LFO Prime--Reverse Engineering my Own Work, And It Still Doesn't Work (Yet!)

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I cobbled together an Analog LFO back in 2003 and didn't document any of it, now I want to make a clone. So far no love: two different attempts failed for different reasons. But I will get this clone of my own work to work someday! Really!

The LFO prime, almost 20 years later.....Which one works? Neither!!!!

In my ewaste pile are two PCB layouts, both don't work, and are too broken to fix with kludges. 

Where did I go wrong? (Always liked that song). A few dumb mistakes of course.  The design is based ont his core 2x op amp osc design you can find all over the internet; here for instance....

for the stage on the left--the feedback is to the non inverting terminal!  Wait, I thought op amp  feedback is always wired to the inverting terminal?  Not here. So I laid out the feedback on the rev1 board and of course it didn't work. To wit: if you want to break an audio DiWhy circuit, wire up the op amps wrong!!

The rev2 board had another stupid mistake--when I look at it of course it doesn't work--how did I miss this?

The idea here is that BIAS DPDT on the top right the switch offsets the circuit output by +5V, so we have a switch to choose between bipolar and unipolar output voltage.

But, the switch adds the gain stage to the bottom left to only the "bias A - Bias B" switch in one of its two positions--dumb! The output won't be the same if the only one signal gets 4x gain. That's what I was seeing for the output of Rev2 on my scope. Not what I want.

I rewrote it like this, new layout is coming.....

Now both unipolar and bipolar should get the 4x gain boost. Much better.  

Using a Hakko 301 tool, I managed to get all the useful parts off the 2x bad boards...that's good.

I fabbed a front panel for this hopefully--before I knew my rev2 design was NG--the drilling came out pretty well, so i hope to reuse that for the rev. 3:

Tape a 1:1 output of the PCB....drill your holes.

Line it up, place in the parts and solder.....using PCB material for front panels all of this is easy.

Lessons learned:

First: always document your DiWhy! 

When I first started this odd quest to make audio electronics myself, and not just buy something, and I got something to work, I wanted to light a cigar, not go through the boring laborious process of  documenting what I built. 

Of course if I wanted to make a second identical circuit or repair or improve my DIwhy creation, well, I had to reverse engineering my own work. That's not alway7s easy....since the original build was perfboard spaghetti, good luck with that.

Second: try not to make dumb mistakes, but sometime you will, right? Let it go, mo! I was pretty happy that I wasn't too upset about this (an odd sentiment on its own), as I have been angry things on the bench that I can't get to work in the past, especially surrounding relatively easy circuits. Not sure why I'm more mellow about my mistakes?  Age?....improved diet?....something like that.

Third: The coolest and best thing about analog electronics is that it always acts the same.  Ohms law always behaves like--ohms law.  Voltage dividers always divide. If you don't give current somewhere to go, it stays put. We are dealing with laws of nature here and if it doesn't work, it's because I misunderstood some law of nature. It's not software! And best of all? It's not going to act differently by rebooting!!  In its own way, analog design is beautiful because of its repeatability. 

How many other things in life are like this?

So, onward.  I will send the revised board out in the next PCB run and try this again.  More coming....

Update: I figured it out, post for a working LFO based on this design is here.