Hi everybody,
I recently was showing a friend a version of the EH Pulsar tremolo pedal that I had built....he agreed it was a great sounding effect with a really cool mechanical sounding chop, but he thought it would sound cool with a slowly sweeping high-pass or notch filter after the effect. So we ran it through a rackmount Filter Factory to check his theory, and it was a cool addition to the sound. We set it for a triangle waveform, high pass filter, resonance was off, and a nice slow sweep speed.
My friend suggested I add such a filter to my pedal, and I thought that sounded like a great plan! Then I realized I had no idea how to do that!
So my question is, how would one go about adding a sweeping filter to the end of a circuit? A very simple one....with a knob for the LFO speed and maybe a knob for depth....it doesn't need a resonance knob or a tap tempo feature or selectable waveforms....a triangle wave sounded best on the rackmount filter, with it set to high-pass.
Maybe there's no simple way to do that and I'm asking the impossible, but if anyone has an idea or could maybe point me in a direction where I could do some reading and learning on this idea it would be much appreciated.
-Ryan
Give a read to "The Technology of Wah Pedals" at GEO for some ideas.
You have two routes here. You can do a sweeping filter similar to a wah pedal by using a variable resistance like the JFET in the EA trem, or you can go voltage controlled with any number of synth filters. I have some designs coming out soon based on OTA state variable filters.
Thanks for the suggestion R.G.!
If I want the filter to just continuously sweep automatically that suggests I need to use a voltage controlled style circuit, as from a synth?
I'll check out the GEO site before I ask any more questions!
Thanks again,
-Ryan
Quote from: RJIf I want the filter to just continuously sweep automatically that suggests I need to use a voltage controlled style circuit, as from a synth?
As much as I love OTA circuits, it's pretty easy to hook up a Twin-T type filter to your LFO. You can use a FET (I use MOSFETs) as a variable resistor.
There's one here in this list from Munky!
havn't tried it, but looks OK.
http://www.geocities.com/munkydiy/schematics.html
Actually, any wah circuit could be modded easily, by replacing the variable resistor by a light dependant resistor & using a flashing led to 'sweep' it.
If you want to get seasick, use TWO slightly out of phase led flashers shining on the LDR :D
QuoteIf I want the filter to just continuously sweep automatically that suggests I need to use a voltage controlled style circuit, as from a synth?
Nah, there are several ways of continuously sweeping a filter shown in the articles at GEO. The "one resistor to ground" wah circuit adapts itself to a single LED/LDR or JFET variable resistor, as does a twin T filter circuit. There are articles there on both.
I didn't built it too, but if you do a search in this forum you will find a topic about it with some reviews. And Gez did this mod, to make it more versatile: http://www.geocities.com/munkydiy/autowahmod.gif
Here is the link for the stock version: http://www.geocities.com/munkydiy/autowah.jpg
Thanks for all the links and ideas, very much appreciated! Those websites are great resources....I've got a lot of reading and breadboarding to do. I've never used LDRs before, definitely have to give that a shot!
Thanks again for the guidance,
-Ryan