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building an active balanced ground? - Page 9

post #121 of 128
3/26/11 at 10:24am
Thread Starter 

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

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post #122 of 128
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 128
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 128
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 128
4/10/11 at 9:31pm
Thread Starter 

That would be awesome. PM underway...


 

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post #126 of 128
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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post #127 of 128
12/13/12 at 11:05am

Any update on this?  I'm interested in hearing about how it sounds in the real world

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post #128 of 128
2/22/13 at 11:19am
Thread Starter 

Whoa, I missed this. The project in the pic above has been on the shelf. One of the a20 boards blew and I don't have a replacement. I do have some b22 boards though... 

 

I did build a strictly opamp version for a member though, and I thought it sounded quite good though ridiculously susceptible to EMI. It used three opamps: one as input buffer and control for a bass boost switch, one for the left and right channels, and one for the ground. I have plans for another one using some proper differential opamps and BUF634's (so 6 chips in total) and no resistors in the circuit... but who knows if I'll ever get around to it.

 

I've gone as far as proof of concept that the implementation works, but I lack the time/resources to take it beyond the "reconfigured cmoy" stage. 

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