Guitar VCF.?

[deadastronaut]

hi guys,

been looking at simple VCF filters, but for guitar use..

i plan to add lfo etc later, but want to nail the filter first..

here is where i lifted this one originally...
http://electro-music.com/forum/topic-45231.html

then put it on breadboard and tweaked a bit to this...


thing is, it gets pretty growly half way, and pretty hissy on the top range too..

am i barking up the wrong tree going this route , if so, is there a more suitable 'guitar vcf' ?..

i planned on using the other opamp for a second filter too...

...hmmmmm...cheers guys.

[anotherjim]

I had this on breadboard a short while ago...

I used the non-self oscillating version since I had no VCA after it. It works good considering it's so simple.
I'd seen the one you refer to - didn't try it because it's so similar the Q&D VCF.

[nocentelli]

Those two look good for simplicity/low parts count, you could maybe diddle with the resistors in the cut-off pot circuit to limit the maximum frequency boost to reduce the hiss. The Eric Archer 9v VCF is more complex, using a dual OTA and a dual op amp, but has a nice range from sub-sonic/inaudible, right up to full range range with some boost at the very top (which is also a bit hissy, but quite useable). It is pretty clean, and the resonance goes up to the beginnings of self-oscillation but it's not too ugly like some other LPFs.

[nick d]

   The VCF I used in my Sonic Attack pedal worked pretty well , but it wasn't simple - even without LFO's there's a dual OTA and 3 op-amps .
     
     Didn't sound too bad though , even if I say it myself .....

[StephenGiles]

Once more - Craig Anderton's Bi Filter Follower is the best "simple" guitar VCF I have ever heard, and doesn't suffer too much from stuttering sweeps. Figure out how to drive the EH Space Drum envelope generator from guitar, and with those 2 you'll have a masterpiece!

[deadastronaut]

^ sounds cool, i'll look it up...

anyway, ive gone with a modded Q&D and its much better now ive chosen its max/min range, no hiss etc..

i discovered an old circuit wizard file on my HD where i was testing this out ages ago where i had dual filters on the go..

high and low versions...pretty cool..so i'll have another tweak with it...then add a nice slow lfo sweep to it...nice with delay too..

[StephenGiles]

Ah ha, dual filters is.......no, are good! I'm on holiday in Spain at the moment, so no circuit files to hand, and we need to keep AC on all night!

[deadastronaut]

put the DC on...

[deadastronaut]

ok, had a bit more of a tinker..

i now have dual vcf's...and they work ok..

however, the vcf2 high 100k pot is scratchy as hell...whereas the vcf1 low 100k pot is fine/silent....weird?..

tried dc blocking cap, but obvously that kills the filter...hmmmmm....ideas?.





edit: nevermind, dodgy trimpot  

[deadastronaut]

anyway heres a clip ...twiddling both filters..(using a recording looper)

just need to hook up an lfo...and tinker more..

https://dl.dropboxusercontent.com/u/7464107/dualvcfclip1.mp3

this is what i'm trying to do...but a bit cleaner than this...

[alanp]

Is there any way to get some resonance going with that filter design? Because that could work very well, resonance cranked up a bit...

[anotherjim]

It should have resonance -  but not very high Q. I found you need to feed it a signal rich in harmonics to get it to really honk. The synth boys in another place were figuring out a way to use two Q&D filters in series -  a dual gang pot for resonance and a level trim in between sections. I'm not sure how the CV control was shared.

[merlinb]

Using biased diodes as variable resistance elements is a big handicap, especially for guitar applications. You shoud be looking at OTAs, LDRs, or at the very least replace the diode with a JFET.

[samhay]

Sounds cool Rob.

As drawn, R13 is redundant. However, instead of the two 1M level pots, you could try a single mix pot at the output of the two filters (do you get clipping with the pots at max?). In either case, you should add some series resistance to the op-amp outputs before you mix them - 1k will work.

[deadastronaut]

hi sam....another epic thread ahead

i'll try that later, i do however have some lm13700n's if there is an alternative schemo/way...

off to see the tall ships at greenwich today...back later

[Strategy]

Deadastronaut, I've been using the EDP Wasp VCF - multimode filter, no onboard modulation.  it has built in switchable overdrive, CV input, sounds amazing...I did a thread on my build and there's some links etc but I haven't put up samples yet
Couple things to consider:
- Its a modular synth circuit so most of the DIY versions are dialed for a higher input signal level so consider using a boost somehwere in your circuit, but it works without too
- As a synth circuit most of the PCB's are not so small I used a 1790 enclosure...a smaller version could probably be put together
- Low parts count!

Strategy

[deadastronaut]

^ sounds cool. link? found it:
http://www.diystompboxes.com/smfforum/index.php?topic=102714.0

arent those EDP VCF's at 15v though..

ideally i need a 9v pedalboard friendly 1590bb one..


@sam i'll try your suggestions today...and yes it clips like hell too..

i'd like to be able to mix between the 2 filters though...but i'll try moving the pots to the outs instead..

would an input buffer help things?...

[samhay]

If it clips, then leave the two 1M pots as trimmers, and set to just-before-clipping. Now, add a 10k pot with lug 1 to the output of 1 op-amp and lug 3 to the other. Take your output from lug 2 and you have a mix pot, which pans from one filter to the other.

[deadastronaut]

cool, i'll try that..cheers sam.

[deadastronaut]

@strategy: any clips of that EDP?

after tinkering more i have this...