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Design Review
After four years, the first thing we needed to do was to determine whether there might be a better overall approach to the design of the preamplifier. After all, there is no point in optimizing a design that is itself less than optimal.
After a careful design review process that included an evaluation of many alternative designs, we concluded that the basic topology of the Nº38 and Nº38S was still the most desirable at anything close to these price ranges. What was needed was a thorough evaluation of new component technologies that were not available four years ago.
Power Supply Improvements
The power supply is the foundation of any electronic product, and critical to its performance. We have found that it is almost impossible to put too much effort into its design and execution. It is that critical.
In fact, if you look at the circuit board of a Nº38(S) or Nº380(S), most of the apparent complexity you see is actually related to optimizing the performance and distribution of the DC power throughout the board. The signal path itself is simple, using a small number of extremely high quality parts. But those parts are served by a robust power supply that includes many more local bypass capacitors than other designs to ensure that active devices have the pure power they need, when they need it.
In the Nº380 and Nº380S, we are using a new AC input module with improved pre- and post-filtering of line noise above the nominal 50/60 Hz line frequency, reducing the amount of high frequency noise (RF and other types) that reaches the transformer's primary windings.
In the new preamplifiers, we changed from standard rectifiers to a discrete rectifier bridge using ultra-fast soft recovery diodes. These parts were first used in the power supply of the Nº36S, and were brand new when we evaluated them for that product-this technology simply did not exist four years ago.
These soft recovery diodes turn on and off faster and more smoothly, generating less noise and more cleanly separating the positive from the negative halves of the incoming AC power. We evaluated the use of these costly parts separately for the two analog channels (each has its own rectifier bridge and power supply regulation) and for the microprocessor control section. It turned out that there were sonic advantages to using the new soft recovery diode rectifiers even in the control area. Thus there are three such rectifiers in each preamplifier: left channel, right channel, and control.
The new preamps also use new, low output impedance regulators, in effect giving every device that consumes power better access to the power it needs. These regulators provide another example of the improvement in basic technology that four years has brought-even such a seemingly basic part as a DC regulator has moved forward enough to make a significant performance difference in a product as advanced as our preamplifiers.
Lastly, after having selected many new active devices in critical areas, we re-evaluated all local bypass capacitors throughout the preamplifiers to ensure optimal matching of the new active devices and their supporting passive parts.
The sonic impact of all these changes to the power supply and its distribution manifest themselves primarily in low end authority and impact. In fact, the improvement in this area is of the sort that you might normally expect when going from a merely adequate power amplifier to a price-no-object model.
Input Buffer Improvements
The input buffer is the first section of the actual signal path, responsible for actively receiving the signal and presenting the next stage (the volume control) with a predictably high quality, low impedance signal-regardless of the variations of the source components used.
The new preamplifiers use new low noise, ultra-fast voltage mode amplifiers in their input buffers.
Interestingly, we had a choice of either voltage mode or current mode technology four years ago. At that time, it came down to a choice between speed (current mode devices were faster but noisier) and noise (voltage mode devices were quieter, but slower). We opted for the speed, and lived with a little extra noise.
In the intervening four years, voltage mode technology has improved significantly. Some of the best new devices are as fast as their current mode alternatives, while having vastly lower noise. In fact, these new devices have a THD+N figure of three one-hundred thousandths of a percent (0.00003%)-since this figure includes noise, these devices are quiet, as well as fast, combining the best attributes of both circuit technologies.
As you may recall, the design of the Nº38 and Nº38S employed gain only when gain was actually needed. Up to and including line level output, the preamps used only attenuation (keeping the signal path as simple and pure as possible). When gain was needed, the input buffer's gain was switched to a higher value. This innovative approach is retained in the Nº380 and Nº380S and avoids the compromises of traditional fixed gain designs which add gain to all input signals only to throw much of it away in the unit's volume control.
The new preamplifiers use new gain switches with superior off isolation to effect this change. What this means is that these switches are more "off" when they are supposed to be off. All conventional switches (including relays) pass some signal at high frequencies due to capacitive coupling across the switch. These improved switches prevent spurious high frequency signals from getting through, allowing the circuit to operate more perfectly.
The audible result of these changes to the input buffer is cleaner, more natural high frequency performance. Subjectively, the highs are more detailed, but without the artificial brightness that often passes for detail in many high end products.
Volume Control Improvements
These preamplifiers use the same high quality Analog Devices precision attenuator used in the Nº38 and Nº38S. Comparing this part to other parts having similar functionality, it remains our first choice. You can think of it as a solid state stepped attenuator, but one with over 4000 laser-trimmed steps.
However, as with all stepped attenuators, the output of this device is a current signal. Preamplifiers deliver voltage, not current, necessitating a current to voltage (I/V) converter.
The Nº380 and Nº380S preamplifiers use a new I/V converter device that is twelve times faster than the part it replaces. It also has six times less current noise (the most important noise characteristic in this application, since the part converts all currents to signal voltage). The combination of speed and lower noise in this part is critically important, and a huge step forward in available technology. Because this part is so fast, its associated passive parts are especially critical-they have to "keep up" with the demands of this speedy active device. Roederstein polypropylene bypass caps and Vishay thin-film resistors were selected from among dozens of high performance possibilities, and provide the best possible environment for the critical I/V converter.
