[Beefy]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Kevin Gilmore deplores rail splitters and active grounds. If you do some searches, you should be able to find some posts if interested.

Without searching, and entirely from memory (which is bad form, but what you gonna do?

)......

Isn't it the case that Kevin thinks active ground isn't that much of an improvement? That if you are going to go that far, you might as well go a step further for fully balanced? If that is the case, then it really is just a philosophical thing.

As for the rail splitters, I don't know much technically but I think that the MMM and PPAv2 prove that they can be fine when used for a low current voltage gain section. You obviously wouldn't want to rely on them for output stages though, because they can't sink nearly enough current on the ground.

 

[majkel]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif lets make a short list of dual-supply-rail amps. the beta 22, the vast majority of the gilmore designs (most of his tube stuff and all of his solid state) and as the OP mentioned the vast majority of power amps in production.

These are statistics which don't say a single word about the sound quality. Sorry, they say... tube amps sound better.

There is 3-channel Beta22 option as well.

 

[NelsonVandal]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif There is 3-channel Beta22 option as well.

... and that's the recommended option.

BTW, amb cleared things up with excellent graphs and explanations in this thread: http://www.head-fi.org/forums/f6/do-...-sound-279041/. In another thread he showed graphs of how crosstalk improves from using active ground: http://www.head-fi.org/forums/f6/how...-sound-200303/. Am I glad people like amb visits DIY-discussions and share their knowledge? Yes.

Still not convinced? Then it's time to do some AB comparisons.

 

[pinkfloyd4ever]

I don't know much about the subject, but I did read somewhere recently (I think diyaudio.com) that for some reason 3-channel just works with headphones but not with speakers. I'm not sure if there's any real truth to that or just that speaker amp makers for whatever reason haven't really tried it much...

 

[amb]

For one thing, with speaker amps we're dealing with much higher currents, and the ground channel must be able to handle the return currents of both stereo channels, and this poses practical difficulties with the power supply, heatsinking and construction. Also, since speakers are naturally 4-wire setups rather than a 3-wire TRS plug, there is less impetus for a 3-channel configuration. If one want to go beyond passive-ground, then fully balanced (or at least bridge tied load) is the logical next step.

 

[NelsonVandal]

Quote:

Originally Posted by amb /img/forum/go_quote.gif For one thing, with speaker amps we're dealing with much higher currents, and the ground channel must be able to handle the return currents of both stereo channels, and this poses practical difficulties with the power supply, heatsinking and construction. Also, since speakers are naturally 4-wire setups rather than a 3-wire TRS plug, there is less impetus for a 3-channel configuration. If one want to go beyond passive-ground, then fully balanced (or at least bridge tied load) is the logical next step.

I can see one benefit of using an active ground channel compared to balanced or BTL - input impedance. You have to use an input buffer/preamp in front of the amp.

Amb, do you think a fully balanced or BTL amp sounds better than a 3-channel amp? Even if you have to use a preamp in front of it? You must have listened to several versions of the B22.

 

[amb]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif I can see one benefit of using an active ground channel compared to balanced or BTL - input impedance. You have to use an input buffer/preamp in front of the amp.

That's true only of something like a β24 where there is cross-coupled feedback. A balanced amp built out of four channels of non-inverting amps (like β22) needs no additional input buffering. Also, as a pure speaker power amp with no input volume control, this is not really an issue, as most sources and preamps have low enough output impedance that a low-ish input impedance of the β24 is not a problem at all.

Quote:

Amb, do you think a fully balanced or BTL amp sounds better than a 3-channel amp? Even if you have to use a preamp in front of it? You must have listened to several versions of the B22.

I don't think a 3-channel is inherently or qualitatively inferior to balanced or BTL, but as I said it's a matter of managing the current and dissipation. If you're going to build a speaker amp with a ground channel that has twice the output current capability as the left and right channels, then it just seems to make sense to go balanced or differential instead. You don't have the problem like you do with standard headphones (i.e., the need to rewire them to 4-wires), and you get a lot more output voltage swing for very little incremental cost.

 

[linuxworks]

Quote:

Originally Posted by tvkalvas /img/forum/go_quote.gif Ok guys... you got me convinced. I will go for the real PPA v2 then, not a two channel modification of it. Also it is easier for me because I can use the pcb from Tangent's shop and I don't have to mess with acids.

but the acids will give a TOTALLY new experience to the soundstage.

oh, wait. you didn't mean that, did you? lol

I second building from tangent's boards. I've built 2 pimetas and a ppa (v1) and its been great so far. highly recommended. the parts don't have to cost an arm and a leg, either.

 

[linuxworks]

Quote:

Originally Posted by amb /img/forum/go_quote.gif ...then it just seems to make sense to go balanced or differential instead. You don't have the problem like you do with standard headphones (i.e., the need to rewire them to 4-wires), and you get a lot more output voltage swing for very little incremental cost.

well put.

the way I'm seeing it, headphones are forcing us to run in non-balanced (common ground, 3-wire mode) because of the plug they come with!

most people don't want to change out too much about their phones (lets ignore people at *this* forum, for now, since this isn't typical, grin). so running phones in 3 wire mode is pretty much a given for most of us.

given *that*, the best you can hope for is 3 channels.

if all headphones came with wire pigtail leads (lol) then this would never ever be an issue and each 'can' would get its own 2 wire pair and be differential and that would be that.

really too bad 'they' picked a trs plug instead of trrs (they do exist, too, btw).