It’s alive! The Fyrall board is assembled, with some of the modifications I discussed previously.
I’m still working out the the panel design. The panel has to come last, because I need to see how the Fyrall behaves before deciding on the panel features. Finishing it up to the point where it operates is a milestone. I discovered that my hairy capacitor choices result in quite low frequencies. I may change these. And I’m still considering whether to put range switches on each oscillator pair. Another thing I discovered, and don’t like that much as a fixed operating mode, is the burst-like nature of the beast. It turned out that the oscillators spend a lot of time not oscillating. They wake up and wiggle around for a bit and then get sleepy again. This is kind of cool, but I’m going to make it into an optional mode. By breaking into the circuit at the ZE node, I found that by applying either 9V or 0V to the 100k resistor (depending on whether oscillator spikes up or down), I can make it oscillate regularly. So I plan to have a switch for each oscillator that can make or break the ZE node connection, and there will be a banana jack available for input or output, to or from the node.
Pictures
Fyrall is a bit weird in that the top of the board is the bottom of the PCB. That is, the pots and LEDs go on the bottom of the board, which will be upward facing. It’s intended to go in a wood box, but I’m doing my clear acrylic thing. Jacks won’t go above the board, but on a panel area adjacent to the board. The LEDs will show through the clear plastic. By the way, those LEDs are jammed so close together, the little Fresnel lenses that disperse their light don’t fit. The intention was to have the LEDs behind epoxy windows, like on the Cocoquantus.
The lower, left LED cluster indicates the (mixed) outputs of the Orranger (CV selector). The cluster in the middle of the Counters indicate the three primary stepped outputs.
The LED cluster at the right side, in the middle of the pots, indicates the (mixed) values of the three oscillator pairs. (The pairs share a pot and an LED.)
To the left of the board on the component side are the three dual selectors (4052) and their output buffer chips. This area also has the U-strip, which I’ve abused so as to add in six buffers for the stepped waves that will be brought to the panel. I’m also bringing out the six selectors coming from the counters, at the OC points. I omitted the 100k resistors, because these are no longer treated as nodes, but as outputs. At the bottom of the photo below you can see how I reused a chip for the extra buffering.
The center section is the counters. The other repurposed buffer chip is to the upper right. Not much around it but a little yellow bypass cap. To the lower left you can spy one of the FET buffers for the “studio out”. There are three on the board. Easy to spot with the two large red 100nf coupling capacitors. The FET buffers AC couple signals to the outside world, and impart a distortion as well that I expect to sound nice.
The right side contains section Z, the six oscillators of the King’s Face. The power conditioning circuitry is here, too. After initial testing I felt the voltage regulator getting a bit warm to the touch, so I added a heat sink. I’m not worried about clearance below the board, because I can give it as much as it needs.
