Nadion Particle Generator (modded stage fright)

[midwayfair]

Stage Fright, with a pretty cool little "Sweep" mod.

I was tinkering around with the trim pot, and trying to figure out what it was doing -- turns out it was adjusting the notch. And I thought, that's really interesting. But it really only had any action on the top half of the pot, and sounded best maxed out.

I was also fiddling with the FET, because I wasn't getting too much action on the 5-stage side. At first I figured I'd just swap it for a J201, because that sometimes offers a higher switching range (see the Shark Fin notes). It helped a little. But then I looked at the schematic, and noticed that the grounded gate meant it was really just acting as a diode. So I started plugging in some diodes, then realized that a higher Fv (up to a point) offered a far more extreme effect. I settled on a blue LED over a 3.3V or 4.7V zener because they didn't work without a blocking diode.

The I wondered -- what would happen if the sweep pot was bigger? Hooked up a 100K pot in series with the LED and got a nice big range. 500k was a little too much. 250K was perfect on the extremes, but bunched up a bit on the sides. A log taper fixed that and now the sweep gets "deeper" (moves toward bass) as the pot's turned up. For an even cooler effect, it also forms a CLR with the LED, so turning the pot makes the sweep AND the LED darker. The ability to tune the notch makes it an exceptionally versatile phaser now.

It was a bit of a pain while boxing. I had the LED sort of hard mounted to the switch, and then I could reach in with a small screwdriver and guide the LED to the bezel.

And for extra super added bonus thought ... if you move the sweep while playing, it sounds flanger-ish. No fooling. You could add a switched expression jack and use an Ernie Ball volume pedal as an expression pedal. Might be worth considering for anyone thinking of an add-on that uses the CV input. (I might build another one in the future and add an envelope control for the CV.)

I will definitely do a demo of this in my next batch.

That said, it wasn't the most pleasant build. There's really no option except top jacks to get this in a 125B, and the jacks leave almost no room for error if you want to use sockets for the LM13700s. Since I still haven't solved the problem of my soldering iron killing chips (I actually lost my first stage fright PCB due to that ... after I desoldered the chips, I couldn't get it to fire up, though I might revisit it with the possibility that the chips were bad), that meant I almost ended up with an effect I couldn't plug into.

I also had a near-disaster when I overtightened the toggle switch (trying to get the PCB as far from the jacks as possible) and broke it ... desoldering a 2PDT is NOT my idea of a good time. I also had to lower the board-mounted pots at the same time.

Finally, let me just say that I'm not really a fan of top mounted jacks when the design has the in, out, 9V, and ground connections at the bottom of the PCB! I don't mean to fault Brian for that part of the layout, as I'm sure things were exceptionally tight on this (and overall it was an easy board stuffing experience), but it just makes the wire running less than ideal. Especially because I don't think the in/out jacks will fit on the side except to do like Merlin and cut off the nubs of some plastic jacks to put them on either side of the switch.

Oh, and my last problem was that some of my LM13700s simply didn't work. They happened to be the set I was using in the first one I built -- not the desoldered ones, but from the same Tayda batch. Since I wasn't careful about separating my Tayda chips from my Mouser chips, I now have to dig through them to figure out if it's the builds or the chips in the OTA pedals that have been having problems. I just wanted to mention this if anyone else is having trouble getting theirs to fire or has a really weak effect ... though I did have one chip that didn't work at all, in a couple of them, it was simply one half of the chip that wasn't working. I found four that were in some stage of death. It could be a lack of ESD precautions (Tayda doesn't ship in protected bags), or just bad chips, I don't know.

[Leevibe]

Sometimes a pedal just fights you all the way. Sounds like you won in the end!

Edit: oh, great job! Nice work getting those jacks top mounted. Love the graphic too!

[jimilee]

Set Phaser to stunning!

[lincolnic]

You've emerged victorious! No phaser will stand in your way. This looks great, as usual.

Any reason behind "partical"?

[bcalla]

Fantastic work, especially your ability to develop mods.  I wonder if I could retrofit the sweep mod into mine without destroying the pedal.  Maybe I need to build another one...

BTW, I was able to get side jacks installed next to the stomp switch.  But I didn't use a board on the switch, and it was ridiculously tight.

[das234]

Fantastic work, especially your ability to develop mods.  I wonder if I could retrofit the sweep mod into mine without destroying the pedal.  Maybe I need to build another one...

BTW, I was able to get side jacks installed next to the stomp switch.  But I didn't use a board on the switch, and it was ridiculously tight.

Ditto on both comments.  I remember building this right after the honeydripper, which is very similar space-wise, so I had figured out how to fit the jacks in on that project (after mis-drilling one enclosure).  Looking forward to the demo.

[jubal81]

Really dig this one and great report on the mods. I think a bogus 13700 spoiled my Space Harp build.

[midwayfair]

Any reason behind "partical"?

Because sometimes I don't pay enough attention.

But if anyone else asks, it's to avoid getting in copyright trouble, or something like that.

[GrindCustoms]

That sweep control is pretty sweet, still have an unused board of this circuit, might give that a try, since the MP1 is my second favorite phaser.

BTW, The pcb layout in a 125B works with the jacks mounted on the side, with a regular 3PDT that you mount low as possible in the enclosure (i.e 1590A) you've got plenty of room to fit enclosed or open jack, with the enclosed jack you would be able to have them sitting under the board and you could also fit the extra jack for the expression pedal if desired... ...and the In/Out pads location on the board would'nt be inconvenient anymore.

[juansolo]

Velly nice 

[pickdropper]

Very cool build and nice report, Jon.  I have a populated board here, I may have to give the sweep control a try.

Btw, on my build, mine never sounded balanced until I changed all the 1n caps in the phaser stage to 4n7.  Now it sounds good (to me) in both 5 and 6 stage mode.  I even went back and changed them on my Andromeda 2 build (wasn't fond of opening that one up again).

[Guybrush]

Issues with the build and still meticulously neat. Great work as always (even if you do make me feel like hanging my soldering iron up)

Sent from my HTC One using Tapatalk

[mah62]

Jon, your builds always make me smile!

Mark

[TGP39]

Fantastic build Jon. You have an insane ability to find really cool mods. I always look forward to your builds and your notes. Steve.

[das234]

I agree.  Jon's builds are unique and always a treat.  The highly informative comments are great too but sometimes they just make me dizzy.