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FDP Forum / Fender Amps: Vintage (before 1985) / tone stack question



now even awesomer
Jul 3rd, 2018 02:51 PM   Edit   Profile  

Good evening all... my Princeton Reverb II has a traditional Fender t,m,b tone stack if you ignore the boost switches. I've been doing some frequency spectrum plots to try to isolate a kind-of upper-mid honk that makes the sound a little brittle, and it's confirmed something else that I thought was just me fooling myself... the mid control doesn't change the mids very much. There are plenty of peaks which shift around as you wind the middle from 1 to 10, but the general region of (say) 500Hz to 2k doesn't change in amplitude much.

Is this normal?
What might I do to get a bit more control?

Thanks for any thoughts!


Too Near Atlanta GA

Amp Tech Emeritus
Jul 3rd, 2018 05:02 PM   Edit   Profile  

It's really pretty normal in my experience. There isn't a great deal you can do change it that doesn't involve circuitry modifications. Perhaps the simplest thing to try would be to remove the 10k mid pot and replace it with a larger value, 25K...up to maybe 50K...that said, you already have a mid boost that would do virtually the same thing...so, to me...meh...the circuit is pretty well designed. Have you tested the amp through another speaker?




now even awesomer
Jul 4th, 2018 03:48 AM   Edit   Profile  

Thanks Willie... the mid boost is too "all-or-nothing" for me... I've just been playing with the Duncan Tone Stack Calculator and I can see your point on the mid pot value. Maybe I'll have a go at that next time I open it up. Can you recommend a brand? (I started to type "can you recommend a pot supplier", but... )

I thought about trying another speaker, but the plots I made show different peaks and troughs dancing around as the mid control is adjusted. I figure the speaker would have some peaks that wouldn't do that. I think the nasty peak that I THINK I can hear is a prominent one around 1250Hz which appears to dip away when the mids are turned down to 4. I'll try that, next band rehearsal.

Once again thanks for your reply!


Too Near Atlanta GA

Amp Tech Emeritus
Jul 4th, 2018 07:15 AM   Edit   Profile  

CTS 25K...




now even awesomer
Jul 4th, 2018 09:12 AM   Edit   Profile  

You're a gent.



Jul 14th, 2018 04:46 AM   Edit   Profile  

Hi, Stratopastor. Got some Rivera amps, so will get the serial #'s to you. Amps are a little scattered around. Send you the #'s as I get to their locations! Cheers to you!

FDP Forum / Fender Amps: Vintage (before 1985) / tone stack question

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