Held needed for building Tim's Q&D VCF

[AmpliFuzz]

I got the parts to tackle Tim's Q&D VCF. On the circuit there's an opamp without remarks. I shown it to the electronics store dude and asked for the most generic compatible opamp and he gave me a UA741CN. Will that work? How should I wire it?

Thanks!
AF

[petemoore]

To a socket. That way you can try something like a TL071 [as long as it's a single OA in a socket wired for single OA] or other higher performance IC.
 The 741 pinout is pin 2 is -in, 3 is +in, 4 Gnd, 5 [I forget NC I think] 6 is output, 7 is V+
 Check the data sheet

[AmpliFuzz]

Checked out the data sheet. You were spot-on. Thanks

Coupla more q's:

1, 5 and 8 go to ground or float?

What advantages will I have subbing a higher-performance opamp?

[AmpliFuzz]

So I built the version which self-oscillates and it worked. Luv it, but I didn't really like the self oscillating so I tried the 'non oscillating with nicer resonant peak' mod, and now it doesn't work anymore  :evil:

The 10k pot just adds or removes hiss and the 100k one does a funky sweepable 'low boom' thing (which sounds much less pleasing that it reads unfortunately) when the trim is high enough. The circuit still passes audio,  but not much correct filtering action going on.

It's even simpler part-wise and I already checked the wiring. The caps are 22nf and 47nf (circuit has a 0.005uf here). What could it be?

d'oh,
AF

[lightningfingers]

if you soldered it the second time round without removing the opamp from its socket- - - - -you may have fried the opamp.

[AmpliFuzz]

I'm pretty sure I removed it - it was socketed. Thanks anyway ...

[Marcos - Munky]

Just a question, what did you used for the CV input?

[Tim Escobedo]

If it was working, it sounds most likely something inadvertently got disconnected or connected somewhere by accident during the alteration. Keen eye and good debugging needed. Not to mention patience.

[AmpliFuzz]

Marcos: nothing is connected. I assumed that if there's nothing connected to the CV input the filter just does its 'fixed' lowpass thing depending on how you set it. Can't wait to try it with some kind of drum pattern feeding it, though.

Tim: right on. Also a great lesson about never fiddling with working stuff with an mildly crushing headache. Before I started (which is like a month ago, mind you) I really couldn't have imagined the quantity and quality of concentration needed to pull off this stuff. And BTW, thanks for those great circuits