USB Oscilloscope

[bkspero]

It was pretty easy to build. A couple of cheap carbon film 4.7K resistors from radio shack, a couple of 47 ohm carbon film resistors, and a 100 ohm potentiometer (variable resistor). I don't know how to attach photos or drawings to this BBS, so I can't help there. Just do a Google search of "H Pad" for the layout.

Wire the following in series: 4.7k, 47 ohm, and one of the end connections of the potentiometer. Also wire in series, the center terminal(wiper) of the potentiometer, 47 ohm, and 4.7k ohm. Connect one input lead to the free end of one of the 4.7K resistors, and the other input lead to the free end of the other 4.7k resistor. Connect one output lead to the spot where one pair of 4.7k and 47 ohm resistors join. Connect the other output lead to the junction of the other set of 4.7k and 47 ohm resistors.

The only difference from a standard pad is that the Pot provides a variable resistance in the center leg so that you can fine tune the height of the output.

I used 3.5 mm jacks and plugs for input and output over plain old multistrand bell wire. All wiring was point to point. The output needs a jack on one end to feed to the line input of the soundcard of the PC and another jack on the other end to connect to the pad. For the input I used a couple of spring probes (the ones that grab onto the connection point) from Radio Shack on one end, and a 3.5 mm plug to connect to the pad. All together it probably cost about $10-$15, with the biggest cost being the aluminum box.

Not sure what you meant when you asked if the attenuation is linear. If you leave the pot in one position, you will get substantially constant attenuation with the voltage levels in this system (ca. up to 50 V). Does that tell you what you wanted to know?

[Nineteen Billion]

What I mean by "linear" is that it has the exact same effect across the entire frequency spectrum.

I'm so used to hearing about how components impart their characteristics upon the information that travels through them. I (with my limited knowledge) just want to know if building a pad like the one you described so well is a sure path to even attenuation. Again, I assert that I ask this only because I know so little about the actual affects of components on the energy they transmit.

[bkspero]

What I mean by "linear" is that it has the exact same effect across the entire frequency spectrum.

I'm so used to hearing about how components impart their characteristics upon the information that travels through them. I (with my limited knowledge) just want to know if building a pad like the one you described so well is a sure path to even attenuation. Again, I assert that I ask this only because I know so little about the actual affects of components on the energy they transmit.

I'm probably even less familiar with details like that than you are. In the specific case of these amps, the adjustments are only made at a single, relatively low frequency (1000 Hz). So the question of frequency response is not important.

If you're interested in broader application, you'll have to do some searching online about H pads to find the definitive answer. I believe, though, that it will be constant within the software's operating range. Remember that the software uses the computer's soundcard for input and output. So the best you can expect for linearity of frequency response is the linearity of the soundcard. And the frequency range will be limited to the audio frequencies (20-20k...and depending upon the quality of the card, probably not all the highest frequencies).

[aphid310]

Got a link to the layout you used? Could always link out to a pic instead of posting. That would rock!

Chris