Thanks, I'll have to give that a look.
building an active balanced ground? - Page 9
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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.
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)
Whooo, it works! Behold the monstrosity...
(not shown: the Fuze providing music)
- 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.
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.
This thread is so interesting that i have tried to build one according to your schematic and successful at the first time. I use 2 JRC4556, no virtual ground, the input ground is fed from true ground because i have no tle2426 and it was powered by 2x9v batteries. It sounds quite okay but high frequency and bass distorted like the batteries are going down past 7v, do you experience this? And i dont have input buffer, this amp is fed from a 2v line out.
No, I never had any distortion like that. When you say no virtual ground, are you omitting the active ground stage entirely? Because that will result in very distorted sound since the "ground" needs the active signal to balance out the modified L and R channels.
You're right. I dont' have TLE2426 so i made a simple divider by 2 resistor and the distortion's gone but now i got about 90mv dc offset, it sound very good but i'm not sure if it's better than the regular 2 or 3 channel . Thanks for your very informative topic :D
Edited by proid - 2/24/14 at 6:42am
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I just read this whole thread and wow. Only on Head-fi.
I admire your motivation to take a purely theoritical idea and create a physical circuit out of it. I still don't understand what the goal of the circuit is, but it's impressive just for being so overkill. I love it.
Here, I fixed the broken link from the original post... http://www.meier-audio.homepage.t-online.de/grounds.htm
Basically, I was attempting to recreate Jan Meier's topology based on his description of it.
Geez, I'm reading over my posts from all those years ago and rolling my eyes at myself now that I (sort of, not really) know better. I did wind up building a working unit, "proof of concept" at it were. Even had one guy commission a cmoy-style amp out of it which I thought turned out quite well (except for a bad susceptibility to EMI).