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.

I haven't heard it myself, but there is a review of the GSpre/GS150, in this months HiFi News magazine in the UK. It gives a pretty much unqualified thumbs up, as you would expect from a magazine with a heavy advertising input from the UK distributor. Not that they would be biased of course. This is part of a telling conclusion:

" Audio Research say it's Galileo Series is not intended as a replacement for the existing Refs, but will coexist with the rest of the ARC product range to provide an alternative aesthetic as well as a platform for new ideas. So, before REF owners feel tempted to upgrade lock stock and barrel, I'd urge them to first try an audition an ARC ref 150 with KT150's in place of the stock KT120s"

Well precisely, except it is not a switch ARC would condone it seems and might void the warranty. The KT150's works pretty well in my Ref 75 though and many are using the 150 tubes in the Ref 150 amp, I believe.

Now I for one, would be very interested in that comparison and if, as I suspect, there isn't a great improvement in the sound, you are paying a pretty penny for an, "alternative Aesthetic", methinks.
Pulled the HI FI News review and clipped some pertinent comments:

"The GS duo not only looks much better
it also sounds way better than the ARC REF 5E/150 combination with **KT120 valves installed** (which
are congested and closed-in by
comparison). The GSPre/GS150 won
hands down, I must say. As well it
should, considering that it costs
almost double the price."


"Audio Research says its Galileo Series
is not intended as a replacement for
the existing REFs, and will coexist
with the rest of the ARC product
range to provide an alternative
aesthetic as well as a platform for
new ideas. **So, before REF owners
feel tempted to upgrade lock, stock
and barrel, I’d urge them to first
audition an ARC REF150 with KT150s
in place of the stock KT120s.**"

Warren Gehl comments:

"So is the GS150 really just a
REF150 with new looks? ‘As with
many designs from Audio Research,
the GS150 is an evolutionary step
from the REF150’, explained
Warren. ‘For while the two amplifiers
share many common aspects, **there
have been numerous parts and
layout changes which affect the

("**" denotes my emphasis.)

Not to bore all with the HI FI lab report, I am very familiar with the Ref 150 specs and lab tests. The two amps test almost identically. Warren Gehls states that "numerous part ... changes" affect the sound. I can count at least 5 changes. Four (4) KT-150 tubes and a slightly different output tranny (minus 1 tap). What other parts were changed ... better coupling caps?? Better resisters? Better front end power supply?

The authors encourage current Ref 150 amp owners to try the KT-150s. ARC says we can't do that yet. But I wonder what the authors would say if they compared the Ref 150 with KT-150 tubes and the GS-150?

I smell a marketing trick: a Ref 150 with a pretty new skin and much better power tubes. I have a funny feeling that loading my Ref 150 with KT-150 tubes will yield a MAJOR improvement. Maybe almost as good as the GS-150. But ARC says NOT YET!

P.S. Not much said about the GS-Pre other than the phono stage was not as good as the Ref Phono 2 SE.

Given where I hold with my system, I am looking for tweaks and changes that have a high benefit to cost yield factor. The DEQX PreMATE is one such change. I think KT-150s will be a another. Next on the list is AC power distribution. And so forth.

If there are any brave souls who have slipped KT-150s into their Ref 150s, please share your comments.
I was in your camp as of the spring. ARC had been life testing for a very long time, but I had 2,000 hours on my tubes and wanted ARC's blessings for the KT150s in my Ref 150. I called Kal who indicated that life testing was not complete and that ARC had not passed on the combo yet. So I, being the conservative type, ordered a new set of KT120s from ARC. Then after reading all of the plaudits on Agon, I pulled out my KT120s after only 500 hours and installed matching KT150s sourced from Upscale Audio. It is a worthwhile upgrade. I am convinced for reasons that I am sworn not to tell, that the KT150s will not harm my amp now or ever. If I could do it again, I would have purchased the KT150s in the spring. The difference between the KT150s and the KT120s are similar to the upgrade from 6550s to KT 120s. A little better all around, especially in the low end.
I too suspect that the difference between the Ref 150 and GS 150 is purely a matter of form. In fact, ARC engineers were told to, in essence, fit the Ref 150 into the GS 150 chassis. In the interim, the KT150 tube was released so the GS 150 was modeled around it. My intuition tells me that the layout for the circuit in the Ref 150 is the preferred layout and the layout for the GS 150 is driven more by the new chassis configuration than anything else. Is it possible something was learned and gained along the way in the new design? Absolutely. It is also possible that, with a truncated circuit path, we may have lost something as well.
01-01-15: Bifwynne
Way too early to come to judgment .... 600 hours is the break-in period.

