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ultra fi

Monaco 845 SET stereo amplifier

as reviewed by Akhilesh Bajaj

 

 

 

 

AKHILESH BAJAJ'S SYSTEM

LOUDSPEAKERS
1978 Klipschorns with Bob Crite updated crossovers, Vintage Altec VOTT system, modified to use 515B woofers in a large BR box with a 511B horn using 808-8A drivers, with a sub to drive the bottom. Stephens trusonic 80-FRs with Vifa dome tweeters and sub, actively crossed, DCA5.5" driver in PAWO horn, run in pure single driver mode with no passive or active EQ, Vintage University 315 coaxials in largish sealed altec boxes. Subs: Hsu research vtf 2 and vtf 3.

ELECTRONICS
Hand built passive using General Electric single wire rheostats and a Mod Squad Line Drive. 5842/45 SETtube amp (James Burgess built), 2a3 Bez SET amplifer, ASUSA 12ax7/el84 SET mode amplifier, Custom built Dynaco ST35 12ax7/12au7 el84 p/p amplifier, Abraxas Audio Built SET amp 12ax7/12b4 output tube, and a Larry Moore built 2a3 SET amplifier.

SOURCES
Berendsen CDP1 and a Modified Philips CD player with TDA1541 chip in Nonoversampling mode.

 

"There is alchemy between triodes and Alnico that is more profound than beer and pretzels, ketchup and French fries and ice cream and cookies." Dr. Harvey 'gizmo' Rosenberg ( http://www.meta-gizmo.com/tri/aroma.html)

Larry Moore, Esq. out of Ohio, has been building amplifiers for over 30 years, starting in his pre-teen years. He has also been a competition bicycle racer and currently drives souped-up BMWs (bimmers) for fun. He was part of the initial wave of SET (single ended triode) amplifiers when it crashed back on US shores several years ago, and counts among his friends folks like Herb Reichert (of 'flesh and blood' fame). As Larry says, he is one of the few Non New York members of the NYC Triode mafia. Larry has been building and experimenting with SET amplifiers for several ears, and it is safe to assume he has tried a multitude of different circuits (input tubes, driver tubes, output tubes, etc). He has also built several high end custom amplifiers for his well-heeled clients. The Monaco SET amplifier is his first production offering, using high quality but non-exotic parts. Conversations with Larry indicate his goal was to create an amplifier that performed well over its price point, but that could be manufactured using off the shelf parts.

Even though I do have an engineering background (and some would say, mindset), my goal in the audio hobby is not to get the best measuring system but rather to get closer to the music. I bought my first SET amplifier about seven years ago, and have bought and sold quite a few since then, currently owning a 45 tube amplifier (driven with 5842 tubes), a 2A3 Amplifier (driven with 5687 tubes), a 12B4A amplifier (with 12AX7 driver) as well as a 12AX7/EL84 amplifier where the output tube is wired in single ended mode. I have also listened to a wide variety of SET amplifiers other than the ones mentioned, including several Audio Note amplifiers in the $1200-$10,000 range as well as kit SET amplifiers in the $500-$1500 range. These have all been heard with a wide variety of speakers, ranging from single driver set ups to horn based setups. The point is to assure the reader that this is not a write-up where the reviewer decides to listen to a SET amplifier for the first time and discovers the "SET magic". I have been living with SETs for a long time, and listen almost exclusively to SET amplifier driven speakers.

In order to facilitate reading this review, it would make sense to state some basic opinions that I hold about SET amplification first. First, measurements don't really matter with SETs (perhaps they matter a little, but not nearly enough to worry about). If finding the best measuring amplifier is important, then there are several excellent offerings in the solid state area. My goal with seeking out SET amplifiers is to find components that bring me closer to the music. In that sense, SETs are more about emotion (how does the music make you feel when played through an amplifier?) than reason (how does it objectively measure?). Second, different tube combinations do sound very different. Based on my experiences, 2a3 tubes tend to be delicate sounding with good bass, while the 45 tube is lacking somewhat in bass but does an excellent job of rendering the human voice and correct instrument tonality. 300B tubes tend to be mellow and deep with a somewhat pronounced lower midrange.

I personally bought one of Larry's experimental one-off amplifiers about a year ago. This one uses a 5687 input/driver tube, driving a 2A3 output tube, both coupled with clarity capacitors, and with electra-print output transformers (http://www.electra-print.com/) built by Jack Elliano for Larry for this amplifier. This particular amplifier has excellent bass and sounds gutsy, with somewhat delicate highs. When I heard Larry was building the Monaco amplifier as a manufactured product, I called him up and a few months later received one of the first I'Os he built.

Information on the basics behind the Monaco is available at http://web.mac.com/ultrafitimes/iWeb/ultrafitimes/Products.html

The Monaco uses a 6SN7GT input tube, that feeds to a directly heated 46 driver tube which in turns feeds to an 845 output tube. There are thus three tubes per channel. The power supplies are solid state rectified, using Larry's proprietary circuit that (paraphrasing a conversation I had with him) somehow manages to achieve the advantages of choke based filtration without the disadvantages. Larry calls this "non-critical inductance input filtering".

