Equalizer 5-band by GGG on veroboard is noisy

[Elijah-Baley]

Doesn't matter. I've got a problem here. After a while the I got a distortion/clipping sound. I had fixed it early replacing C13, but it comes back now.

This is the voltage, the battery is a bit low: 8.45v.

IC1
1 4.85
2 3.96
3 3.95
4 7.94
5 5.84
6 5.89
7 5.89
8 3.95
9 3.95
10 3.22
11 0.00
12 3.21
13 3.94
14 3.94

IC2
1 3.94
2 3.94
3 3.21
4 7.85
5 3.91
6  3.20
7 3.90
81.51
9 0.95
10 0.94
11 0.00
12 3.16
13 3.20
14 3.85

[Kipper4]

Ic2 pins 8,9,10 do those look right ? Without looking at the schematic I can't tell for sure.

[Elijah-Baley]

I link again scheamatic and even the layout, because it could be slightly different.

[...]
http://www.generalguitargadgets.com/pdf/ggg_eq6bg_sc.pdf
[...]

[...]

[...]

Anyway, the circuit doesn't work as first, when it worked fine but with noise. Now, the sound is a bit dull, the frequency pot works, but the gain pot doesn't work properly, it doens't control the volume, just the tone change a bit.

I'm gonna replace the other 10uF caps one by one because those was taken off by a failed and noisy Little Angel abandoned time ago. Honestly, I don't trust in it so much. We'll see.

[PRR]

> gain pot doesn't work properly

It has a cap which should NOT be in there. Same error on schematic and on Vero drawing (though different part numbers?). The fix for an already-build board is to short the cap. (If the cap were not in yet, you would insert a jumper and save the cap for another project.)

[Elijah-Baley]

There's somthing really weird here, because I replaced other caps 10uF, resolder some point on the board, and switched between them the IC, just to see. I tested the circuit and for a while it worked fine, a lot of volume (and a bit of white noise, the first problem), and the gain pot worked well. While I was turning the other pots the gain pot work bad again. It is like a compressor, I have slightly more volume at low setting, at high setting the sound is compressed and a bit distorted.

About the schematic... I can try to take off that cap and put a jumper, but it should be verified.

[rankot]

About the schematic... I can try to take off that cap and put a jumper, but it should be verified.

C13 is definitely in a wrong place - it is not needed at all.

[Elijah-Baley]

What about the orientation of C14? Look at the layout, look at the schematic.
On the Sabrotone layout, and on the its page, it seems has been corrected, but... I'm not sure.

[Kipper4]

The orientation of C14 looks fine.
Where you thinking it is anode + to Gnd?
If you look there's a cut at A7 which isolates it from the Gnd.

[Elijah-Baley]

Thanks for the image, PRR.

I could wrong, but look this:

[...]

Schematic: Input goes in the positive of C7 (C14 for Sabrotone).
Layout: Input goes in the negative of C14.

Here the discussion, even about the orientation of C14: http://www.sabrotone.com/?p=99
They said: "negative side of C14 goes to input", just like the layout, then it should be work, even if I can't explain it.

[PRR]

> Input goes in the positive of C7 (C14 for Sabrotone). ... Input goes in the negative of C14.

This is don't-care. Actually C7-C14 should be non-polar. There is zero DC volts across it. However polar electros work very well this way. EITHER way.

MY problem is that C8-C13 should NOT be there at all.

And one possible symptom is that things work erratically. (IC1? does not know what DC to be at, and can get stuck.)

[Elijah-Baley]

I soldered socket pin for C13 and C14. Used a 1uF film cap for C14 and a jumper for C13. But it still doesn't work. Tried also a 1uF for C13, no changing. Gain pot works like a sort of compression pot, encreasing it I lose a bit of volume.

IC1 stuck? What I have to do?

[Kipper4]

MY problem is that C8-C13 should NOT be there at all.

[Elijah-Baley]

Yes, I tried even to jumper it, but there's no difference. I still have the same issue with the gain pot, low volume and a bit of clipping.

[Elijah-Baley]

I tested the circuit again, immediately with a jumper instead the C13 cap. C14 like in the schematic. It worked.

I don't know why today it's working. Is it because of this?

[...]
(IC1? does not know what DC to be at, and can get stuck.)

I got, anyway, just that bit of white noise, like at the first test. I have to try to put it in the drilled box.

[Elijah-Baley]

I probed the signal. I get the slight hum in the first part of the circuit. After the first gain stage and before the gain pot.
http://www.generalguitargadgets.com/pdf/ggg_eq6bg_sc.pdf

[...]
Any circuit with highly selective gain stages like an EQ is going to have a tendency to be noisy.
[...]

I'm trying the circuit in front of the amp, is it because of this it is so noisy in the distortion channel?
What is the typical position of the eq in a pedal chain?

You might get more headroom out of it using the dual supply.
Or a charge pump +9v -9v maybe a icl7660.
[...]

I can decrease the hum with a charge pump?
What of these two?

[rankot]

If you build voltage doubler, it is much better to use LT1054 than 1044 or 7660. If you have to use 7660, make sure you use 7660S and not 7660A, because S can be used with frequency boost.

[Elijah-Baley]

Thanks!
I know what the voltage doubler does, but I don't know what the +9v/-9v does.
And what about my eq?

[rankot]

I know what the voltage doubler does, but I don't know what the +9v/-9v does.
And what about my eq?

Voltage inverter is something you need for this EQ if you want to run it on ±9V, and you have only +9V supply. So you build this inverter and it produces -9V, then connect that -9V to point B on EQ schematic (http://www.generalguitargadgets.com/pdf/ggg_eq6b_sc.pdf), connect +9V to point A and ground to point C. You will have double headroom, but I don't think it will reduce the noise you have.

I have also built similar EQ (4 band) and it has some noise, but not much. If all EQ pots are in the middle, there should be no noise at all!

[Elijah-Baley]

I should to find the point A, B, C on the sabrotone layout, but if you think it is nothing to do with the noise...
I am almost sure the boards is ok and the eq is right so.
Probably it has to be used after the distortion.

[rankot]

Do you have noise when all EQ pots are in the middle?