Product Review - Music
Labs Preamplifier and Power Amplifier - February, 1996
By David Moretti
Music Labs ML-8 Preamplifier; Solid state line level stereo preamplifier; Power spectrum DC - 400 kHz +0 -3 dB; THD <0.002%; Gain 3 dB; Input impedance 56 kOhms; Output impedance 47 Ohms; Size 3 1/2"H x 17"W x 10 1/2"D; Weight 10 pounds; $1,545; Audio Labs of Melbourne, Unit 3, 9-11 Beach Street, Port Melbourne, 3207 Victoria, AUSTRALIA; Phone 61-3-9646-9889; Fax 61-3-9646-9898. USA Distributor: Music Labs USA, Inc., P.O. Box 148, Denver, NY 12421; Phone 607-326-7689; Fax 607-326-3436; E-Mail [email protected].
Music Labs ML-825 Mk II Power Amplifier; Solid state push-pull two channel power amplifier; 250 watts/ch rms into 8 Ohms; Power spectrum 0.002 Hz - 150 kHz -3 dB; THD < 0.002%; Gain 30 dB; Input impedance 10 kOhms; Slew rate 95 V/us; Damping factor 100; Size 5"H x 17"W x 15"D; Weight 36 pounds; $2,995; Audio Labs of Melbourne, Unit 3, 9-11 Beach Street, Port Melbourne, 3207 Victoria, AUSTRALIA; Phone 61-3-9646-9889; Fax 61-3-9646-9898. USA Distributor: Music Labs USA, Inc., P.O. Box 148, Denver, NY 12421; Phone 607-326-7689; Fax 607-326-3436; E-Mail [email protected].
Twenty years warranty parts and labor. Not very many amplifier manufacturers can offer this. Music Labs does, and it is obvious from the build quality that I noticed right away after unpacking these beauties. Only two knobs (input selector and volume), along with the on/off rocker switch, adorn the glossy black front panel of the preamp, and the power amp only has the on/off rocker (see photo). Red LEDs indicate power on. There is no turn on/off thump, which is a result of solenoids that click plainly, preventing signal flow until the circuitry is stabilized. Input and output jacks (RCA on ML-8, RCA and balanced on ML-825) are solidly constructed. There are pins in the balanced inputs of the ML-825 that must be removed before using those particular jacks.
Now, the sound. Oh, the sound! I am a tube (valve to you guys in the U.K.) fanatic, and, for better or worse, I can't help but always compare a solid state amp to my very nice tube gear. Usually, the solid state stuff has some harshness compared to good valves, especially triodes. But, with the ML-8, it was very difficult to discern the difference. I was really amazed. Now, I might say that for the price, it should be good. But, there is some not-so-great audio gear out there that is expensive, solid state and tube. You don't necessarily get what you pay for, but you get what you deserve if you don't listen carefully before you shell out. However, the ML-8 is one fine piece of engineering, and well worth its price tag. Line level passive preamping is popular now, and the ML-8 is just that. Very little, if any gain. Just an extremely transparent, impedance matching switch you might say. No phono stage, but it does have a tape loop. Extremely low noise and hum. Very detailed sound, no coloration at any of the frequencies that I can hear. I wish I could afford one. The newest version (we may get one later, and we will update the review then) has balanced outputs (the ML-825 already has balanced inputs) and a remote control. The only negative comment I have about the ML-8 and ML-825 is that the chassis top rattles a lot when you tap it. I know about rattle. My bass amp rattles everything on stage, particularly the snare drum at certain frequencies. A little thicker metal, or perhaps some damping, would reduce this problem. The feet of the chassis are very nice, but the chassis still rattles. The idea of a resonating chassis affecting the electronics, and thus, the sound, is a controversial topic, but hey, it rattles, and it bothers me.
