Wah sequencer, Vanishing Point, help?

[The Tone God]

I decided on using the Morley Power Wah, since there was a pcb for it in the Schematics 2 section.

Dang you beat me to it. You didn't let me finish my post. lol.

Ah, but now. What to drive? Is this just feasible for just a wah circuit with a resistor to ground?

Any effect that uses a resistor to ground to control can be used. Some people didn't like the filter in the The Original Vanishing Point so as to let people use their favorite circuits I left out the audio section. Some people may want to use inductor based filters and others twin-T filters. I think the twin-T is the easier way to go.

You can look at GeoFex's Technology of Wha pedals article. I was also going to suggest checking out Morley's website as they post schematics for their whas which use optocoupler to ground filters. You can also take a look at sites like GGG and Tonepad for wha boards that you can throw together and use.

Goodluck and enjoy.

Andrew

[Michael Allen]

Ok! Here's my suggested box layout. The 1590BB and this stuff should fit nicely. I based the parts on the dimensions I got from mouser, and the size of the circuit boards. I drew this with TurboCAD after a day of messing around. Turned out well! Imagine that the PCBs are mounted to the bottom of  the box though....

Small row of boxes are the control switches and the small cylinders are the control LEDs. The larger cynlinder is the speed control.

This is gonna be rad!

[The Tone God]

Great stuff! Now your starting to look like a pro.

Two reminders though. In that CAD drawing are you using the exterior diamensions as your case size or interior dimensions ? You lose a few millmeters from the exterior diamensions for the wall thickness. Also are you taking into account the posts in the corners of the interor used for the lid screws ? When I did my quick CADing the pots seemed alittle closer then that because of the two above mentioned points.

Just a few thoughts.

Andrew

[Michael Allen]

Ooh, good point on the interior. I hadn't thought about that. I'll try and readjust for that.

It doesn't really matter on this drawing because i'm not using it as a template. Just a rough idea of setting stuff up inside. I'll try and use illustrator  or something like that, maybe a 2d Cad to set up the drill template.

[Michael Allen]

One more question on the pots.

The LED for the photocell needs 2ma. The LEDs for the stages need 20ma. So 22ma with a 9V supply and a forward voltage of 1.8V means a resistor of 327ohms? I used the calculator from AMZ.

So a resistance of 327 ohms will allow the LEDs to light all the way up I assume. Then using V = I*R what do you mean by "how much current you want to drop" ? In other words how do I get the final pot value that will allow darkness to fully lit? Right now I assume 10k would get the job done....

[Transmogrifox]

This sounds interesting. Just for reference, what is the link to the page with the VP?

I'm chest deep in my envelope filter design/build right now but expect to be done in a couple weeks.  It has an external modulation jack option and it may be fun to make the sequencer as an external device to modulate it...or maybe put it in the box if I have room--though it's getting pretty full.

[Transmogrifox]

Never mind, I found it.  I actually already have a design based on the identical concept of clocking a digital counter rapidly, then stopping the clock at certain time intervals to produce a pseudo random sequence.  I used an 74LS93 TTL binary counter (16 sequence when summed) appropriately.  The sequencer worked well--I was using CMOS gates to control the filter in a binary fashion--too much clock tick in the signal source---didn't even work well with Analog Devices high-end  switches---need to go back to the LED/LDR standby.  Seems to be about the best so far.

[The Tone God]

It doesn't really matter on this drawing because i'm not using it as a template. Just a rough idea of setting stuff up inside. I'll try and use illustrator  or something like that, maybe a 2d Cad to set up the drill template.

Usually I do a 2Ds with seperate images from the each axis lining up to each other. I place centering lines on each part to line up the parts in the drawing but also so I can use the drawing later for a drilling template.

The LED for the photocell needs 2ma. The LEDs for the stages need 20ma. So 22ma with a 9V supply and a forward voltage of 1.8V means a resistor of 327ohms? I used the calculator from AMZ.

The 327 would be the current limiting resistor which I gave a suggested value of 1K to be safe. You could go with a more common value resistor like 330 or 470 to make life easier and give a safety zone.

As for the pots it kind of tough to say. Its not just the LED's current/brightness but how sensative the LDR is as well. Usually I adjust these types of things to my tastes when I have it together. I can understand you don't want to order ten pots only to find out they don't have the range you want so then you have to order another ten. You could order a couple of different values and test them out with your optocoupler then order the rest of them. Thats about the only to be happy with the outcome.

