EQ Pedal Take 2

[PoopLoops]

I didn't get any replies to my previous thread, and I assume that's because I just vomited up my (numerous) thoughts incoherently.  So let me make it specific and easy to read.

I would like to make a parametric EQ pedal based on this design:



Which is taken from here:  http://www.geofex.com/Article_Folders/EQs/paramet.htm

My only problem is I don't know which op amps to use.  In my electronics classes we pretty much stuck to 741s and a few other cheap general purpose op amps.  Secondly, the way I see it is that the bottom 1M pot adjusts the peak frequency, the middle 10k pot adjusts the bandwidth, and the top 10k pot adjusts the volume.  Is there a way I could have a volume pot for each "section" with only one knob for adjusting the bandwidth?  The peak frequency would be static in this case with pre-determined inductors instead of having to simulate them.  I can't figure out how to do this.  I assume just having all of these "sections" go through the same resistor wouldn't work, but then again they are all going through the same op amp, so I can't be sure.

Thanks in advance!

[oskar]

My only problem is I don't know which op amps to use.

TL072, 4558, NE5532... for instance.

Secondly, the way I see it is that the bottom 1M pot adjusts the peak frequency, the middle 10k pot adjusts the bandwidth, and the top 10k pot adjusts the volume.  Is there a way I could have a volume pot for each "section" with only one knob for adjusting the bandwidth?  The peak frequency would be static in this case with pre-determined inductors instead of having to simulate them.  I can't figure out how to do this.  I assume just having all of these "sections" go through the same resistor wouldn't work, but then again they are all going through the same op amp, so I can't be sure.

I'm not sure I've understood you correctly but are you familiar with dual ganged pots? That's what you need if you want to controll the resonance of both section with one knob.

[PoopLoops]

Awesome, thanks for the suggestions.

No, I don't know about dual ganged pots.  I'll look into them.  Thanks.

EDIT:  Okay, those things are almost impossible to find.  Apparently 4-ganged pots are only known from wild myths and legends from far away lands.  Ahh well... I guess a more realistic solution is to just use 4 trim pots and find settings that I like. =/

[oskar]

No, I don't know about dual ganged pots.  I'll look into them.  Thanks.

EDIT:  Okay, those things are almost impossible to find.  Apparently 4-ganged pots are only known from wild myths and legends from far away lands.  Ahh well... I guess a more realistic solution is to just use 4 trim pots and find settings that I like. =/

I knew there was something I didn't get. I still don't get it... why 4-ganged?    I thought basically that you wanted to control the two resonance pots with one knob... where do I go wrong here?
Anyway, if you want a flexible filter maybe you should check out the ones used in the world of synthesizers?
http://jhaible.heim.at/tonline_stuff/hj_wasp.jpg
that link is the closest I could think of, because your earlier post also mentioned distorting things...   

[PoopLoops]

I knew there was something I didn't get. I still don't get it... why 4-ganged?    I thought basically that you wanted to control the two resonance pots with one knob... where do I go wrong here?

Sorry, I wasn't really clear.  The schematic I posted uses two "modules" for high and low frequency control (or really any 2 frequency bands you pick), whereas I want to add two more of those things so that I have 4 different frequency bands to control, in my case low, low mid, high mid, and high.  Or, low, mid, high, ultra high (for harmonics).  Whatever.  In any case, I'd like to be able to control all 4 resistors with one pot, but I guess I can just go with 2 dual ganged pots, or hell, two push/pull pots.  Might as well control all 4 individually in that case.

Anyway, if you want a flexible filter maybe you should check out the ones used in the world of synthesizers?
http://jhaible.heim.at/tonline_stuff/hj_wasp.jpg
that link is the closest I could think of, because your earlier post also mentioned distorting things...   

Thanks for the schematic.  Yeah, I want to also make a distortion pedal.  I had hoped I could just add the EQ and distortion electronics into the same box, but I figured I'd ask for one thing at a time so that people don't look at my post and just click the "back" button when the see the wall of text.

I found some schematics for distortion pedals (there are a ton as I'm sure you know) and I just need some advice as to which ones are "good" and which ones are "cheap".  I found a few with 1 transistor by itself and a pot or something.  Pretty simple and I don't think it would be versatile or sound very good.  I also found a lot that replicate the Boss Metal Zone.  I just need to look into whether I want to replicate it and then I can decide whether or not to go with one of those pedals.

Do you have any specific suggestions for distortion pedals?  I'm interested in getting a sound similar to Iron Maiden, early Metallica and Iced Earth, or Megadeth on Rust in Peace.  Basically very crisp sounding, not muddy like a lot of death metal is.  And kind of bright sounding.  Covering the low end is what bass players are for (i.e me as well!)  I guess that's down to EQ though.

For some music samples, it would be like these:

http://www.youtube.com/watch?v=mYlUe-SDqA0&feature=related
http://www.youtube.com/watch?v=t-G9O5KbyBM&feature=related
http://www.youtube.com/watch?v=UX2jrWifKak
http://www.youtube.com/watch?v=dTaD9cd8hvw

Sadly Youtube videos aren't that high quality, and basically all of those sound a bit "lower" and muddier than what you'd hear on a CD.

