I've built a few pedals, built a bunch a pedal models in LTspice, and have some electronics knowledge from university (ok, in 1982..).
I've been looking specifically at the design of the filters in some of the popular pedals to try and figure out what the designer wanted. There's been a lot of discussion on clipping on various boards, but not much on filters, and to me, filters are what gives a pedal its mojo.
One major problem with this is when a pedal is described by the designer as 'transparent' - which to me means no tone coloration ie flat EQ across audio band - but the frequency response of some of these 'transparent' pedals in LTspice shows that the EQ is nowhere near flat across the audio band. However, I don't want to get sucked into a discussion on transparency as I prefer to look for distinctive, colored tones in any pedals I might design as it's good to stomp on a pedal and get a whole new sound.
One design issue that the EQ of some pedals changes a lot not only with 'tone' controls but often with 'gain' controls too - this is easy to understand if you are conversant with active filter design using op amps - changing the value of any resistors in the negative feedback loop will change the EQ if there are capacitors in the loop as well. For example, the last pedal I built was a Clark Gainster clone, and adjusting either the gain or the presence control has a marked effect on EQ as both are variable resistors in the loop (as shown below). Are there any successful designs out there where the designer has managed to separate gain and EQ?
Another issue is that clipping adds higher harmonics that weren't there before, so only filters after the clip can affect the new harmonic content.
I wonder if the more experienced members of the forum have heard of anything like a pedal design cookbook which has a variety of modules (ideally in LTspice) with guidance on how to adjust the parameters to achieve the end goal?
One other key piece of info would be a comprehensive understanding on what EQ gives what tone - the Duncan Tonestack tool is a start, but that doesn't cover pedals. I'm sure someone has done this before so if anyone knows of a resource please post.
Lots of topics there. I'm hoping this thread might become a useful resource for those seeking a better understanding of the design of the filters in guitar pedals so we know what to do to get them to sound just the way we want.
I've been looking specifically at the design of the filters in some of the popular pedals to try and figure out what the designer wanted. There's been a lot of discussion on clipping on various boards, but not much on filters, and to me, filters are what gives a pedal its mojo.
One major problem with this is when a pedal is described by the designer as 'transparent' - which to me means no tone coloration ie flat EQ across audio band - but the frequency response of some of these 'transparent' pedals in LTspice shows that the EQ is nowhere near flat across the audio band. However, I don't want to get sucked into a discussion on transparency as I prefer to look for distinctive, colored tones in any pedals I might design as it's good to stomp on a pedal and get a whole new sound.
One design issue that the EQ of some pedals changes a lot not only with 'tone' controls but often with 'gain' controls too - this is easy to understand if you are conversant with active filter design using op amps - changing the value of any resistors in the negative feedback loop will change the EQ if there are capacitors in the loop as well. For example, the last pedal I built was a Clark Gainster clone, and adjusting either the gain or the presence control has a marked effect on EQ as both are variable resistors in the loop (as shown below). Are there any successful designs out there where the designer has managed to separate gain and EQ?
Another issue is that clipping adds higher harmonics that weren't there before, so only filters after the clip can affect the new harmonic content.
I wonder if the more experienced members of the forum have heard of anything like a pedal design cookbook which has a variety of modules (ideally in LTspice) with guidance on how to adjust the parameters to achieve the end goal?
One other key piece of info would be a comprehensive understanding on what EQ gives what tone - the Duncan Tonestack tool is a start, but that doesn't cover pedals. I'm sure someone has done this before so if anyone knows of a resource please post.
Lots of topics there. I'm hoping this thread might become a useful resource for those seeking a better understanding of the design of the filters in guitar pedals so we know what to do to get them to sound just the way we want.
