Circuit polarity

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theojohn4
 
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Joined: Sat Jun 14, 2014 2:34 pm

Circuit polarity

Post by theojohn4 »

I'm at the VCO section, and it says I need a variable power supply for testing. I have one with a 3V setting however I'm not sure what polarity I should be plugging it in with, is it centre negative or centre positive, and would I be able to find out using the multimeter or is it something that just has to be told?

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antto
 
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Re: Circuit polarity

Post by antto »

you need a DC power supply

the build manual says: "Test the adjustable power supply and verify it's outputting 3V."
that is, 2 wires (or so), and your multimeter should measure some steady positive voltage between them (3V is okay in this case)
alternatively, you could use two 1.5V batteries in series, as suggested in the manual, again, you will have two points where you should be able to measure ~3V

so then, the build manual says: "Apply the Control Voltage using the adjustable power supply."
that means, connect one of the two wires of the supply (or batteries) to ground on the x0xb0x circuit, and the other wire (the positive one) to R90
if you're confused which wire should go where - when you measure +3V with the multimeter - whichever wire you had attached to the ground on the multimeter is the one you should attach to ground on the x0xb0x, and thus the other wire is the "positive"

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antto
 
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Re: Circuit polarity

Post by antto »

the purpose of all this it to supply a control voltage (aka Pitch CV) to the VCO, at some mid frequency (3V is the voltage for C3, but at this point the VCO isn't tuned yet, so the actual frequency will be off, but still somewhere there)
if you don't supply a control voltage - the VCO might "oscillate" at some weird frequency (could be uber-high, or uber-low) in which case you won't be able to easily tell if it actually works or not

if you have another x0xb0x (a working one) you could inject the CV from it instead of using variable power supply or batteries (that's what i did)
just connect ground to ground on the two x0xes and R90 to R90

theojohn4
 
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Joined: Sat Jun 14, 2014 2:34 pm

Re: Circuit polarity

Post by theojohn4 »

Oh right, I was under the impression that meant a variable wall wart that you could plug into the power jack. Thanks for your help.

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antto
 
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Re: Circuit polarity

Post by antto »

nonono..
during all voltage-related tests on the mainboard - you have to have the IO-board powered up and J4 connected to the mainboard, so that the analog section (the synth) gets 12V/5.33V/Ground

don't plug anything other than the 9VAC adapter into the IO-board (unless you know what you're doing)

so for the VCO test - you have to use the 9VAC adapter plugged into the IO-board, J4 connected to the mainboard, and also apply ~3V to R90, in order to have the VCO running and oscillating at some sane frequency

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