Don't forget heat shrink tuning either. Opaque black is good.

It has an external modulation jack option and it may be fun to make the sequencer as an external device to modulate it

I made a suggestion similar in the Original Vanishing Point article's mods section. I think its pretty myself althought I haven't tried it.

I agree that this way of creating "randomness" is easier then trying to solve it mathamaticlly using indivdual logic bits. The optocoupler just made life easier from just about every perspective (i.e. interfacing to audio, noise, softening of switching, etc.) The 4066 swtiching in the Original Vanishing Point was pretty good as well. It didn't pop at all but I did a few hacks to make it work.

Andrew

[Transmogrifox]

I better look at the original VP schematic--sounds really cool.  I'm interested in how you made the 4066 work without popping...[EDIT]>>took a look, hmmm.... not much different in the implementation.  The difference is that I was using a state variable filter instead of the T-type deal.  I suspect the lack of inherent DC potential between the terminals in the T filter tend to prevent excessive popping.  In the state-variable topography, there is a very high dependence on DC characteristics of the op amps.  An exceptional DC performance op amp is general a rather abysmal audio amp, so I am probing the pulse-width modulation scheme using an analog switch.  I did the math and found this is a very high-precision linear filter sweep technique, superior to most, that is, in theory.  I intend to post the derivation of this at some point when time allows to digitize it.  The inherent problem with getting a wide linear sweep range is the speed of the switch chips and comparators or CMOS inverters used to generate a variable pulse.  You can get a 100:1 resistance change if you have a rise/fall time of less than 50ns on a 500ns wide pulse at 100kHz (lower frequency requires less stringent specs on switches---too low you have aliasing and noise).  Needless to say, I need to find an analog switch that meets that requirement that doesn't cost $10 a chip.

I think this method (back to the digital clock "randomizer") gets closer to random since these cmos, or op amp (bistable vibrator based oscillators) are generally noisy oscillators, in that the frequency drifts, and the pulse-width drifts as well, so it helps keep the  counter from landing on a predictable bit sequence pretty well.

[The Tone God]

I better look at the original VP schematic--sounds really cool.  I'm interested in how you made the 4066 work without popping...

Yes the Twin-T its less DC dependency. I was having some popping problems with the 4066 switch when I was tying the stage pots to ground. I suspect the complimentray FETs inside the switch were getting bitchy so I decded to connect to 1/2 V+ instead. That made the 4066 happier and got rid of the pops. Alittle careful grounding and most of the noise was gone. I also drove the indicator LEDs with transistors off the switching lines since I have had situations with LEDs pulling too much power from the line and causing instabilty with a 4006 switch.

I haven't played much with state varible filters so I can't help out too much there other then to suggest maybe using some kind uC with a PWM and a nice filter. Sorry. I think recently there was a thread about MXR using an opamp PWM to control a 4016 in one of their phasors instead of FETs. I thought that was kind of cute.

Looks like we were both on the same track for the random feature. Ah great minds.

Andrew

[Michael Allen]

OK, these should be the final layouts if all turns out well. Andrew, do you think that the second layout would cause clock bleed since the boards are in close proximity? How about the first one since the speed pot is so close? Just wondering. I'm going to try and throw together another one with the boards as far apart as possible....

[Michael Allen]

How about this one:

http://img.photobucket.com/albums/v368/soma_hero/seq3d_v4.jpg

That's a battery in the middle. Just to see if I could fit it. I can leave it out. I think I like this one the best...

And by the way. I've nailed the 3d business! It's all about adjusting the working plane. Chaning the view and then setting the plane to current view. That allows you to change to each face of the box and move the items along that face until they arrive where you want them. Nice! I've now got full 3d layouts of these boxes. And a dril template!

[The Tone God]

I would lend towards the last layout you posted. Keeps the two boards away from each other. My only suggestion would be to swap the stage and speed controls. Clock noise is happening around the speed pot. The stage selector has less noise involved with it. See if you can tighten up the pots alittle more since it rubbing against the wall. You should leave alittle bit of space to buffer against drilling accuracy. When you wire the pots/leds run the wiring up to the top of the box and around the sides to keep it away from the audio.

Other then that it looks good.

Andrew

[Michael Allen]

Well here's my *essentially* final layout. This is the rendered view of the outside. Pretty sweet what you can do with these programs and the dimensions of what you're working with!

[The Tone God]

I dig. Like the colour choice as well. Can't wait to see the real thing.

Andrew