Saturday, May 16, 2015

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...

16 comments:

krivx said...

Looking at your noise generator, you have the noise source feeding a stage with gain of ~6, then another amplifier with a gain of ~25 at DC and more gain at audio frequencies (prob x100 or more).

Do you need that x6 amplifier? Looks like you could drop it and remove some parts.

Your second stage has a 1k/1k common emitter - a common collector buffer might work better here (+saves a resistor :))

Is there some LPB-1 inspiration going on?

The state-variable filter does look odd...

crochambeau said...

Ousting the early low gain stage is certainly something I'll look into once I have the 2nd & 3rd sections bulletproof.

The initial stage of the 2nd section was swapped out for a trimmable common emitter gain stage, I don't need to provide any current, just tickle the triac on and off. The 1K/1K configuration was the result of my messing with it until it worked (at 9 volts only). This is the section that's getting the most scrutiny at the moment, I love the sound it's making now, it's just tempermental. I've got three other triac configurations to try and will drive them from every BJT configuration until I have something that's reliable.

Yeah, I think the LPB-1 was the common emitter footprint I started with.

I don't think it can be called a state-variable at this point, started there and then I blindly beat on it until it could only crackle. The opamp section in the second version had a complete facelift, first section was set up like a differential amplifier, second section was a voltage follower splitting the supply feeding non (IIRC) inverting input of the first, third was gain & fourth just terminated. They each have a different voice, jury's still out on which one I'll settle on. Thanks for the input!

krivx said...

What's the triac doing? Gating? I've never used them before, don't understand why the gate is held at 9V.

crochambeau said...

Triac is gating, but the white noise is working the gate, the 9 volts is what is just the supply that comprises the signal for the next stage. It's an odd device, as configured the V1 appears on the gate as well, and the relation of voltages and current (when it's conducting) contribute to what's conducted, an on and off trigger based on thresholds provided by the signal, not external control.

I feel like I'm butchering the explanation, which may not be based in complete understanding on my part. Anyway, the little zener regulator there was an aborted attempt at a stop-gap fix I tried when I observed the circuit wouldn't behave (turn off) at different supply levels.

krivx said...

I might read up on triacs. I am used to seeing them in phase fired controllers where the gate is connected to one of the terminals through some resistance. That configuration makes sense (to me) for a signal to gate itself. I don't really get what's happening here, it feels like the gate should have a varying signal and not just DC.

Thanks for sharing, it's odd that more people don't for noise stuff.

crochambeau said...

I'll share my findings on it for sure, I also have a bunch of SCRs to play with - but one thing at a time..

crochambeau said...

Regarding gate & the triac, I depicted it incorrectly on the schematic. The white noise is fed through the DC blocking cap to the gate and MT1 is connected to DC voltage.

Thanks for the catch!

krivx said...

Ah that makes more sense. Does that mean you get 9V minus a couple of PN junction drops on the output of the triac when it triggers? That would give a noise-controlled ramping signal instead of gated noise but maybe those are functionally the same. It would be cool to see some scope shots.

crochambeau said...

No, the output signal at the triac is small. Once pushed into conduction it'll latch up and require a reset.

In all honesty, with a self incurred deadline to have this thing sorted by the weekend I've shelved using the triac right now. I'm getting close to what I need with transistor bias and cascading sections.

When I get to working with one again I plan on including a provision to interrupt current and allow the triac to turn off. I'm hoping it can be done without just making it an oscillator.

krivx said...

are you doing pcbs for these?

crochambeau said...

A friend has offered to draft a layout, after which I do plan on getting a quote from an in state company for a small run. Would you be interested in just an unstuffed PCB or would you prefer kits?

The former may be achievable in a relatively short period of time (say 1-2 months) the latter is somewhat off the table at the moment, as I'm tied up with builds and R&D.

I'll get around to uploading the revised schematic in a day or two. It has deleted the triac and LM324 and added a 741.

krivx said...

PCBs are always nice for international orders, you can ship them quite cheap. I must say that the enclosures you're making (right?) look very nice though

crochambeau said...

Thanks for the kind word regarding enclosure. Yeah, those are being hand fabricated from sheet steel, not quite one at a time but in pretty low numbers for a days work. If I had better tooling I wouldn't be averse to offering up empty enclosures, but as it is they are too labor intensive to allocate to anything but my own builds. SOME DAY

Sounds like PCBs are on target.

Marcus said...

What a fantastic machine! May I please have the updated schematic if it`s available? Or are PCBs now available? Thank you!

crochambeau said...

Hi Marcus! I have not got a schematic in user friendly state just yet, though I am about to test the waters regarding offering the PCB and a BOM. It's still a somewhat temperamental build, so I'll update this after the builder gives me feedback. Thanks for your interest!

Marcus said...

Thanks very much, looking forward to it!