[sdiy] Odd bug-search problem - Steiner multi-VCF

[Rykhaard D.A.M.I.A.N.]

Hey all.  I wasn't going to post about this bug, but after 2 hrs. of
minor bug fixing on the perf. board version of the filter that I spent
the day building, I'm still completely stuck and stumped, as to why I
have approximately 5V on my Ground.  (I.E.  Ground is not showing as 0
volts.  It's showing with a +5V offset.  )

I did a paper PCB layout of Ken Stone's Steiner multi-VCF Rev. 1
schematic, but I I built a perf. board version FROM Ken's Rev. 1
schematic - varifying my PCB layout as I went, and correcting a couple
of drawn errors that I'd made.

I've gone over the circuit, countless times, with the scope and my
Fluke meter.  I can't for the life of me, find where (or FIGURE why)
my Ground would be at roughly +5V rather than 0 volts. :(

Problems that HAD occurred, in case this might help:

I have no 47uF caps at the moment.  In 2 of the places required - I
used 100uF caps in series.
BUT - I originally had them (and the series 22uF caps) in bi-polar
connection. :O  Duh.  I fixed that.
The pair of 22uF caps that I had in series, were at the point of
buffering the -V power supply.  I didn't need that as I already had it
buffered on the board, where I'd built and HAD working - a discrete
Exponetial VCA.  (Not working any more, since the problem with the
Steiner came up.)

I HAD oscillation coming out from the output.  Looking at the scope -
I thought it could be the TL071 output opamp saturating, as it were a
squarewave that changed in pitch, adjusting the Resonance and CV pots.

Anyhoo ...... lacking tons of theory, I haven't been able to figure
what could be causing the huge offset on the ground line.  Anyone??

Oh yeah - due to the output opamp saturating (if that's the case) I
thought that the other user's recommended addition of a 180K resistor
to the 47K feedback resistor, could be amplifying things too much.
I changed the 180k resistor to a 100k pot - and NOW - the TL071 is
simplying outputting -15V.

7 hrs. from the start until giving up for the night, on bug solving. 
It'd be great if anyone could give me a tip as to what this could be -
as I'd much RATHER keep the perfboard with the Multi-VCF and VCA on
it, to combine with my Ken Stone Shimmer unit and drum trigger
converter, to put into a panel together with a couple of Thomas Henry
AD EGs. :)  As it sits for the moment though, (with to me - bug
solving on a perf. board, being absolute HELL), I'm just going to go
straight to laying out real PCBs for the whole mess. :P :)

Thanks for any possible help on this. :O :)

--
Take care,
Warmth and Peace,
Ryk

http://deathlehem.bravehost.com/damian.html - my modular synthesizer,
D.A.M.I.A.N.;s webpage
http://deathlehem.bravehost.com/design.html - D.A.M.I.A.N.'s design section
Mar. 0406 update :)