Parametric eq noises scares me

[Eb7+9]

Yeah, I know what you mean. I'm not a pro, indeed, I just know something more than one year ago, but it's true, I use to build pedal effect or circuits on stripboard. Totally amateur.
Anyway, a lot of us are guitarists or musicians, and if someone plays the device built himself strengths and weaknesses could hear. Often noise, oscillation, ticking... are reported.
Well, it's another topics.

As far as circuit performance is concerned there is no real accounting here // the moderator shows little teeth and even less knowledge in electronics ... anybody can snowjob all they want here and present ideas that hold no water, that's been par for the course for the duration of the forum ...

Enjoy your stay here but don't expect solid knowledge to be shared ... and don't forget that those who really know their shit might not want to share the knowledge you seek simply because it might conflict with their professional aspirations ...

[Elijah-Baley]

I built the veroboard layout of this 3-band parametric with Frequencies and Q variable.
In stock schematic it works fine, every controls is ok. But I got the white noise, the same white noise that make me to abandon the old 5-band. In flat is a bit better, but if I boost or even cut some band, at any Q or Frequancy set it add noise like it was a high gain pedal. I have some DIY high gain pedal less noisy than this. I can get good sound with this EQ, but it's useless if it adds white noise in the background. It's always better play without it.
It's like I need a noise gate to play clean, it sounds like a joke.

Is this white noise normal? I think yes, but how could it be?

[Eb7+9]

some gyrator circuits are better than others in terms of hiss ... and then there are active inductor circuits ... unfortunately the "simple" gyrator types chosen above are the worse ones, and noise increases as we introduce higher resistance in these circuit - in this case to tune inductance ... a loose-loose situation imo ... yes it works - but pretty useless for low level signals ...

I once tried w low-gain active inductors for fun - based on the Shinei ckt ... a little active noise as expected, but still manageable ...

a dual opamp GIC approach can be made even better for noise, and it's also tunable without comparable drawbacks ... I used those in my early 360 clones and they worked well ..


http://www.lynx.net/~jc/pedalsClassAeq.html

[Elijah-Baley]

[...] unfortunately the "simple" gyrator types chosen above are the worse ones, and noise increases as we introduce higher resistance in these circuit - in this case to tune inductance ... a loose-loose situation imo ... yes it works - but pretty useless for low level signals ... [...]
[/url]

Great!
But I guess I seen some pedal schematic with this kind of gyrator: Boss HM-2 (just two bands) and Boss GE-7 (6 bands + a sort of another extra band). Why they doesn't sound so noisy? The GE-7 could be a bit noisy, but I know that replacing the low current IC with some low noise IC it's very better.

Thanks for the link.

I can't see much pedals to use inductor in the parametric eq, I think there's another way to get it. What type I should use to get a 3-band parametric eq noiseless for an acoustic preamp?

[Eb7+9]

I seen some pedal schematic with this kind of gyrator: Boss HM-2 (just two bands) and Boss GE-7 (6 bands + a sort of another extra band). Why they doesn't sound so noisy?

The GE-7 makes use of pre-emphasis/de-emphasis filtering at the front and back to improve signal-to-noise in the higher "hiss" noise region ... their choice of 100k/82k leg resistors makes things noisy, prob. for sake of using smaller caps (manufacturing trade off ?!) ...

notice in my active inductor circuits my leg resistors are 470r which brings down the noise a lot ... but I'm also using larger caps

The GE-7 could be a bit noisy, but I know that replacing the low current IC with some low noise IC it's very better.

Thanks for the link.

I can't see much pedals to use inductor in the parametric eq, I think there's another way to get it. What type I should use to get a 3-band parametric eq noiseless for an acoustic preamp?

can't get away from noise completely, all you can do is work to improve you're s/n ratio ...

as noted try to use a lower noise GIC (variable) inductor emulator or something lowZ discrete like mine, consider the type of topology you're going to use (opamp based like BOSS or low gain single-ended like SHINEI), if you're gonna use opamps use the good low-noise stuff, also consider inserting this eq stage late in your preamp where signal has already been built up, and lastly consider using an emphasis/de-emphasis strategy like BOSS does ...

If you already have an acoustic preamp then all you have to do is crank up the preamp going into the eq and attenuate at the output of the eq. as required ... this is the most important way to maximize your S/N ...

but also a different application to sticking an eq. in front of a Marshall where noise gets maximized in the process of creating frequency selective dirt

[ElectricDruid]

can't get away from noise completely, all you can do is work to improve you're s/n ratio ...

+1 This. Completely this.

Also recognise that there isn't one answer. Instead you usually have to do several things at once to get a low noise result. Changing the op-amps helps, but won't be enough on its own. Lower value resistors helps, but won't be enough on it own. Pre/de-emphasis?...etc etc..all this stuff together? Might just work.

The final part is the signal going in. If you've got some hiss on your input, and you put it into a perfect completely noise free pre-amp and then boost one of the bands by 20dB, you're going to get significant and objectionable hiss at the output. And that's with *no noise added by the preamp at all*. You need a really quiet input signal, and that's hard with a guitar.