BF Princeton Reverb - wider range for treble pot

[Bluefinger]

Hi,

what's the best way to make the treble pot on a stock BF Princeton reverb circuit roll of more highs? I use it for harp sometimes and even with a darker speaker it still sounds too bright with the treble control at 0

thanks!

[mozwell]

Does that have a fixed 6k8 resistor instead of a mid pot.
Looking at Duncans Tone Stack Calculator, with treble on minimum, reducing the value of the 6k8 resistor will suck a lot more highs out. The treble control still works the same as before, its just the range of the pot is higher....
Try paralleling a 470 ohm resistor across the 6k8 resistor in the tone stack & see if that works for you

If you find that with the 470ohm resistor, the treble control is hard to adjust for a guitar (too much range on the treble pot) you could always put a switch in series with the 470 ohm resistor so you can have both settings.

[Pedro Vecino]

Disconnecting 10pf capacitor paralleled with 3.3M resistor will reduce the treble.

[Bluefinger]

Does that have a fixed 6k8 resistor instead of a mid pot.
Looking at Duncans Tone Stack Calculator, with treble on minimum, reducing the value of the 6k8 resistor will suck a lot more highs out. The treble control still works the same as before, its just the range of the pot is higher....
Try paralleling a 470 ohm resistor across the 6k8 resistor in the tone stack & see if that works for you

If you find that with the 470ohm resistor, the treble control is hard to adjust for a guitar (too much range on the treble pot) you could always put a switch in series with the 470 ohm resistor so you can have both settings.

yes, it does have a fixed mid resistor. I'll try that and see how it works for me ... I'm not quite sure since i don't want to reduce the mids (which reducing that value would do) but who knows.

thanks ...

[Bluefinger]

Disconnecting 10pf capacitor paralleled with 3.3M resistor will reduce the treble.

that sounds like a plan ... thanks!

[mozwell]

Pedro
Download Duncans Tone Stack Calculator TSC
This is a great FREE tool !

go to the FENDER tab at the top
Double click on the mid pot itself and change the value to 6.8k
Slide the mid pot wiper (sliders are under the schematic) to maximum

This your current tonestack
If you slide the treble wiper from left to right you will see the frequency response curve change.
With treble pot on minimum you can get to -25dB at 10kHz
Mid frequency is around 400Hz with -25dB

Double click on the mid pot and change the value to 470
Slide the mid pot wiper to maximum
Mid frequency is around 400Hz with -32dB (slight drop in mids)
Move the treble pot wiper and you will see you get up to -45dB at 10kHz, much more treble reduction

You could also add a low pass filter, add a cap from the wiper of the volume pot, to the anticlockwise terminal (0V). Try 10n and see if that does what you want. If its not enough treble cut, increase the capacitor value, if its too much, then reduce the capacitor value.

Anyway, taking out the 10p cap, adding a 10n cap or adding 470 ohm in parallel with the 6k8 are all easy to try.
Hopefully one of these will work for you.
These are also easy to do with a switch, so you can have "normal" or "harp" mode with the flick of a switch

[pdf64]

The tapped treble pot of the 6XX series brown Fenders rolls progressively more treble off as it's turned past the tap point towards full CCW http://schems.com/schematicheaven.ne...6g7a_schem.pdf
https://www.tedweber.com/wp354at

[Bob M.]

Bluefinger,

I had a SF Princeton Reverb with too much treble and was playing it with the treble control on '0' and it still had too much treble. That didn't suit me as there was no way to lessen the trebles. My answer for this amp was suppressor caps on V1 a and b, between cathode and plate. I spent some time fine-tuning the cap values but it came out really good and now I can play the treble control at about 4 or 5 for a normal amount of treble and it sounds just fine. I saved this 'mod' as a last resort but in my case it worked great and did the job properly. For harp, I would think that this would be just the right cup of tea.

Bob M.