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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
2,206 posts
 
Jasper,

What does the impedance curve of the ML CLX look like, especially in the critical power range (50 to 750 Hz)?

The 16 ohm tap has the highest output impedance of the 3 taps. As a result, if there is an impedance "bump" at a certain frequency range, the Ref 150 will produce more power at the "bump" and the SPL will be correlatively augmented. By contrast, the 4 ohm tap has the lowest output impedance of the 3 taps (approx .6 ohms I believe) and will produce the smallest power variance as a function of frequency.

My speakers have an impedance curve that looks like a roller coaster ... but significantly, the impedance curve in the critical range of 60 to 500 Hz ranges between 4 and 6 ohms. I happen to use the 4 ohm tap. That's a good match for the amp because the bulk of the power demand is in that frequency range. Also, the 4 ohm tap has the highest damping factor .... therefore better control of the woofers

But look ... use whatever tap you think sounds best. You won't hurt the amp. Having said that, the amp's capacity to deliver clean power in the "power range" (i.e., 50 to 750 Hz) may be somewhat compromised if the impedance match between the speakers and the amp (via it's primary windings) is not be optimal, i.e., much lower than 16 ohms.

I'm sure Al (Almarg) can chime in and clean up my attempt at a technical explanation.
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almarg
9,670 posts
 
Hi Bruce & Jasper,

I couldn't find an impedance curve for any of the versions of the CLX, but the Anniversary version is spec'd at 6 ohms nominal and 0.7 ohms at 20 kHz. As with most electrostatics, the impedance presumably descends more or less progressively through the treble region, reaching that very low value at 20 kHz, while being at much higher values in parts of the mid-range and in the bass region.

So the higher output impedance of the 16 ohm tap on the Ref150, relative to the output impedance of the other taps, will interact with those impedance characteristics in a manner that will tend to de-emphasize frequencies in the upper treble region. Given the relatively low output impedances of all of the taps on the Ref150, though, as compared to many other tube amps (resulting in part from the amount of feedback it uses), that effect figures to be modest in degree. There might also be a bit of an increase in amplifier-generated distortion in that region, due to the mismatch between the speaker's very low impedance at high frequencies and the nominal impedance that tap is designed to work into. But that effect would probably be mitigated by the relatively low energy levels that are usually present in the uppermost octave or two.

The bottom line, as Bruce said, "use whatever tap you think sounds best."

Regards,
-- Al
gpgr4blu
1,082 posts
 
I'm a huge ARC fan as well. Hopefully, they make it right over time. Get back to 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.
bifwynne
2,206 posts
 
Gpgr4blu ... couldn't agree more. We may be recycling the same inside news from the same person that the GS line is targeted for the Chinese/Asian market, but I heard that bit of information too. I still find it hard to understand ARC's pricing/value proposition for the GS line. Short of a major "Ref 10" type redo, which is based on the 40th Anniversary linestage on steroids, I just don't get it.

IMO, I would not part with the kinda cash ARC is asking for the GS line, even if it could levitate spoons and bend them in mid-air.
bifwynne
2,206 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
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