Equalizer 5-band by GGG on veroboard is noisy

[Elijah-Baley]

Hello.
I'm working on this circuit: http://www.sabrotone.com/?p=99
All pots work fine, but there is too hum, like a distortion pedal.
It is based on this: http://www.generalguitargadgets.com/effects-projects/eq/6-band-graphic-eq/
In my first test I forgot the two ICs and I missed R5
All componets seem ok.

Where's the problem?

Thanks guys!

[Kipper4]

Hi EB
Is the issue that when you raise the gain of you favourite freqauncies it clips the op amp?
If so maybe try reducing the unwanted ones and reduce the ones you want too so as not t clip the op amp.
Maybe stick the o scope on it. It might give you some clues.
I've never got this to work but I'm glad you have. Maybe I'll try it again soon.

[Elijah-Baley]

Thanks Kipper4.
It works fine, I mean all the pots are very useful. It is like a Bass/Middle/Treble but with two more pots, and it doesn't make the thing difficult.

The only issue is this noise always on. I can't use it in front of my amp using the distortion channels.
The gain pot controls the volume, and I get just a bit of clipping at very high setting of this gain pot, but setted like that the pedal becomes a volume boost, anyway the clipping is just a bit and it doesn't a real problem. And then I tested it with humbucker pickup.
I guees it is not a clipping problem, because it sounds clean.
Seems to me it is not even a problem of some frequency pot, because the hum change frequency following the tone of the equalization, but it never encreases nor decreases.
The volume of the hum is joined to the overall volume. I can hear more hum just beacuse I have more volume (gain pot of the eq or volume of my amp).
It is very tricky, and unfortunately it is not very built. But I really don't want to abandon this pedal.

[Kipper4]

You might get more headroom out of it using the dual supply.
Or a charge pump +9v -9v maybe a icl7660.
Also is your power supply regulated? If the power supply is not regulated it may introduce some additional noise.
Sounds like your using it as a kind of booster......so if you use it just as a eq with unity gain is it better?

You'd be surprised what a well tuned 2 band active can do.
If you look at the eq in the boss fa1 ,breadboard it and tweek to your ears and gear, you might like it.
If your happy with the 6 band. Go for it.
Happy playing EB.

[Elijah-Baley]

I'm testing the circuit with a battery.
My intention is to use it like an eq.
I'm using it at unity gain, but it's definetely noiser than bypass.
I don't know what kind of problem could be.

[rankot]

I have built similar circuit powered with ±15V, and it works fine, no distortion at all. But I swapped + and - inputs on gyrator op amps when designing PCB, so controls behave strange. I will order new PCB with corrected inputs and I will report my experiences with that board. However, I put JFET preamp in front of this and it is working fine, and there is some (but not much) noise when EQ pots are not in the middle; when in the middle, no noise at all. Maybe using another op amp will eliminate that noise? I use TL074, but I will try with something else, too.

[Elijah-Baley]

I thought it can works at 9v without any issue. I'm using two TL074, I guess it should be low noise.
Anyway, I want to be more clear. I got no distorion at all, the sound is clean, but the noise I get is: do you know the noise of a gain channel?
I found a casual video. Just listen few seconds at the beginning before the guy start to play.
www.youtube.com/watch?v=iIFqlSowsSQ
That hum come from the high gain channel, and that is the kind of noise I get. Indeed, if I active the gain channel of my amp the noise is intolerant. In the clean channel it's really disappointing thought it isn't so loud, but I can hear if I play softly or hardly.

[ElectricDruid]

Is it boxed up yet? If you've got a veroboard floating about in a room with mains power wiring running about to your amp and so forth, I wouldn't be surprised if it picked up some hum/noise.

Actual mains hum could be down to it not being shielded, or it could come from the power supply, but you said you are using a battery, so that rules the second possibility out.

Any circuit with highly selective gain stages like an EQ is going to have a tendency to be noisy. If you put five of them together, it's going to get noisier. If you'd got an error in one of the gyrator stages which boosted the Q of that stage, that might make it worse.

Beyond that, I'm not a massive fan of that low impedance inverting gain stage on the front end of the circuit.

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

They've gone with an inverting gain stage because the output mixer is inverting (I'd guess) so that gives the pedal no inversion overall. But that means the gain stage design is a big compromise.

Tom

[Elijah-Baley]

It isn't boxed yet, indeed. And I thought that was my lost possibility to solve, but I use to drill the boxs only when I'm sure enough that the circuit works right. I didn't know that an eq could be so noisy or pick up noise. Usually my distortion pedal circuit was really quite. (Big Muff, Rat, BSIAB II, Fuzz Face Si...)

