Op Amp Circuits and boards

Some Op Amp Gain Circuits

One of those simple electronic things that is useful: get some gain circuits going using op amps, for whatever you need to apply a gain stage or buffer to.

This started when I was trying to rebuild an old mixer circuit with 2 attenuator stages and 2 gain stages.

I needed a small board and schematic for a dual Op Amp 5532 or TL072 or whatever, and came up with this.

Board layout looks like this:


Here is the schematic and the board. I created gerbers and sent this off to EASYEDA in China to have some boards made.

Worked first time! How about that? I tried to make the boards flexible, if you know anything about simple op amp circuits, you can AC couple betweens stages, stick a pot in negative feedback to have adjustable gain, make the 2nd stage a buffer by jumpering over the resistors, etc. As audio electronics go, this is pretty easy stuff.

OK not satisfied with that, I needed an VCLFO for a studio I was building, so I dug out a really old LFO board I had lying around in my junkbox, from a now-defunct outfit called "Electronics for Musicians".

Wait, EFM? Who are they and where do I get this stuff? Not so fast partner....This outfit was apparently run by a single lone wolf tech dude named Tom Gamble.....Fitting name because if and when you got your boards from EFM was a gamble?

I remember grumbling about vanished paypal funds to EFM back in the day (2005?)

But Tom and his outfit was like a girlfriend you complain about. But then when she leaves for good you miss her, dig?

(Tom are you out there? Are you still with us? Don't let my bitching scare you off, you are missed!)

so anyway here I am 12 years later and I still have a few unbuilt boards from EFM. LFO5A one of them.

And if you ever followed EFM at all, the EFM LFO5A board has all the EFM issues: egregious chip frying trace errors, BOM is incorrect, outputs are all over the map as far as P/P voltages and so on.

I have to think Tom liked to design circuits (and was good at low parts count designs, which for DIY circuit building is good?) but hated the OCD part of getting everything on the board just right; I admire this, but I am not like that.

To correct all of the P/P output issues on the LFO5A board I downloaded this Dave Kendell mod schematic to correct, as part of the invaluable forum page for the LFO. (the original forum is gone, this is a copy)

This is built for the LFO5A as a daughterboard but is generic enough that I figure it can used for any reasonable audio or DC gain up/gain down or buffering need.

For this one here is the board:



Here is the schematic:

OK, for EAGLE users, board is here and schematic is here. I made gerbers and sent them off the China....we'll see if it works.

UPDATE!It works! EFMLFO5A works great with the addition of this gain board. I may do a circuit board for the LFO itself if I ever need another.