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?

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

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.

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 overall the design is generic and modular enough that I figure it can used for reasonable audio or DC gain up/gain down or buffering solutions as they come up.

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 had another project where I needed to use a few of the gain stages, so I modified a few resistor values, left about half the board unpopulated, slapped the board on with some 90 angle clips, and we were good to go.

Model 210 Mixer

I was hired to build a mixer for a small installation (this was quite a while ago) and there were a few requirements: the mixer had to be small and have both fixed and variable outs on 2 jacks. the metal work required that there only be 5 ports (1/4 inch?) for the following: 4 inputs, 1 fixed output, one variable output. what to do? Here is what I came up with. The thing I remember being tricky is that port 4 is variable as input and adjustable output, and a dual pot was used since I could only fit 4 pots in a very limited space. I liked this little design so much that I fab'd one for myself, I don't recall doing a PCB for this, it was all built on perf. Hand drawn schematic (?) is here. I lost this documentation for a very long time, having recently dug it up. Oh yeh the mixer used pair of Burr Brown OP627's which cost a whole lot but were very nice.