GGG EQ Prebuild questions

[jswingchun]

Okay, Mr EQ didn't do what I needed so now I am thinking of building the EQ on GGG. I was planning on the 5 band plus gain build.

This would be for bass guitar, so I know that:
I should probably up (double?) the input and output caps.
I should use the provided chart and match the parts to frequencies that would be useful for bass guitar

I saw a post suggesting a person could use internally mounted trimpots in place of the regular pots. I like that idea a lot. This is going to be a set it and forget it kinda eq.

Anything I should know about using trimpots instead of regular pots?

If I get these trimpots from smallbear, do the numbers on the trimpot equate to the lugs on a regular pot?
http://www.smallbearelec.com/Detail.bok?no=160

Anything else I should think about/be aware of before I start getting an order together?

[Dave Simpson]

You're probably going to want to do some of these to fix the little problems with the design.

1. Disconnect point C from ground, and use point B as ground instead. That makes your negative battery terminal or negative supply voltage ground, so the pedal will work with others on the same supply. Point C is now your standard 4.5volt vref like you get in most FX pedals that use opamps.

2. Connect the input and output jack socket sleeves and the bottom of the final 10k resistor to point B, so that they are connected to the new ground. If you're using the GGG layout you can do this just by moving the jumper that normally connects those to point C to point B instead.

3. Flip the input cap so the positive end faces the 100k resistor and remove the 10uF cap in the feedback loop of the IC1b and replace it with a jumper. That will correctly bias the opamp now that it's referenced to 4.5volts instead of ground.

4. Install the 220K resistor immediately to the left of IC1, between pins 3 and 5. To tie the input of this opamp stage to ground, instead of letting it float.

[jswingchun]

You're probably going to want to do some of these to fix the little problems with the design.

There are seriously that many issues with that layout and no mention of them on the GGG site?

Just to make sure I understand....

1. Disconnect point C from ground...

This is handled in the next step you mentioned, by moving the jumper, correct?

2. you can do this just by moving the jumper that normally connects those to point C to point B instead

Okay, I found this one.

3. remove the 10uF cap in the feedback loop of the IC1b and replace it with a jumper

I'm not educated enough to know what that means. I assume it is the cap right above point B and C. The right hand one of the two in the center?

4. Install the 220K resistor immediately to the left of IC1

I think I found where that one goes. It would match the 220K resistor to the left of IC1b?

[Dave Simpson]

You got it, except for the 10uF capicator.  It's the one on the bottom left side. It's circled in the diagram.

[jswingchun]

Excellent, thanks for the heads up.

Still wondering about this part from my original post:

If I get these trimpots from smallbear, do the numbers on the trimpot equate to the lugs on a regular pot?
http://www.smallbearelec.com/Detail.bok?no=160