The ML-825 is the power amplifier that compliments the ML-8 preamp. It uses four Motorola MJ15003/004 bipolar output transistors for each channel. The power supply has a 650 watt toroidal transformer and twenty 4700 uF/63 V capacitors. The use of numerous small capacitors, instead of a few large ones, results in less resistance and inductance, and also a faster response to signal demands. Of course, this type of design is more expensive to manufacture. The use of only four bipolar output devices for a 250 watt amp surprised me, in that we usually see more (six or more) in the output stage of other amplifiers with this much power output. However, the MJ15003/004 series is rated at 250 watts each (some other amps with more transistors may use devices with lower power capability per transistor). The ML-825 has a voltage rail of 55 Volts, so each transistor can produce 4.5 amps of current and maintain its safe operating area (SOA). (Each transistor sees a constant 55 volts, while the current varies with the voltage to the speakers, depending on the strength of the input signal. This is a characteristic of amps with a low output impedance, say 0.1 Ohm, and is why such amps are called "Voltage Source Amps". So, if you divide the 250 watt maximum that each transistor can produce, by the 55 Volts that it constantly sees, you get the 4.5 amps maximum current.) Theoretically then, even one pair of these transistors (it's a push-pull amp, so at least one pair is required) could produce the 250 watts, except that the power supply is a limiting factor here, as it is in most power amplifiers. Thus, with these particular output devices, four is more than sufficient for a 250 watt output, even into 4 Ohms where the current demand increases, and still maintaining SOA. In fact, the additional pair of transistors is what allows good clean power into a 4 Ohm load. Although using more transistors, e.g, six or eight, would allow delivery of high current into 2 Ohms, (one reason some manufacturers use numerous output devices in each channel), this would also increase the second order harmonic distortion, something Music Labs opted out.
The sound of the ML-825 is well suited to the ML-8 preamp. Extremely fine detail and very fast. The use of the numerous small capacitors is partly responsible. The slew rate is one indicator of quick response, and the 95 V/us of the ML-825 is fast indeed. Although the manufacturer states that it is biased for about 20 watts into class A, the amplifier barely got warm at idle, suggesting to us that the bias for our review unit was more towards about 5 watts of class A. Music Labs says that some local distributors may reset the bias. That was probably the case here. However, I don't have a single complaint about the sound. Heat just plays heck with the circuits over the long haul anyway, and 5 watts of class A is plenty for most listening sessions.
We connected the ML-8/ML-825 set to our reference speakers, and we could get 93 - 95 dB SPL of clean, detailed music, without audible distortion, even from planar magnetics, which are not the easiest speakers to drive. In the past, the lab group has turned up the volume to determine the maximum clean SPL that could be obtained from a test amp. As a musician, I stopped exposing my ears to high SPL a long time ago, and I use earplugs when I play in our jazz ensemble, or listen to other live groups for that matter. So I have convinced the boss that we should just test them to a maximum of 95 dB and let it go at that. This is more than enough loudness, and actually, constant exposure to this level will damage your ears, even if the amp is not clipping. What good is it to have a fine amplifier like this if you don't have the hearing to enjoy it?
As a bassist, I am very tuned to the low frequency sound quality. The ML-8/ML-825 are superb at this. I tested them to the limit with a tape I made of a particular way of plucking the bass strings. It gives kind of a metallic twang to the bass, and it is hard to put into words, but I'm sure you have heard it in pop music. Anyway, the transients of the pluck are difficult to reproduce in an audio playback system. No problem for the Music Labs. In fact, I wish I could get this type of pluck in my "on the road" amp, but, on the other hand, my power pentodes look so nice when they have that blue glow as I crank up the beat.
To sum up, the Music Labs preamp and power amp are awesome. Some amps like to dance with Hootie and the Blowfish, while others are more suitable for a string quartet of chamber music. But, from Coltrane to Copland, and Mozart to Mingus, the Music Labs sing like a Byrd. Although they are not meant for home theater use, I still am saying, "May the force be with you."
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