Guitar Loading vs Input Buffer/Filtering

[aziltz]

I've been thinking about filtering at the input lately, especially bass cuts and treble booster range controls.

Something like the ROG Omega actually *changes* the input impedance with its "Range" Control to add/cut bass, changing the load on the guitar.  Naturally this is going to work best first in-line, and would sound different with different guitars.  I plan on building it very soon, but from what I've heard from clips it really sounds killer.

Does anyone have any thoughts on how using an input buffer to drive variable high-pass filter ("Range" or "Bass") would work instead?  Can you achieve the same effect with the right filtering and an input buffer?  Obviously both of these methods are used a lot, but has anyone compared them in the same application?

Loading can be a magical effect IMO, however it tends not to fight nice with other boxes before it. 

Thanks.

[Gus]

You got two things going on.
One the input resistor loading affecting the pickup
Two the HP filter

Now if you used a big input cap(flat to a few Hz) with say a 22K input resistance to a buffer then to a HP and compared it to a RM or Omega input there is a difference.  Think about what the input Z is with changes in frequencies to both setups
pickups loading with frequency changes between both.
  Does it matter?

one can change the input resistor to 22K and increase the input cap value etc at the first buffer
http://www.aronnelson.com/gallery/main.php/v/gus/plus.GIF.html?g2_imageViewsIndex=1

[aziltz]

Think about what the input Z is with changes in frequencies to both setups
pickups loading with frequency changes between both.
  Does it matter?

this is wherei wasn't sure how to quantify it.  and certainly a simulation would show the designed frequency response, but not the pickup loading.  At least at the simplest level.


thanks for your thoughts though.  i'll probably build an omega and then tweak the High Gain Fetzer to get what I want and compare.

[Ben N]

Hey, Gus (or whoever),
Would it be fair to say that the Rangemaster type input creates a sort of bandpass or shelving response, since the lowered impedance causes the slope of the HP filter to level off at some point?

[aziltz]

Hey, Gus (or whoever),
Would it be fair to say that the Rangemaster type input creates a sort of bandpass or shelving response, since the lowered impedance causes the slope of the HP filter to level off at some point?

That's an interesting suggestion.  I noticed that the Omega Input has a intentional bandpass, where the High Pass section can be controlled, and that is where the input impedance changes.

[Gus]

This is a good question.  I have done test in the past with different input resistance and input cap values for a HP.  I have 3 RC starting points for an input opamp based fuzz distortion and overdrive buffer RCs.

What I did was build a fet input follower circuit, I used a fet so I could go to 1meg and have a 1 meg input.  I varied the input RC and noted the tone changes.  There are hints in my schematics.

It was a strat to the test unit to the amp