Blues Jr and Duncan Tone Stack Calculator

[jasonvilla]

Hey all, I've been messing around with my blues jr again and have been modding the tone stack. Been trying to get rid of some lower mids because I THINK its causing it to sound overly boxy. However I could be totally off on this. Anyways, I think I set up the calculator correctly... I wanted to get rid of frequencies around the 500hz range. The amp is pretty stock except it has the cathode follower mod and theres a .1 bass cap. If I change the mid cap to a .047, from .022, the calculator says that it will lower the 500hz range. I tried this and it sounds a bit different but it made the amp quieter. Not really what I was trying to do. Heres a picture of how I have it set up. Any comments/suggestions would be greatly appreciated. Thanks!

[HotBluePlates]

Change your Bass control to a Linear type (not the Log type which is shown now).  Make C2 22n to simulate what you actually have in the amp now.

Turn the Mid pot to zero, Bass/Treble full up.  The Tone Stack Calculator oughta show plenty of cut at/near 500Hz.

[jasonvilla]

I forgot to mention I also have the twin stack mod!

[jasonvilla]

Well, you're completely right. Theres already a pretty big dip at the 500hz area with my current config and knob settings. Hmmm, Maybe I need to be taking out upper mids. 

[HotBluePlates]

We'll need a link to a schematic and/or description; just saying "XXXX Mod" doesn't communicate what is changed in the circuit.

... Theres already a pretty big dip at the 500hz area with my current config and knob settings. Hmmm, Maybe I need to be taking out upper mids.

It's often hard to translate "what I hear" to "frequency I'm hearing" or "how the circuit should change".  A cheap used graphic EQ pedal can be very instructional in this regard (like a Boss GE-7, maybe off of Craigslist).

"All knobs at Noon" doesn't necessarily mean good sound in a Fender amp.  For some things, I like Bass near 1-2, Mid at max, Treble to taste (maybe 4-6).  Sim that on the Tone Stack Calculator and see what you get...

[jasonvilla]

Sorry! Two pins on the mid pot are jumpered on the "twin stack mod"  SO it looks like the tone stack calculator is already set up this way.
A graphic EQ pedal is a very good idea!!! I recorded the amp on a setting I liked and adjusted the eq in Logic. Thats how I came up with the 500hz range.
I did run the calculator where I had the knobs set!

[jasonvilla]

Also, since the stage before the tone stack is now a cathode follower should I set the Zsrc to 1.3K(the value found in the Marshall setting) from 38k?  Thanks!

[jjasilli]

Google cathode follower impedance.  Amp Books has an online calculator.  Open the calculator & enter your values.  It will give the output impedance for your CF circuit.  (Note I think that your slope resistor is a rather high value for a CF driver.)

[PRR]

> should I set the Zsrc to 1.3K

OK.

We could quibble that the very-small-signal impedance is nearer 1K, but that makes no difference. We can quibble that the 5F6a driver is not any ideal cathode follower and goes to quite high impedance for loud yet typical signal levels.

"Boxy sound" would lead me to study (replace) the speaker and the cabinet. If the "boxy" persists, little time lost. But some speakers or their boxes just ARE "boxy" sounding. Sometimes an inch of fuzz-stuff on each side wall takes the boxy out. Some cones aim for boxy sound, good for some styles and bad for others.
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> your slope resistor is a rather high value for a CF driver

True in that he does not "need" a CF to drive a hi-Z tonestack. However the 5F6a driver has other flaws/virtues even when its apparent drive ability is not used.

[HotBluePlates]

... I recorded the amp on a setting I liked and adjusted the eq in Logic. Thats how I came up with the 500hz range. ...

Does Logic have a way for you to get a spectrum plot of your after-EQ track? [EDIT: apparently yes, though the video is old.]

Seems like a smart thing to do is look at your guitar track after the EQ and see how it has changed.  Or since you know you apparently boosted at 500Hz, look back at Logic and see how many dB the boost was (it would be nice to know the width of the boost, but just for feel).

... I did run the calculator where I had the knobs set!

If the image in this post was how you had the knobs set, you had a pretty strong dip between 500-600Hz.  And your Mid pot is down around 2-3.  Turn up that Mid pot, and the dip will lessen.  Might even sound like your Logic-EQ'd track.

In some ways, the typical tone stack is not intuitive.  You might expect that setting each control at half is "flat frequency response".  It's not.

And when you play amps with true "flat frequency response" the auditory impression isn't "flat response".  Guitar is a midrange instrument, and most pickups make it even more mid-focused.  This can be a very good thing in a Mix.  But we're so accustomed to 60's amps (and their variations) which have a pronounced mid-dip in the tone stack that we come to think that mid-dip is "flat".  It may be "balanced among highs, mids & lows" for the instrument by itself, and yet still not be "flat response".

In a track, every instrument will be heard if they contribute energy where other instruments don't.  It's no accident the kick drum, snare & cymbals put energy in a different part of the audio spectrum.  Your guitar will be more audible if you don't try to put a lot of energy in the 80-200Hz range where the bass may be competing for space.  It's no accident that acoustic guitars in a band track often get EQ'd to occupy similar frequencies as the hi-hat (mixed to mainly hear the rhythm that player is strumming), to get out of the way of voice & other guitars.  Might be a good idea with multiple guitar parts to have very-different sounding guitars, and/or very-different EQ for each (they might sound garbage when solo'd, but blend well together).

https://www.youtube.com/watch?v=aNwWzJLAwkI

[jasonvilla]

Sorry BluePlates but either I wrote it wrong or you misunderstood! I wanted to CUT signal around 500hz. But I might have been off with that guess because when i adjusted the tone stack to cut around 500 it didn't help much. So Im trying to pick up a cheap EQ pedal to see where I really need to cut signal! :)