Wah-ndering about something...

[garcho]

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

^ Tim Escobedo has a few filter with LFO or envelope "snippets", if you haven't checked that stuff out, you should. So many great starting points.

Wah is basically bandpass, and of course sounds like what we all know and love. But I like that lowpass filters keep the low end intact, and sound just as funky.

[strungout]

Hmmm... So, I put the LDRs and LEDs on my breadboard. LDRs wah (with my fingers) and the LEDs light up with picking strength. Now, this: I put them in shrink tube and it doesn't work... I was trying some xvive VTL5C3 and I thought they were't workng but my own rolled ones don't either. Tried putting them in series (the LEDs), parallel. Nothing.

Any ideas?

Oh, and I'm using diffuse yellow 5mm and GL5549 (100k-10M)

[ElectricDruid]

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!

It has an input mixer too, so there should be a highpass output from there as well.

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

I'd have to add level-shifters, or otherwise run the op-amp stages at 5V, but it's not impossible by any stretch, and turning the whole LFO/PWM bottom half of that schematic into an 8-pin chip you just plug in is definitely an appealing prospect!

[strungout]

EDIT: Ha! Stupid mistakes... The resistor for the resonance was too low (10k). Changed it to 680k and boom, this thing wahs and quacks pretty well with my LDR/LED combo. Needs some work, but I'm on the right track. I'll post a soundclip tomorrow.

It has an input mixer too, so there should be a highpass output from there as well.

Oops, yeah, that's what I meant 

[11-90-an]

Is the formula for gain of the CMOS inverters still -(R2/R1)? (Just like the standard inverting op-amp ckt?)
               R2
            |-~~~------|
            |   |\          |
---~~~-|--|  >o----|----
      R1      |/

Sorry for badly drawn illustration...

A good read: http://melbmcu.weebly.com/cmos-gate-as-analogue-amplifier.html

[strungout]

I got it working with the VTL5C3. Added a 1M pot for resonance control and adjusting it produces a nice sweep. THe soundclip is with the VTL5C3. At the end, I just disconnect the pot and it does that weird whistling wah thing...

https://soundcloud.com/user-165425177/autowahedfilterfx

[ElectricDruid]

I got it working with the VTL5C3. Added a 1M pot for resonance control and adjusting it produces a nice sweep. THe soundclip is with the VTL5C3. At the end, I just disconnect the pot and it does that weird whistling wah thing...

https://soundcloud.com/user-165425177/autowahedfilterfx

Yeah, the "resonance" control in this SVF is actually a "damping" control. The circuit will oscillate *unless* there's some feedback to reduce it. So when you take the pot out, it whistles. It also means the pot works backwards. You'd expect "more feedback = more resonance" (e.g. low resistance=more resonance) but in fact it's the other way around - higher resistance=less feedback=higher resonance.

It's not the only way to connect it up. Some SVFs hard-wire the bandpass feedback and use the lowpass feedback to control the resonance instead (in which case it works the other way around) and I even saw one that used the separation between the two integrator's frequencies to control the resonance. It will only resonate if the two stages are well matched, which is why the FilterFX generally doesn't *quite* oscillate with the pot out - between the two integrator cap tolerances and the two LDR tolerances, it's unlikely to be matched well enough (although it might happen).

I like the sound sample, except for the whistley bit. The rest sounds good.

[strungout]

@Tom: Thanks for the info! I wasn't sure why adding more resistance produces more resonnace, haha.


Hmm, so... putting the Vactrols' LEDs in paralell sorta effs up their sweep (or sensitivity). Resonance control won't do anything this time. They work very well in series thought. Hence the problem: I'd have to switch the VTL5C3s to series (they're in parrallel in the FilterFx) along with switching to the EF control voltage...

Another thing I was thinking about is sending the CV of the EF into pin 2 of the StompLFO (I'd only have to switch between pedal and auto operation and still use the same LEDs without having to switch them). The schematic says expression pedal or 0-5V control voltage. Have to mesure what output voltage I get from the envelope follower.

Or yet again, as Rich suggested, connect it right behind the 'control' transistor as the output of pin 3.

Ok, well, I'll got try some stuff!

[ElectricDruid]

@Tom: Thanks for the info! I wasn't sure why adding more resistance produces more resonnace, haha.


Hmm, so... putting the Vactrols' LEDs in paralell sorta effs up their sweep (or sensitivity). Resonance control won't do anything this time. They work very well in series thought. Hence the problem: I'd have to switch the VTL5C3s to series (they're in parrallel in the FilterFx) along with switching to the EF control voltage...

Yeah, in general you're supposed to put LEDs in series to make sure you've got the same current through all of them. But in the case of the FilterFX, I wanted to run two vactrols and an LED, and I wasn't sure if 5V would be enough forward voltage for *three* LED drops. I could have wired them to the 9V supply, but then that would risk putting noise into the audio, what with the load of three LEDs being switched on and off rapidly. What to do? COMPROMISE, same as ever!

Another thing I was thinking about is sending the CV of the EF into pin 2 of the StompLFO (I'd only have to switch between pedal and auto operation and still use the same LEDs without having to switch them). The schematic says expression pedal or 0-5V control voltage. Have to mesure what output voltage I get from the envelope follower.

Yes, that should work, good idea. With the Depth CV at zero, the output will follow that voltage on Pin 2. If you can control the amount of envelope you apply there, you'd be able to mix a bit of envelope with a bit of LFO using the depth controls. The FilterFX lets you do this with the expression pedal - you can mix a bit of LFO-wah into your manual wah.

