Wah-ndering about something...

[11-90-an]

Just wanted to know what inductorless wah circuits would be nice for a wah-autowah(lfo)-envelope_contolled_wah 3-in-one pedal...

I was thinking about the colorsound wah, but I prefer to hear everyone's favourite wahs and opinions... 

[ElectricDruid]

If it has to be LFO or envelope controlled, I'd be looking at something either LM13700-based or vactrol-based.

There's plenty of Mutron-Style circuits for vactrol-based, including my own effort (actually based on the ESP pages SVF not the Mutron, but it inevitably finishes up looking very similar):

https://electricdruid.net/filterfx-lp-bp-hp-lfo-filter/

For LM13700, there's the Snow White Autowah. The filter itself is a state-variable like the Mutron, but with OTAs instead of vactrols:

https://4.bp.blogspot.com/--dV3lzyt4Zw/T_xAYx1DuYI/AAAAAAAABuw/gfMLjzLKOV0/s1600/mpswaw.gif

I haven't tried this, so I can't comment on how good the envelope follower and OTA Iabc current drive is. Those are the tricky bits on a pedal like this.

Good luck!

[Kipper4]

I like the colorsound but always end up swapping the caps to suit the sound I want.

[11-90-an]

When you say swapping caps, i give you mean the caps in the twin-t filter... right?

Anyone else have any other input?

[ElectricDruid]

I like the colorsound but always end up swapping the caps to suit the sound I want.

How would you add LFO or envelope control to that? FET in place of variable resistor? Or single vactrol? Or PWM CMOS switch, I suppose, but that seems a bit loopy.

[11-90-an]

I was thinking of those options, and I wanted to try an OTA, but it seems like it's not as simple as sticking it in there and passing the lfo or envelope through Iabc...

I never considered PWM... i think that's way too out of my league, though...

[ElectricDruid]

There's plenty of circuits that pretty much *do* just stick an LFO or envelope through a resistor to Iabc. It's not the greatest method perhaps, but it works. You just have to remember that the Iabc input is two diode drops above -ve supply (Have I got that right? - sanity check, someone, please!).
It's a current input though, not a voltage input, so you can use some current source circuit instead. It looks like the Snow White does this, but I didn't study the circuit closely.

PWM only makes sense to me if you're using a microprocessor where you can easily generate PWM waveforms. Otherwise, you finish up with a lot of circuitry, and it's *more* complicated than other techniques, like FETs or OTAs, since you need your LFO or env follower, but then you also need a high frequency oscillator and a comparator to turn the LFO/env output into a PWM waveform.

[skyled]

The Tycobrahe Parapedal wah is inductorless and quite extreme. I'd love to see it with an autowah option. There's also the Frostwave Funk-a-Duck which is the Korg MS-20 filter and an envelope.

[Kipper4]

When you say swapping caps, i give you mean the caps in the twin-t filter... right?

Anyone else have any other input?

Yes correct.

[11-90-an]

So now I think I'm going with the Colorsound wah / vactrol combination...

For my LFO, I found this ramp/triangle/sawtooth LFO that I think I would use...
https://www.circuitbenders.co.uk/forum/index.php?topic=1893.0
Here's my redrawn schem...

If there are any problems about this LFO, please do tell...

For my envelope follower/detector, I quite confused as to what would be a good option, I was thinking Mutron III style, but I have yet to breadboard it... (It's quite late at night now )
But also, the SWAW also has a good envelope follower, but since it is made for OTAs, I'm not quite sure if plugging vactrols will immediately work, or changes are necessary...
http://revolutiondeux.blogspot.com/2012/07/mad-professor-snow-white-auto-wah.html

Also, I do have a question...
Can the envelope detector in the Engineer's thumb be used in this application...?

All your opinions would really be useful...

[Paul Marossy]

The Tycobrahe Parapedal wah is inductorless and quite extreme.

I built one years ago but didn't have the right pots. The thing that makes that one hard to build is getting dual pots in the right configuration with the right values.

[strungout]

I think my favorite filter is the mutron style. Good options, nice, different, sounds.
My favorite EF is that of the MXR Envelope Filter, because of it's 'response', but a lot of it is the attack knob. I need to be able to control the start of the sweep so it doesn't go up to fast.

I just finished a Filter FX and with all it already has, I was telling someone about how it would be the almost ultimate wah if it had an EF. That'd be a lot of options for one box!

[Kipper4]

I just finished a Filter FX and with all it already has, I was telling someone about how it would be the almost ultimate wah if it had an EF. That'd be a lot of options for one box!

And if you used the envelope an envelope detector and put it on a switch (switch between the Stomplfo's output pin 3 or the envelope detectors driver output you should be able to make it work.
You might need to restrict the Volts at the detector driver output to 5V similar to the Stomplfo V output.

Lm358 come to mind for detector and driver.
I feel sure one of my previous Stomplfo designs might have a suitable detector already. Might be worth a site search. Try.  Flo Rider  or Stomplfo (typo on my behalf when they first started using them)
in the search.

Hollow if you need help with the detector and maybe show us the mxr scheme....

Happy building.
Rich

[strungout]

EDIT: couldn't find much in the way of EFs with those two keywords... :1 But I did get the MXR's EF to control an LED (last time I couldn't get it to work...). Progress. Only problem is the LED is on all the time. It goes brighter when I pluck the strings. Ill BB a filter with LDRs and see what kind of action I get.


Hey Rich, hadn't checked back in a few, but here's the MXR Envelope Filter:



I'll go search for your stuff and others, see what I can find.

[11-90-an]

EDIT: couldn't find much in the way of EFs with those two keywords... :1 But I did get the MXR's EF to control an LED (last time I couldn't get it to work...). Progress. Only problem is the LED is on all the time. It goes brighter when I pluck the strings. Ill BB a filter with LDRs and see what kind of action I get.

Cool! How did you connect the LED to the EF? Did you just connect it straight to the "to TG" in the schem you provided? Or did you still use the CD4066?

If this is as good as you say it is, then I'm gonna have to attempt to make a op-amp version due to lack of CD40XX parts...

[strungout]

@ 11-90-an: Yup, I connected it straight after the last inverter, the one that 'reverses' the sweep, didn't use the 4066. I added a pot to ground in serie with the LED, as a depth control. Atm the EF is the only thing on my BB. Gonna build up a filter (SVF) and see what kind of action I get out of the LDRs.

I think an opamp version would be great. As is, I have four unused inverters... bit of a waste...


EDIT: And I'm looking into Harry Bissel's 'morph lag' which has both an attack and decay controls:



Also this, seems to implement the morph lag:

[ElectricDruid]

That's an amazingly unconventional bit of circuit. The two things that are fairly standard about it are that it's a SVF, and the envelope follower. Aside from that...PWM to control the filter cutoff, inverters used in their linear region instead of op-amps throughout, weird stuff, man!

Makes me wonder if the StompLFO output could drive a 4066. Might make for a good simple phaser.

[strungout]

Hmm I'm too much of a noob to have noticed it, but now that you mention it, I recognize the SVF in the MXR. That means you could mod it to tap the lowpass and bandpass outs... cool!

[11-90-an]

Makes me wonder if the StompLFO output could drive a 4066. Might make for a good simple phaser.

Try replacing the PWM circuit in Freppo's Parasit Phaser...

[duck_arse]

the MXR circuit is notorious for not working unless fed particular brands of IC's made under the right moon phases etc. the lower right 4 invertor section is very picky about not/working.