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B22/Active Ground Query

post #1 of 204
9/20/09 at 6:31pm
Thread Starter 
So, I've been told that a four board B22 can't also accommodate unbalanced headphones without a fifth channel board to act as an "active ground."

The person who told me can't explain why, and I'm afraid I see no reason for why it should be the case.

Can someone here explain why it can't accommodate unbalanced headphones without a fifth channel board to act as an "active ground"?

Thanks.

k
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post #2 of 204
9/20/09 at 6:38pm
When using unbalanced only two boards are utilised. See two board passive ground option on the AMB website.
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post #3 of 204
9/20/09 at 6:42pm
Thread Starter 
Quote:
Originally Posted by johnwmclean View Post
When using unbalanced only two boards are utilised. See two board passive ground option on the AMB website.
Yes, I know all that and I've seen all that.

But I see no particular advantage nor any need for it. However I was told that it was a requirement in order to work.

k
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post #4 of 204
9/20/09 at 6:44pm
They are incorrect. You can use a 4 board balanced B22 to power single ended headphones by only using two active channels. You only need a 5th board if you want the single ended output to have an active ground channel.
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post #5 of 204
9/20/09 at 6:47pm
With 4 board, can SE and balanced headphone outputs be used simultaneously, or do you need a switch to toggle them?

Or is the switch we see on many 4-board builds to control the balanced / unbalanced inputs on the amp?
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post #6 of 204
9/20/09 at 6:48pm
Thread Starter 
Quote:
Originally Posted by mugdecoffee View Post
They are incorrect. You can use a 4 board balanced B22 to power single ended headphones by only using two active channels. You only need a 5th board if you want the single ended output to have an active ground channel.
Yes.

And as I said, I see no particular advantage or benefit of the active ground channel.

k
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post #7 of 204
9/20/09 at 6:53pm
Thread Starter 
Quote:
Originally Posted by IPodPJ View Post
With 4 board, can SE and balanced headphone outputs be used simultaneously, or do you need a switch to toggle them?
I see no reason why it can't drive both headphones simultaneously.

Of course with just one volume control, the balanced headphone will always be driven louder than the unbalanced headphone assuming both headphones are the same.

k
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post #8 of 204
9/20/09 at 7:20pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
I see no reason why it can't drive both headphones simultaneously.
Agreed, one channel will see some sort of weird parallel load which may affect both headphones but I don't think it'll cause a failure of any kind.

As to the 3ch vs. 2ch argument, it's really a matter of whether or not you believe that the lower measured distortion results matter (see amb's site for these) and also whether or not you want the extra expense and heat of the 3rd/5th channel in your build. Me, I've built both, but never had both 2 and 3ch versions at the same time so I can't really comment all that well the sonic aspect of it. I do know that I've never found a 2ch version lacking for good sound when built well. Hopefully later tonight I'll have both a 2ch and 4ch amp to compare, that I hope will produce audibly different results.
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post #9 of 204
9/20/09 at 7:23pm
A ground channel is not required to support unbalanced headphones. All the different configurations are well explained at the β22 website, under the "Wiring & ground" and "Other options" sections. The "Tech highlights" section explains why an active ground is beneficial. It's about avoiding signal ground pollution, especially with reactive loads where output voltage and current could be shifted in phase.

Also see the following thread about an additional benefit of active ground topology (as well as balanced topology) with regards to reaping full synergistic benefits with class A operation:

http://www.head-fi.org/forums/f6/do-...-sound-279041/
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post #10 of 204
9/20/09 at 7:33pm
Thread Starter 
Quote:
Originally Posted by n_maher View Post
As to the 3ch vs. 2ch argument, it's really a matter of whether or not you believe that the lower measured distortion results matter (see amb's site for these)...
I've looked and I can't seem to find any measurements regarding this. Only the statement "This results in lower output impedance, greater linearity and reduced stereo crosstalk" in the Technical Highlights for the B22. Can you give a link to the measurements you're referring to?

Quote:
I do know that I've never found a 2ch version lacking for good sound when built well.
Not surprising.

I was reading a thread on here yesterday where "amb" was describing the benefit of the "active ground." Basically its basic purpose was to maintain constant current through the power supply which you also get when running "balanced."

However I see no problem arising from the lack of the active ground unless you're not adhering to good grounding practices. So it seems to me that the active ground really just serves as an "idiot proofer," which would certainly be of some good for a DIY-based product.

Quote:
Hopefully later tonight I'll have both a 2ch and 4ch amp to compare, that I hope will produce audibly different results.
*ahem*



Thanks, for the input, Nate!

k
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post #11 of 204
9/20/09 at 7:44pm
Thread Starter 
Quote:
Originally Posted by amb View Post
The "Tech highlights" section explains why an active ground is beneficial. It's about avoiding signal ground pollution, especially with reactive loads where output voltage and current could be shifted in phase.
Yes, I'd read that. But I can't say as I agree with much of it.

For example:

The ground channel amplifier sources or sinks the return current from the transducers, which would otherwise have been dumped into signal ground or power supply ground.

There is no separate "signal ground" and "power supply ground." They're both the same node, and all of the current flows into and out of that node.

And:

This shifts responsibility for the high current reactive load of the headphones from signal ground to the tightly regulated power supply rails, thus removing the primary source of signal ground contamination.

Again, all of the current flows through the ground node.

The primary source of "signal ground" contamination is improper grounding practices.

Quote:
Also see the following thread about an additional benefit of active ground topology (as well as balanced topology) with regards to reaping full synergistic benefits with class A operation:
Yes, I read that yesterday. But I don't see that it has any particular benefits if proper grounding practices are exercised.

k
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post #12 of 204
9/20/09 at 11:32pm
http://www.head-fi.org/forums/f6/4-b...ml#post5787509
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post #13 of 204
9/21/09 at 3:15am
Thread Starter 
Quote:
Originally Posted by digger945 View Post
Thanks, digger.

Though I didn't find the measurements terribly informative. Primarily because they were made using two physically different amplifiers. There's no way of knowing exactly what the ground scheme was in each amp (beyond just the issue of using an active ground or not) and grounding isn't the only thing which can contribute to crosstalk.

k
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post #14 of 204
9/21/09 at 10:33am
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
I've looked and I can't seem to find any measurements regarding this.
Hmmm, I'd swear that either amb or someone had done comparisons of a 2ch vs. 3ch beta22. But I can't find them now either, crud. And if they weren't for the beta22 maybe they were in the M³ section? Ugh, my feeble brain...

I didn't get to do any relative comparing last night but the 4ch beta certainly sounded very good.
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post #15 of 204
9/21/09 at 1:09pm
Thread Starter 
Quote:
Originally Posted by n_maher View Post
Hmmm, I'd swear that either amb or someone had done comparisons of a 2ch vs. 3ch beta22. But I can't find them now either, crud. And if they weren't for the beta22 maybe they were in the M³ section? Ugh, my feeble brain...
Just went through the entire M³ section and didn't see anything except the standard measurements. Nothing comparative vis a vis active/passive ground.

Perhaps you were thinking of the measurements that digger posted?

Quote:
I didn't get to do any relative comparing last night but the 4ch beta certainly sounded very good.
Sweet!

By the way, I just noticed the Resistorous Conflagorous in your particulars. What's the story behind that? What, did you re-enact the firebombing of Dresden in one of your amps or something?

k
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