Monumental absence on the blog-front, my apologies. I like to have something of an orderly line of thinking in this format, and frankly it seems as if I've been ensconced in avalanches of R&D or convoluted puzzles to the point that settling on a single train of thought would be detrimental to the process. Since there has in fact been physical realization of something, I can just shut up and talk about that! Haha, thanks for understanding.

Pictured above is the preliminary assembly of the first two sections of a three section noise generator. The initial prototype is essentially a lifted collector white noise section cascading into a low pass section which in turn feeds a malformed state variable filter (not yet stuffed, obviously). I can't really call it that, because while it began life as a state variable it became mangled. I'm not going to elaborate further, because with the second generation prototype that section is facing a deep revision. The sonic goal of stage 3 is a pop-corn type crackle with adjustable intensity, please stand by.

Let's fast forward the initial build and actually listen to it:

Something of an acquired taste, perhaps. Seems also to have aggravated the youtube compression algorithms, I can provide a clean recording on request (but seriously, the second generation is shaping up to be improved, so why bother!)

Guts! Nothing much more to add here. I have slapped a primitive voltage regulation into it because I built it with a spot on 9 volts supplied by my bench supply, and every single wall wart I tried once built made it go haywire. Here's the believed to be accurate schematic of the initial prototype:

If you're a lunatic and want to build one yourself, I would advise contacting me instead of going off this schematic - unless you want to be saddled with all the issues that are under resolution with the current build. Amongst design flaws that are resolved at this point: the loading down of the low passed crumble output control when other stages are turned up got cleaned up with a common collector buffer.

Layout on the proto-board is also taking a more direct path.

With the exception of the initial noise source stages, I identified gain stages and buffers - then settled on a uniform configuration of values to simplify assembly. This created additional problems with the triac, but since the operating characteristics of each and every one seems different (I'm pulling from a really old bag, so it's anyone's guess if this is due to my circuit conditions or age/sloppy manufacturing tolerances) I needed to allow for calibration anyway. Now I can dial the triac up to the point where it's *not quite* stuttering and cutting out, which has improved the crumble of stage two substantially.

So there you have it, I may update on stage three once I get it sorted (lower right knob needs more travel/interaction), or we might take a look at something else. I'll try and touch base before another season goes by...

Perhaps I should change the running title to "broken stuff" instead of "machine log", especially since most of what I focus on isn't technically machinery in the first place. Nah.


Here's a GenRad 1390a noise generator.


The power switch was already sheared when I bought it, and being a three position rotary wafer it will not be as simple as slapping a SPST in there.


Gutshot.


Here's the heart of the noise generator, a 6D4 in a magnetic field, sort of the tube era equivalent of a lifted collector. Okay, not really a firm parallel there, but work with me here.


I think this unit saw some service, as there are a few thermal stains on the chassis. I'm pretty sure the shake and bake coating on this cap has more to do with a "sticky" shell picking up airborne debris than heat, but the airborne material was probably agitated by the heat and magnetic charge of the powered device to begin with.


More selenium, which reminds me I have a backlog of simple surgeries to perform with no excuse..