Gallery, Projects and General > Project Logs
Extending the soundscape of a hexaphonic guitar pickup
sorveltaja:
While waiting for the ordered parts, I made a 15V split power supply pcb: http://musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/wallwartbtmcopper.gif :
It needs an ac wall wart to power it. I have only one, that is for 12V. I was ready to order 15V one, but then thought: hold on, doesn't dc wall warts have already an ac output in them, that is rectified by using diodes to make dc voltage?
So I had to look, what I have in my boxes of 'stuff'. Surprisingly, there was 15V/500mA dc adapter, that didn't seem to belong to any device, that I use. I managed to open its enclosure, and took some measurements with multimeter. Yep, it could perhaps be used for the purpose.
Only two wires needed for straight ac output. Actually I'm going to use its dc wires for that, as they have a nice strain relief clamp already. No extra wires or holes needed.
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But there is one very serious precaution, though: to do something like that, one must be extra careful, as there is live 220V(in Europe) involved, when that adapter is connected to mains.
Disclaimer: If in any doubt, don't do it. If one still insist doing it, that one takes full responsibility, of what he's doing.
Only once I've had 220V shock, and yes, it was indeed very nasty, so I'll do my best to avoid messing with it.
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But enough of that. The 15V split psu will be a 'master' one, that feeds lower ones(like devices, that have 9V regulator in them). But we'll see, what comes out.
When looking inside of that previously mentioned ex-tape recorder enclosure, there was dust and a phase shifter:
I doubt, if it's still in working order, after two decades, due to corrosion of the pcb traces. As can be seen, two ic's are configured to substitute original op-amps(super-rare 4739's). White blocks are diy optoisolators(led/ldr), to replace original Clairex CLM6000's(that were probably never available outside US, but what do I know).
Quite a mess, that is worth only for looting socketed ic's, pots and switches.
I'm considering of rebuilding that, but what comes to optoisolators, they need some fiddling(when using ordinary leds and ldr's) to get them to the 'working range'.
Or just re-use the components inside white blocks, and look, what kind of mods I did use back then, to get them to work.
Sea.dog:
They're not cheap, but still available - https://www.ebay.co.uk/itm/Clairex-CLM6000-Single-LED-Optocoupler-/322610705324
sorveltaja:
Seadog, yes quite a price for single led/ldr -pair. One way, at a fraction of the cost, is to make ones using a heat shrinking tube.
If memory serves, it wasn't that difficult to get ordinary led/ldr pairs to work, as required in that phase shifter. In schematic, there is a 470k resistor in parallel with ldr, and 200 ohms current limiting one in series with led. The circuit itself:
Playing with those two resistor values should do the trick. Nowadays the leds are much more brighter(and/or efficient?), so they need to be tamed down, to fit for the rest of the circuitry.
Ldr's responses (could) vary between maker/model, so some tinkering with them also, I guess.
More about that, when I get to building the actual device.
Ordered parts came today, so I managed to finish the 15V split power supply circuitry. I also did the previously mentioned ac-mod for the 15V dc wall wart.
I'll have to admit, that I got a bit nervous, when testing those out. I had already a box of fuses, and some other measures of precaution, just in case, that something goes horribly wrong.
But it went well, and they work nicely together. Fortunately there are very rare occasions, where I have to do projects like that.
Next thing to do is either:
- print an enclosure for that split power supply(not sure yet of its final assembly, though)
- build that phase shifter
- build the vocoder
- drink few more beers
Somehow I have again this familiar feeling, that I'll have to start with the most complex one, that is vocoder(well maybe not that complex, but considering its parts count).
Yep, vocoder it'll be.
In the end, I think I should provide some audio clips every now and then, considering so far built devices/circuitry. But easily accessible/usable audio recording interface is still missing.
I'm thinking something like a usb-based ones. But we'll see.
sorveltaja:
The pcb for the vocoder needs thorough cross-checking, using the schematic(down-sized to fit for the page):
Luckily most of it is repeated 'blocks', like op-amp and compander sections in the middle. Only the component values vary between them. But still, tedious task to do, so I'm expecting to take a break of it at some point, and do something else, like building the phase shifter.
What comes to the previously mentioned audio recording interface, there seems to be a lot of those usb-based soundcards.
Without knowing too much about them, something like Behringer U-Phoria UMC22 could do the job for 39 euros, but it's currently out of stock on local supplier:
sorveltaja:
Cross-checking that vocoder pcb is indeed very slow thing to do. I had to restart from the beginning a few times, to find better ways to approach it, and perhaps learn something in the way.
So far I've found several missing traces, and errors, when compared to previously drawed one, using that blurry image.
But after all, no matter how long it takes, I guess it could be worth the effort. If not, there are always plenty of other vocoders to choose from.
In the meantime, I have also had some ideas, like making the filter sections 'variable', using headers for their capacitors. Originally the cap values are for 200, 400, 600, 950, 1300, 2200, 3000, and 4900 Hz. But we'll see, once I get there.
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