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I've been through the Parasound Halo 2 review a couple of times, and wanted to ask a "woody" question.

Do you think there is an 'objective' measurement on this piece that would correlate well with its superior soundstaging?

If I knew what it was, I would give up the magazine, become a manufacturer, and become rich beyond my wildest dreams!!!

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I tried thinking about channel seperation, but most preamps have better channel seperation 'skills' than almost all recordings do.

Ayup.

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I was taken by your comment that even mono recordings had more space, which would also argue against channel seperation being responsible for its superior performance.

You could definitely hear some instruments as being behind the others, which I believe correlates with greater retrieval of recorded detail, such as subtle differences between the reverberation tails of closer and farther-way soundsources.

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Could it be a lower noise floor that might allow more lower level spacial cues to be better reproduced and, therfore, paint a better sonic picture of space?

The low noise floor is definitely part of it.

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Can a preamplifier (or amplifier) have certain parts of the audio spectrum where it alters phase?

Not once feedback is wrapped around the circuit. But I do wonder if the polarity of the _crosstalk_ is a factor in some designs. To my shame, it is not something I look out for in my testing.

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The Parasound was listed as non-phase inverting, I was wondering if electronic devices like this preserve the same phase over their whole range of reproduction?

Yes they do. It's inherent in their flat frequency response (phase and frequency responses in a minimum-phase system like an audio circuit are mathematically related. You have one, the other comes along for free.)

John Atkinson
Editor, Stereophile

First, it is great that JA has an up-to-date measuring system, the SYS2722.

Halo JC 2 is excellent in THD spectrum, no high harmonics. Very low noise. THD does not rise with frequency too much. CCIF IM 19+20kHz has a bit higher 3rd order component, about -83dB. JC2 is a discrete, moderate feedback design, so it is understandable. It should not be audible.

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The Parasound was listed as non-phase inverting, I was wondering if electronic devices like this preserve the same phase over their whole range of reproduction?

If the preamp is phase inverting, can't that be addressed very simply by cross wiring the speakers? (ie attaching the positive cable from the amp to the negative terminal on the speaker and negative cable from the amp to the positive terminal on the speaker)

Yes.

Correctness in the full dynamic envelope, from a whisper to a shotgun blast...without any given frequency emphasis, tends to be one of the more salient points that creates the idea of spaciality in mono recordings. Tubes tend to be good at this, depending on the designer of the given gear. Solid state performs the trick less often, in my experience. I've been involved with/in many a conversation with John Curl on the DIY Audio forum, and he's always struck me as a quite literate man when it comes to analog circuitry. He has one of the most important components down quite well, which is to keep his mind and ears---open.

Shit. Now it looks like I gotta buy another preamp. Remember the final scene of The Raiders of the Lost Ark? An entire warehouse full of "lost arks"? Well, that is my garage -- 20,000 preamps.

Seriously, I only have 5. Two tubes, and, among the other 3, a pure passive (the Audio Synthesis "Passion" and the active/passive Adcom GFP 750) and the McIntosh C-46. Preamps do color the sound more than any other single component other than the loudspeakers.

The Adcom, believe it or not, is the most neutral preamp I have ever heard, as near as I can tell from extended listening. For around a grand. And, if your source components and speakers are dynamically compatible, you can run it passive. A John Curl design. I guess the guy knows what he is doing.

I enjoy the (for want of a better term) "palette" of my 2 multi-bucks tube preamps (the big VTL and the ARC) a bit more, SOME of the time (depending on the software), but we are talking 5 figures, here, versus around a grand for the Adcom.

Not being a gearhead, I have no idea which elves running through the boxes and wires are responsible for the various differences, but I am glad I have a carefully-selected variety to choose from. The preamp, in my opinion (remember, as a concert-goer who listens mostly to full orchestral music) can add that indescribable "life" in the upper midrange that other components don't seem to capture (other than the loudspeakers, of course, which have an overpowering influence on tonal balance).

So, I guess Mr. Curl rules. If he can do what he did with the Adcom GPF 750 in an active design, for 5 grand, I guess I have to hear it.

It's about time somebody came up with a great preamp for under $10,000. God knows, nothing else is getting any cheaper. I can't wait to hear this piece.

So, any of you having a garage sale on your preamps?

I'd like that Adcom...

Actually, the GFP-750 is a Nelson Pass design. Same as the GFA-585. A few others I suspect, but those two for sure. The basic circuit is at least his, we don't know where the given designer ends - and the influence of the given company begins.

John has seemingly done quite a few designs for/with Parasound.

John has this neat unit called 'The Blowtorch'. IIRC, it is based on one of his designs that was too expensive to make it to market or survive effectively in it-these things happen. They've been playing with it extensively over at DIYAudio, through about 200 people making different variations thereof. I might be slightly off on the correctness of the story, but it goes something like that. Par for the course at DIYAudio.

Those two guys hang out on the DIYaudio forum, and for the same reasons: they like to help and to share. Gotta help create the new audio designers! Thankfully, somebody does. A few designers spend time there as well. The DIY audio guys can be a great but..sometimes, er, cranky bunch. Makes the little wars here look like calm walks in the park. And that's with their moderators using big hammers..and often!

The GFP-750, being a decent and relatively simple circuit (parts count, layout, design, etc - one has to be smart to get to the point where one can design the simple things that work!), responds quite effectively to modification.

As for audiophiles? I'd have to say that out of the hardcore of the hardest core of audiophiles...the DIY crew would have to be that group. The same issues as we have here, as in cables vs none, parts quality vs whatever, everyone gets represented.

Imagine a bunch of Scots who each make their own Scotch, drunk, in a bar, arguing over Scotch, and you'll have the flavour of how the conversations can go over there. (At DIYAudio)

KBK said "Imagine a bunch of Scots who each make their own Scotch, drunk, in a bar, arguing over Scotch, and you'll have the flavour of how the conversations can go over there. (At DIYAudio)"

YIKES!