[sdiy] Why DIY stuff doesn't work

[Paul Schreiber]

Not that this is directly the case, but here is my "indroduction" to DIY (1974).

A friend was an Electronotes subscriber, and I too decided on a VCA as my first 
circuit. Hell, it was my first circuit *period* because I was a ChemE and was 
making model rockets at the time.

So, I get Dave Rossum's simple VCA (LM3086 + 1 op amp) and connect it up. Zip, 
nada, nothing. Disconnect power supply, 'ring it out', check pinouts. Checked 
power supply, it was an HP lab supply with meters, it read 15V. Flat-line scope 
trace. He's dead, Jim.

About this time the lab TA walked by, leaned over and looked. After a few 
seconds he giggled and said "You have a power supply problem". I looked, showed 
him the HP supply.

The supply had 3 banana/screw terminals clearly marked: + - and GROUND. I had 
wires on all 3 to my circuit.

The TA looked at my 'deer in the headlights' stare and said "That's not a dual 
supply, it's only +15V". I thought this TA was an idiot, the supply HAS 3 POSTS 
that say + - and GROUND am I blind or what.

He then calmed explained that the '-' was not REALLY "MINUS" and he brought over 
2 supplies, hooked them up for me and the damn thing worked perfect. I was that 
the heck GROUND was and he said something like 'frame ground' and the only 
'frame' I knew about was a picture frame.

I then noticed batteries have + and - terminals too and cursed EEs everywhere 
that went into marketing.

Paul S.