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" A -12V power connector may not be readily available in your computer.The standard disk drive power connectors are +5 and +12. I added analternate power connector in my system by tapping my power supplies'-12, GND, and +12 wires. Be careful not to get these mixed up!"Its quite vauge what he means and I havent been able to get in touch with him to ask but I thought It would be OK to simply cut and feed off the -12V. But something has now gone very wrong with my computer.
the op amp i'm using is a TL082 and my voltage in is +12 ... Do you think the 10uF caps are big enough? Would there be any harm in upping them to 100 uF?
Hi,If you have the +/-12V already, using a voltage inverter is a stupid extra that can go wrong (and inverters are pretty inferior to a real +/- supply).It's not at all vague what he means. Tapping into means to keep the circuit intact and jut adding a tap.If you have done as you describe (cutting the -12V wire), you have disrupted the negative supply to whatever else needs it in your computer.Just make a tap!And then you have to filter the supplies, as they're nowhere near the clean supply you need for a 'scope buffer.
If you mean bulk filtering of the power rails then that depends on many variables. For low current devices 10uF is usually enough. What can be more important is smaller de-coupling caps right near a device's power and ground pins. 100nF is a common value to start with.If you mean the 10uF caps on the 7660 schematic then no they should be 10uF for the frequency that the 7660 runs at. Also, be sure to get the data sheet for the exact 7660 you buy and check the cap values recommended. There can be differences among 7660's made by different manufactures. By the way. I just noticed an error in the schematic in your first post. D8 in backwards and will always conduct.
I am mistaken after looking at the circuit again. I first thought D3 was to clamp input voltages from exceeding the negative rail.
The diode D3 is in series with the 4.7k Ohm resistor. This will have (12-.7)/4700 = 2.4mA of current.I'm not really sure of the purpose of doing this.
This is to establish a -12V (~-11.3V) clamping rail and keep a (very) good symmetry, although you may argue that it's a wee bit overkill, as the signal will be clipped anyway, so who cares about symmetry at that point (but that's very HorrorWiz & Hillbilly).For a sound card 'scope front-end I wouldn't go to any of these lengths, when a single supply buffer (w. virtual earth) will still do better than the sound card and the overvoltage protection can be made simpler as well - nobody in their right mind will be probing anything connected to the mains with it (I hope), without galvanic isolation of either the PC, the circuit or preferably both.Further, all the good intentions about load etc. was shot when it was "adapted" with a 10nF cap on the input.-3dB low cut off is ~15.5Hz (the -3dB high cut off is >360kHz, far beyond the capabilities of even the best sound card) - I'd change this to 100nF or more, depending on the lowest frequency of interest (or keep it DC).I have attached the original amp to show how amputated the suggested cicuit is, relative to the original - and I rush to repeat that, for a sound card scope, both are over the top.
I just built it because on the Zelscope software site they say you need it if you want to measure more than 1V into your soundcard. I thought it reduced the size of the signal amplitude, like the opposite of an audio amp. For example if I wanted to probe 10V the amp would reduce it down to 1V but the same waveshape. But I know its not that simple.
Perhaps I should bang up a circuit with proper protection - just for the heck of it Anyone got requests for needed ranges?