FilterFX - 12dB/oct autowah thing with LP/BP/HP and 8 wave shapes

[ElectricDruid]

Hi All,

I'd like to show you what I've been messing about with the last week or so. It's a vactrol-controlled state variable filter inspired by the Mutron, but actually owning more to the SVF design on the ESP pages than the original Mutron circuit. The control signals for the vactrols come from one of my PIC-based LFOs, so I've got tap tempo and eight waveforms to choose from. The waveforms are:



The prototype is not the most beautiful thing you've ever seen, but it's functional enough:



The dangly red wire on the RHS is the highpass/bandpass/lowpass selector. I hadn't got a suitable switch handy (I was asking about this in another thread). The vactrols are VTL5C3's. There are Xvive clones of these that aren't too expensive and are pretty widely available. Or roll your own, obviously.

The schematics are here:

https://electricdruid.net/wp-content/uploads/2018/03/FilterFXSchematicPg1.jpg
https://electricdruid.net/wp-content/uploads/2018/03/FilterFXSchematicPg2.jpg

Finally, here's some sound samples.First, a basic funky riff with some lowpass autowah:

https://electricdruid.net/sounds/filterfx/Funky1.mp3

Next, something similar, but with highpass filtering taking all the fundamental out (mostly with the Ramp Up waveform):

https://electricdruid.net/sounds/filterfx/Funky3HP.mp3

A lead solo with lowpass filtering using the Random Slopes waveform for a less repetitive wahwah effect:

https://electricdruid.net/sounds/filterfx/LeadLPSH.mp3

Some rhythm guitar with lowpass and then highpass filtering using the Random Levels "sample and hold" waveform. This can get pretty abstract:

https://electricdruid.net/sounds/filterfx/RhythmLPHP.mp3

Finally, some strumming and playing about with the different waveforms available and fiddling with the Rate and Depth knobs a bit. This is wild filter mayhem:

https://electricdruid.net/sounds/filterfx/StrummingWaves.mp3

I've got a few tweaks to do to it perhaps. For example, I can't decide whether to add a trimmer to the first op-amp to provide some gain if necessary. The trouble with that is then you'd probably need another trimmer on the output to compensate. Also the current 5 knobs+ one switch is too many knobs, and I'm thinking that swapping the Resonance knob for another three-position switch (high/mid/low res) would be better, since I pretty much only ever use the maximum position anyway.

All thoughts, comments, and improvements welcomed!

Tom

[Kipper4]

Sweet Tom.
Is that with the new 8pin dip lfo chip?
I need to try those.

Rich

[ElectricDruid]

Is that with the new 8pin dip lfo chip?

It is indeed - the "StompLFO". Some years ago there was a discussion on here about an 8-pin PIC LFO, and a couple of other people did one, but I never got around to it until this winter. It's looking like it might be a handy little chip. I'd like to do a simple tap tempo tremolo with it too. The original TapLFO is great n'all, but pedals based on it tend to finish up with about two dozen knobs for all the options. So a slightly simpler and less tweaky version for people who actually want to play the guitar instead of twiddling. And I'd love to try it for a chorus - especially with the two random waveforms.

I need to try those.

What can I say? *Everyone* needs to try those! lol

Tom

[EBK]

Thought for a sec that the second knob was labeled "Druid Rate", which had me stumped.  Shows that I need to read all of the labeling before trying to figure out what each knob does.   

[Mark Hammer]

Sounds nice.  What would put it over the top would be expression-pedal control, and/or envelope control.

[blackieNYC]

This is exactly what I've been looking for.  Exactly, right down to the random LFO.
Untiiilllll... I saw the lightwah, with that optical control. I for one do not want a separate expression pedal. I guess I have two piorities - filter w random LFO, and I'm never going to have a wah pedal on my board.  Just the real estate. Obviously this isnt everyone's cup o'tea.  Is an open LDR light-controlled wah even remotely consistent? The Lightwah  is a late entry into my list of considerations.  I'm sure I could build it into this.  (If I did, I wonder how this would compare to the light wah?)
Sync input-nice! External LFO?  External trigger might be interesting too.
I don't know about front end gain control, but don't you think output volume will be necessary?  I'm sure some sounds can jump out and bite you.
Here's an idea - should a pedal such as this, which may enjoy being placed before a fuzz face like few others, have a cheap little transformer based pickup simulator - inside the box? Switchable?
Can I say this? I've asked smallbear to get the LFO chips. Very excited about them. Heck, I was very excited about building the LFO from scratch, but this is wonderful.
One more edit - how does the speed control affect the "random" waveforms? Hopefully it does.

[ElectricDruid]

Sounds nice.  What would put it over the top would be expression-pedal control, and/or envelope control.

Thanks Mark.

Expression pedal is easy, envelope control is a whole other thing.

For the expression pedal, you can wire the Freq/Offset pot via a stereo jack so that inserting an expression pedal takes over from the existing pot. Since the PIC isn't fussy about the pot value it should work with pretty much anything. Also the jack provides the +5 and ground connection, so you don't need a CV pedal, although you could wire it for one of those too if you wanted.

Of course, you could add an envelope follower too, but I was desperately trying to keep it simple!

Tom

[ElectricDruid]

Sync input-nice! External LFO?  External trigger might be interesting too.

Yeah, one thing I haven't tried yet is syncing it up to a synth sequence, but I shall give it a whirl. The LFO will sync to incoming pulses.

I don't know about front end gain control, but don't you think output volume will be necessary?  I'm sure some sounds can jump out and bite you.

