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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

Showing 2 responses by almarg

almarg's avatar
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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
almarg's avatar
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almarg
9,670 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
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