Probably a stupid question but I'm not sure what to search for at this point. I'm trying to do a very simple diode test (half wave rectification I suppose it's called) using an ac source. The source is a 440hz signal off of my computer soundcard (generated and played via a .wave file). It's a balanced output soundcard, so I'm just using one of the 2 outputs. Either single balanced output connection shows up fine as an AC wave on my tektronix 465b scope. There's no dc offset or anything. I don't even need to connect the ground scope probe end to the soundcard ground at all. The reference seems to be adequately earth ground (according the the scope's assumption). side note: basically I'm trying to use the sound card as a bench signal generator of sine wave output to do some very fundemental testing of caps, diodes, transistors, etc. Could be my first mistake perhaps.... Ok, but I'm not completing a circuit. I'm just testing voltage. So I add a IN4004 diode on the end (of the positive ac signal connection) and test the voltage. What I get is a smaller ac wave. I don't get just the positive portion of the ac wave. And even if I put on a resistive load I see current of 0-30mA (hopefully won't blow my soundcard!). I'm not sure how to measure that correctly. Does it have to be a reactive load??? I feel lost. Please help me to comprehend! THANK YOU VERY MUCH Ahead of Time! I'm sure of the many here who are well versed in electronics can help me get over this simple hurdle! And I hope I'm not posting in the wrong place for this as well. I guess you could call it "homework" but I'm not in any formal school so Ill assume it's ok. Thanks.