Eq schematic simplification

[Emetal]

I found this DIY EQ: http://www.runoffgroove.com/mreq.html

I myself only have a need for MID boost, do not need any of the LOW and HIGH functions. Could I simply throw away the parts of the circuitry I have circled in red on the scheme or I still need to build the whole device? Also what part of the MID circuitry I can also omit since I do not need CUT but only the BOOST part?

[JazzGuitarGimp]

The CD4049UBE is a logic gate: a hex inverter to be exact. It's not going to pass audio. It kind of looks like an inverting op-amp stage was intended for each of the four logic gates. You could use a TL072 for the op-amp, but you'll either need a bipolar power supply, or you'll need to make an artificial ground by making a voltage divider with two 10K resistors in series, connected between +9V and GND. You'll get 1/2 the battery voltage at the mid-point on the divider, which you'll want to decouple with a 1,000uf or so electrolytic cap. Don't delete any of the Mid-circuit components, but there is not reason you couldn't use a SPST switch, and just connect it to the side that will give you a Mid-Boost. But it is safe to delete the Hi- and Low-band circuits as you have indicated.

[LOUDthud]

The 4049UB, 4069UB or 74C04U have been used to pass audio since the Nixon administration. See if you can find National Semiconductor (now owned by TI) application note AN-88 (corrected). You must use Unbuffered gates, usually there is a U in the part number.

They do tend to draw lots of current at voltages above 5V. With a 1K in series with a 9V battery, all 6 gates will draw about 4mA. Without the 1K about 17mA. Connect unused gate inputs to ground so those gates don't draw current. A resistor from output back to input will bias the output near mid rail.

The one strange thing about CMOS is that as the supply voltage goes up, the bandwidth goes up but the voltage gain goes down. So at higher voltages, they can oscillate at ultrasonic frequencies if the layout is not right. You can connect gates in parallel at lower voltages to increase the output drive. At 3V supply you can make an overdrive pedal, but they tend to sound a little fizzy.

[JazzGuitarGimp]

LOUDthud, are you saying this part gas a linear, analg output? Even if so, i'm not sure why someone would use it as an opamp when opamps are plentiful and cheap.

[Emetal]

Well since the guys at http://www.runoffgroove.com/mreq.html did build it and proved it is working let's assume that CD4049UBE is passing audio, if that is settled, than are you guys saying I can build it exactly as I marked it on the scheme, right? Or if there is cheaper or less current consuming version with some other opamp can somebody draw me a schematic I am not that good with this, I just know the basics

[gui_tarzan]

I don't remember the version but I built a 4049 fuzz box back in the mid 80s and it absolutely does pass audio. It has a very cool distortion characteristic but is sucks batteries dry in a hurry.

[LOUDthud]

Got the ap note number wrong, it should be AN-88. Here's a link: http://www.fairchildsemi.com/an/AN/AN-88.pdf I have no idea why it's on a Fairchild website.

CMOS sounds great for guitar because it produces low order distortion and clips softly. The higher the supply voltage, the softer it clips but the amount of feedback in the circuit also changes the clipping. Very tube-like in the right circuit. I like to use it at low voltages, ~3V where it only draws micro amps but you need something to buffer the output, a JFET or (ugh) an opamp.

[Tillydog]

...can build it exactly as I marked it on the scheme..?

Yes.

Make sure you get the chip with the UBE suffix.

It is a logic chip, but early(-ish?) CMOS is quite good as a linear amplifier. The reason it uses (relatively) high currents is that it's operating in class A!

(It'll still not use much more current than an LED would)

As said, tie the inputs you don't use to gnd or vcc. Don't leave them floating.

[Emetal]

Thanks a lot Tillydog and everybody else

[Emetal]

I'we build it and it is working Best place for it is in the loop between preamp and poweramp.. no noise at all, if placed in front of an amp it does get noisy a little. Now I am curious how would the whole thing sound with Lows and High's circuitry gotta do it when I catch more time

[JazzGuitarGimp]

Good job! And I learned something new - it's a good day all around!

[teemuk]

...are you saying this part gas a linear, analg output?

It passes as an amplifier. But "linear" is somewhat misleading term for it though. In practice the operation is linear only at a very narrow range of the transfer curve.

... i'm not sure why someone would use it as an opamp when opamps are plentiful and cheap.

Because it distorts and the knee of non-linearity is much rounder than in any generic opamp....?

But yes, using logic chips in EQ is kinda like building a distortion with EQ as gain control so I'm not overly sure why they chose that component aside from the facts that it was fascinating and happens to provide some gain. Then again its ROG, I don't even have to try understand all the quirks in their designs. At least they sort of work, which isn't always the case with "Internet designs".

Here's the application note, by the way:
http://www.fairchildsemi.com/an/AN/AN-88.pdf
Note the time they wrote the original one (1973). The soft clipping characteristics of CMOS gates have been known that long and used almost as long in several guitar amps or effects.