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# building an active balanced ground? - Page 3

Bump. Any help guys? Any at all?

If anyone's wondering, I did ask Jan first if it was ok, and he was fine with me creating this thread.

Quote:
Originally Posted by Armaegis

Quote:
Originally Posted by qusp

Quote:
Originally Posted by Armaegis

Why would you need to double the ground channel? You're tapping two sets of wires off it, so your voltage is the same in each except now you have two of them, so it all balances out.

just because there is 2 wires does not mean there is double the signal strength, the way I see it you would indeed need to either double the channel, or double the signal strength and tap twice; tapping a single channel twice will simply give you half the signal strength on each wire

Er... we're tapping a voltage signal correct?  Tapping it twice does not diminish that signal. The channel will need to pump out more power since it's feeding both sides, but the signal remains the same.

At least this is how I understand things (it's sort of like a parallel circuit... sort of).

An issue I see though is that since loading is complex and impedance changes with signal, things might imbalance... but I guess this is a problem inherent in a normal setup anyways and isn't something that can be accounted for (at least not with my limited knowledge of amp and headphone design).

incorrect, if we were at the boundaries of how much power could be pulled through a single wire then perhaps there would be a benefit from tapping the same signal twice, but since we are nowhere near it 2 wires makes no difference, provided sufficient wire gauge the amp doesnt care if there are 2 wires or 1, it still has the same potential. what matters more for drive here is current.(thats why you see amps and conductors rated by Amps or watts, not voltage) there is always 2 headphone drivers and there is still the same power/potential in the ground channel amp regardless of how many wires you attach and unless a single wire isnt large enough for the power that it needs to carry then a second wire matters nothing

to put it another way Voltage x Amperage (current) = Wattage (power). in a given circuit such as this, the voltage source is static and will remain the same regardless of the size of the conductor, what will be limited is the amount of current and therefor wattage that can be carried before the wire resistance limits it and burns out the cable. the voltage will be the same no matter the size of the conductor, increasing the size of the conductor will not increase the voltage.

of course there are other factors that can be improved by the use of a dedicated signal and return for each channel, but that is out of the scope of this post.

Quote:
the voltage will be the same no matter the size of the conductor, increasing the size of the conductor will not increase the voltage.

to add to this, given large enough size to cope with the power (wattage) the size of the conductor does not matter. under load however there may be a small amount of voltage drop if the wire is too small because of the resistance of the wire.  if there were 2 voltage sources (ground amps) with 2 wires then of course there would be more power capability,

anyway thats enough explanation, sorry for the little bit of OT guys but I thought this needed explaining.

Edited by qusp - 1/9/11 at 11:38pm

Er... when I said signal, I meant voltage not current/power.

The overall power consumption in an active balanced ground config should be the same as regular config. The only difference is that some of the voltage signal is taken off the left and right channels and is provided by the ground channel. The potential (voltage) difference from left-to-ground and right-to-ground is still the same.

Holland made the comment (I think, unless we've beed misreading each other) that the voltage signal in the ground channel shoul be doubled since it is connected to both the left and right channels. I say no it doesn't, because voltage does not get split.

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Has anyone else tried the circuits? I've got really lousy equipment, so I don't know for certain if my diagrams are wrong (I hope they aren't) or if I've just wired something wrong/improperly.

Quote:
Originally Posted by Armaegis

Holland made the comment (I think, unless we've beed misreading each other) that the voltage signal in the ground channel shoul be doubled since it is connected to both the left and right channels. I say no it doesn't, because voltage does not get split.

Not quite.  I said that to solve the equations put forth by Meier.  I said logically it would be the same (divide by 3), but it will fail the equations put forth.  Since it's not my theory, I cannot comment further.

Well regardless, has anyone else tried cobbling together a circuit? I'm going to try a different configuration tonight (my config #1 on the paper) and fiddle with some gains. I'm sure there's actually a better way to accomplish these circuits... I've got no reference material so have been working off the opamp page on wikipedia (I know, I know).

