[akgfan]

I came across this double channel oscilloscope:
 
http://www.zeitnitz.de/Christian/scope_en
 
You only need some high impedance buffer - fet or opamp and connect it to line-in on your soundcard. It has some limitation due your soundcard quality, but it's very good for checking operation points of transistors in amp if you get some distortion.
 

 
You can use also resistor voltage divider in front of buffer. I have 1M-1M or 10M-1M.
 

 
If you need tone generator, you can use Audacity and click on Generate-Tone in menu. Or use a headphones burn-in program Biwavegen (Generator-Pure test tone and Play).
 
I wanted to buy DSO Nano, but I don't need it anymore. This is very useful program.

 

[amb]

Sound card based scopes have been discussed before, try doing a search.  The A/D sampling rate of sound cards means that it can't do much beyond audio frequencies, which makes it basically useless for checking ultrasonic behavior of amps (such as looking at square wave response), etc.  For such purposes you need at least tens of MHz capability, if not 100MHz or more.  Ironically, that is what I use an oscilloscope for most of the time...
 
For checking noise and distortion, FFT software such as Rightmark Audio Analyzer and a good sound card is far more useful.

 

[akgfan]

Yes, I know. It's good only for operations points IMO. I was doing a search and found gazillion different topics.
 
RMAA doesn't work for me. I get a feedback or something. It says that signal is low and when I slightly turn volume up signal gets distorted and it's very strong.