To compare, what I am not looking for is something like this:

http://www.youtube.com/watch?v=3RkIks85g6k
http://www.youtube.com/watch?v=sRmRm8JC6hg

I like these bands, but don't want to sound like them.  I like the instruments to all stand out instead of blending together into one stream of notes.

Anyway, thanks for all your help.  I'm not expecting you or anybody to know exactly what I should build, but I'm throwing this out there on the off chance that someone can point me in the right direction.

[Mike Burgundy]

Fwiw - for normal use a fixed Q (bandwidth) is fine. If you want a really flexible EQ which you can use for tone-shaping (wide-band, low Q) AND for problem solving (High-Q, narrow band, f'rinstance to eliminate feedback on one difficult frequency) you'll want adjustable Q on all bands - individually. I personally think having one control for all bands will severely limit the added value of the extra control on the pedal.

[oskar]

In the end of the soundchain all these bands are pushing an amp. Probably most of them Marshalls...
These are recordings and what happened to the sound after it left the speakercone?
But one thing many of these guys are using is probably graphic equalizers somewhere.

Hm. But if you're really serious about distortion....    http://www.youtube.com/watch?v=1WcsV7hQ1V4

[DSV]

For some ideas of a really basic but effective equalizer you can check my preamp (schematics are in post 6):
http://www.diystompboxes.com/smfforum/index.php?topic=71425.0

The pre-equalizer has got two bands with low Q (wide), for gain-shaping, whereas the post-eq is an Baxandall tone stack, with a mid control based on an equalizer band. Finally, the cab-sim part is provided by 2 LC networks, each being a 2nd order low pass filter.

[PoopLoops]

Fwiw - for normal use a fixed Q (bandwidth) is fine. If you want a really flexible EQ which you can use for tone-shaping (wide-band, low Q) AND for problem solving (High-Q, narrow band, f'rinstance to eliminate feedback on one difficult frequency) you'll want adjustable Q on all bands - individually. I personally think having one control for all bands will severely limit the added value of the extra control on the pedal.

Yeah, that's a good point.  I'll have to think about this.  One of the reasons I don't want 9+ knobs on this thing is because I have ADD and I would spend more time playing around with sounds than actually playing. :p  This was definitely the case with my Bass POD, which is why I am selling it hahaha.

In the end of the soundchain all these bands are pushing an amp. Probably most of them Marshalls...
These are recordings and what happened to the sound after it left the speakercone?
But one thing many of these guys are using is probably graphic equalizers somewhere.

Good point.  But the kind of distortion they are using still plays a pretty big role.  I'm not expecting to sound exactly like them, but going with something like a Boss Metal Zone clone apparently isn't what I want, since form the reviews I read people say it's the noisy and muddy kind of distortion that I'm not looking for.

Hm. But if you're really serious about distortion....    http://www.youtube.com/watch?v=1WcsV7hQ1V4

I love that video!  hahahaha  Now I need to import a walnut from Finland or Norway so I can build my own.

[bassmasta17]

Hm. But if you're really serious about distortion....    http://www.youtube.com/watch?v=1WcsV7hQ1V4

schematic... i need one...

[PoopLoops]

Umm... I'm having some trouble calculating the frequencies to set each "band" to.  So I'll have 4 sets of knobs, one for deciding peak frequency, one for Q, and one for boost/cut.  I don't know what frequencies to set the peak to.  For example for guitar I know the low E is about 102Hz, but that doesn't tell me anything because I don't know if that's what I want to be boosting or if that would make it sound bad, you know?    Is there like a "safe" bass frequency range I could set as my peak?  Then the same for low mids, high mids, highs? 

[Ben N]

Not claiming any expertise in EQ circuits or how they behave, just in semantics: "resonance" doesn't exactly mean bandwidth, but rather more like the ratio between the bandwidth and the peak. As for building the thing and how many knobs you need, where to set things like the Q, why don't you breadboard it with everything pot-able hooked up to a pot, and play with a it a while. See what tends to stay in one place, measure and substitute a fixed resistor (if you're sure) or trimpot (if you want to be able to come back to it). See what tends to get tweaked a lot for different tones, and keep that as a pot. No doubt you will find that for your distortion needs, there a lot of things (like bandwidth) that you can set and forget, once you play with it a bit. Or make all the Q and freq controls trimpots, then set to taste.
BTW, you can simplify your life by substituting highpass and lowpass filters for the high and low bands, especially if there are going to be four of them.

[PoopLoops]

Hmm... good point about the high/low pass filters.  Yeah, I plan to breadboard everything first before I do any soldering.

As for distortion, I decided to make a separate pedal for that and keep that one very simple, on/off, gain, and output volume.

[Ben N]

I don't get credit for that suggestion--like many other good ones, it came originally from Mark Hammer, who has put up a few thoughtful posts about how much eq is enough to cover guitarists' needs.