Or yet again, as Rich suggested, connect it right behind the 'control' transistor as the output of pin 3.

I'm not so sure about this. The pin 3 output is a 0-5V digital pulse stream at 2MHz! I'd have thought it's going to get messy putting a changing analog voltage in there too! But you never know, it might work.

[strungout]

Just a quick update: the pin 2 idea worked like a charm. It even sounds better to my ears. To follow with the schematic, I put the LED in parallel, with its accompanying 470 ohm resistor and I'm lovin' it (screw you Ronald!).

Now I'm gonna go play with the pots, see what moar I can get out of this 

[ElectricDruid]

Just a quick update: the pin 2 idea worked like a charm. It even sounds better to my ears. To follow with the schematic, I put the LED in parallel, with its accompanying 470 ohm resistor and I'm lovin' it (screw you Ronald!).

Now I'm gonna go play with the pots, see what moar I can get out of this 

The CV inputs on the StompLFO are digitally filtered by the chip, so perhaps that helps in this case? Feeding the envelope into pin 2 should smooth the envelope a little more, anyway.

Glad it's working out for you.

[strungout]

BTW, at first I connected the EF control voltage straight into pin 2 of the StompLFO. LOTsa ripple. Then I realised I forgot to add the 'filter I/O protection' through which the expression pedal passes. Much better.

I have a slight, barely-audible, not-really-that-bothersome, problem: with the EF CV connected and the depth pot turned down to 0 -- so as to only have the envelope control without the LFO -- there is some ripple in the decay... but I think it might be from the LFO?
If I was using switches, should I use them to disconnect power to the LFO/EF instead of just switching from the output of one or the other.

Soundclip. It has the same action of the sweep as it had on the LFOgly Face I built, except clean:
https://soundcloud.com/user-165425177/autowahedfilterfx02/s-6HkufwB8GUp


@11-90-AN: How's your stuff coming along?

[ElectricDruid]

I have a slight, barely-audible, not-really-that-bothersome, problem: with the EF CV connected and the depth pot turned down to 0 -- so as to only have the envelope control without the LFO -- there is some ripple in the decay... but I think it might be from the LFO?

So does it respond to the LFO frequency control? If not, it's not that. If it does, it's definitely that!

With the Depth pot at 0, there *shouldn't* be any LFO output. Is it possible the pot doesn't quite zero correctly?

[strungout]

@Tom: Yeah it did, but since I realised I forgot something (namely the 1N5817 and 47 Ohm in series with the power supply) and fixed that, it doesn't do it anymore...

At first I thought the LFO was bleeding through, cause the ripple was sort of 'consistent' with the rate pot. But everything seems to have worked itself out. The decay resembles the MXR EF's now. One question I've been pondering: Which cap controls the decay rate in the MXR EF?

Side-note: I didn't use the 3K in series from the MXR EF. It cuts the sound. But the 5817 + 47 Ohm does the job.

[Kipper4]

Sorry I did a site search.


https://www.diystompboxes.com/smfforum/index.php?topic=123551.msg1168957#msg1168957

I can't see much useful with mxr circuit suitable or easy to implement in a Stomplfo circuit.

Rich

[Kipper4]

Might be worth thinking of this type of detector

https://www.diystompboxes.com/smfforum/index.php?topic=119101.60


and No do not isolate power to the lfo or Envelope detector (e.d.).

Just switch between their outputs.

Isolating power to the lfo may mean, a delay on start up.
Isolating power to e.d. May mean a some signal does not get processed adequately.
May be an an advantage. But there are ways of doing it with attack decay controls that may be more effective and predictable.

Check out the grey paper in my signature too.

[11-90-an]

So i've stated before that I'm attempting to make the Envelope follower of the MXR envelope filter with op-amps...(since i'm a cheap-o)

Now everything else seems quite straightforward, but my only problem is the high frequency clock... Do you guys have any idea on implementing this?

[garcho]

I'm attempting to make the Envelope follower of the MXR envelope filter with op-amps...(since i'm a cheap-o)

Envelope followers without op amps are rare designs. Find every envelope controlled effect schematic you can and compare them all, you'll figure it out. The goal is to turn AC amplitude into DC, with the least amount of ripple. The main controls are attack, decay and output bias. Often, these don't need to be "knobbed out". They can be hard wired. Why not use one of those op amp designs as a starting point instead of CMOS?

Now everything else seems quite straightforward, but my only problem is the high frequency clock... Do you guys have any idea on implementing this?

If you're not just making the MXR filter, why do you need CMOS? Do you understand what the clock is doing? Also, CMOS are cheaper than op amps, so there goes being cheap. How will your envelope follower control anything? Are you making a filter with an OTA? Will the filter be op amp based? Because then, basically, you'll only be able to control it with a LED/LDR setup. So your envelope follower will have to light up an LED. If you want envelope control, you need to find a filter that responds to control voltage (or current a la OTA).

[11-90-an]

Yes, I know about those things you said... 

I wanted a envelope follower that also has a "reverse sweep" option...
I know the Mutron III has that, but I want to try something new... 

I bought 10 TL074 for about $1 give or take a few... cheap enough? 

I'm planning on using a vactrol..

[11-90-an]

https://www.nicolascollins.com/texts/electronotes.pdf

I there any advantage to this ckt rather than the Morph-Lag?