Shunting highs: What's your favorite approach

[Nolatone Ampworks]

Hey folks,

I'm working on a prototype that has just BRUTAL shrill highs. As in OUCH (with a strat or tele bridge pickup dialed max treble, rolling back on tone control tames things).

I've been experimenting with various low pass/high shunt methods, and I'm curious what your favorite is.

Some things I've experimented with:

* small value cap across PI plates
* small value cap from plate of preamp tube to ground
* small value cap across plate load resistor
* rc filter by means of large grid resistor miller capacitance of the tube itself.

On the shunt methods I'm using I'm having to use a much larger "small value" cap than I had expected to tame the icepick. For instance, a .047uf sounds really nice and round with the strat bridge pickup at the brightest, though it'd be too dark with, say, a humbucker. I'm shocked it takes that much. I would expect less treble to get through with a cap that size!

[Rosewood]

Series resistance does it for me.

[RedMan]

Sounds like a cut control might work for you. That way you can dial it in to suit your guitar/liking

[RedRock]

The 4 best IMO:

1. A small value, 100 ohm to 10k ohm, grid stopper resistor on the
input grid pin. But as the value goes up, the tone is changed
more.


2. A small value cap, 1 pf to 8pf, on leg on input grid pin, one leg on plate
pin. This one means business. See the Fender Prosonic.

3. A cap, 47pf to .002, from plate pin directly to ground. This preserves
the attack of the note best.

4. A small cap, 50pf to 250pf, across the input jack is not bad.


All the above are done on the pre amp tubes except 4.

[darkbluemurder]

Series resistance and cut control would be my choices.

[RedRock]

Cut controls like the one used in the Vox AC30 are nice, but on a 2 channel amp,
they will cut the highs on BOTH channels, even if one channel is ok; also
you are stuck with the cut control's fixed value cap, usually a .0047, and you
may need to fine tune your high shunt to a greater extent.

[drgonzoguitar]

Sounds like a cut control might work for you. That way you can dial it in to suit your guitar/liking

:agree

[Nolatone Ampworks]

I've used a cut control and it's a great device. What I'm going for though is to limit how bright the amp can go in any setting.

I've witnessed this: If there is a bad sound to be found on an amp, most people when demoing the amp will find it, and that bad sound tends to stick in their heads like a fiery car crash!

The one thing I haven't done with this one is review the plate voltages. I suspect they are running a bit high. I should have done that before but got off on a tangent.