Parametric Mids

[fuzzo]

Hi, I want to build another FX pedal but I don't know which. So, maybe a parametric mids to replace my boss Ge7 (placed before my disto/overdrive/fuzz to boost mids)

Someone has built a parametric EQ ? a  parametric Mids EQ ?

(maybe something similar to "maestro parametric filter")

thanks !

[Mark Hammer]

Look at the documents on www.geofex.com for some examples of easy parametric EQ.

[fuzzo]

you mean this one ?

yes, I'm reading it.

[Mark Hammer]

That's it.

[fuzzo]

Hi,

I read this very good article and I think I need just one EQ section. Actually I use a boss GE7 before my overdrive/fuzz to boost 400Hz to have a sound more fat and present.

So, this schematic seems to be very simple and easy to build for this application.

[fuzzo]

i did a schema, looks good or not ?

http://img98.imageshack.us/my.php?image=parametriceqpi3.png

[Mark Hammer]

Though not fully parametric, I have used this particular circuit many times with success.

The circuit assumes you are using a bipolar supply, or are feeding it a signal that is already sitting on a 4.5V reference.  Note that it provides a gain of 2x as shown, though you could increase this by making the 10k resistor that goes to ground a little smaller.

C1 and C2 can be replaced with several caps in series, so that you can use a toggle or rotary switch to select among values.  For instance, if you had each of those caps replaced with a .1uf and .047uf in series, then you could have a choice between a boost at 200hz, 425hz, and 625hz.  Like I say, not quite parametric, but certainly flexible.

Note that it only does boost and not cut.  In your case, that is exactly what you want.

[fuzzo]

yeah I know this pedal, maybe  i'll do  too ! (I did a stripboard of this frequency booster). 

But I don't know why but I want to do a bigger project than a simple 9V pedal, to have more dynamic in using a -15V/0V/15V supply. But I have to find a "rack box" before making this parametric EQ.

Otherwise, my schemo (based on geofx's schematic) is good or not ? Here too, I could use a rotary switch to select bass, middle, treble. Just C1 and C2 change.

thanks for your help.

[Mark Hammer]

I would answer your question (schem good or not?) but I can't see things on photobucket or imageshack at work (they are blocked).

[fuzzo]

ok maybe this link ?

http://www.hiboox.fr/go/images/divers/parametric-eq,37ae2fde373efc36f1c5dc34a5982fbe.bmp.html

[Mark Hammer]

Nope.  Still blocked.  I'll look once I get home, where there are no filters.

[Mark Hammer]

Okay, looked it over and it seems fine.  Based on what you say you want it for, I'm not sure you need more than two ranges.  That should cover enough of the bass and treble for your tastes.

Just a tip.  When you leave caps with a "free end" unconnected to something, you may often hear a pop when you connect them with a switch.  One way to avoid the pop is to use two caps in series.  Remember that if you use two same-value caps, the effective capacitance will be half when in series (e.g., .047 + .047 = .0235).  If you use two 15n caps in series for SW1b and two 330n caps in series for SW1a, and replace SW1 with a DPDT toggle that either leaves both caps in series or shunts one cap of each pair, you will have two ranges without experiencing any pop when you switch ranges.

[fuzzo]

hi,

fine. Actually, I wanted to do just a parametric Mid, but in reading geofx page, I understood C1/C2 change to select the range, so why not ?

When you talk about "two range" you mean which ranges ? treble/bass ? low mids/high mids ? Or a mix between (bass-low mids / high-mids-treble) ?

Actually, the range nombers will depend of the box.

For the "pop", isn't important, I don't care , I don't use the selector range when i'm playing. I've the same thing on my crybaby 535Q and I've no problems with it. But thanks for the tips!

[Mark Hammer]

By "two ranges" I simply meant a higher and lower range.  I don't know what you'd call something that sweeps centre frequency from, say, 200hz to 2khz.  For the purposes of boosting a resonant frequency in a guitar signal, you wou'd really have no need to go much lower than 200hz, or much higher than 4khz.

[fuzzo]

Ok thanks for your help.  I take notes about all that.

I must finish my current projects (I have to buy missing parts) and I continue to think about this parametric EQ.

[fuzzo]

I cannot edit my last post, so I do another one.

If I put an input JFET buffer  I can remove the first AOP used in buffer , and connect directly the output of jfet buffer with the 2k7 R ?

[fuzzo]

I bump my old thread, I'm still thinking about building one of these Parametric EQ .

Well, the mt2 tonestack looks interesting especially the fact you can control bass and treble with a semi-parametric EQ.plus, I take the volume control presents on GE7 to have a perfect balance with the bypassed signal.  So I kept that idea and drew that :



What do you think about it  ?

Should I put the "parametric mids" in parallele with the bass/treble control ?

Distortion could appears with that kind of circuit ?

[fuzzo]

any suggestions/ideas/critics about my new schematic ?