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Extending the soundscape of a hexaphonic guitar pickup
sorveltaja:
When checking solderings, there was only one bridge. But then I found multiple errors also. They were easy to fix, by adding a solder bridges to pairs of IC legs.
Still no cigar. Finding bugs by using an audio probe seems to be more difficult as I expected, as there are too many interactions with pots/knobs, and switches involved, which affect the results.
So I think it's not worth of the effort. What I'm going to do, is to crop all the extras(stereo-, loop send/receive, fuzz, and bypass options) out of the schematic/circuitry, making it a lot easier to make sense of the signal paths.
Then start from scratch, using same method as mentioned before; divide circuitry to blocks. Breadboarding first, and only after certain block is tested and working, draw a pcb for it, and build it.
I already have all the needed IC's, pots, and jacks. Some caps and resistors could be scavenged from the already built circuitry.
sorveltaja:
Today I did some drawing, of how the blocks could be breadboarded. Both the instrument- and microphone input stages consist only single amp. So does the output stage.
The heart of the device is between:
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On the left side is one of the bandpass filter pairs, which share the same component values. In total there are 8 pairs of them, for 200, 400, 600, 950, 1300, 2200, 3000 and 4900 Hz. Obviously different frequencies require also different capacitor values. Other than that, all the pairs are identical, and use the same pcb layout. Should make easier to build the blocks one by one.
Plan is to make separate pcb's for each pair, so that they could be handled like 'modules'.
For those I'm going to use dual op-amps, instead of quad ones used in that already built circuit. I happened to find more than enough duals from my shelves, and also few single op-amps, that I'll use for input- and output stages.
On the right side is one of the 571 dual companders. I might have used one or two in some projects in the past, but never actually fiddled with them. But now there is a good chance to hopefully make sense, of how they work, at least during testings.
So here we go again, and next on to the breadboarding.
sorveltaja:
Both input stages were breadboarded, and tested. I did draw pcb's also:
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So I printed the transfers, did some ironing, etched the boards, and drilled the holes. Only after that, I noticed that they were reversed... Sometimes the printed transfers need to be mirrored but not this time. The way, that I draw the layouts, they should be printed as they look on the screen. If there is some text in them, only that should be mirrored.
To keep the project going, I made new ones using non-mirrored transfers, and now the boards are in etching bath.
sorveltaja:
Today was spent mostly by drawing new layouts for buffers(the 'clarifier' mod for the vocoder):
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First is the old layout. Second is the new one, divided to two separate boards. Both have only one input, and 8 outputs. I thought that it would be more handy to gather the outputs together, so headers will be used. There are no ground connections in the buffer boards, as was mentioned by the builder of the mod.
As can be seen, there are no other components than quad op-amps and a few jumpers, so I didn't bother to breadboard it. If the IC's are fine, it just should work.
sorveltaja:
Input and buffer boards almost finished:
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Only one of them doesn't have a header, being mic input board, as it was the first one that I did draw and build, and didn't consider of using headers.
But after that, I got back to my senses, as using them(headers) should minimise the wiring hassle between stages. That way, testing of the 'modules' is also a lot simpler thing to do.
Next thing to do, is to add necessary wires for the boards, and test them together. If that goes well, then on to the bandpass filters.
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In the end, today I got the tax return, and ordered hopefully a good guitar. It's a "buy a pig in a poke" gamble, so we'll see about that, once it arrives.
If it's good enough, it means, that I can dedicate the old 'frankenstein' -guitar solely for the hex pickup system, which was used on that build thread.
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