The Monaco amplifier retails for $6250. It is 12.5" wide, 25.5" deep, and 11.5" tall. It is a very heavy amplifier, at around 80 pounds. I would strongly recommend getting a friend to help you move it around, unless you are into serious weightlifting.

The amplifier puts out 10 watts into 8 ohms. It uses James 6123HS output transformers, a military grade power transformer that weighs 35 pounds by itself and has an extremely low DCR (DC Resistance). The coupling capacitors between the input and driver tubes are Angela paper in oil signal capacitors, while the coupling capacitors between the driver and output stage are West German Mundorf capacitors. The input jacks and speaker binding posts are of reasonably high grade, though the speaker binding posts are somewhat inconvenient in that only large spades or banana posts can be used; there is no hole for a naked wire to be used. Overall, very good quality off the shelf parts have been used in this amplifier.

The amplifier consists of a heavy top plate that has all the components mounted under it, resting on a Corian® base. The amplifier is heavy to move around, and some sort of carry handles would have helped. Since the contours are so smooth, I recommend wearing leather gloves (and using a friend) when moving the amplifier, lest it slip out.

The overall aesthetic appearance of the amplifier is more boxy-industrial than soft-round-living-room, though to me that lends it a certain kind of chic (bear in mind, I also happen to think that Altec VOTT (Voice of the Theater) speakers look industrial-chic). The artwork on the top plate is nice looking, and a casual viewer should be able to tell this is an expensive, heavy duty piece of equipment. The base is available in a multitude of colors of Corian®, so one can certainly pick the base to match one's décor. I was overall quite happy with the appearance, though if one is looking for a softly rounded sculpture, this amplifier is not the one to get.

Unpacking and set-up

The amplifier came in a large wooden crate, with foam on all sides. Unfortunately, there was a large open crack in the crate, and it looked like something sharp and heavy had hit the side hard enough to split the side and open a large crack directly in the side. The amplifier itself had a cracked base (and as you know, it takes a LOT to crack Corian®!). I lifted the amplifier outside the crate, and moved it upstairs to my music room. The amplifier was shipped to me with Sylvania 6SN7GT tubes, RCA 46 tubes and inexpensive, valve art Chinese 845 output tubes. After inserting the tubes, and using a stock IEC power cable I had lying around (the amplifier did not come with one), I turned it on. It seemed to perform fine, so Larry asked me to go ahead with the listening. After listening to it for a couple of months, I met up with Larry in St. Louis, where he changed the base to a white one.

Listening

There are two reasons I was interested in reviewing the Monaco. The first was Larry's experience with SET design, as mentioned before. The second reason was that this is the only production amplifier out there (to the best of my knowledge) that uses an 845 output tube and a 46 driver tube both of which are directly heated tubes (DHT). As mentioned in http://www.webace.com.au/~electron/tubes/valves.htm, "in directly heated tubes the cathode is heated by itself and is called a "filament" because the electrons are emitted directly from it, just as in a light bulb. Filament warm-up time is quick so current flows soon after the tube is switched on. In indirectly heated tubes—i.e. where the cathode is physically separate to the heater, the cathode is called a "cathode", to describe its true function. Cathode warm-up time is slow, so current flows some time after switch on—usually controlled by tube design to about 11 seconds from cold to full warm-up."

The utilization of DHTs for both driver and output stages (and in some extreme cases for even the input tube, though not for this amplifier) are at the cutting edge of the SET experimentation scene. I was curious to learn how this amplifier compared to the more "run of the mill" SET amplifiers to which I was used to listening: the ones that use a combo indirectly heated input-driver tube driving a DHT. This would be the large majority of SET amplifiers available today.

I listened to this amplifier over a period of over three months. Larry had already burned in the amplifier for a week before shipping it. Overall, my impression of the amplifier is that it did not change significantly after the initial burn in. However, it definitely required at least a 10 minute warm-up at each session in order to sound its best.

I used two different setups to try and understand how this amplifier reproduces music. For the first setup, I used a pair of single driver speakers that use a D'Charles Audio 5.5" full range driver in a PAWO horn. A single driver setup like this helps reduce speaker related confounds, as long as it has a reasonable frequency response, such as this one does. For the source, I used a Berendsen CDP-1 player, which is a $2200 player made by Berendsen in West Germany. The speaker cable used was 10-gauge cable, bought from a large electronics store, hand trimmed with no terminators by yours truly to the minimum required length, which was about 5 feet. Interconnects used were simple Radio Shack gold plated ICs, 1-2 meter, again as short as required. Power filtration was a PS Audio ultimate outlet feeding into an Isobar isolator.

