SA: PC sound card oscope

don't make this SA, see last section.

8/26 2012

11/25/2012

For audio experimental, the most cheap spectrum analyzer is PC based[except the PC], a simple buffer circuit do all the work you need. then you can use a free version trueRTA or the SoundCard oscope do all the audio related analyze work: the O-Scope, spectrum analyzer, THD meter , all in one.

there is 2 mazing adapter circuit F.Y.I.

http://xoscope.sourceforge.net/hardware/hardware.html

http://www.zen22142.zen.co.uk/Circuits/Testgear/pcscopeprobe.htm

My version Probe

I use xoscope's input protect and oscilloscope probe compensation circuit and use Rodney Byne's buffer: the MPF102. that does work, for 1:1 probe, it works well, but for 10:1, the 60Hz power line interference can not be eliminate, so i use 1x only, that's enough for me now.

the beautiful box make it a cute instrument of my Lab.

Using is test a simple sine oscillator, Audio, I'm Coming

THD 3%

protection

1. input: 0.6V :cause if you power down/or off , and connect a power siganl to it...., mpf burned

2. output 100R+0.6Voutput + addtinal capcitor protection: some pc sound card had a 2.5V dc offset !!! damit !

LOOK HERE!

the buffer i built derived from Rodney Byne's one . but i add two pair of protection diode. that's would introduce the distortion while input level reach 300mVpeak. make it um-convenient to meter distortion. thanks Rodney Byne remind me this.

so D3,D4, D2,D5 should be remove. and power on before you start to use it ! (thanks Rodney again).

Simple dummy "buffer"

i use a very rough "dummy protection" circuit: 0.47uF serial with a 560R resistor as buffer circuit, and it works very well than this buffer. use this very simple circuit sound card can handle <1.5Vpeak signal and noise floor drop to -110dB with a decent audio cable.

use this "buffer" the signal level you get is a little bit small than the accrual level, cause the sound card input impedance is not "infinity".