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building an active balanced ground? - Page 9

post #121 of 126
3/26/11 at 10:24am
Thread Starter 

Thanks, I'll have to give that a look.

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post #122 of 126
3/26/11 at 1:59pm
Thread Starter 

Hmm, I just measured the DC offset on my INA134/137 resistorless circuit. I've got about 1.3mV off each opamp to input/reference ground. When measuring from output left/right to output ground, I get aroun 0.1mV. Not bad I suppose. My multimeter can't go any more precise than that.

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post #123 of 126
4/10/11 at 7:36pm
Thread Starter 

Argh, so close yet so far. I finished building the s22 and 3x a20 boards intending to hook them up to my active balanced ground circuit... except one of my a20 boards is blown (the other two are just fine though). Grr, and no spare parts on hand either. Sigh, I don't suppose anyone has a spare MJE243 and MJE253? (Q5/Q6 from here)

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post #124 of 126
4/10/11 at 8:24pm

I'll be ordering from Newark this week. If you don't mind a bit of delay I can add your parts to my order and forward them to you when I receive them. Which would be probably Wednesday or Thursday.

 

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post #125 of 126
4/10/11 at 9:31pm
Thread Starter 

That would be awesome. PM underway...


 

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post #126 of 126
5/5/11 at 10:35pm
Thread Starter 

Whooo, it works! Behold the monstrosity...

 

(not shown: the Fuze providing music)

IMG_5073.JPG

 

- Sansa Fuze for music

- s22 providing power (+/-18V) for the ABG circuit and the three a20 boards

- the ABG circuit feeds OL, OR, OG each into its own a20 board

- connect output from each a20 board to the headphone

- no resistors on the current ABG circuit, using INA134/137 which are differential receiver chips that have built in resistors

 

At the moment I've only tested it with cheap airline headphones so I don't really know how good it sounds. The a20 boards are extremely susceptible to temperature variations and produce voltage offset due to that, so I'm going to rig up a temporary cardboard box to protect it from drafts (like from my arm movement or breathing) before using my good headphones.

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