I don't know if there is some error in the gyrator stages you mentioned, because I don't know what exactly it is. Seems to me there's no mistakes with resistor or caps.
Could be a voltage measurement of the ICs useful? Unfortunately, those can't tell me anything, perhaps one of you guys can help me.

About the inverting gain stage, I post here the veroboard layout, because it is a little bit modified.



Thanks.

[Kipper4]

I'm gonna try and explain the gyrator as best I can. Not my forte.

First off the gyrator is a replacement for an inductor. How am I doing?

There are 6 gyrators one for each EQ stage.
Ggg schematic



Ic1A
Ca1
Cb2
R6
R7

Is a gyrator
I hope that helps.

[Cozybuilder]

I don't know if this is the problem, but I see 3 things:

1) Vref is connected directly to the +input of the first IC amplifier (A1+in, pin3), while Vref is applied through a 220K resistor for each of the tone shaping ICs. It might be quieter if Vref also goes through a high value resistor to A1+in. As is, potential thermal noise? Confusion arises from the GGG schemo showing that input going to ground, not Vref, but he gives options for both 9V and 18V power options.

2) R6 is connected to Vref (4.5V) rather than case ground. For a 9V system, it should go to case ground (0V) (GGG R25)

3) C1 is connected to Vref, not 0V (GGG C9)

Using the Sabro layout you posted and referencing the GGG schematic,
#1 above could be done by the following:
  -Cut at 5f
  -Move R5 between 2a & 2c
  -Move R2 between 4c & 4e (flip it)
  -Extend jumper from 3h to 3c, no connection at 3f
  -Shorten jumper from 7f to 7i, no connection at 7b
  -New 220K between 7b & 7e
  -New jumper 6e to 6f

#2 could be changed by:
  -move R7  to 11a & 11c
  -remove the jumper between 3i & 3n
  -move top of jumper (starting at 8j) from 8a to 9a
  -new jumper between 7n to 8a

#3 could be changed by:
  -move C1 so it is now 3k & 3n

edits for clarity and additional mods

[Kipper4]

Double post

[kaycee]

I've built this, don't remember mine having any hum, been a while since I've used it though.

[Elijah-Baley]

Kaycee, did you build the veroboard layout?

[...]
There are 6 gyrators one for each EQ stage.
Ggg schematic

Ic1A
Ca1
Cb2
R6
R7

Is a gyrator
[...]

Thanks for helping. But caps and resistor seem ok. I'll check anyway, again.

I don't know if this is the problem, but I see 2 things:

1) Vref is connected directly to the +input of the first IC amplifier (A1+in, pin3), while Vref is applied through a 220K resistor for each of the tone shaping ICs. It might be quieter if Vref also goes through a high value resistor to A1+in. As is, potential thermal noise?

2) R6 is connected to Vref (4.5V) rather than case ground. For a 9V system, it should go to case ground (0V)

Using the Sabro layout you posted, #1 above could be done by the following:
Step 1:
Cuts at 5e and 5f
Move R5 between 2a & 2c
Extend jumper from 3h to 3c

Step 2:
Shorten jumper from 7f to 7i
New 220K between 7b & 7e
New jumper 6e to 6f

#2 could be changed by:
1) move R7  to 11a & 11c
2) remove the jumper between 3i & 3n
3) move top of jumper from 8a to 9a
4) new jumper between 7n to 8a

Thanks. Before to make this mods I wanna be sure there's no my mistake. The layout should be verified.

[kaycee]

Yes, vero from the Sabro layout, lots of pots to wire up!

[ElectricDruid]

Cozybuilder's points about the grounding are all very good. If the grounding is wrong, it'll be noisy.

Those GGG designs with various power supply options always confuse the hell out of everyone. Does anyone really use two 9V batteries to get a bipolar supply in a pedal? Isn't that just expensive?! Designing for a single 9-18V supply would be much better, I reckon.

Tom

[Elijah-Baley]

Talking about the Sabrotone version, how we could explain this?

I've built this (Sabro version), don't remember mine having any hum, been a while since I've used it though.

Thanks Kaycee!

Maybe I really can eliminate the hum boxing it up.

[kaycee]

Looks like I made a 3 band version 



Been a while since I had it out, I knew it had a lot of knobs, but not enough apparently 

Is very quiet though, just a 9 volt supply

[Elijah-Baley]

Thanks.
I preferred the 5 pots + gain pot version.

[Elijah-Baley]

I just drilled the box for the Bit Commander http://www.diystompboxes.com/smfforum/index.php?topic=117042.msg1085787#msg1085787
And it has 6 drill pots. I wanna try to solder the jack input and output, fit the 6 post, and probably to solder the DC jack, too. No footswitch nor LED, and close the box.
I wanna see if it can mute the hum.

Just a quickly question: what about the capacitars 10uF? Could be someone which it could give this noise? I can exclude C13 and C14 already replaced.