Here's an idea some may wanna try

[iknowjohnny]

Every now and then someone finds a trick that stands out and shares it here. I think i just found one and i thought some may wanna try it. This works on marshall style MV amp like an 800. At least it works amazing on mine. I built this amp a long time ago but it's always been a sort of work in progress to which i've conducted experiments on ever inch of the circuit ad nausium. This may be the best trick i've found yet.

The amp has a JCM 800 style output section thats very close to a 2204 from the cathode follower on. But I have a NFB pot thats 100k in series with a 33k resistor. My search has for years been getting the best high end possible because i find when you get it right and from the right place in the circuit the tone opens up and it becomes alive and resonant. Generally i leave the NFB pot full resistance so i have 133k all together (off the 16 ohm tap) which makes for a pretty open bright sound. I don't like a lot of NFB. But when i turn the treble past about 1:30 with the presence up say 1/2 way or even less, the treble becomes very harsh. If i turn the presence all the way down then i can turn the treble up a bit more. If i unhook the NFB completely the treble cannot go past about 11:00 w/o being too bright.

So i got to thinking how the tone sounds so good with the treble turned up and the presence all the way down, but with no presence it's too dark even when the treble it way up. Then it hit me....no NFB=much too bright, nfb with presence down=better tone but too dark. So why not disconnect the presence completely but put a bigger pot in place of the 100k that i use to control how much NFB it has. That way without the presence where it's usually too dark but has a great resonant tone, turning the NFB pot PAST 100k by replacing that pot with a 250k would allow me to brighten the tone with no presence. So i could set the treble and mids where the tone was balanced in a way i like, then remove just the amount of nfb necassay to brighten it up.

I gotta tell you, this worked far better than i ever expected and i would suggest anyone with a similar amp try it. The tones i can get now are not only much better in overall tonal quality, but i can get many different levels of bright/crunchy or darker and smoother and everything in between. Before it was a situation where i'd try and find the sweet spot and leave it there. Now there are many different flavors that are all usable. I am loving this ! I have tried so many NFB tweaks and tricks it's mind boggling, but why i didn't think of this till now is exactly why i'm such a tweak freak. No matter how long you do this every now and then you find gold. This may be the best one yet. Just add a 250k pot inline with the NFB resistor (u can adjust pot or resistor value later to taste) and lift the presence cap. Takes a few minutes, give it a try and post your results.

[Reeltarded]

Neat.. Question: were you using early or late presence setup before?

I always end up around 56k on the 8R tap but with the amp around half way up none is also really good for me. I like the idea of constantly variable NFB. It might turn out that the only controls an amp might need is volume, slope, and NFB.

[iknowjohnny]

Neat.. Question: were you using early or late presence setup before?

I always end up around 56k on the 8R tap but with the amp around half way up none is also really good for me. I like the idea of constantly variable NFB. It might turn out that the only controls an amp might need is volume, slope, and NFB.

Early or late? You mean was i using the presence up (bright) or down (dark)?
If thats what you're asking, i used it both ways. But when i used it down so i could turn the treble up more it would be too dark. Thats when i thought to remove it altogether which would be even darker and allow me to brighten it up by using less NFB. Because i always felt that no nfb sounds so much more alive but was always too bright. Removing the cap allowed me to remove even more NFB without being too bright.

I think this works as you suggest, a all in one tone control. But thats not to say i would want to do that. I prefer being able to shape the treble and mids then use the NFB pot to darken or brighten the overall tone in a more global way than treble or presence pots can. Because it acts like a single knob tone cutting highs or adding them but also affecting the entire range unlike a treble or presence.

[Reeltarded]

Three basic Marshall pres rigs: early is 5kL with a .1u that gets DC scratch, second is .68u which digs into the mids in a different way..

Then the later 25kl with .68u and a 4k7 resistor with no DC on the pot. This one is terrible.

Sorry to sidetrack. I was just wondering.

[iknowjohnny]

5k/.1uf. I've tried 25k pots and .68uf, 1uf, 2.2uf, etc. They all cause the same thing to one degree or another, which is to say an inability to be able to get that alive open sound with exactly the right degree of cut. It's just "right" if you know what i mean. Maybe the 25k pot might have been enough to take the presence out of circuit to enough of a degree that i could add a big NFB resistor/pot and get what i am getting now. I don't think so tho, and it's that cap that was the culprit anyways. it's just so much better getting the brightness this way than with a presence cap.

[Reeltarded]

Yeah yeah. Whatever works is good. I like no NFB with a cut control too. I have an amp with that and a fixed resonance that is really good at punch.

Thanks! You made me think of something.

[iknowjohnny]

Yeah yeah. Whatever works is good. I like no NFB with a cut control too. I have an amp with that and a fixed resonance that is really good at punch.

Thanks! You made me think of something.

Then you should really try this ! I say that because i have done that (no NFB, cut control) several times and this works a lot better. Tried it with several caps and found a .022uf does a fair job. But the reason i say you should try this is that if you like that, you'll find this the same kind of thing but it works a whole lot better. With no NFB and cut control i found myself constantly trying to find the sweet spot and it was never 100% satisfactory. With this there are lots of sweet spots and every one is a lot more satisfying with a lot more punch. To my ear it's not even close. Try it !

[Bob S]

The hair on the back of my neck just caught fire.
Must try this.

[iknowjohnny]

If u do please post back w/results. I'm thinking i may use a bit more resistance. Maybe replace the 33k with 100k since i never seem to want to turn the NFB pot down very far anyways and if anything i could use even less NFB. Really digging this more and more. Seems like the missing ingredient between vintage marshall tone and more modern, that grindy punchy cut thats still fat and not thin or harsh. Hope it works for u as it's working for me.

[M Fowler]

I'm just the opposite I hate NFB and presence controls. I like the Cut control and if I have to have NFB set it with a resistor only.

I find most amps are too bright.

[matt h]

l(deleted)

[iknowjohnny]

Well guys, if you haven't tried it then i suggest you do b4 u decide a cut is better. Like i said, i've done that myself many times and it was my preferred method in some ways, but overall it didn't quite cut it for me and this blows it away. Note that if you never tried this with no presence and a large enough pot then you didn't hear what i'm talking about. The whole point of this is removing the presence because WITH a presence no amount of nfb or lack of will get you what i'm getting now. Even the low end is very improved. It's very different than a cut with no nfb, and while i realize tone is subjective, there are things that are generally agreed upon by most people like sustain is good, dynamics/touch are good, etc. And this does several things like that much better than cut/-nfb. It brings the stuff we all like much better, yet works in a very similar way to cut with no nfb. Try it, then tell me u prefer the cut. I'm just trying to share something that blew me away, and if you know much time i have spent tweaking this amp you'd realize it's not easy to impress me. Theres not much else i HAVEN'T tried.

[John_P_WI]

IKJ, curious how does this differ in design from a generic fender, ala twin, except for the addition of a much greater and variable resistance in the feedback path?

[chief mushroom cloud]

I have a repair customer w/ bf fender vibrolux and super that he cut out the nfb resistors...most amazing fender amps I ever heard
I don't use nfb in anything now.....

[Reeltarded]

The rawness you perceive at first can be controlled with a couple knob taps... but in a huge gain monster I like de NFB to set the tantrum level.

Tantrum is what i am going to call variable NFB from now on.