck H]

I use to use a BOSS GE7 EQ pedal with the mids bumped, the lows and highs rolled down just a little and the level set as desired for a boost pedal into my Marshall amps whenever I wanted a bigger and beefier tone. The BOSS EQ is a little noisy but there are surely better options now. Something like this would give you the bump on demand and leave your original tone intact.

Also, where is the jangle coming from in your particular amp? Is it an effect from overdriving the 6V6's or is it in the preamp? That it gets lost when you try to change the to preamp signal EQ would indicate that it's in the preamp, I think. If you can increase low mids in a fairly narrow band that might work better than the broader band modifications you've tried already. I'll look into it and post when I have a suggestion.

[Chuck H]

Re reading the thread and having experimented a lot with Marshall preamps I'm actually thinking that part of what you need to preserve is your current OD EQ balance. If you increase low mids it will always get sloppier WRT low end definition and that's part of this amps charm. If you decrease highs you'll lose the nuanced attack and definition. So I'm wondering if you couldn't keep things just as they are with the amp and change the overall EQ balance with a different speaker. One that is either not as bright as what's in there or one that is known to have beefy mids. Have you tried the amp through a different cabinet yet?

[Chuck H]

FWIW my favorite speaker for adding some beef that still has good clean tones and enough HF definition is the Celestion G12H30 Heritage model. When I want more cut and upper mids, which is my usual tone, I use the G12H30 Anniversary or Vintage 30's. My favorite so far is a combination of these two. They're all nice and efficient which seems to lend a livelier "feel" that I can't live without.

[daz]

Re reading the thread and having experimented a lot with Marshall preamps I'm actually thinking that part of what you need to preserve is your current OD EQ balance. If you increase low mids it will always get sloppier WRT low end definition and that's part of this amps charm. If you decrease highs you'll lose the nuanced attack and definition. So I'm wondering if you couldn't keep things just as they are with the amp and change the overall EQ balance with a different speaker. One that is either not as bright as what's in there or one that is known to have beefy mids. Have you tried the amp through a different cabinet yet?

I agree, thats the way i see it too but i don't wanna buy speakers that fail to do the trick because a year ago i moved to a rural area and everything i buy that turns out to be un needed ends up as a waste of money because i can't sell anything here. My garage is already full of wasting gear. And shipping and fees and all that are not worth it, specially with things like speakers. One of my all time fav speakers is in it now, a celestion 100. But it's a 4 ohm because i bought it for a modeler which uses a 4. Luckily the OT in my amp has a 4 ohm tap. But i wonder if that could have anything to do with it. I have heard different taps sound different. never noticed that myself but then i never used a 4 ohm in a tube amp that i recall unless it was two 8's in parallel.

[pdf64]

Yes, I was thinking of a different speaker too. But then I wouldn’t expect a 100W Celestion 4ohm speaker to be toppy. Such that other speakers seem likely to be toppier, a change in the wrong direction tonally.

[daz]

It will take some more experimentation but i think i got it. There was just too little OD. Sounds counter intuitive but i upped the stage 3 grid leak to 1M from 150k and now theres more OD which i actually wanted but NOT at the cost of THAT sound. But i had the gain on 10 all the time because it was just enough for that classic rock tom petty kind of tone and i use a pedal for more drive. But by upping the gain i found that lowering the gain to around 2-3 o'clock i get the same sound but it has more body, even with a bleed cap on the gain. Plus i have the bonus of more gain when i want it which is great. It's weird but i have just as much brightness but i don't actually hear more low mids or bass yet somehow it doesn't sound thin anymore.

[Helmholtz]

Glad you found a solution.

Upping that grid leak from 150k to 1M likely increases low end (depending on coupling cap value), as coupling cap and grid leak form a high pass filter.

[daz]

Glad you found a solution.

Upping that grid leak from 150k to 1M likely increases low end (depending on coupling cap value), as coupling cap and grid leak form a high pass filter.

I actually don't hear certain increase or decrease in any given area which is odd. Just a sound that seems fuller is the only way i can describe it.

Heres the thing....i would likely not have used a 150k there but in the past i think i probably did that to lower gain. But i always used 1.5k or 820R cathode resistors on the 1st and 2nd stages so i probably did the 150k on the stage 3 grid to lower gain there likely due to blocking from too hot a signal. BUT, at some point i changed the resistors on 1 and 2 to 2.7k and 4.7k respectively (which is where they were when i pulled the amp out of storage) and forgot that i had that 150k on the grid of 3 leaving me with too little gain to retain enough body to the sound. Anyways, that was several years back so i am just guessing at what i did and why. Funny that i spent a lot of time back then and never got it where i was happy and now i guess because time has changed my perspective on some things i pull it out of storage and in a couple days i have a sound closer to anything i ever built to the sound in my head ! Anyways, it will required more playing and some band use to be sure it;ls where i want it. Kinda afraid to put a loop in it now for fear it will lose that sound.

[Helmholtz]

What's the value of the coupling cap?

[daz]

.022uf

[Helmholtz]

.022uf

Ok, so lower cutoff will shift from maybe 40Hz down to 6Hz. That's both below the range of a guitar.

[daz]

I think it just has to do with the extra gain. That fattens things up and even when turning the gain down to where it's the same as before on 10 it just has more body to it. i