GEOFEX Simple Easy Graphic Equaliser

[Woolly Mother Mammoth]

I'm building the GEOFEX Simple Easy Graphic Equalizer and I'm in need of some help. I've built the 1khz section (for now) and the op-amp (RC4558P) part so far.

All I get is hum, which use to be an indication that there is something wacky with the ground connection, but I can't find any weird/bad or wrong connections.
What bothers me is the 5th, 6th and 7th leg of the IC, they all got exactly the same voltage reading.

More info on the equalizer can be found here: http://www.diystompboxes.com/smfforum/index.php?topic=84033.0

Q4 (2n3904)
E: 3.92
B: 4.19
C: 9.0

IC (RC4558P)
1 4.72
2 4.72
3 1.21
4 0.0
5 4.43
6 4.43
7 4.43
8 9.0

[Woolly Mother Mammoth]

whoa, before anybody wastes their time! Found a bad connection between C18 and R24

Another question, is this circuit really in need of a buffer? Read about it in the other GEOFEX SEGE thread.

[Woolly Mother Mammoth]

Bump  

Need help on how to recalculate the 150hz section into 200hz, to get rid of some mudd. I'm demanding, I know!

Been trying my hardest to understand slotbots explanation but without any luck.

f = (2*pi*sqrt(Rq*R2*C1*C2))^(-1)

so

it means just R in ohms and C in Farad like 1 meg ohm = 1 000 000 ohms

1 uF  = .000 001 F  => .047uF = .000 000 047 F

u is a suffix meaning *10^-6 and M is *10^6

K is *10^3 so for exampke 6.8K is 6800 becasue 10^3 = 10*10*10 = 1000.

f I understand right its R1 X R2 X C1 x C2 divided by 2 X Pi divided by 1

not quite how i would phrase it.


an example. say c1 is .01 uf and c2 .02 uf, R1 = R2 = 22k

first calculate c1*c2*R1*R2 = 22K*22K*.01uF*.02uF = 96 nS^2 ( thats nano seconds^2)

now take the square root of that you get 311mS

result * 2 * pi = 1.95 mS

now the whole denominator is calculated so take 1 over that. ie 1/result = 1/1.95ms = 511.54 Hz



edit: sorry i didn't see you asked for the 60 Hz.

same steps....

c1*c2*R1*R2 = 6.8K*6.8K*.1uF*1uF = 4.624 uS^2

sqrt(4.624uS^2) = 2.150mS

2.150mS * 2 *pi = 13.51 mS

1/13.51mS = 74.0135 Hz

so its around 60 Hz.


and also for Q its a bit easier. it look s like the q chosen was ~ 1.58

for all the filters C2/C1 is 10
sqrt 10 = 3.162
and .5* 3.162 = 1.58

[R.G.]

Need help on how to recalculate the 150hz section into 200hz, to get rid of some mudd. I'm demanding, I know!

Been trying my hardest to understand slotbots explanation but without any luck.

There is one more layer of complexity in this. The setup of this kind of equalizer is a bit complicated. The bandwidth of the filter sections, all that Q= (mess of stuff)/(some more stuff) ^-pi is important to get the sections to sum to nearly unity.

And in the simplistic version with one pot and one LC per section, the Q is a variable, lowest at 0db boost/cut, and highest at max cut. There are constant-Q equalizers, but they're quite a bit more complicated.

When you shift one of the sections, you have to shift all the others so that away from +/- 0db, they give not-too-ripply a response from adjacent frequencies.
So if you shift one section up 50Hz, you have to shift the other sections too, exponentially-proportionately, so you get a flat response and not too much interference between adjacent sections. You have to recalculate them all. Not that it's all that tough, but it's probably necessary.

[Woolly Mother Mammoth]

There is one more layer of complexity in this. The setup of this kind of equalizer is a bit complicated. The bandwidth of the filter sections, all that Q= (mess of stuff)/(some more stuff) ^-pi is important to get the sections to sum to nearly unity.

And in the simplistic version with one pot and one LC per section, the Q is a variable, lowest at 0db boost/cut, and highest at max cut. There are constant-Q equalizers, but they're quite a bit more complicated.

When you shift one of the sections, you have to shift all the others so that away from +/- 0db, they give not-too-ripply a response from adjacent frequencies.
So if you shift one section up 50Hz, you have to shift the other sections too, exponentially-proportionately, so you get a flat response and not too much interference between adjacent sections. You have to recalculate them all. Not that it's all that tough, but it's probably necessary.

Thanks R.G for taking the time explaining it to me. I think I'll skip the recalculation and just build it straight forward.  My math skills are in great need of cultivation.

I got two sections  ready and functional, the 150hz and the 1khz (at least from what I hear) or are they dependent of the rest of the sections to affect the accurate/desired frequencies? 

[Woolly Mother Mammoth]

I also noticed that it is a very noise/hissy one, both with boost and cut. Especially when I place it in front of my Black Fudge Fuzz, where I need it so badly. 

Any ideas why, could something be improved or is it just the way this circuit is?

[R.G.]

I also noticed that it is a very noise/hissy one, both with boost and cut. Especially when I place it in front of my Black Fudge Fuzz, where I need it so badly. 

Any ideas why, could something be improved or is it just the way this circuit is?

It's not a naturally hiss-prone circuit. The gain is low and the impedances are low. It does include gyrators, which can be hissy, but that's a bit unusual in this circuit.

