Tubes Asylum: REVIEW: Antique Sound Lab KMP60FOX Amplifier (Tube) by Bob G Questions about tubes and gear that glows. FAQ

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Model:	KMP60FOX
Category:	Amplifier (Tube)
Suggested Retail Price:	$2199
Description:	Tube mono bloc
Manufacturer URL:	Antique Sound Lab
Model Picture:	View

Review by Bob G ( A ) on February 24, 2002 at 15:00:08 IP Address: 12.225.10.8

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INTRODUCTION: I have been meaning to write a review of these mono blocs for some time now, but after having received my March, 2002 issue of Stereophile, wherein lie reviews of two other brands of 6C33 based tube mono blocs, I’m just not going to wait any longer. It goes without saying that whatever is written here is just my opinion of what I hear in my living room from my system. The experience one has while listening to recorded music entails listening to the entire playback system, not just a specific component, of course, but I’ll attempt to separate out the qualities of the amplifiers, themselves. If you bore easily reading of others’ tales of equipment ownership, please move immediately to “The Basics” or “The Sound”.

THE PATH: My first system was tube based–an Eico integrated amp and a single Jensen speaker. I got into stereo with Dynaco electronics, which I assembled from kits, and I enjoyed music from these for many years. I jumped the boat to solid state in the early 70's with a Marantz receiver, which I later realized intrigued me most because it had more buttons and knobs than most anything else around. After that, a variety of solid state and hybrid devices came and went–each with it’s own strengths and weaknesses.

The feeling that I was really starting to enjoy the music more consistently came when I moved to a tubed preamp, and after mating that with a Bryston 4BST, I began to enjoy listening to music with more pleasure and satisfaction than ever before. Speakers, cables and source components were changed along the way, but at the heart of it all, I found the performance of the preamp and the power amp (or the synergy of the two) was the key to musical satisfaction.

So there I was, enjoying the music as never before, feeling very good about my choices of equipment, proud that I had been able to put together a system that sounded this good without spending all of my savings, thinking that maybe this would be my last set-up...then the concept of going to all tubes started to sink in. It seemed, in reviews, that the sound of most solid state amplifiers ended up being compared to the sound of tubes, with the latter being the benchmark, so maybe I should have the benchmark–whatever that was.

THE SEARCH: I began reading and re-reading every article I could find on tube amplifiers, both in print and on the web. Opinions here at the Asylum were quite helpful. I kept mental notes as I went along, eventually noting that certain features, certain brands and certain tube types were quite often associated with equipment that earned praise. Since I did not want to spend the big bucks for this experiment, I began concentrating on attempting to find something with the features that I perceived to be important, in the used market. To make this long story a bit shorter, let’s just say that one day I found an ad at Audiogon for a set of Antique Sound Labs KMP60FOX mono blocs. At the time, I hadn’t found any reviews of this model, but I hadn’t found a negative review of any ASL product. The concept of going to mono blocs was intriguing, but a bit scary, considering I would have to completely reconfigure the built-in system of shelves I had for my audio gear. The asking price was about what I would have hoped to get for my Bryston on the used market, and it turned out the ASL’s owner was using these amps to drive the rear speakers of his home theater system and wished to go to solid state for that particular function. We agreed to make an even trade, which meant my out-of-pocket expenses would be limited to the cost of shipping my Bryston to the other fellow.

THE BASICS: Before agreeing on the trade, I made email contact with Joseph Lau, in Hong Kong, the designer of Antique Sound Labs electronics. His knowledgeable answers, both then and after I had used the amps for a few weeks, gave me confidence that I had made a good choice. Following is a list of features, some of which you can read in the ads and some of which I learned directly from Mr. Lau, that describe the KMP60FOX.
Output power: 60 watts.
Tube configuration: two 6C33's and five 6SN7's per side (all triodes).
Push/pull, transformer coupled, cathode follower circuit.
Solid state, choke filtered power supply.
Full wave rectification.
Fast recovery diodes in power supply.
Rel Caps.
Indirectly heated output tubes.
Point to point wiring (6SN7 sockets and power supply storage capacitors plug into the only printed circuit board, everything else is point to point.
1% metal film resistors.
Bias meter and adjustment pots externally accessible.
Gold plated input jacks (RCA) and output terminals.
Output terminals for 4, 8, and 16 ohm speakers (ground is common).
Ceramic tube sockets.
All aluminum chassis.
Very large and heavy transformers.

THE SOUND: When I first turned my FOX’s on, I saw a flash of purple lightning in one of the output tubes and that amp’s fuse blew. A week and a half later, with a new “Mig” tube in place, I finally got to listen to my new (to me) amps. Some aspects of the sound were very good, but all was not well. There was no depth of sound stage and instrument location was inconsistent–it was as if certain frequencies were out of phase. More emails to Mr. Lau produced concern and suggestions on his part, but neither of us could point to the cause. Replacing the Sovtek 6SN7's with Chinese tubes brought a warmer, more relaxing sound, but some of the detail was lost and the depth situation stayed the same. I replaced the stock Bennic coupling caps (two per side) with Hovland Musicaps, and although the detail improved and the sound stage became wider (beyond the speakers), the presentation was still flat and “phasey”.

A couple of frustrating weeks after installing the Hovland’s, I changed interconnects between my preamp and the ASL’s, just to see what would happen. This particular IC isn’t very detailed sounding, but I noticed right away that things sounded more “right”. I left the system running all day but didn’t sit down to do any critical listening till early evening. And then I said “Ahhhhhh!”. There it was. I couldn’t believe that these interconnects had transformed the sound, so I put my original DH Labs BL1's back in, and I said “Yes!”. Now the detail was back and the depth was still there. I don’t know to this date what happened, but in one day, the sound changed from unacceptable to wonderful. I have since replaced another output tube and all of the smaller tubes and at no time has the depth problem returned.

