Wednesday, February 25, 2015

Notes Towards a Mister Grassi Workshop

The essentials of the paper circuit micro-cottage include a needawl- an awl made with a sewing needle for punching the paper circuit. Besides that, the standard tools are a soldering iron, lead free solder, de-soldering braid, and strippers, nippers, and pliers.

Here you can see the back side of a Mister Grassi, with many components threaded and solder-beaded together. Note the temporary disarray of some leads as they wait for other connections- don't be disturbed by the presence of wire, especially if it will serve you in the future.

Next is a picture of the same Mister Grassi, cleaned up a little more, and with some large interstitial traces added. Note that I constructed the central traces with bare wire, and how some outer traces maintain insulation. They tend to be more flopplier there on the outer rim, so you need to protect them from touching each other. In the bottom middle of this picture, you can see I did a special trick with the green wire- you can strip its insualtion a little bit in the middle, and work it apart, to insert a perpendicular connection.

Worry less about following the lines, but rather following the separations; these wires must not touch where they aren't supposed to! Next we start talking about encasure, but first, I need to put the hairy capacitors in. Mister Grassi has twelve, and I usually specify a range between one and ten nanofarads; codes 102, 152, 222, 332, 472, 682 and 103 are the E6 preferred numbers, that give a wide spread from high audio to bass. Any material should be fine, either plastic or ceramic, but long leads helps if you could find the older, green jellybean style. Note that they might not be green anymore, more like brick red (panasonic) or yellow (nichicon) but they will still be polyester film.

Zooming out, the decade range from one nanofarad to ten is theoretically for a diversity of tones that produces a wide range of data noises in the circuit. Actually, you could get just as wide a range of tones by leveraging the precision tolerances of industrial capacitors; by relying on a five or ten percent spread, then many sidebands are generated by the harsh data heterodyne of Mister Grassi's arbitrary logic. 

My son and I are in a noise band, of Mister Grassi and imitative utterance obligati. Each new Mister Grassi adds a unique song-piece to the arsenal, for they are all different as per the discussion on hairy capacitors.

For the case, I use the traditional stereo oblong (see final pictures below). After the circuit board is done and thoroughly tested, move on to installing twelve nodes in the top of the case. Use brass rod or wood screws. Flip the case over and wire each node with a hank of solid copper wire. There are six stars and six crosses on the Grassi board, that connect to these nodes in an arbitrary arrangement for latent finger-muscle memories.

The sides of the case have been slats of wood, paper mache, thin plywood upholstered with fake fur, and simply cardboard. I choose double-wall thick corrugated cardboard and found it quite sturdy for this application. I might cover it with a decorative and protective layer of multi-colored gaff tape. It is mounted with screws and washers.

This case not only protects the circuit board, but it also forms a resonant space, like a hollow thorax to give the speakers a personality and isolate them for maximum diffusion projection. The final touches are almost done.

Here you can see my final grassi box. This form has been with me for a while now. I use it mostly for grassis, but have put other beasts in it. It has two speakers angled to project away or towards the performer, depending on preference. It is slightly arched so the face material can clamp down, with the use of wooden cauls here. I decorated it with a little green felt. I sank the nine volt battery snap into a pool of epoxy, so you can simply attach or detach it upright. I never do an auxiliary output jack; this is almost an acoustic instrument and I prefer to not amplify it otherwise. Since the body of it can be held and shaped acoustically, I find it better to mike it like a real instrument!

The Mister Grassi whom I made in this article uses a slightly improved design, the new Mister Grassi paper circuit. For reference, here is the old one. The difference is in a slight standardization of resistor values, and a replacing of the LM386 amplifier chip with NJM2073. The reason is for the purpose of a completely electrolytic-free circuit. The NJM2073 has two amplifiers, and can work in bridge formation, so it doesn't need the big electrolytic capacitor that the single 386 does. It's an important goal to eliminate electrolytics because they decay and need replacing; they are a major contributor to obsolescence in electronics. A musical instrument can be un-obsoletable, meaning that a musician will always find use for it, be it simple or outdated or ponderous or primitive.

On the soldering bench at Calarts, there sit several Mister Grassis. Nathan Shaw seems to have decorated with sharpie and replaced the cardboard sides with clear polycarbonate! Elizabeth Aubert used the classic Joanne's plastic fur...

1 comment:

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