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

[Mark Hammer]

If there are to be two stompswitches, then the toggles need to go between (in the space just below), controls 2&3, and 3&4, such that there is maximum distance between the user's steel-toe work-booted size 13 foot and the toggles.

The proposed volume pot should probably be able to dial in a level somewhat below bypass, and somewhat above, such that the user can engage the pedal for rhythm OR solos.  Keep in mind that upping the resonance also increases the output level.  So if a user wants to bring in sweeps for rhythm work, they want to be able to avoid surprising shrieks.

Not to beat the horse mercilessly, but my own experience and view is that downward sweeps often have to start a bit lower, and not simply replicate the min/max sweep points of an upward sweep.  That obviously bears no relevance for some of the modulation patterns the chip is providing.  But it likely does have some relevance to the sawtooth waveform which, even though repetitive, IS fundamentally a downward sweep.

[BetterOffShred]

[ElectricDruid]

If there are to be two stompswitches, then the toggles need to go between (in the space just below), controls 2&3, and 3&4, such that there is maximum distance between the user's steel-toe work-booted size 13 foot and the toggles.

The proposed volume pot should probably be able to dial in a level somewhat below bypass, and somewhat above, such that the user can engage the pedal for rhythm OR solos.  Keep in mind that upping the resonance also increases the output level.  So if a user wants to bring in sweeps for rhythm work, they want to be able to avoid surprising shrieks.

Not to beat the horse mercilessly, but my own experience and view is that downward sweeps often have to start a bit lower, and not simply replicate the min/max sweep points of an upward sweep.  That obviously bears no relevance for some of the modulation patterns the chip is providing.  But it likely does have some relevance to the sawtooth waveform which, even though repetitive, IS fundamentally a downward sweep.

All good points, Mark.
I agree about the different sweep ranges. You finish up adjusting both the base Frequency and the LFO Depth when you change the waveform. Different shapes need different settings.

Tom

[Kipper4]

I can look at doing a tremolo with the chip Tom.
I'll start a new thread when I've had a play with it on the breadboard.

[garcho]

I have a thing on the breadboard with Tom's LFO 8pin chip and let me say it's a breeze to implement and the only LFO i've made that compares was a complicated mess that took up so much real estate i scrapped it. Highly recommended!

[Kipper4]

I have a thing on the breadboard with Tom's LFO 8pin chip and let me say it's a breeze to implement

Jelous here.

[ElectricDruid]

Which PIC did you settle on?

It's a 16F18313 in the end, one of the recent enhanced midrange chips.

Code and details are online here if you're curious:

https://electricdruid.net/electric-druid-chips-the-next-generation/

[samhay]

Thanks for the link (and for sharing the code, even if it is in assembly).
That looks like a very useful little chip. Will have to add some of these to the next Farnel order.
PDM is a nice feature - I guess it would be much easier to get this to drive something other than an LED (like a JFET).

[Hatredman]

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.   

Makes sense to me: "Druid Rate", "Filter Depth", "FX Wave".

.sig goes here.

[blackieNYC]

In suggesting a output volume pot, I mean - does it sound like it needs one, when listening to the amp (as opposed to phone)?

[ElectricDruid]

In suggesting a output volume pot, I mean - does it sound like it needs one, when listening to the amp (as opposed to phone)?

I dunno to be honest. The prototype has no bypass switch, so it's hard to tell. More experiments needed before a final decision can be made there, I think.

T.

[Mark Hammer]

In suggesting a output volume pot, I mean - does it sound like it needs one, when listening to the amp (as opposed to phone)?

Much like tremolo, when you take away portions of the signal, via filtering, or by arriving at a lower average overall level, it's helpful to be able to balance bypass-vs-effect level.

[garcho]

^ but unlike tremelo, filters have resonance. i would throw a super simple compressor in there (opto, NE57x etc), no need for compressor controls, just auto-squish the pointy peaks. of course, that means a bigger PCB...

[KarenColumbo]

omfg - almost forgot about those beauties! Ordered a couple

[ElectricDruid]

Ok, I've got a Rev.1 (definitely "prototype") PCB layout done for this:





As it says, I need to check the switch footprint before I pull the lever on this, but once the switches arrive, I'll get a few prototype boards made up and see how it looks and make any tweaks necessary. Usually there's a couple of small things, but I'm not envisaging anything major.
This Rev.1 includes components for the optional sync input for the LFO and also a location to add an expression pedal input (that's what the cut-out on the right is - gives room for the extra jack).

More soon..ish,
Tom

[Mark Hammer]

I see that Godlyke/TWA has adapted your TAPLFO chip for an expression-pedal input source.

http://www.effectsdatabase.com/model/twa/sidestep

[blackieNYC]

ED - I have one on the breadboard.  What is the "onset - base frequency before modulation"?

My HP and BP outputs are working, but the LP isn't doing anything that I can hear. Passes audio.

On the breadboard, there is a lot of LFO noise in the audio output - did anyone experience this on the breadboard? I ave filter caps in place.

[ElectricDruid]

ED - I have one on the breadboard.  What is the "onset - base frequency before modulation"?

It sets the "bias level" if you like. Imagine you turn the depth down to zero - what level do you get? That controls sets that level. As you turn the depth up and up, it becomes a moot point since at max depth the output is 0-5V whatever you do.

On the FilterFX specifically, if you turn the depth down, you can use the offset control to manually sweep the filter over the full range - add an expression pedal for wahwah. Or you can have a limited depth and just filter the treble or just the bass or whatever.

My HP and BP outputs are working, but the LP isn't doing anything that I can hear. Passes audio.

That's pretty weird for a SVF, since all the outputs interact, pretty much. I'd check you've got the feedback paths correct - those are easy to get wrong; R6 and R7. Note they *don't* go back to the same place. IC1.2 is a differential mixer not a simple mixer.
Beyond that..dunno - a problem with the integrator caps C2 and C3 maybe? They're pretty critical too.

On the breadboard, there is a lot of LFO noise in the audio output - did anyone experience this on the breadboard? I ave filter caps in place.

What does the LFO noise sound like? Actual LFO feedthrough would be ultrasonic, so you won't hear that, but you might get some ticks or bumps or something. But I'd get the filter working first and then see what the situation is. I have a feeling this might fix itself.

HTH,
Tom

[blackieNYC]

It cleared up somehow.  I must have had a short on the breadboard in that last op amp stage.

The Depth and the Offset both seem to have all the action at one end of the pot.  Particularly the Offset.  I'll try a log pot, or maybe a series resistor.

The Sweep LFO setting - I can't tell - what is that supposed to do?

[ElectricDruid]

It cleared up somehow.  I must have had a short on the breadboard in that last op amp stage.

Remember to give thanks to the Gods of the Breadboard for your blessings, or your circuits will remain ever faulty.

The Depth and the Offset both seem to have all the action at one end of the pot.  Particularly the Offset.  I'll try a log pot, or maybe a series resistor.

Could it be that the optos aren't acting very linear? The controls for Depth and Offset are supposed to be linear pots, and they have a linear action. The pulse-density drive of the LED should give a pretty linear conversion to LED brightness too.

The Sweep LFO setting - I can't tell - what is that supposed to do?

It's a "hypertriangular sweep" - in this case approximated with the bottom of a sine wave (which is actually how it's done in some of the analog implementations I've seen). There's a picture in the datasheet:

https://electricdruid.net/datasheets/STOMPLFODatasheet.pdf