My poor-man's audio probe.

DarrenF

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I've been needing an audio probe to trace audio signals from their generation thru circuits to the amp.

I understand some people use small amplifiers. And I've heard of headphones being recommnended. I didn't want the complexity of a powered amplifier, and I didn't like the idea of low input impedence like headphones would provide.

I ended up using a piezo "buzzer" from Radio Shack. #273-074: http://www.radioshack.com/product/index.jsp?productId=2062403

Just wired a lead to the - leg to a clip, for attaching to a convienent ground. Then another wire with a probe-like tip to the + leg.

Works well, IMHO. Not high-quality audio, of course, but adequate. The level is typically pretty low. I need near silence, or I need to put it right by my ear. But it allows me to hear audio. I've probed things from the output of an AY-3-8910 output, all the way to the final speaker output.
 
I've been doing the powered speaker method, but have been having an issue lately. The last time I made one, it worked just fine. I could probe the input and hear nice loud sound out of the speakers.

But then a year later I try again with another pair of speakers, and probing the input is super quiet (need near silence like you said), and probing the output it loud - almost like the speakers aren't amplifying the sound at all. Tried it with two different sets of powered speakers, but no change. Kind of annoying when tracking down a hum. I can't tell from the quiet input whether the hum is there. I hear it on the output...
 
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