I am interested in learning how the GS-150's innards differ from the Ref 150.
Bifwynne (System | Reviews | Threads | Answers | This Thread)

01-02-15: Tsushima1
Several hundreds of hours would have been ideal, It is unfortunate that this particular unit has just the 100 hours on the clock as I rather suspect my loan period will not extend quite that far.

Another run out sees the clock just ticking over the century mark, midrange opening up a smidgen! Vocal inflections? *particularly* impressive, even in comparison with my 100K hours Ref 150/ KT120. Soundstage ? although having expanded outwards a tad from the frontal plain of the Martin Logan CLX's comparative to 60 hours, I am far from replicating the projected 3D soundstage, verging on surround sound, that I can achieve with my Ref 150 in combination with its 16 Ohm tap.

Imaging and separation? Even at this stage, most impressive!

Returning to vocalisation. Even at this point in break in time it is clear to me that the nuances in diction and phrasing were being elevated to a point beyond that which I had previously considered as quite excellent, via my Ref150, these evolutions of inflection may be subtle, yet are perceivable enough, in taking the listener that one step closer to the old cleche that is 'Sinatra in the room'

However, A most compelling and pertinent question yet remains.

Just how close is a Ref150/KT150 to the GS150?

Especially were one to be an oddball like myself that utilises the 16 Ohm tap, phased out on the later GS Amplifier.

For anyone interested, more anon.

Jasper ... why are you using the 16 ohm taps? What type of speakers are you driving?
Thanks Gpgr4blu .... then why the huge price increase in the GS-150? Where's the value? Is ARC asking its loyal customers to pay for just aesthetic and silly meters?

If so, William Z Johnson is rolling.

I hope that ARC publishes a tech explanation on its web site that explains the tech differences between the Ref 150 and the GS-150 that justifies the huge price increase. I would expect a wholly new everything.

If this is just about aesthetic, ARC's good rep takes a big hit IMHO. And I am a fan. Just sayin'.
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... ML CLX anniversary, flying in the face of received wisdom I know! However, with certain Genre viz.Girl n Guitar, Jazz, etc.etc, I trade off a smidgen of control in return for the effects that I mention in my previous post.

My own Ref150 is now ready for return, therefore my time with the loaner GS will shortly come to an end with approximately 130 hours on the clock.

Whilst my sonic impressions of the GS are unlikely to evolve much, if any, further that my considerations at the 100 hours mark, I would state tho, having now become accustomed to its 'Retro' look , that I will quite miss its 'easy on the eye' aesthetic styling, precision of diction, and the subtle yet perceivable additional head room it has brought to the system.


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.
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."

-- Al
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.
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.

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 ~

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.
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?
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
"So is the GS150 really just a
REF150 with new looks? �As with
many designs from Audio Research,
the GS150 is an evolutionary step
from the REF150�, explained
Warren. �For while the two amplifiers
share many common aspects, **there
have been numerous parts and
layout changes which affect the

The question that I BELIEVE up until has not been answered definitively is whether there is any difference between the Ref150SE and the GS150 other than the latter's fancier case/meters. One poster in another thread suggested based upon a magazine review that the GS150 "blows the Ref 150 out of the water" (which I doubt) but what about the GS150 vs. the Ref150SE? Does the extra money buy a better circuit layout or parts inside? So as a registered ARC owner, I just emailed ARC that exact question last evening and just got this response;  "they are sonically the same." If you watch Mike Fremers two videos on Youtube of the ARC factory tour, there's a short section/exchange in which Warren Gehl says he uses the Ref150SE as his benchmark for subjective listening checks on all outgoing amps (unless I misunderstood the exchange and video).That explains that. I love the looks of the GS150-more than the staid looks of the Ref150SE. But is it worth the extra dough for the bling? Is ARC's Italian ownership going a bit over the line in making ARC gear resemble the stablemate McIntosh kit without the McIntosh blue meters? I have to wonder but again, I would take the beautiful GS150 any day of the week and Sunday too if they were close in price. I am biased-I just bought a dealer demo Ref150SE to go along with a brand new Ref 6 to replace a 25 year old tubed preamp and a 12 year old VS110. I'm happy but poorer! I have a fluke meter for my VS110 so I'm set in that respect.