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Audio Research GS150 Musings

Good day my fellow ARC Agaricus Bisporus.

In light of the relative ambivalence that seems to have descended upon ARC's latest, and Should we to believe the "word' on the street, greatest stereo amplifier, I thought that I would initiate this thread for the most part as a vehicle whereby any early adopters of this particular model might comment upon their considerations of the amplifier thus far, and hopefully utilize the same, as a place where they may log their considerations as they journey through the Roller Coaster ride that is ARC break in.

I hope that I will be excused for the somewhat laxidaisic cut n pasting that follows, however I plead the 'Humungous Hangover' defence!

" For my part I have listened to the same GS150 at 60 hours, then with 166 hours on the clock, and whilst there were signs of an opening up in the midrange, I felt the amplifier to to be rather 'Tight', and still a Tad constrained in some areas of tonality, texture and harmonics, particularly on acoustic strings.

Whilst considering comment made thus far in respect of the KT150, I was expecting to be impressed with the lower registers, even at this point in what can be something of a roller coaster ride where break in of ARC is concerned, however this particular GS is still quite some way off, in reproducing the gravitas evident in for example, Der Ring des Nibelungen, as imparted by my Ref150 even at 300 hours on the clock.

However! Even at this early juncture, It is in the upper mid-range, ascending, where the GS has ,for me, impressed the most. The retrieval of filagre micro detail is quite excellent, the GS seeming to impart additional 'air' and light with an effortless extension to the very upper registers. Smooth, clean and accurate, whilst remaining quite organic and utterly convincing in nature.

Jasper."
tsushima1
bifwynne
2,069 posts
 
P.S. Correction to my post to Jasper. What I should have said is that the output voltage variation (not power) is tightest off the 4 ohm tap and therefore the amp performs more solid state like ... that is like a constant voltage source. This corresponds to the fact that the output impedance (about .6 ohms) of the 4 ohm tap is the lowest of the 3 taps.

So, if the ML speakers were voiced to be driven by a low output impedance SS amp, the 4 ohm tap might (??) produce the flattest frequency response, assuming the MLs spec flat as a threshold matter.

But having said that, as Al said, the ultimate output may sound better at a higher ohm tap based on listener preferences (i.e., preferred acoustic coloration) and/or the impedance match (or maybe better said, mismatch) of the amp and speakers especially if the amp is called upon to produce large amounts of power.

As Al said, generally, most amps are not called on to deliver huge amounts of power in the treble frequencies.

In the end, go with what ever sounds best.

BIF
tsushima1 OP
148 posts
 
Thank you Gentlemen, as I posted above, I do like to run this combination counterintuitive to received wisdom. For your info a link to some test measurements taken during the HiFi World review ~

http://www.hi-fiworld.co.uk/index.php/loudspeakers/65-reviews/252-martin-logan-clx.html?start=2

Jasper.
bifwynne
2,069 posts
 
Jasper, I'd appreciate Al's thoughts, but looking at the impedance graph of the ML's, they look like a giant capacitor. Notably, in the all critical power region (50 to 750Hz), impedance is quite high.

The graph is hard to read, but it looks like impedance is between 10 to 15 ohms in the frequency spectrum where the amp is called on to deliver power. It wouldn't surprise me that you like the sonics off the 16 ohm taps. As suggested, you might want to try the other taps to see which taps sound best.

For example, you might find bass to be tighter and punchier if you use the 8 ohm taps ... I expect a high DF. The 4 ohm taps might give you the tightest bass and the high end might be less bright

Al, any comments?
almarg's avatar
almarg
8,673 posts
 
Jasper, thanks for providing the link. Bruce, yes an electrostatic element can very reasonably be thought of as a giant capacitor, although the resulting impedance variation as a function of frequency will be modified by the step-up transformer that is usually used to drive the element.

I wouldn't expect a great deal of variation in bass response to result from differences in impedance interactions between the different output taps and the speaker's impedance vs. frequency characteristics, though. The reason being that the relatively low output impedance of all of the taps on the Ref150 (for a tube amp) results in all of those output impedances being much lower than the speaker impedance at low frequencies. So with respect to the effects of impedance interactions I would expect the most notable differences among the three taps to occur at higher frequencies, where amplifier output impedance becomes increasingly significant in relation to speaker impedance.

Also, of course, the concepts of bass damping and woofer control that come into play with dynamic speakers are essentially inapplicable to electrostatics.

Although it seems possible that the distortion characteristics of the amplifier could be significantly affected at low frequencies as a function of which tap is used. John Atkinson noted in his measurements that "over most of the audioband, and when the load impedance is very much higher than the transformer-tap value, the Ref150 offers low distortion." Although it should be noted that that comment was based on measurements performed at power levels of just a few watts or less, and it could be a different story at power levels approaching the amp's maximum.

Best regards,
-- Al
knghifi
1,667 posts
 
01-03-15: Gpgr4blu
I'm a huge ARC fan as well. Hopefully, they make it right over time. Get back to superior engineering at a reasonable price.
ARC IS producing superior engineering at a reasonable price.

If ARC has decided to make its products look better for the Chinese market, it can be done with a reasonable (1 to 2k) price increase so as not to lose its base here in the US.
DISAGREE! ARC should charge what the market bears. Passion alone doesn't pay the bills.
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