I own the VS-115. I can't say enough positive things about it. I've read old posts from other members who claimed it sounded 80-85+ percent as good as the now discontinued Ref 110. If you decide to spring for the VS-115, use KT-120 tubes. They make a big difference. If you check the A'gon ads, I recall seeing one or two used VS-115s for sale for around $4K or less, which is a very good deal considering a new VS-115 retails for $7K.
Two caveats. The VS-115 has been around for a while. I wouldn't be surprised if ARC comes out with a replacement model soon. Not to say that's bad. It may even put a downward pressure on the used VS-115 market.
The other point relates to maintenance. I've owned my VS-115 for about 3 years. So far only one maintenance issue, but I suspect this applies to most tube amps.
On occasion, usually when I replace power tubes, a new tube may arc taking out a bias resister. The part costs about a buck -- it's the labor cost and out of service time that is annoying. Fortunately, I live near an ARC authorized service tech who makes house calls. He charges me between $80-$100 to soldier in a new resister, usually within 1 day after I call him.
If you're handy with a soldiering iron and can stay away from lethal high voltage sources, you can replace the resister yourself. Otherwise, be prepared for the occasional blown bias resister.
I bought a VS115 brand new from my local AR dealer. Within the first week, a resistor blew up, probably the same as Bifwynne referred to in the note above. I think this isn't acceptable and the AR engineers should figure out a fix and make it free to VS115 owners. When it happened, it scared the crap out of me because the resistor made a loud pop and I later found the blown resistor on the shelf below the amp. I returned the VS115 that same week for full credit towards my current McIntosh MC452 SS power amp and I'm happy. The experience was great since my dealer, Paragon Sight and Sound in Ann Arbor, MI took care of me.
At a fraction of the cost of that ARC (which I had considered buying at one point) I bought a new "factory upgraded" Jolida 502p about a year and a half ago, stuck KT120s in it, and am very happy with it...reliable, quiet, and powerful...unlike myself. I was lead to it (and the VS) because I wanted an "old school looking" amp with XLR inputs. I'm sure other's get sick of my mentioning this amp, but Jolida rarely gets reviews in the press and I think they're a cool little company (the MD guys) that deserves more attention. Like a puppy.
Smatsui, not sure you laid out all the relevant facts about your resister problem. But based on what you did say, I surmise the VS-115 was under warranty since the resister problem occurred within one week of taking delivery from your dealer. When one of my bias resisters blew, my amp was still under warranty. ARC sent a tech to my house to fix it -- free of charge.
Bias resisters do double duty as fuses when a tube arcs. Tube arcing goes with the territory with tube amps. Now . . . as to engineering, I understand some manufacturers make self biasing amps with mini fuses for each power tube. Don't remember the models - sorry. OTOH, it is my understanding that ARC intentionally passed on that configuration to keep as much artifacts out of the circuit as possible.
I have heard of bias resisters making quite the racket when they do their job. Can't say I heard one took a ride out of the amp, but I guess sh*t happens.
If the problem you experienced was indeed as I surmised above, ARC would have fixed it in your house, the fix taking all of 30 to 40 mins. And I want to emphasize, power tubes are glitchy when new and have a tendency to arc during break in. If they do arc, something has to give or the circuits could fry.
Here's my bottom line: as soon as I get beyond the "tube break in nervosa period," I have little if any problems with my VS-115. And the double bottom line is that the amp sings.
I'm glad you found another fine amp to pick up the slack. But all of my electronic gear is ARC and except for the occasional pesky tube arc, I have no complaints. In contrast, after tweaking this and that, my rig is very musical and enjoyable.
If Gary (Hifigeek1), an ARC authorized tech, catches this thread, perhaps he can weigh in with his comments.
ARC tests their tubes at hard labor for 24 hrs. prior to putting them in your amp at the factory. No other tube reseller does this. Tubes are not perfect and they do fail. They warranty the tubes for 90 days and any damage it caused would be covered under warranty. The resistors are doing their job when they shatter. They are flameproof resistors. This is normal.
I'm not sure what relevant facts that I left out. My dealer would have given me a brand new replacement VS115 within one week if I wanted it. That is not the point. I did not want another VS115 after my experience. The KT120 tubes were fine. The center rear transformer also was humming loud enough that I could hear it in my listening position and it got pretty hot as well. When my dealer asked me if I wanted a replacement I told him that I did not want to wonder if this would happen again.
I think the VS115 is a fine sounding amp. I wouldn't have bought it in the first place if it wasn't. I just question its reliability.
Glad to hear that Paragon Sight & Sound took care of you. I have been in that shop a couple of times as I live in the Detroit area. And while I have not purchased anything from them it is reassuring to know that they support their customers and that I can feel comfortable should I ever purchase something from them.
I've had my Jolida for a relatively short time compared to the tube guitar amps I've used since 1966. In all those years of constant gigging I never had a single incident of a tube failure taking out any other part of the amp...some tubes did fail here and there (extremely rare) but were replaced with zero damage anywhere else. ARCs issues, although seemingly often covered by warranty, seem strange to me...but then so much seems strange...NURSE...wheel me out of the sun!
