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> Tapping An Audio Output
kellys_eye
Posted: February 13, 2012 05:37 pm
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I'm looking for the easiest way to tap the output of a bridge-tied-load audio amp chip (you know the ones, two amp stages working in push-pull).

Other than feeding the output into an audio transformer I can't think of any suitable method - putting a preset across the output doesn't help as I can't get a reference 'zero' on the pcb.



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Sch3mat1c
Posted: February 13, 2012 07:55 pm
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Google "differential amplifier circuit". Essentially, the active electrical equivalent of that there audio transformer. If the outputs are balanced, it will suffice to draw from just one (so you get half the swing), but that isn't necessarily guaranteed.

Tim


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tekwiz
Posted: February 13, 2012 08:19 pm
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What about pulling your signal from the INPUT to the bridged amp?


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kellys_eye
Posted: February 13, 2012 09:39 pm
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It's a cheap chinese knock-off audio recorder/playback module (I got FOUR of them, each came with three button cells, a microphone, a speaker and two push buttons, for the total sum of around $10 - delivered!)

The onboard chip is a 'poxy lump so only the mic and output are available to me.



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AwesomeMatt
Posted: February 13, 2012 09:49 pm
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QUOTE
for the total sum of around $10 - delivered!


One time thing or is there somewhere I can get in on it?

I have a few Staples "Easy" buttons to crudely convert tongue.gif.
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kellys_eye
Posted: February 13, 2012 10:40 pm
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AwesomeMatt
Posted: February 13, 2012 11:55 pm
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*samples a couple*

Thank ya smile.gif
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MacFromOK
Posted: February 14, 2012 02:04 am
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That listing has now expired, but I found the same item here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...em=190637038351

$1 USD each +1.39 shipping to the US.

Ordered 3 for $7.17 total. beer.gif


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AwesomeMatt
Posted: February 14, 2012 03:12 am
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QUOTE
$1 USD each +1.39 shipping to the US.


Gah, I paid 4.19 pounds, which is like, $6.50 US, for 2.

Damnit. *shakes fist*
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Village Idiot
Posted: February 14, 2012 04:14 am
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Maybe I don't comprehend the problem, but I don't understand why you can't take the signal from one side of the output, and pass it through a DC blocking cap. Then reference it to the power supply ground.
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tekwiz
Posted: February 14, 2012 09:15 pm
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QUOTE (Village Idiot @ February 13, 2012 07:14 pm)
Maybe I don't comprehend the problem, but I don't understand why you can't take the signal from one side of the output, and pass it through a DC blocking cap. Then reference it to the power supply ground.

Was wondering myself. I used a similar device a couple of years back in a sound effects project I built for someone, along with a LM1875 20W audio amp chip. I used capacitive coupling from one speaker lead & it worked just fine. huh.gif


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MacFromOK
Posted: March 04, 2012 08:18 pm
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Dave, did you ever get connected to the output like you wanted?

Mine arrived yesterday. Just opened them up and all 3 seem to function properly. beer.gif


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AwesomeMatt
Posted: March 04, 2012 09:26 pm
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Mine still have not arrived.
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AwesomeMatt
Posted: March 07, 2012 02:23 pm
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Mine arrived today. Neither of them work.

No LED when I press either button. No audio records when I press either button and hold the other to play back.

Hrmph. Might just be dead batteries, but, arg.

[Edited]Nope, not dead batteries. Just don't work.

[Edited2] I'm an idiot. That transparent plastic tab is not to stick it to a greeting card, it's to block the battery from touching hte circuit board during shipping. *sigh*... humbling.
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kellys_eye
Posted: March 07, 2012 05:32 pm
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laugh.gif

dork laugh.gif


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johansen
Posted: March 07, 2012 07:42 pm
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LOL. not quite as bad as the idiots who forget to take the transparent tab off their new $89 cpu heatsink, and then try to return them because their processor burned up.


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MacFromOK
Posted: March 07, 2012 11:39 pm
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Hehe. Well, at least they work... beer.gif

I removed the batteries to store mine (re-installing those plastic T-shaped insulators was more trouble than it's worth). Just moving the units around will sometimes make them play, even if nothing is touching and no buttons pressed (these were in a plastic "ziploc" bag btw).

I guess your body acts like an antenna (and/or cap?) and it doesn't take much to trigger the "play" circuit. This happened with at least two of the three (more than once), so I assume it isn't a fluke.


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AwesomeMatt
Posted: March 08, 2012 05:01 am
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QUOTE
I guess your body acts like an antenna (and/or cap?) and it doesn't take much to trigger the "play" circuit. This happened with at least two of the three (more than once), so I assume it isn't a fluke.


Mine were triggering randomly too. Once just when I thumped the desk next to them. Any time I started soldering them they triggered (if I neglected to disconnect the battery meanwhile). Got some demon voices out of them while soldering.
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