OK gotcha, sorry I misread you as stating that tapping twice was somehow going to increase the power. I know you were talking about signal, matters nothing though whether talking signal or the PSU to support it. indeed if it has to 'balance' 2 signal channels, then by rights it should be double the strength as the signal channels, otherwise it would not work. regardless this is all conjecture, as none of us know exactly what is going on with what Jan has done. I think it will take some time for enquiring minds to tinker with their amps and find out real component values etc

Which is why I was hoping for some other people to maybe give it a try. I've run the simulations on Tina-TI and they do work. I haven't been able to reproduce it in person, but I highly suspect that I'm just wiring something wrong and have problems arising from my lack of proper power supply/ground.

hang on, why dont you have a proper power supply ground? this is a signal processing trick, signal ground may be 'floating' so to speak, but power supply should still be grounded. no chance with me giving it a try sorry mate, while I find it intriguing, I have far too many builds on the go already to be playing with another one.

I've got a really terrible/shameful setup right now. I have 3AA batteries in a holder providing the V+/V-, and using the output headphone sleeve for ground.

Maybe I should try digging through a salvage box for an AC/DC adapter, and construct a virtual ground with a simple resistor divider?

Argh, so close and yet so far.

I redid the circuit using method one, and created a virtual ground with a resistor divider except I also tied the virtual ground into the sleeve ground (dunno why, but it works better; I get lots of static without it). So here's the thing: it works... but only one channel at a time.

- the leftmost opamp is just there as an input buffer (input and feedback resistors of 400)

- the centre opamp I used to generate L* and R* (resistor values of 1.2k, 4.8k, and 7.2k)

- the rightmost opamp generates G*

- the outputs are at the far right of the board

I've got a test file that basically verbally says "Left Right" back and forth into the appropriate side. With that, I can tell how much of each input channel comes out from the output channels.

I'm basically just using alligator clips to connect L* to the tip, R* to the ring, and G* to the sleeve. For testing purposes, I also connected the original G to the sleeve to hear the unaltered signals.

- connecting L* and G: allows me to hear what the L* sounds like, which is essentially 3L/4 and -R/4 (though I can't hear the "-" obviously which is just an inverted signal)

- connecting L* and G*: I hear the full L, and the R is canceled out (this is what I want)

- I get similar results using R* with G vs G*

- connecting G* (to one of the sides) and G (to ground): I could hear (-L/4 -R/4), which is what I expected

edit: I suspect I'm also running at the lower voltage limit of the opamps as I'm still just powering it with three AA batteries

But here's the fly in the ointment

- if I connect L*/R*/G: I can hear sound on both sides with equal loudness as to be expected

- if I connect L*/R*/G*: it sounds the same as above and I don't get cancellation (levels might be different; it's hard to tell here)

So why doesn't it work when I have all the channels connected? (On a whim I tried doubling the voltage of G*, but that made it worse)

edit: could it have anything to do with the fact that I'm connecting the headphones directly to the opamp outputs?

Edited by Armaegis - 1/13/11 at 10:18am

I've just noticed that if I only have L* and R* connected (and no ground at all), I still get sound coming out of the headphones. Hmm, so I guess that means they're connecting somewhere... I don't know if that means there's a short somewhere (I can't find one) or if I'm getting signal passed through the G, or something else I haven't accounted for.

yet another edit: since I'm using method one which uses a differential opamp config, part of the signal routes directly into ground. Hmm, I wonder if that pollutes my ground and mucks up the other channels. If nothing else, maybe that's where the connection between the L* and R* would be forming when I don't have either G or G* attached

edit 3: or maybe all three channels bleed through to one another when they're connected? that's kinda what it sounds like... argh, I really wish I had an oscilliscope!

Edited by Armaegis - 1/13/11 at 10:28am

Bump?

I'm still thinking I have grounding issues here. Here's a dumb/dangerous question: can I stick a wire into a ground socket on my wall and tap that into my breadboard as signal ground?

notes to self:

playing pure test tone across both channels

- if only L* and R* connected, get almost no sound (I think there's cancellation here if you do the math... need to double check later)

- if connect G, then get sound

- if connet G*, it is louder than G

edit: doing the "math"

- L* and R* connected but no ground, the resultant signal on both sides is essentially L-R (or R-L). Playing a pure tone across both channels should results in cancellation, which is what happens

ARGH. This is really frustrating. Some things make sense, but others don't.

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