synthy filters for guitar..

[DougH]

This is a treasure trove of modular synth circuitry:

http://www.musicfromouterspace.com/

I was going to get into playing with some of this stuff but never did. Nice sound samples, PCB's available, some stuff designed for guitar, etc, etc...

[rring]

Yes - forget the ring modulator - in the schematic you can just see an example of how I use the filter.  The ease in adjusting the curve and steep cut off allows for great modulated filter effects and envelope effects, etc. In general when I just play around with these type of filters on a breadboard - I can generate very synth like sounds with few parts and little effort.

[deadastronaut]

@gary:  cheers for the links.

what IC is used for the Q&D, just an op amp?..
http://folkurban.com/Site/QDVCF-714.html



Will this one run on a lm13700n ?
http://folkurban.com/Site/9VpoweredMS20SallenKeyLPVCF-690.html

[garcho]

 yes and yes, cheers!

[deadastronaut]

goody gumdrops..

before i breadboard these up, has anyone added a nice slow  lfo or envelope detect  to either or both  already?..

[garcho]

I've made a similar MS-20 style filter and used LFO for the cutoff frequency, definitely synthy. You can get great sci-fi sounds, too.

Here's some advice from Taylor:

His MS20-ish design is better for a more typical synth filter sound. You can lower the resistors from the CV pot to the Iabc pins of the OTAs to get higher frequency range with it, which I definitely recommend.

The Q+D VCF does a surprisingly good job of faking a lowpass resonant filter considering how basic it is. But it distorts very easily because it's using a diode trick to get voltage control.

from Paul Perry (frostwave), MS-20 champion:

In most circuits, there isn't a difference between the 13600 and 13700.

[deadastronaut]

Cool, i have the Q&D on breadboard at the mo.....ive trimmed it down to basics a bit more...no resonance , etc.

been tapping whilst changing the freq pot, its pretty cool.....interesting.

i'll try the ms20 later...

[Strategy]

I just finished Wasp VCF from a modular synth design. Runs on +9V and has multi modes: LP, BP, HP, Notch! And, the one I did has switchable overdrive! I have not made sound samples yet as I have to replace a bad potentiometer and have not had much time for circuits. But here are links in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=102714.0

*EDIT: I did this as a pedal format "standalone" not as a synth module! works well - might need an LFO or Envelope follower but I use LFO from my Gristliezer right now, patched to the CV input of Wasp VCF.

[deadastronaut]

^ cool that looks very interesting..i'd llove to hear it.

being a total synth noob i don't really understand this CV lark though....

[Mark Hammer]

CVs are regularly in use by guitarists in their pedals.  It's just that we tend not to talk about them, or plan around them.  For example, virtually every modulation effect uses a control voltage to make something happen.  Many (though not all) expression pedals use a CV to control something.  Where we tend to get confused about  such matters is that in a guitar pedal, a CV is connected directly and exclusively. 

So, for example, consider the EA tremolo.  The LFO produces a control voltage, and the current from that is applied to the gate of a JFET, that acts like a voltage-controlled resistor, and varies the gain of another transistor.  It IS a CV-based effect, BUT...it is a closed system.  That is, the CV from the LFO is connected directly, and not made available to other pedals. 

In contrast, were one to have a modular synth, you'd likely have a standalone module with one or two LFOs, and a bunch of jacks for patching the LFO outputs to other circuits in other modules.  It is primarily the open-ended aspect of control-voltages that differentiates how synth players use them, versus how guitarists use them.

Of course, being open-ended imposes certain requirements.  Guitar pedal X might only make use of control voltages between this min and that max, and has the luxury of having its own self-contained LFO that provides that particular range.  In the synth world, it is assumed that - as standalone modules - one does not know where an envelope generator or LFO or joystick or breath-controller is sending the CV to, or indeed how many devices it will be "shared" by.  So they are designed around standards, such that system A might assume CVs ranging from 0-5v, system B might presume a 0-10V range, and system C might assume 0-15V (somewhat rare).  Both the circuits providing the control voltages, and the circuits being controlled by those CVs assume a particular standardized range of possible CVs.

What all of this means is that many synth filter modules CAN be used for guitar.  What is required is a suitable source of control voltage that matches the requirements of the filter.   So, although a Dr. Q / Nurse Quacky will provide an envelope voltage to control a filter, it may not provide enough of a voltage to make a synth filter sweep very far within its range.  Consequently, either the sensitivity of the filter needs to be modified to anticipate a more restricted range on CVs, or else the circuit providing the CV has to be modified to deliver a wider voltage range, so as to make the filter behave in the desired manner.

There, clearer?

[deadastronaut]

^ brilliantly explained...thanks mark.

[moosapotamus]

I just finished Wasp VCF from a modular synth design. Runs on +9V and has multi modes: LP, BP, HP, Notch! And, the one I did has switchable overdrive! I have not made sound samples yet as I have to replace a bad potentiometer and have not had much time for circuits. But here are links in this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=102714.0

*EDIT: I did this as a pedal format "standalone" not as a synth module! works well - might need an LFO or Envelope follower but I use LFO from my Gristliezer right now, patched to the CV input of Wasp VCF.

I'd love to hear what this sounds like, too.

~ Charlie

[garcho]

So, although a Dr. Q / Nurse Quacky will provide an envelope voltage to control a filter, it may not provide enough of a voltage to make a synth filter sweep very far within its range.

Can the control voltage from, say, the envelope follower in the Dr. Q, be amplified for sweep like a LFO? For instance, can one easily* tap into the envelope voltage, run it through an op amp and send it on its merry way?

[deadastronaut]

i had a thought last night of using both opamps with 2 Q&D filters..

just breaded both up and sound great...one filter is as per escobedo's..the other has 1uf/4.7n caps..sounds nice and thick...

if i can add a nice smooth slow lfo to both it should sound pretty good imo....tinker tinker..

[deadastronaut]

https://dl.dropboxusercontent.com/u/7464107/2q%26dfilters.mp3

q&d experiments clip

1st hi filter...

2nd low filter

3rd both filters..

[samhay]

I was looking at the Q&D filters only a few weeks ago, and thought they looked interesting. With that demo, they have moved rather near the top of my list. What LFO are you using?

[deadastronaut]

No lfo at the mo, just tapping and turning pot...

[garcho]

Sounding good D'Astro! I'm gonna breadboard two of these in series and hook `em up to the ol' TAPLFO. This is going to turn into a fun project, I can feel it...

[deadastronaut]

cheers man, lfo and envelope follower would be cool too.

bit busy for the next few days, but it sounds so nice its defo going to be on my breadboard for a while...

i'll post up a schemo of what i have so far later if i get time .

[aab0mb]

check my last post about the remote wah mad and the gain control.  very synthy for a wah pedal....  Cheap mods to make if you have a wah lying around.