"Notch Filter" in Tube Guitar Preamp?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi,

I just finished building the preamp section of a blackface Super Reverb in a large "pedal" format. It sounds great, but after playing it, I decided to just have fixed resistors in place of the mid and bass pots and so have some orphan holes. When playing dirty, I pretty much always have a Boss eq pedal in front of the amp, and the only thing I do is scoop the 400 and sometimes 800hz bands 3-6db. Knowing this, would it be possible to incorporate a passive notch filter in the output stage to target these frequencies? If it would make things more realistic, it would not have to be adjustable. If I could target about 5db of reduction in the 400-600HZ range, I'd happily just use a switch to choose either it or the direct signal.

Thanks!

Joe
 

PRR

Member
Joined 2003
Paid Member
> that 400hz dip that really makes the magic

Make the caps 700/400 or 1.75 times bigger.

If you now have 0.1u and 0.022u, try 0.175u and 0.038u.

Or since this is just a test, and those computed values are whack, tack a 0.068u (or 0.05 or 0.1) across the 0.1, a 0.015u (or 0.01u or 0.02u) across the 0.022u.
 
Thanks! I'm getting some good results starting with the Tone Stack Calculator using the Big Muff stack and modifying it. Tonight I actually alligator clipped a version I'd derived into my preamp the results were promising. Will keep this idea around though.

Thanks again!

Joe
 
So in the end I took PRR's idea about parallel caps in the main tone stack and opened up the Fender model in the Tone Stack calculator. I had tried the combo mentioned first in the live circuit and that didn't seem to do it. But when in the TSC I started playing with the cap value of the .022 and realized that increasing it alone moved the scoop like clockwork from the 700hz area over to the 400. So I alligatored a .047 across the .022 in circuit and, perfecto! I added some additional capacitance, but that started taking me from scooped to hollow so I'm going to leave it at .047 across .022. In fact, I'm going to put the .047 on a switch so I can retain the original vibe as well, and will probably put the mid-pot back in too for maximum control. In fact, think I'm going to swap the 10k pot for a 25k so I can get into raw/tone stack bypass territory.

Thanks again for the help!

Joe
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.