27-11-2011, 02:21 PM
I made an excellent audio signal tracer out of an old pair of PC speakers. The type I am talking about have both amps in 1 cabinet, the second having only the speaker. What I did was to find the input wire that feeds the amp and speaker in the cabinet and cut it where it joins the PCB. Put a wire link from the speaker output of the other amp to where the wire was cut. Use the remaining input wire as the signal input. The addition of a DC blocking cap and a BNC socket completed the job. Doing this mod puts the amps in series.
Tests show that I can easily resolve 1mV RMS without too much internal hiss. One advantage of doing it this way is that, because the signal inputs go directly to the volume controls, each amp still has its own gain control. This gives a wider range of signal handling(assuming you don't overload the input amp. The volume control for the second amp also acts as a DC bleed for the previous speaker coupling cap.
The volume controls on mine are 50kohm so not too bad an input impedance.
I am doing mostly audio work these days so I have not got round to building a diode probe and trying it yet.
Al
Tests show that I can easily resolve 1mV RMS without too much internal hiss. One advantage of doing it this way is that, because the signal inputs go directly to the volume controls, each amp still has its own gain control. This gives a wider range of signal handling(assuming you don't overload the input amp. The volume control for the second amp also acts as a DC bleed for the previous speaker coupling cap.
The volume controls on mine are 50kohm so not too bad an input impedance.
I am doing mostly audio work these days so I have not got round to building a diode probe and trying it yet.
Al