Maybe you're right. Pity, I'm trying to keep the knob-count under control, not add more. Oh well!

Here's an idea - should a pedal such as this, which may enjoy being placed before a fuzz face like few others, have a cheap little transformer based pickup simulator - inside the box? Switchable?

Easily added if that's your objective, for sure.

Can I say this? I've asked smallbear to get the LFO chips. Very excited about them. Heck, I was very excited about building the LFO from scratch, but this is wonderful.

Cool, thanks. I'll make sure we get some winging their way!

One more edit - how does the speed control affect the "random" waveforms? Hopefully it does.

Yes, it does. The LFO rate is used as an underlying clock in both cases, and every time the clock "ticks", a new random value is chosen. For the random level, that value becomes the output until the next tick. For the random slope, the chip does a linear interpolation between the last value and the new one until the next tick.
So in both cases, you have some control over how rapid/frantic the sound is, but no control over the detail.

Tom

[Mark Hammer]

Sounds nice.  What would put it over the top would be expression-pedal control, and/or envelope control.

Thanks Mark.

Expression pedal is easy, envelope control is a whole other thing.

For the expression pedal, you can wire the Freq/Offset pot via a stereo jack so that inserting an expression pedal takes over from the existing pot. Since the PIC isn't fussy about the pot value it should work with pretty much anything. Also the jack provides the +5 and ground connection, so you don't need a CV pedal, although you could wire it for one of those too if you wanted.

Of course, you could add an envelope follower too, but I was desperately trying to keep it simple!

Tom

Well, anything that would provide some real-time control is fine by me.  So what you describe nails that.
As well, looking at then datasheet, I see that the 4 different parameters are voltage-controlled.  Sounds to me like a job for my Source Audio Hot Hand 3!  Those units output 0-3.3V control voltages.

Ever tinkered with using discrepant fixed-resistor values for the two vactrol stages in the filter, like Lovetone did with the Meatball?  They used a higher-value resistor in parallel with the vactrol/LDR for the first one, and lower value for the 2nd.  I can't say that I've ever heard equal-value resistors (the traditional arrangement, which you use) directly compared against discrepant-values.

[stringsthings]

Sounds excellent!  This would give me a great excuse to get one of your flanger boards ( and/or delay boards )
with the filterfx pcb ( when it's ready, of course ).

[bluebunny]

Do we have an emoji for "gets wallet out"?

[vigilante397]

Hang on, you've had this going since March 4? And I'm just hearing about it now?!?!?!

Sounds killer, I'm definitely in

[BetterOffShred]

Do we have an emoji for "gets wallet out"?

Hang on, you've had this going since March 4? And I'm just hearing about it now?!?!?!

Sounds killer, I'm definitely in

Yeah Man, I'd be into this project as well.   It's pretty Juicy.   Effects loop?

[ElectricDruid]

Ok, I've got a question for you all: How to do the panel layout?

Currently it has four knobs (Frequency, LFO rate, LFO depth, LFO waveform) and two switches (LP/BP/HP and Hi/Mid/Lo Resonance).
Does it need a volume/output level control too? How would you arrange 5 pots and two switches on a 1590BB enclosure? Do people expect enough room for their fingers around the knobs?

Personally I tend to favour big knobs and widely spaced and I try to keep things simple to accommodate this (not always successfully), but I see some fiddly designs out there where people have stuffed as many Davis 1900 clone knobs (about the narrowest that's available?) onto the panel as they can. And I'm not talking about the 1590A pictures thread either...

Your thoughts are welcomed!

Thanks,
Tom

[287m]

Do we have an emoji for "gets wallet out"?

Sticker enough? get this money

Ok, I've got a question for you all: How to do the panel layout?

Currently it has four knobs (Frequency, LFO rate, LFO depth, LFO waveform) and two switches (LP/BP/HP and Hi/Mid/Lo Resonance).
Does it need a volume/output level control too? How would you arrange 5 pots and two switches on a 1590BB enclosure? Do people expect enough room for their fingers around the knobs?

Personally I tend to favour big knobs and widely spaced and I try to keep things simple to accommodate this (not always successfully), but I see some fiddly designs out there where people have stuffed as many Davis 1900 clone knobs (about the narrowest that's available?) onto the panel as they can. And I'm not talking about the 1590A pictures thread either...

Your thoughts are welcomed!

Thanks,
Tom

1590BB?
5 pots inline. and the 2 switch is below the 2 & 4 pots. Symmetry?

[vigilante397]

Leave off the volume, keep it at 4 pots/2 switches and I want it in a 1590B

[ElectricDruid]

1590BB?
5 pots inline. and the 2 switch is below the 2 & 4 pots. Symmetry?

Nice, that could work. What's the spacing on those pots? They look pretty tight to me. Oh, and I forgot to mention it has a tap tempo foot switch as well as the 3PDT...still, we've got lots of room at the bottom, so no problem there.

T.

[ElectricDruid]

Leave off the volume, keep it at 4 pots/2 switches and I want it in a 1590B

Yeah, that'd be nice. Don't know what you'd do about the tap tempo foot switch though. Can you put two foot switches on a 1590B? I suppose horizontally it would work...hummm...

T.

[vigilante397]

Can you put two foot switches on a 1590B?

I have before, but only once. I smash my footswitches as far as I can to the bottom of the box, then I just had one in each corner. Maybe not the best option. 1590BB is fine then I suppose

[samhay]

Very nice.
If you want to be able to tweak the input gain, you could always do this with a switch that also pads down the volume so you add a switch instead of a pot. Not sure that helps much.

Which PIC did you settle on?