Amp design and low end drive

[lespaul3]

So... new to the forum... been repairing stuff for 20 years and building from scratch for a few years... but I'm not a good tweaker or modifier.

I have a question that has eluded me thus far when it comes to designing a certain tone into an amp.

I love when an amp "rips" on the lower strings, such as the intro to "running down a dream." I've found alot of amps that do not have the rippy lower end (could be "woofy" or just piano-ish)...and I've found a couple that have "some" of that low end rip... To my ear, the lack of rip on the low end seems that the distortion/drive just doesn't extend into the lower frequencies of the guitar (may rip higher on the neck, but clean up lower), but I am not sure that this is the way to view it. I know it has some interaction with guitars used... and I gave up humbuckers and LP's for SG's and Jr's to go more in that direction, which has helped quite a bit with the woofy part.

In trying to define this "tone" I'm talking about...I hear the term "farty bass" thrown around quite a bit... and I'm not sure if that "running down a dream" tone is a perfect example of farty bass, or is the antithesis.

Anyone have any design suggestions to help push an amp more in the direction of it being cranked and still ripping? Is my question about desiring ultra tight, or ultra loose bass? Am I barking up the wrong tree??

I've kinda got in my mind that the answer may be "interstage coupling capacitor size" but I don't know if I need my amp to have more bass capability so it craps out, or less bass capability (smaller coupling)... or if I'm even on the right trail!

All suggestions welcome. Currently, I am a guitar-cord-cranked amp sort of player, and am generally on smaller amps with alnico/jensen/weber type of speakers.

Thank you in advance.

[Stevem]

One thing to keep in mind is that on many guitar tracks you have heard over the years is that what may at first to seem like one or two tracks, is 4 to 6 layers of that same part being played and you will of course never get that out of one amp!
One thing that will help you sin your quest is a to use a output transformer that is 20 watts over what is needed for you level of max power output and to use SS rectifiers and not a tube and if the amp is 30 watts or more and is to mostly run cranked out, than 150 uf of first node power supply filtering and a choke type set up should be in the amp.

[danman]

I had this issue with several of my builds(1987 & 2204 marshall clones) and I found that adding a fixed resonance cap inline with the NFB and impedance selector really tightened up the bass and gave me that thump I was missing. Looking back now, I really think I would have preferred the 100watt circuit for the extra headroom and tighter bass it provides. As the poster mentioned above, having a strong power supply section and higher filtering may help in giving you what you're after.

[Structo]

I would try a switch on the NFB.

Does this amp have a Presence control?

I added a switch on my Dumble 100w clone.
The switch is on the pot so when I rotate counter clockwise, it turns off.

It really makes it sound raw and is pretty good for lower volumes.

[iknowjohnny]

You didn't say, but whether you are trying to get this at home volumes, stage volumes, with preamp based OD or cranked amp OD are all things that must be addressed because those will change things radically. Note that petty and his band are big on vintage gear cranked up vs master volume tone and no doubt thats how they record. Using that petty song as an example i'd wager what you are after is cranked vintage vox tone which you aren't going to get exactly without....well, a cranked vintage vox !

[Tone Lover]

Cranked vintage Vox, amazing what an amp with no NFB does in the bass area.

[tubeswell]

More iron in the OT core will give better bass response. Less iron will result in quicker magnetic flux saturation of the core and loss of bass. (This is because bass frequencies are longer, and so the amount of time that the current spends in +ve or -ve voltage territory for a bass frequency, is longer than for a treble frequency, and so the magnetising current - which is a form of energy - needs to be in the core for a longer period of time in order to get induced between primary and core and then between core and secondary. Smaller cores dissipate this magnetic flux more quickly than bigger cores - in the same sort of way that a capacitor with small plates can only pass higher frequencies. So bass frequencies can't 'hold on' in smaller cores as well as they can in bigger cores - if that helps with an intuitive grasp of the physics)