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Audio probe

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philmurr View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Topic: Audio probe
    Posted: 10 Dec 2016 at 2:49pm
I've been doing some work lately on some faulty sound boards and old drum machines, and found it quite tricky to work out exactly what part of a circuit was faulty.  You can't really use a logic probe to help, and a 'scope can give difficult to understand readings.

I had a look around for an audio probe (which is used to probe parts of a circuit and hear what's going on), but couldn't find one at a reasonable price, so armed with the LM386 amp datasheet I set out to build my own.  A PCB was designed, plus around £7 of components later and I've a working audio probe.

The probe connects to the power supply of the circuit under test (usually the 0V & +12V of the sound section), you just need to plug in a pair of headphones as it doesn't have a built-in speaker.  The sensitivity and volume are adjustable, and you just touch the probe tip to the part of the circuit you want to "listen to".

It helps answer the "is the power amp or some other part of the sound circuit faulty" predicament as it can prove the working bits of a circuit to narrow down to where a fault actually is.

Photos of the one built unit are below (the probe tip is a nail, until the proper tips I've ordered arrive from China!)








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Ace` View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ace` Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 2016 at 3:16pm
Nice work Phil this looks great, I want one. Smile
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ianski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ianski Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 2016 at 3:27pm
Yeah that is cool. As someone who also works on musical instruments I'd find this useful. If you are selling any I want one too :)
Looking for: Nice working monitors for my US games.
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philmurr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 2016 at 5:02pm
Thanks guys - I have some spare PCB's for sale but won't be assembling any more units.  You can make them yourself for less than a tenner!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mykill Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 1:26am
Dose this use a common ground,it tried somthing similar but wasn't sure we're to run earth to the speaker ,I ran mine off a 9v battery and wasn't sure if it was grounded
Don't touch the red wire
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philmurr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote philmurr Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 8:20am
Not sure what you mean in this case by a common ground or running an earth to the speaker.

The probe is powered by the game's power supply so there aren't any grounds to common, and you plug in headphones to hear the amplified sound

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mykill Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 12:33pm

ill try it running on the power from the arcade
Don't touch the red wire
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RSwanson Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 5:34pm
That's handy, but you're going to have to be ultra careful with those sensitivity and volume knobs!
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5 Years of Supporting ukvac.com!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurray Banana Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 5:50pm
Mine arrived today, thanks a lot phil 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nes4life Quote  Post ReplyReply Direct Link To This Post Posted: 14 Dec 2016 at 8:24pm
Got mine
NES4Life
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Owner of ... too many cabs!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ace` Quote  Post ReplyReply Direct Link To This Post Posted: 15 Dec 2016 at 1:06pm
Mine arrived today, thanks Phil. Hug
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jinq-sea Quote  Post ReplyReply Direct Link To This Post Posted: 04 Aug 2018 at 10:10am
-oops-

Edited by jinq-sea - 04 Aug 2018 at 10:12am
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