Product Review -
Densen Audio DM-10 Integrated Amplifier - May, 1995
By John E. Johnson, Jr.
Densen Audio DM-10 Integrated Amplifier. Integrated pre- amp/power amp, 75 watts rms output per channel into 8 Ohms, four line-level inputs, two tape inputs and outputs, frequency response 2 Hz - 400 kHz + 0 dB - 3 dB, THD less than 0.01% at rated output, signal-to-noise ratio greater than 95 dB, input impedance 22 kOhm, black metal chassis with brass control knobs, weight 24 pounds, $2,499, Address in Europe: Densen Audio Technologies, Kronprinsengade 32, 6700 Esbjerg, DENMARK, 45-75-18-1214, or in North America: Sonic Integrity, 9820 Bell Ranch Road, # 102, Santa Fe Springs, California 90670, 310-944-0160.
Densen Audio BEAT B-100 Integrated Amplifier. Integrated pre- amp/power amp, 60 watts rms output per channel into 8 Ohms, five line-level inputs, one tape input and output, one passive pre-out (for use with additional power amplifiers), frequency response 2 Hz - 200 kHz + 0 dB -3 dB, THD less than 0.01% at rated output, signal-to-noise ratio greater than 95 dB, input impedance 22 kOhm, black metal chassis with brass control knobs, weight 19 pounds, $1,299, Address in Europe: Densen Audio Technologies, Kronprinsengade 32, 6700 Esbjerg, DENMARK, 45-75-18-1214, or in North America: Sonic Integrity, 9820 Bell Ranch Road, # 102, Santa Fe Springs, California 90670, 310-944-0160.
When we first heard the Densen DM-10 at the Consumer Electronic Show in Las Vegas, January, 1995, we knew that this was a product we wanted to review. Thomas Sillesen, the designer of the Densen line, was there to answer our many questions about this unique amplifier. We obtained not only the DM-10 for testing, but the new BEAT B-100 as well, and, as you will see, both amplifiers are very special in sound quality as well as their design.
Unpacking the amplifiers is an experience in itself. The box and foam rubber protection weigh as much as some amplifiers! Each amp is black with large brass knobs. The power on/off switch is on the back. There are only two knobs on the front, one for volume control and the other for selecting the inputs. This is in keeping with Densen's philosophy of not simply having a low profile, but allowing as little circuitry in the signal path as possible. Even the RCA connectors on the rear of the amplifiers are soldered directly to the PC board.
There is an on/off thump with the DM-10 and B-100, but they are minor. The thumps are due to the lack of any additional circuitry which would eliminate the thump but possibly degrade the signal. A red LED in between the two brass control knobs illuminates when the units are on, and slowly fades when turned off. In fact, the LED on the DM-10 took 45 minutes to completely turn off since it is connected to the power capacitors.
One of the most important design characteristics of these amplifiers is the lack of global negative feedback. The presence of negative feedback has several purposes, among others: to improve the linearity of the amplifier (reduce harmonic distortion), to improve the frequency response, to reduce parasitic oscillation, and to reduce the output impedance. Negative feedback can produce distortion of its own, however, and too much of it becomes obvious when listening to sibilants (the "s" in words), where it sounds as if someone is hissing at you. There are proponents and opponents of negative feedback, regardless of its shortcomings, and Densen has chosen the design route of using no global feedback which is very difficult to do in a solid state push-pull amplifier. This requires the use of extremely linear (and expensive) transistors, careful grounding, and a PC board layout so the + and - conductors are not next to one another. This not only results in a reduction in the problems listed above, which are normally corrected by the use of negative feedback, but also improves phase linearity and speed.
The sound of the DM-10 and B-100 is somewhat like a single ended triode tube (SET) amplifier, and that is a complement indeed. The upper portion of the audio spectrum is laid back, not quite as much as the SET, but just a little, and the mid-range is glorious, just like the SET. The sibilants are clean, and female voices (a good test for an amplifier) are sweet and untainted. Unlike the SET, however, the bass region on the Densens is powerful and deep. There are some subtle differences, too, mostly noticeable in the background of the SET sound. They are probably the result of even order harmonic distortion - a hallmark of the SET - that do not occur to any significant degree in the Densen amplifiers. In any case, this is one of the very few amplifier designs we have ever tested that has this type of sound characteristic, and we consider it an extremely desirable one. Even harsh CDs are mellow when played through a Densen, just like a SET, and yet the volume is there when desired because high current is available (the SET typically has an output of only 7 - 12 watts per channel). The basic difference between the DM-10 and B-100 is in dynamic range, and perhaps a bit in the detail of the upper mid-range as well as the high end. The Alps potentiometers for volume control are marvelously smooth and noise free, allowing a very gradual increase in sound levels even in the 7 - 10 o'clock region.
The tape inputs and outputs are not tape loops. In other words, they can only be used for tape recording and playback rather than for a "loop" containing an equalizer (for tone control) or other circuit such as a surround sound processor. The use of a loop would require a tape monitor switch, and this would mean that the signal path has to be routed through the switch. Since the DM-10 and B-100 are designed with the shortest signal path in mind, tape loops are out of the picture. However, either amplifier can be used with a surround sound processor if the processor has the capability of routing the unprocessed signal through when it is turned off.
The DM-10 uses two toroidal transformers (one for each channel), and the B-100 uses one which supplies both channels. There are separate windings for the output stages (bipolar transistors) and the remaining portions of the amplifiers (the DM-10 as well as the B-100). For the DM-10, there are 40,000 microfarads of capacitance for the input stages and the same for the output, while the B-100 uses 10,000 microfarads for the input, and 30,000 for the output. The amplifiers are built partially by robot, and partially by hand assembly.
Because the DM-10 and B-100 use no global negative feedback, the damping factor is very modest. Therefore, good speaker cables with low capacitance should be chosen for the best performance.
Both the DM-10 and the B-100 are among the finest integrated amplifiers we have ever heard. Their elegant sound is matched only by their looks. We highly recommend that you audition these superb components.
John E. Johnson Jr.
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