How hard to lower the frequency of treble boost in my preamp

[jibreel]

How hard would it be to lower the frequency of the treble boost in my BATT tube preamp? I love this preamp. Boosting the treble is very bright. And not boosted it becomes high end muted.

Any suggestions would be appreciated.

The front of the pre is a little confusing:
The 3 buttons boost bass mid and treble.
The 3 knobs are: gain / tone blend / master.
The labels for the buttons and knob are underneath the buttons and knobs.

The tone blend control is unique. Kind of a one knob tweaker that sweeps from deep low to transparent high.


BATTSchem.pdf

[brendanbassist]

Doesn't look like it should be too hard from the pictures you posted. Glancing at that schematic, I'd guess that you'd want to change the capacitor next to that 10M resistor (can't make out the value of the cap), but its been a while since I really studied circuits and I don't have time to do a proper analysis.

[UncleFluffy]

There's a couple of things you could try - either increasing the 100p cap next to the 10M resistor as brendanbassist points out, or adding a trimmer (2M2 would be a good ballpark starting point) resistor in series with the boost switch. Increasing the cap would probably be easiest. Every time you double the cap value you will drop the frequency an octave.

There's 270V in that circuit and it will hang around for a while after you disconnect the power. Please be very careful.

[Passinwind]

Just lowering the hinge frequency by only changing the 100pF cap will quite possibly make it even brighter. You will probably want to mess with the high rolloff too, if you take that tack. A resistor in series changes the hinge frequency too, so it's a bit of an interactive puzzle. Looks pretty easy to work on in any case.

[jibreel]

Thanks all. And thanks for the voltage warning. I will have a tech work on this.

[billfitzmaurice]

Originally Posted by brendanbassist

Doesn't look like it should be too hard from the pictures you posted. Glancing at that schematic, I'd guess that you'd want to change the capacitor next to that 10M resistor (can't make out the value of the cap), but its been a while since I really studied circuits and I don't have time to do a proper analysis.

Correct, but rather than changing the frequency I'd reduce the boost level. I'd bypass the 10m resistor with a 1m pot instead of the switch. Lowering the boost frequency wouldn't tame the brightness, it would just extend it lower.

[Mingo Sanders]

Originally Posted by jibreel

The front of the pre is a little confusing:
The 3 buttons boost bass mid and treble.
The 3 knobs are: gain / tone blend / master.

Here's what's confusing me: the attached photo has 3 knobs: bass / mid / treble. Is this the right schematic for the unit in the attached photo?

[jibreel]

[quote=Mingo Sanders;11797478]

Originally Posted by jibreel

The front of the pre is a little confusing:
The 3 buttons boost bass mid and treble.
The 3 knobs are: gain / tone blend / master.



Here's what's confusing me: the attached photo has 3 knobs: bass / mid / treble. Is this the right schematic for the unit in the attached photo?

As is my original post: The front of the pre is a little confusing:
The 3 buttons boost bass mid and treble.
The 3 knobs are: gain / tone blend / master.
The labels for the buttons and knob are underneath the buttons and knobs.

[jibreel]

Originally Posted by billfitzmaurice

Correct, but rather than changing the frequency I'd reduce the boost level. I'd bypass the 10m resistor with a 1m pot instead of the switch. Lowering the boost frequency wouldn't tame the brightness, it would just extend it lower.

Thanks Bill !!!

[JohnMCA72]

[quote=Mingo Sanders;11797478]

Originally Posted by jibreel

The front of the pre is a little confusing:
The 3 buttons boost bass mid and treble.
The 3 knobs are: gain / tone blend / master.



Here's what's confusing me: the attached photo has 3 knobs: bass / mid / treble. Is this the right schematic for the unit in the attached photo?

The photo isn't very clear because of the angle it was shot. The knobs & buttons don't have anything directly to do with each other. Labels for the knobs are underneath, hidden from view in the photo.

[brendanbassist]

Originally Posted by billfitzmaurice

Correct, but rather than changing the frequency I'd reduce the boost level. I'd bypass the 10m resistor with a 1m pot instead of the switch. Lowering the boost frequency wouldn't tame the brightness, it would just extend it lower.

After reading the OP's problem again, you're right, lowering the amount of boost would probably be better than lowering the frequency.

[Mingo Sanders]

Originally Posted by jibreel

The labels for the buttons and knob are underneath the buttons and knobs.

Now I see it.

[MAMMOTHvolume]

Do you use it with the el84 in the circuit? If so i'd try lowering the grid resistor or bypassing it with a fairly small cap. It seems really big for a el84 amp and would definatly dull the whole sound.