"Funky MF (Multimode Filter)" - LM13700 Multimode Envelope Filter

[Mark Hammer]

Thanks for chiming in, Rick.  I'll unsolder the 324, socket the space, see if it behaves any better with an 084, and report back when done.

[Mark Hammer]

Well, I tried a few different quads: a TL084, a TL054, an LM348, and a an MC3403.  The 3403 was the best-behaved of the lot.

I should add, better than the LM324.

[avandelay]

The "volume" opamp and pot seem to only add gain.  I would like to eliminate the gain.  Can I eliminate that whole opamp or does it serve another purpose and should I just bridge across where the pot is located?  I'd experiment but it's already soldered up.  Thanks for any advice.

Jeff

[Mark Hammer]

Pulled it out again today to take another stab, as I slowly work my way through the bin of things that came close to working but not close enough to box up.

Yup, bi-fet quads don't work at all.  I used my last 3403 for an OD-1 clone so I can't reproduce what it did, but a second stab at using different Bi-Fets was unsuccessful.  Put the 324 back in the socket, and it worked again but has the same issue, namely that there is a very pronounced thunk at the onset of each sweep.  Additionally, if the resonance is set higher, it will "lock up" and emit a high-pitched oscillation that won't stop until I turn the sensitivity/Range control was turn way down.  Perhaps that can provide some clues as to what is causing the misbehaviour.  Could the 220k/100k pair providing a bias/offset to the control current be a possible solution?

[rankot]

Schematic in the first post seems to be dead. Anyone can repost?

[Mark Hammer]

Here's what I'm working from.  Note that one stage shown as assigned to the TL062 is actually assigned to the LM324, and vice versa.