Resistor blowing, with tube arcs, and shorts, is only true with ARC amps and is IMO a reliability issue. ARC in the Twin Cities will "never" send a tech to your home for any repair! The amp always goes back to the factory for any repair!
BAT, Quicksilver, VAC, Atmosphere, Manley, Rouge, and VTL amps "never" blow out parts if a tube arcs!
It is a poor design choice by ARC!
I now live in fear of my Jolida being destroyed by a tube arc...not likely to happen, but still...also, is this all stemming from the fact that ARC and "arc" are the same letter grouping? Coincidence? hmm...I smell a conspiracy...or my tubes melting...or something
Sorry Don, there are a lot of amps which will take out a resistor in the bias circuit when a power tube blows. ARC has a lot of company, including I suspect some of those you mentioned. But I agree it is a PITA especially when you aren't handy with a soldering iron. Usually it is simple to replace the resistor.
BTW, since you have stated that it is a "poor" design choice, what design would be preferred, and how would its utilization affect the performance of the amp? I suspect that designers may have concluded that using the resistor as a fuse was a preferred solution as opposed to inserting a fuse in the bias loop. But I'm not a designer.....
Smatsui, I'm sorry to read about your troubles. It's hard for me to react to your situation, other than I'm glad you found an amp that suits your needs.
Just a couple of responses to your last post. Yes, the power tranny does get quite warm, but that is normal for the VS-115. As far as humming is concerned, I wonder out loud if what you heard was the power caps charging. I've heard humming too at start up, but it goes away pretty quickly after warm up. Perhaps Gary (Hifigeek1) could add another comment or so to put your observations into perspective.
There are no reliability issues with that amp that I am aware of.
My VS115 is one of the earlier ones with the 6550's. At some point I will upgrade the tubes to KT120's. I've also blown one of the resistors in the amp. I ended up replacing the resistor myself--it's a 10 minute job if you know how to solder. Apparently this is a common problem.
Other than that, I love this amp. When I put it in my system, it totally changed the sound of my system in the area of midrange accuracy, imaging, and 3-dimensional soundstaging. I was using Classe solid state electronics before.
Compared to some tube amps, this is a very wideband amp. With laboratory test equipment I have measured its frequency response into an actual loudspeaker load as flat out to 20 kHz and -3 dB at 50 kHz. This probably helps account for why this amp does not sound rolled off in the highs and has very good detail.
I also have an LS-27 and Reference CD-7, so you can see I am sold on ARC.
Jake, what loudspeaker did you use when you tested the VS-115's FR? Also, what output taps did you use?
Bifwynne - The speakers under test were Thiel CS2.3 driven from the 4 ohm tap. The CS2.3 are a notoriously difficult load for amplifiers, with large swings in impedance over frequency and a minimum impedance of 2 ohms. However, the Thiels and the VS115 match up extremely well, far better than with solid state amps. I currently have the Sonus Faber Cremona M and get pretty much the same results with the VS115.
@Jake, your results line up with the test results from Stereophile and Soundstage I posted above. Did you also have a chance to near-field mic the actual SPL outputs of the Theils. That would seem to be the ultimate test.
I switched over to the 4 ohm tap and am getting used to it. Very different acoustic presentation, probably because the 8 ohm taps has a higher output impedance than the 4 ohm tap, ergo permitting a touch more output variation in the high impedance parts of my speakers, mainly the 2.2K to 4K Hz region of the freq. band. Per Atkinson at Stereophile, the SPL variation is almost half.
Bifwynne - I have a Radio Shack SPL meter but it's not really accurate enough to make good near field measurements.
The 4 ohm tap does have lower output impedance than the 8 ohm tap. However, if you are driving an 8 ohm load you'll get more power out of the 8 ohm tap. My Sonus Fabers are nominally 4 ohms so I use the 4 ohm tap.
Jake, out of curiosity I googled to find bench tests of the Thiel CS2.3. May have looked at the wrong site, but the test results I found showed impedance remarkably holding at a near 4 ohms almost across its entire FR spectrum. As expected the impedance curve had the normal two spikes in the bass region, but that was it.
I'm not saying every amp could eat a constant 4 ohm load for lunch, but I was surprised that past 100 or 150 Hz, impedance hovered at 4 ohms. I must have looked at the wrong speaker. If you have a link to the bench test results you had in mine when you made your post, I'd be very grateful if you'd either e mail me or post it here.
I re-checked the net to view the bench tests for the Thiel CS2.3 speakers. What I saw in fact was bench test results for the CS2.4s, which as I said had an amazingly flat 4 ohm impedance plot from 50 or 75 Hz through the audible acoustic spectrum.
Do you know whether the CS2.3 was configured differently? I ask because you posted that the 2.3s had modulating impedance plots? Do you have any idea what the SF Cremonas impedance and phase angle plots look like? Couldn't seem to find any hard data on the net.
