Building a synth filter in a wah/exp type enclosure.

[beedoola]

I'm looking to build a synth filter type circuit housed in a wah enclosure, basically a wah but more balls like a synth filter.

I'm looking into two of Tim Escobedo's circuit snippets - an MS-20 type filter and another called "Q&D VCF" anyone built either of these?

http://folkurban.com/Site/QDVCF-714.html

http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html

[Taylor]

I've built both. They're both great sound-to-parts-counts ratios. For truly synthy stuff you really want a 4-pole filter, but these get complicated quickly.

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.

[beedoola]

Hmm, is there any other circuits you'd recommend? Even synth ones? As long as I can fit it into a wah type enclosure....

Maybe a really filtery sounding wah?

[egasimus]

I've been thinking about the same thing as you.
http://electro-music.com/forum/viewtopic.php?t=47831
This is my layout for the Polivoks VCF. It's really simple - however, I haven't tested it, neither on +/-15v nor on 9v.

[beedoola]

did you breadboard the circuit prior to making the layout?

[slacker]

Parapedal

schematic and layout here http://www.geofex.com/

[egasimus]

did you breadboard the circuit prior to making the layout?

Nope. But someone else breadborded the same circuit on that forum. Google 'polivoks vcf' for schematic.
Also, a new version of that layout is on the way.

[beedoola]

sweet man! I'm getting super giddy about this!!! can't wait for the layout. Gonna get some parts. could you post the BRD. file for etching when you get the next layout working?

Thanks

[beedoola]

anyone know where I can get the LM4250 and LF442 chips?

[egasimus]

LF442 is not mandatory, I'd use TL0*2 or NE5532. Also, have you looked for alternatives of LM4250? (uA776, LM776, MC1776, NTE888, etc..)

[SISKO]

http://www.diyguitarist.com/DIYStompboxes/MyStompboxes.htm

Scroll down, around the lasts pedals there is a Parapedal. Paul (from diyguitarist) made one, maybe you should contact him to know how this pedal sounds, pcb, etc

[artifus]

http://www.diystompboxes.com/smfforum/index.php?topic=37073.0

this can be quite synthi sounding too.

[space_ryerson]

I've been wondering about how a TB-303 filter would sound on a guitar. IIRC, the 303 runs on 9V.

[liquids]

Not to be 'that guy' but...I am.  

I've spent a lot of time with filters lately (did anyone at all see that I drew a schematic for the EHX Microsynth's filter, using LM13X00s?  I'm not making this up).  And the more schematics I see, I see that A Voltage Controlled Filter (VCF) is a VCF, if you know how to control it.  They all do the same things more or less within a chosen range...and if you understand them at their core, than nearly any range can be chosen no matter what version you start with.    

Envelope filters, often differ more in sound moreso due to the envelope response and control, than the filter itself...

The parapedal is a fine circuit and probably can do the same as the Polivoks etc.  And easier ones than either (for this idea) exist too.  Now, the polivoks seems to require a 'mojo' chip or part, but I dunno why (read: doubt) it would end up being that much different than any other 2-pole VCF (OTA or State Variable Filter based or both etc) with variable resonance, if you know what the resistors & caps do, listen for their quirks like distortion, and tweak/control the variables.  

But yes, if not, than this circuit vs that circuit will be a critical difference....

I agree that a two pole filter is a big difference that a 4-pole (and the three pole filters out there), and the classic moog is 4-pole and all, but if you look around, really, plenty of synth guys use and drool over 2-pole filters with their resonance cranked, just like the polivoks is, just the same. the WASP is another example... of which there are dozens...

The major differences lie in their QUIRKS.  Taht is, things like their response to Control Voltage (or envelope generator), the format the variable resistances take (OTA? Potentiometer? FET? LED/Photoresistor?) and other little things like, if/when&how they distort.  

Most significant of all, are you using/choosing a Low Pass (LP) High Pass (HP) or Band Pass (BP) option/configuration.  Many filters I've seen are capable of yielding all three, but 'tweaked' for one in particular or a compromise for all three options etc...

I've been thinking about this very idea on and off while I tinker with filters...classic wahs are cool and can be highly resonant just the same if you understand what the caps & resistors all do, but they are almost exclusively, BP and a little quirky in their control of the resistance (theres that thing again).  I also hate the limitations (and cost) of Wah enclosures/pots.  But it's fun, give it a go.  Just learn what the R's & C's are doing in the process (breadboard anyone?) so you come to see that they are all offspring of the same thing - the interaction between cutting frequencies & feedback (primarily negative feedback).  

Ah well, I'll go back to my cave now...

[liquids]

Oh yeah, and PS, the MS-20 Tim tinkered with is a 2-pole and a much loved resonant filter...

but Tim E's version, while simple, misses and changes and simplifies a lot from the original.  It can be 'improved' in many ways, and something between that and the late OTA-based MS-20 filter's particulars can be configured as well...one's curiosity, creativity, and persistence are the limiting factors for your achievement and realization of your (or possibly any) idea!

...

[wavley]

Let me play matchmaker

http://www.diystompboxes.com/smfforum/index.php?topic=92064.msg787223#msg787223

Welcome to eHarmony-Central 

[beedoola]

Not to be 'that guy' but...I am.  

I've spent a lot of time with filters lately (did anyone at all see that I drew a schematic for the EHX Microsynth's filter, using LM13X00s?  I'm not making this up).  And the more schematics I see, I see that A Voltage Controlled Filter (VCF) is a VCF, if you know how to control it.  They all do the same things more or less within a chosen range...and if you understand them at their core, than nearly any range can be chosen no matter what version you start with.    

Envelope filters, often differ more in sound moreso due to the envelope response and control, than the filter itself...

The parapedal is a fine circuit and probably can do the same as the Polivoks etc.  And easier ones than either (for this idea) exist too.  Now, the polivoks seems to require a 'mojo' chip or part, but I dunno why (read: doubt) it would end up being that much different than any other 2-pole VCF (OTA or State Variable Filter based or both etc) with variable resonance, if you know what the resistors & caps do, listen for their quirks like distortion, and tweak/control the variables.  

But yes, if not, than this circuit vs that circuit will be a critical difference....

I agree that a two pole filter is a big difference that a 4-pole (and the three pole filters out there), and the classic moog is 4-pole and all, but if you look around, really, plenty of synth guys use and drool over 2-pole filters with their resonance cranked, just like the polivoks is, just the same. the WASP is another example... of which there are dozens...

The major differences lie in their QUIRKS.  Taht is, things like their response to Control Voltage (or envelope generator), the format the variable resistances take (OTA? Potentiometer? FET? LED/Photoresistor?) and other little things like, if/when&how they distort.  

Most significant of all, are you using/choosing a Low Pass (LP) High Pass (HP) or Band Pass (BP) option/configuration.  Many filters I've seen are capable of yielding all three, but 'tweaked' for one in particular or a compromise for all three options etc...

I've been thinking about this very idea on and off while I tinker with filters...classic wahs are cool and can be highly resonant just the same if you understand what the caps & resistors all do, but they are almost exclusively, BP and a little quirky in their control of the resistance (theres that thing again).  I also hate the limitations (and cost) of Wah enclosures/pots.  But it's fun, give it a go.  Just learn what the R's & C's are doing in the process (breadboard anyone?) so you come to see that they are all offspring of the same thing - the interaction between cutting frequencies & feedback (primarily negative feedback).  

Ah well, I'll go back to my cave now...

so what circuit would you suggest?