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Mid range scoop - WHY?


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7/17/2004 9:44 PM
Terry Shipman
Mid range scoop - WHY?
Ive looked at the tone stack settings of a number of amps after guitarists have played their sets and noticed that quite often their chosen settings is with mid control is maxed, or close to it.  
 
It seems to be an accepted fact that the tone stack of a guitar amp always seems to have a mid-range dip. Why is this? It seems almost a traditional thing, but how did it originate and why?  
 
I'm not losing sleep over it, but if somebody more knowledgable can shed some light on it I would be grateful.  
 
TIA  
 
Terry
 
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7/17/2004 11:41 PM
Ray Ivers

Terry,  
 
I think the reason that most guitar amps use passive tone stacks is that they're cheap, familiar/traditional, and effective for a lot of things. But as you noted, most of them just allow you to reduce the midrange, not boost it - and personally, I've never liked the 'affecting everything but bass and treble' response of the standard Fender-type midrange control, preferring at least some kind of targeted mid boost/cut at some definite center frequency, like 400 Hz. It's possible to modify the standard Fender tone stack for a mid boost (Q of maybe .5) but then the bass control becomes the mid control, the old mid control loses its effectiveness, and you end up with a mid/treble tone stack (which IMO is still preferable for amps with the tone stack between the 1st and 2nd gain stages, especially when combined with a fixed bass cut at this point).  
 
OTOH, in a master-volume design with the tone stack after the distortion, the passive Fender/Marshall type tone stack usually works pretty well, I think (although IME most of the Marshall MV guys want more bass - I know I do). I recently used a modified Fender tone stack in a Marshall MV amp, it came out quite well (more bass, more scoop if needed, better mid-control action, and more range out of every control).  
 
Ray
 
7/18/2004 7:17 AM
Terry Shipman

Ray,  
 
Thanks for your informative reply. I would be interested to see details of the modified Fender tone stack you mentioned in the Marshall MV amp as I'm interested to see the differences from the normal arrangement.  
 
TIA Terry
 
7/18/2004 6:41 PM
Ray Ivers

Terry,  
 
IIRC I used a 68K slope resistor, either a .05uF or .1uF bass cap, and I wired the 25K midrange pot in the "Fender fashion" as a variable resistance. I also used a .01uF mid cap to move the bass control range up a bit and increase max boost, and then paralleled the 1M bass pot with another 1M resistor to get a little less sudden action out of it. I think I also used a 220pF treble cap as well. The reason I did things this way was so I could keep the original pots; if you're doing it from scratch I would recommend using a 10K-Audio taper mid pot and a 250K-A or 500K-A bass pot.  
 
Ray
 
7/18/2004 6:38 AM
dod
IMHO, it's simple... it sounds good. I'm not trying to be glib. Remember, a guitar amp produces tone, it doesn't replicate it like a hi-fi amp.  
 
All you have to do is run a guitar DI with the frequencie flat and you'll see (hear).  
 
doddy
 
7/18/2004 8:28 AM
Terry Shipman

Hi Doddy,  
 
Thanks, I know what you mean. Plugging a guitar into a hi-hi amp is a pretty bland experience, but that may have a much to do with the lack of timbre, non-linearity and built-in harmonic distortion of even the most basic guitar amp.  
 
A lot of the smaller amps such as the Champ, Princeton etc, without the traditional Fender/Marshall/Vox tonestacks sound ok, within their limitations. Although accepted they do have a "small" amps sound, is that perhaps one of the differences that defines their "sound" as opposed to the sound of the bigger amps.  
 
What I'm trying to understand is whether the natural mid-scoop of the traditional Fender/Marshall tonestacks used in the larger amps is a technical limitation of the original design that has become the accepted sound, or is it something actually preferred by guitarists.  
 
This goes back to my comment in my original post that I've noticed quite a few guitarists when setting the amp to the tone they want seem to choose as much mid as they can get. I would say that that they are typically younger up and coming guitarists playing heavy rock/punk style music. I would be interesting to see how they would set the mid if it had sufficient range to actually boost the mids.  
 
Cheers,  
 
Terry
 
7/18/2004 9:43 AM
Chris - CMW amps

Hi Terry & others  
 
The most "information" is in the mids.  
 
I remember a gig with another guitarplayer, kinda "bedroom no mids kinda guy". He was using a 100+ Watt amp with his fav. settings ( no mids ) and I was using a 50 Watt ss amp adjusted to "my taste". It was almost impossible to hear that guy on stage and in the room while my "tones" where all around.  
 
I guess the famous Fender/Marshall/Vox tonestack is used because it does have fewer parts then ( let's say ) a Baxandall tonestack so easier/cheaper to produce.  
 
Mo' mids mo' fun :D  
 
Chris
 

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