cut control in preamp?

[iknowjohnny]

Is there a way to implement a cut control somewhere further upstream than at the el34 grids? The reason i ask is i prefer the high end attenuation of a cut more than other methods, but it kills the gain at that point and therefore amp's volume goes way down. I was thinking that if i were able to implement a cut pot in the preamp i could add more gain after it so the PI sees the same level. I do realize it may not sound the same, but if it's doable i'd like to at least try.

[gearhead]

A cut control is, AFAIK, basically a low pass filter. Cap and pot in series to ground. Where to put in and what values are something else.

[iknowjohnny]

No, it's actually from grid to grid at the power tubes and works by phasing out frequencies chosen by the cap that the pot gradually connects to both grids. the less resistance the more highs are cut by phase cancellation. at least thats how i think it works. in any case it's not a cap and pot to ground. if it were i could put it nearly anywhere. (and in fact i DID try that at one time back when i knew less than i do now, if you can believe thats possible )

[Andy Le Blanc]

Parallel the vol pot with another 1M pot and put a 100p to 500p between the wipers of both pots.
Acts to the ear in similar way, as a presence or variable brite.

[iknowjohnny]

Parallel the vol pot with another 1M pot and put a 100p to 500p between the wipers of both pots.
Acts to the ear in similar way, as a presence or variable brite.

not sure i get what you mean in a couple ways...1)-how to do it and 2)-what it accomplishes

My issue is not that it doesn't work good, just that it kills the amp's volume. What exactly does this do different and if it helps with the volume issue, can you elaborate on the wiring? Thanks.

[Andy Le Blanc]

here's an example... it won't kill the volume, I've tried it and its not too bad.
scab into something and check it out.

[iknowjohnny]

Thanks, i'll give that a try tomorrow and let u know if it works.

EDIT: been staring at that trying to get a mental picture of what it's doing, but is it nothing more than a cap and pot to ground as gearhead mentioned? I realize it's different since the pot's input is also connected to the stack's out. But i can't get a picture of how that affects it different ly than a cap and pot to ground.

[Andy Le Blanc]

the cap value acts on the "brite" frequencies. It wont eat too much of the mid.
Its a bypass/bleed. It sounds like a presence and is a "pre" control.
I was surprised at just how usable it is, very simple without huge losses.
Try a a 500p, two 500p series, and parallel.

Its your choice of cap value and its location, all the way up its just a brite cap,
all the way down it's a treble bleed, but the cap value is small, and being on
the vol. pot. wiper it wont affect the circuit as critically as a larger cap to ground will.

[iknowjohnny]

Will do, thanks. I'll let you know how it works out. Have you ever seen amps with this or is it your own idea?

[Andy Le Blanc]

I've seen variations in a few manufactures, that solton amp used it.
One of those old tone controls, good for preserving a high impedance between
just a couple stages to reduce losses.

[iknowjohnny]

hmmm...i checked my wiring several times and i'm sure it's as in the drawing. But it's not cutting highs, it's adding them ! At full counter clockwise where the least highs are its normal, IE: same as if i disconnect the control. As i turn it clockwise it adds highs !

I have it like this....the right lug is grounded as the master is, the left lug goes to the master's left lug, and the cap goes to the wiper of both pots. I tried several values but that doesn't really matter because it doesn't cut highs.

So anyways, the original question still stands....anyone know of a way to implement a cut control in the preamp? Is it possible to do it between the grids of 2 pre stages? Guess i can just go ahead and try that.

[Andy Le Blanc]

Its good to try, not all solutions are always the right one.

In the wreck pages in the universal stage, there's explained using a small value cap to bypass the plate resistors, there's a few ways to voice that way.

You might have to go with a fixed RC filter some where in the gain structure.

whats the project?

[Structo]

It sounds like you have the pots wired backwards.

[iknowjohnny]

no, which way it turns to cut or boost highs isn't the point. the point is i need to cut highs, and when turned fully to the side where there are the least highs, it sounds exactly the same as when you disconnect it. So it's boosting high end. With the pot turned the other way the highs go thru the roof.

Anyways, no matter because it does the opposite of what i need so i just need to know if there is a way to implement a cut in the pre.

[Jana]

A capacitor and resistor in series going to ground. The resistor is a pot. The values of each will depend on where it is in the circuit. Think a simple tone control for a guitar--that's all they do is cut the highs.