The reason I am so curious is because I'm trying to gather some real life anecdotal information about how our amps perform when driving speakers with goofy impedance and phase angle plots.
Btw, how do you even measure the output performance of the amp and speaker combo? I have a digital meter that I use to bias the amp's tubes. But I have no idea how to check actual output with the amp hooked up to the speakers. Or how to check output impedance (with no load) off the 4 and 8 ohm taps. Can you advise?? I kinda would like not to damage my gear just to satisfy my curiosity.
Thanks and have a great Memorial Day weekend.
Bifwynne - The CS2.4 has a somewhat smoother impedance plot than the CS2.3. Here are the measurements done on the CS2.3 in a Stereophile review: http://www.stereophile.com/content/thiel-cs23-loudspeaker-measurements. You can see the impedance dips to 2 ohms in the lower midrange and goes through big swings in the bass region. The phase angle varies all over the place, too.
I've seen impedance plots for the SF Cremonas but I have the newer Cremona M and I'm not sure if the data would be similar. The Cremona M is supposed to have "improved" drivers and a different crossover network.
To measure frequency response into an actual speaker load, I use a Tektronix audio signal generator driving one of the auxiliary inputs of my ARC preamp and I attach a Tektronix oscilloscope across the speaker terminals. I bought both Tektronix units on eBay quite cheap. I dial back the signal generator output levels so I see about 1V at the speakers and everything is happy.
Measuring the output impedance of the VS115, or any other amp, is a bit more involved. The easiest way is to get an impedance analyzer that works at audio frequencies. The analyzer is connected directly across the speaker terminals of the amp and it injects a low level signal back into the amp to make its measurements. I have an RF impedance analyzer but it doesn't go down to audio, so I've never done this myself.
Hope this info is helpful.
Thanks Jake. I think the impedance/phased angle plots are demanding as reported in Stereophile mainly because of the 2 ohm dip and general 4-5 ohm range. But other than that, the impedance is quite flat between 4 and 5 ohms across the freq. band. The low bass peaks are typical. Nevertheless, it does demonstrate the VS-115's impressive performance capability. How many amps out there can push power into such low impedance loads??
Bifwynne - I should mention that a network analyzer (sometimes called a "vector network analyzer, or VNA) can also be used to measure the frequency response of an amp into any load. The same instrument will measure the output impedance of the amp as well. My home lab includes a VNA for RF but unfortunately it does not go down to audio frequencies.
Out of curiosity, what speakers are you using with your VS115?
Paradigm Sig. 8 v3. I've had a devil of a time getting reliable and timely info about the specs, but finally got through. The S8s have a 21-22 max ohm peak between 1K and 2K Hz; and a 4 ohm min. in the bass region. I've been in private contact with one of our tech members and he did some math calcs that indicate the VS-115 should be able to drive the S8s with a relatively flat output response because the amp's output impedance is low for a tube amp. Soundstage and Stereophile bench tested the VS-115 and Ref 150 and they share similar electrical attributes re: NF (about 12-13), DF (about 7 or 8) and output impedance (approx. 1.1 ohms off 8 ohm tap; about half that off the 4 ohm tap). Based on his calcs, FR may be off +/- .5 db at the peak, which ain't so bad.
VS-115 maintenance tip. Just replaced the four 6H30 cathode follower tubes. May have run them out to almost 4000 hours. BIG, BIG difference. The amp definitely sounds better: tighter bass, more transparent, and so forth. I think in the future I will switch out the 6H30s before they have 3000 hours of use.
Any recommendations for new tube set other than the Audio
Research Brand. Can I use any 100 ohm 1 watt bias resistor
or need to order one from A. R. ? Thanks, Gerald
Have the VS 115
Gerald, for some reason ARC recommends using their parts, e.g., bias resisters. I don't know why. They only charge a buck so per resister. Selling "matched" resisters can't be a big profit center. So, I would order the resisters from ARC.
As to tubes ... I think the main stream brand is Tung Sol KT-120s, but there may be other KT-120 manufacturers. ARC charges about $100 a tube, which is twice as much as what other reputable vendors, such as Upscale Audio and so forth. I've gone both ways with tubes. I don't think ARC's KT-120s sound better than anyone else's KT-120s.
But there are two advantages going with ARC. One ... it has been my experience that ARC does a better job of matching tubes. An ARC matched pair biases very closely.
Two, if a tube arcs within 90 days of purchase, I believe ARC will replace it. They may also repair any damage caused, e.g., open bias resister. I'd check the last point.
Btw, I used to own the VS-115. Traded up for a Ref 150. I think the VS-115 is a super-duper amp. Enjoy.
ARC recommends using their parts especially when it comes to the resistors around the output tube circuit because they are flameproof wirewound resistors. These parts are used to minimize circuit board damage when an output tube arcs. Instead of using a plain wirewound resistor where the resistor might heat up and scorch the board, a flameproof resistor basically pops and opens thereby minimizing damage.