I would suspect oscillation first. Solder a 0.1uF ceramic capacitor between pins 8 and 4 of the opamp and see if it changes.

[Woolly Mother Mammoth]

It's not a naturally hiss-prone circuit. The gain is low and the impedances are low. It does include gyrators, which can be hissy, but that's a bit unusual in this circuit.

I would suspect oscillation first. Solder a 0.1uF ceramic capacitor between pins 8 and 4 of the opamp and see if it changes.

As usual YOU my good sir is invaluable for this forum. Hats of!

I'll try to learn something from this from all of this, even though I'm still very confused about the calculation.

[Woolly Mother Mammoth]

The .1uF made no difference. Guess I'll try some other caps and see what happens. The noise/hiss are strongest from around the mids, if that info is of any value.

[R.G.]

Another good theory all shot to blazes.   

I'll think some more.

[Woolly Mother Mammoth]

Another good theory all shot to blazes.    

I'll think some more.

Much appreciated, also it is more of a noisy figure than hissy.

[R.G.]

Hmmm.

The worst sources of noise in this thing are likely to be the gyrator sections or the normal thermal hiss of the resistors. That last should be very small, given only that all the solder joints are well made and the resistors are undamaged.

Thinking about the gyrator sections, a noisy transistor is a possibility. Beginners are so ready to say that the parts are bad instead of there being build bugs, I hesitate to ever admit that parts can be bad - but clearly they can. In the interest of experimentation (if you're willing) you could try this:
- pull out capacitors C2, 4, 6, 8, 10, 12 and 14. This disables the resonant filters entirely.

Is it still noisy? If so, it's something about the opamp or else the noise is getting in through the power supply and/or ground.

If it's not still noisy:
- add back in capacitors, one at a time. Test and note carefully if noise increases with each cap a little, or mostly from one capacitor. If it jumps a lot with one of the caps, then there is something funny about that section, possibly a noisy transistor.

[Woolly Mother Mammoth]

Hmmm.

The worst sources of noise in this thing are likely to be the gyrator sections or the normal thermal hiss of the resistors. That last should be very small, given only that all the solder joints are well made and the resistors are undamaged.

Thinking about the gyrator sections, a noisy transistor is a possibility. Beginners are so ready to say that the parts are bad instead of there being build bugs, I hesitate to ever admit that parts can be bad - but clearly they can. In the interest of experimentation (if you're willing) you could try this:
- pull out capacitors C2, 4, 6, 8, 10, 12 and 14. This disables the resonant filters entirely.

Is it still noisy? If so, it's something about the opamp or else the noise is getting in through the power supply and/or ground.

If it's not still noisy:
- add back in capacitors, one at a time. Test and note carefully if noise increases with each cap a little, or mostly from one capacitor. If it jumps a lot with one of the caps, then there is something funny about that section, possibly a noisy transistor.

I tried what you suggested, sort of anyways. I pulled both 150hz and 1khz lug 2 connections and R5 and R11 connections to 4558s 7th and 6th legs. It results in somewhat less noise, I noticed that when connection lug 2 to the 1khz (section 4) the noise increased a lot.

[Woolly Mother Mammoth]

One thing I forgot to mention, the RC4558 IC needs 18v so I change from 9v to 18v. Still the same amount of noise, though.

EDIT: Ok, to make one thing clear. Only when I have my fuzz engaged with the EQ first it gets super noise. But no noise if I use either the EQ or Fuzz separately.

[R.G.]

One thing I forgot to mention, the RC4558 IC needs 18v so I change from 9v to 18v. Still the same amount of noise, though.

The 4558 doesn't need 18V. It works fine at 9V.

EDIT: Ok, to make one thing clear. Only when I have my fuzz engaged with the EQ first it gets super noise. But no noise if I use either the EQ or Fuzz separately.

It is possible that the two do not play well together.

[Woolly Mother Mammoth]

The 4558 doesn't need 18V. It works fine at 9V.

wha.. wait..hold on a minute...

Your right! I don't know where I got that info from, strange..

It is possible that the two do not play well together.

Sure it could be the case, but I better check the fuzz for any weirdness just incase.

[Woolly Mother Mammoth]

My gosh.. this build is just full of suprises! Bare with me..

When I daisy chain my fuzz and this eq AND place the eq after the fuzz, no problem. BUT when I place it infront of the fuzz I GET NO SOUND AT ALL!? Ground loop or what?

Sorry, I'm just loosing my mind a bit here..

[R.G.]

When I daisy chain my fuzz and this eq AND place the eq after the fuzz, no problem. BUT when I place it infront of the fuzz I GET NO SOUND AT ALL!? Ground loop or what?

I believe that Mother Nature is whispering in your ear that all the wiring is not the way you think it is.

[Woolly Mother Mammoth]

I believe that Mother Nature is whispering in your ear that all the wiring is not the way you think it is.

I can hear her..

[Woolly Mother Mammoth]

Tried it again today (after a good nights sleep) and it turned out I had a bad patch cable. Do I feel like a total idiot, yup.

I change the input and output jacks from some cheap plastic to sturdy metal jacks and boxed it up, which of course help me out with the higher noise and 60hz-ish hum. Still some hiss going on but I'm pretty sure the 15Khz section can dim that out.

R.G, I want to thank you for spending your time helping me out, much obliged.