My main listening room is about 8 feet high by 11 feet long by 15 feet wide, and quite well damped. I compared the Monaco to two other amplifiers that I own: a custom 45 SET, built by James Burgess out of California and Larry Moore's 2A3 SET. The material listened to included several female vocalists (Eva Cassidy, Nana Mouskouri, Jheena Lodwick etc.).

The 45 SET did a great job on the human voice and in transparence, but was noticeably lacking in bass, especially compared to recent push-pull tube amplifiers I have used with this setup in the recent past. However, the 45 did a better job of making the overall musical experience more believable (the experience can be described as if one is listening to the person live in a slightly bass-shy room), and made me feel closer to the music. The 2A3 was significantly better in the bass and sounded better than most other 2A3 amplifiers I have heard. However it fell a little short of the custom 45 amplifier in terms of tonal correctness and overall believability.

The Monaco was then inserted into the signal chain. The Monaco delivered something I have never heard before: it provided a sense of believable realism (for the human voice and for the overall musical performances) that exceeded the 45 and provided bass that exceeded the 2A3, both in quantity and quality. The bass was as good as any push-pull tube amplifier I have heard, and the transparence was at least as good as anything I have heard before. The decay of the voice and instruments like the piano was excellent, and the level of retrieval of low level detail was also excellent.

The next setup was one where most of the listening was done, over a period of about two months. This consisted of the same Berendsen source, but the speakers were my 1978 Klipschorns, which are setup on the ends of the 15 feet wall of the music room. These have updated capacitors in the crossover, but are otherwise stock. Over the last several years of owning them, I have thrown every kind of SET amplification I could come across at them. They are rated at 104 dB efficiency, which means a watt or two is sufficient to drive them. Certainly, the 10-watt Monaco would provide more than sufficient dynamics. The Klipschorns easily reveal the character of the upstream components, and each SET amplifier I have used with them has sounded quite different.

Different types of music were played over the extended listening period, including female vocals, classical (e.g., Ravel, Beethoven, Mozart, etc), Blues (e.g., Monster Blues CD sampler) and also the Chesky Ultimate Audio Demonstration disc, by Chesky records, which I like to use since it isolates the qualities one looks for in a good system.

As soon as I heard the Monaco in this system, I knew that Larry Moore was not going to be getting it back. It is certainly the best amplifier I have heard when mated with my Klipschorns. The main improvements over every other amplifier I have used were the bass (both in quantity and quality), and more importantly the level of transparence. The attack and decay of every instrument was defined so that the sense of realism was greatly enhanced over every other setup I have had in my listening room. I cannot recall hearing a more realistic sounding setup. Every other quality (highs, midrange purity and so on) were very good to excellent. A final quality that really stood out was the tone, wherein every instrument sounded really like that instrument. After hearing a piano piece or a vocal on the Monaco, any other amplifier I had sounded inferior. The overall sense of realism and of listening to a real music performance, as opposed to just hearing different pieces of music coming from speakers, was superb.

The Monaco is not perfect. It proved to be very sensitive to the input tubes used (at one point I switched to a NOS pair of CBS tubes, but quickly went back to the Sylvanias which just created a more balanced presentation). It was also very sensitive to the kind of preamplifier used. I used only passive pre-amplification, and there was a buzz when using the ModSquad line drive preamplifier. When I switched to my home built dual General Radio wire wound rheostat preamplifier, the buzz disappeared. Larry thinks it may be a grounding issue with the Mod Squad, and I did not bother to investigate further, since I was too busy enjoying the music! Third, there is a slight buzz in the power transformer (when one puts an ear to it), and according to Larry, the amplifier is very sensitive to the power cord used, as well as the AC supply. However, this in no way interferes with the music.

Conclusion

The Monaco represents the best effort of a very experienced SET amplifier builder to provide a very high quality product using quality, off the shelf parts, as opposed to exotic components. It's main strengths are its transparence, bass control and tonality. Larry attributes its excellence to the fact that both output and driver stages are DHT, and to his proprietary power supplies. The amplifier is difficult to move around, and very sensitive to the AC power and to tube rolling (rather like a finely tuned sports car). It is certainly amongst the best amplifiers I have heard. I bought my review sample off Larry, and actually had to sell some gear to be able to afford it, but some things in life you just have to do. After listening to what it did in my system, there was no way I could NOT buy it. It has become my reference amplifier in my systems.

Given its sensitivity, I have no doubt the Monaco can change behavior by playing with the preamplifier used, AC power supply management, speaker cables, power cords and/or tubes. I suspect each owner will spend some weeks experimenting with it before getting it to sound the best in their respective systems. I very strongly recommend this amplifier for folks who have speakers higher than 92dB sensitivity (the higher the better). This amplifier deserves the best source and speakers you can use, and given its performance, is an excellent value at its price. Akhilesh Bajaj

Monaco 845 SET
Retail: $6250

Ultra Fi
web address: http://ultrafitimes.com
email address: larrymoore@ultrafitimes.com
TEL: 513. 697. 1187
 

 

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