So, how do these things sound? Let’s start by saying that your enjoyment of these amps, as with any tube amp, will be directly connected to the type of tubes you are using. When it comes to the 6C33's, you don’t have any choice–as far as I know, they are (were?) all made in the same factory. Your choice of 6SN7's, though, will produce almost any presentation you want, from flat and boring to warm and rich. Here’s the fun and curse of tube rolling. NOS is the way to go, in my opinion and that of Mr. Lau. I ordered a sampling of two each NOS types by Sylvania, Ken-Rad and Tung-Sol. All are marked VT-231 and I was told they were all made in the 50's. The position that makes the most difference in sound is the one that is common to both the push and the pull sides of the amp, which is the first tube the input signal sees. Other than in that first position, the other positions are currently filled with a mix of two NOS and two of the Chinese tubes. It works for me.

I liked my Bryston amp a lot, but I think my involvement with the music was more intellectual than emotional. The ASL’s are the opposite–they produce music that is emotionally involving first, but they hold up well to critical analysis too. Bass from the Bryston was deeper and tighter, with the ASL being on the fuller, more tuneful side. As much as I enjoyed the rock-solid underpinnings of the Bryston, I miss that less than I welcome the more musical bass from the ASL’s. The all important midrange is good with both amps, but there is a richness in the ASL sound that is captivating–tube amps are famous for this and the ASL is no exception. Cellos, violins and double basses exhibit there wooden construction more prominently than with the Bryston, and the sound of bows passing over strings is much more realistic. The fundamental notes are there, of course, but the harmonics are displayed with satisfying, sometimes thrilling, accuracy.

Higher frequencies with the ASL could sound rolled off to those used to typical solid state sound, but I think this is mainly due to the lack of grain provided by the tubes. Sometimes I’ll be listening and wondering if maybe things have gone “soft”, when a triangle or a cymbal will be struck, or the highest note of a piano will be played and then I realize that it’s all there, it’s just clean and glare free. Throughout the frequency range there is a truth of timbre that is continually stimulating and involving. Acoustic instruments, especially, sound more real. Before the ASL’s were in my system, I didn’t realize I was missing the “boing”of a piano’s lowest notes and the the “plink” of the highest notes. And I still don’t understand why one amplifier can reproduce the decay of an instrument better than another–after all, the sound is on the CD or the record. Right? Is it the noise floor? Whatever the reason, one of the things I noticed early on with the ASL’s is how much longer it takes for some notes to fade away.

Both the Bryston and the FOX do very well at sound staging. With the right recording the music extends beyond the speakers and this is especially noticeable with the tube amps. Maybe part of this is because they are mono blocs, but I like it just the same. It is easy to follow a particular instrument, whether that instrument is part of a rock group or part of a full orchestra. Being able to pick out individual singers in a chorale group is quite fun.

When it comes to details, hearing musicians turning the pages of their music, or hearing them move their feet is a real kick, even if it doesn’t have anything to do with the music. To some this might be a distraction, but it adds to my involvement. These little things, through the ASL’s, add to the realism of the presentation and can best be described as three dimensional–even visual, in my opinion.

A quick word on dynamics–sometimes startling, but always, in every way, appropriate to the music. And for those who might ask about noise, these amps produce absolutely no audible hum or other noise–either of themselves or through my speakers.

OTHER CONSIDERATIONS: When I first set these amps up I used the same interconnects and speaker cables I had been using with the stereo amplifier. I quickly learned that, with both mono blocs sitting on shelves below my other components, I needed to have a fan blowing air over them at all times to keep their heat from cooking everything else. After I decided I was going to keep these amps, I switched from short interconnects and long speaker cables to long interconnects and short speaker cables. Each amp now sits directly behind it’s own speaker, with only 18 inches of cable between them. Now, the considerable heat all those tubes produce just rises innocently into the room. This arrangement sounds better, too.

I should say something here about the owner’s manual. Although the schematic is included, it does not mention anything about how to adjust the output tubes’ bias, nor does it mention that the amps should never be turned on without a load. I learned these things through emails with Mr. Lau, but they should be in the manual.

CONCLUSION: So how do these amplifiers sound in comparison to the BAT’s and the Joule’s? I have no idea. All I can say is that, in my opinion, Joseph Lau has designed an extremely satisfying pair of mono blocs, in the KMP60FOX’s. For me, they are satisfying intellectually–they have the “right stuff” in terms of circuit design, parts selection and quality of construction. They look great. They are cost effective and give great “bang for the buck”. And most importantly, they play wonderful music for me every time I turn them on.

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Product Weakness:	Owner's manual. Sound can be contoured by tube rolling.
Product Strengths:	Musical sound. Build quality. Value. Designer is easily accessable by email. Sound can be contoured by tube rolling.

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Associated Equipment for this Review:
Amplifier:	N/A
Preamplifier (or None if Integrated):	AMC CVT1030
Sources (CDP/Turntable):	See inmate systems.
Speakers:	Magnepan MG12QR
Cables/Interconnects:	See inmate systems.
Music Used (Genre/Selections):	Classical, acoustic, jazz, rock.
Time Period/Length of Audition:	11 months
Other (Power Conditioner etc.):	See inmate systems.
Type of Audition/Review:	Product Owner

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