State Variable Filter circuit, anyone?

[garfo]

I'm hungry for a pedal that has an active Alembic/Wal style filtering effect.Apparently there's a perfboard going around that doesn't work.
Has anyone successfully made this kind of layout???

[kothoma]

I'm hungry for a pedal that has an active Alembic/Wal style filtering effect.Apparently there's a perfboard going around that doesn't work.

No, the perfboard layout here certainly does work.
It's just my poor skills at working with perfboard that caused the fail.

[garfo]

I'm hungry for a pedal that has an active Alembic/Wal style filtering effect.Apparently there's a perfboard going around that doesn't work.

No, the perfboard layout here certainly does work.
It's just my poor skills at working with perfboard that caused the fail.

oh, cool!!!did you make some change to it?I'm thinking of putting it in a pedal instead of using it onboard with the bass.Also, is it possible to use a treble kind of boost like in the Wal???

[kothoma]

Only thing I changed was the taper of the f-pot. I used a dual-C50K to have a "linear" feel.
Maybe I should also have changed the taper of the Q/res pot. ATM there's not much action beyond 12:00 with a lin pot.
I meditated some time about making the gain external but decided against without remorse.

I put it in a 1590B.

Although it is a lowpass filter you can get a treble boost if the f is dialed in very high (up to 4 or 5 kHz) and the resonance pot controls the amount of boost.
Give it a try, all in all it's a simple and inexpensive build.

[garfo]

Only thing I changed was the taper of the f-pot. I used a dual-C50K to have a "linear" feel.
Maybe I should also have changed the taper of the Q/res pot. ATM there's not much action beyond 12:00 with a lin pot.
I meditated some time about making the gain external but decided against without remorse.

I put it in a 1590B.

Although it is a lowpass filter you can get a treble boost if the f is dialed in very high (up to 4 or 5 kHz) and the resonance pot controls the amount of boost.
Give it a try, all in all it's a simple and inexpensive build.

Have you got any idea on how to increase the frequency peak?what cap should be increased or decreased?

[kothoma]

The peak is controlled with the resonance pot, that is, the height of it.
The peak is always at the cutoff frequency of course, controlled with the dual pot.

[garfo]

And when you move the ressonance peak to the treble side, o you pose the bass?or does it balance both frequencies and acentuates the peaq!?

[kothoma]

No sure if I understand your question.

...does it balance both frequencies...

There's only one frequency knob (with a dual pot, "stereo" you could say) that controls the cutoff frequency. Everything below is passed (lowpass), everything above is attenuated.

Have a look at the graphs:


Let's start with the blue line. Zero resonance. No frequencies below the cutoff frequency (4.8kHz here) are affected. Those above get more and more attenuated.
If you lower the cutoff frequency (more to the left) then the highs start to vanish earlier. If you set a higher cutoff frequency (OK here it is already at the max) then more highs remain.

On top of that cutoff frequency you can dial in a resonance peak with the resonance pot.  That's shown in the other two lines at different settings of the cutoff frequency. The pink is in essence a treble boost.
Lower resonance not only makes the peaks lower, it also makes them wider, until they are flat at zero resonance.
Everything left from the peak is unaffected (OK there's a slight boost to all frequencies).

Hope this helps.

[garfo]

I will enjoy this board.By the way, the 100k trimpot , what is its function, is it an overall gain?

I'm hungry for a pedal that has an active Alembic/Wal style filtering effect.Apparently there's a perfboard going around that doesn't work.

No, the perfboard layout here certainly does work.
It's just my poor skills at working with perfboard that caused the fail.

[kothoma]

Yes, the first stage is a little booster and the 100k trimmer sets the gain.
You could make it external to adapt to different pickup levels, but I preferred set-and-forget.

[garfo]

I will make measurements and readings and establish a minimum and maximum gain and use a footswitch dpdt to switch between resistors.

[kothoma]

Sounds reasonable. Good luck with your build and let us know the results!

[garfo]

By the way, where did you get a stereo rev log 50k pot???

[kothoma]

Oh yeah, none of my favorite stores seemed to carry these. So I ended up getting them from China:
http://www.ebay.de/itm/2-pcs-C50K-Reverse-Log-Taper-Dual-Potentiometer-Pots-20mm-S-6pin-with-Nut-Washer-/360744984955?pt=LH_DefaultDomain_0&hash=item53fe13a17b
I paid US $5.69 including shipping (Economy Int'l Shipping) for two and later $9.99 including shipping (Economy Int'l Shipping) for six. Strange prices.
Needed somewhere between 3 and 8 weeks to arrive, don't remember exactly.
Look like Alpha pots to me. Fine quality. Had to shorten the shaft a bit.

But a dual-B50K should also be OK.

[garfo]

Thank you very much for your help.
As soon as I have some spare time I will try to build that tool box for my bass.