These volume control changes greatly improve dynamics. This can be heard on the obvious sorts of musical choices-piano, timpani, etc.- but is perhaps even more impressive in its unexpected manifestations. The quiet spaces between notes are quieter, vocals are more full bodied and real, and the overall sense of realism is enhanced. Put on a good recording of a tenor or soprano, and you may be surprised at how much more power their voices seem to have.
Output Buffer Improvements
The Nº380S uses new, ultra-tight tolerance, matched-pair output transistors in the discrete output buffer circuit. These are the devices that are responsible for forwarding the signal on to the power amplifier.
These devices were first used in the Nº33 voltage gain stage, and subsequently in the Nº33H. These transistors are extremely costly, allowing their use only in the "S" version, but offer greatly improved matching and thermal tracking. This leads to better response symmetry between positive and negative halves of the circuit, as well as between non-inverting and inverting sides of the balanced signal path.
We also use faster, lower noise current buffers for greater power supply responsiveness. These devices provide a rock-solid source of DC power to the output transistors described above. Similarly, we support the critical output buffer circuitry with improved, lower ESR capacitors for lower power supply impedance at high frequencies.
The audible result of these changes is finer detail, a sense of ease in the presentation of the music, improved microdynamics, and improvements in imaging focus and soundstage reproduction. In effect, low-level details (including the ambient decay of the acoustics of the room in which the music was performed) are reproduced more accurately thanks to the improved tolerances of the new parts.
User Interface Improvements
While we were reevaluating everything else in the preamplifiers, we took the opportunity to incorporate a variety of changes in how they are used by their owners. While none of these improvements affect sonic performance in any way, they add significantly to the experience of owning and using these products every day.
Improvements to operational software include:
Refinements in volume control software result in greater sense of precision and control over level adjustments
Faster volume control ramping speed when operating from Mark Levinson Communications Link system (especially from Nº39 and Nº31.5 remote controls)
Balance LED now remains lit when balance is off center- a visible reminder that balance is not centered when in normal (monitor) operating mode
Additional input names have been added-SAT (satellite), DVD, DMX
The RECORD output is now enabled as a factory default simplifying connection of a recording device. The previous preamplifiers required the user to "turn on" the record outputs by programming an input with the name of a recordable device and then assigning the corresponding RECORD OUT connection. INPUT 3 is now set as a recorder from the factory. We still strongly recommend taking the time to program the preamplifiers as appropriate for any given system, maximizing ease of use.
The Nº38 and Nº38S required camping on the MODE button to save programming changes. Changes are now also saved when the unit "times-out" and returns to normal operation, which is more consistent with other 30 series products. Both methods will work, avoiding confusion for those familiar with the operation of the Nº38 and Nº38S
The power up sequence indicates correct model names in the unit's display-Nº380 or Nº380S (the older preamps both showed "No38")
Industrial Design
The Nº380 and Nº380S industrial design is quite obviously derived from the Nº38 and Nº38S with the units sharing the same chassis and overall appearance. We have however made a subtle but noticeable change to the right front faceplate assembly that easily distinguishes the Nº380 and Nº380S from each other and their predecessors.
The model names are now engraved into a polished and anodized, machined name plate set into the preamplifier's front panel. The Nº380 is black anodized with white lettering, while the Nº380S is clear anodized (silver colored) with black lettering. The appearance is striking and can easily be identified from a distance.
Differences Between Nº380 and Nº380S
With all the changes described above, you might well wonder whether there are any real differences between the Nº380 and the Nº380S. They do share a huge number of common improvements, but there are significant differences still, as well.
First of all, the Nº380S has the four layer cyanate ester circuit board technology of its predecessor, while the Nº380 uses a two layer FR-4 glass epoxy circuit board (like the Nº38). As before, the four layer design of the "S" version gives us the ability to have large uninterrupted plus and minus power planes sandwiched between the signal and ground layers, enhancing the distribution of power and keeping current paths as short as possible. Moreover, cyanate ester has proven itself over and over again in products that can support its higher cost: Nº33 Reference amplifiers, Nº33H amplifiers, Nº36S, and of course the Nº38S all have used cyanate ester boards to their great advantage. In the right application, it makes a big difference.
The Nº380S also uses voltage mode amplifiers that are about two-and-a-half times more costly than their counterparts in the Nº380. While both the 380S and the 380 parts come from the same company, have similar overall characteristics, and offer better performance than the parts they replace in the earlier preamps, the more costly ones used in the Nº380S provide a further performance advantage in high frequency clarity and definition. There is an improvement in musical detail and "ease" in the "S" version that is directly attributable to these more costly parts.
The "S" preamplifier also uses 36 Vishay resistors that cannot be considered in the lower priced preamplifier, for the simple reason that these resistors cost about 100 times as much as the corresponding parts in the Nº380! Even in the "S" version, we listened to every possible location for these ultra-premium resistors, and used them only where they justified their expense. (Our jobs would be much easier if we could simply use the most expensive part everywhere-but often the best part is not the most expensive part, and the only way to be certain is to do the rigorous listening tests we do.)
Finally, as mentioned before, the "S" version preamplifier uses extremely expensive matched transistor pairs in the discrete output buffer. They provide a further improvement in fine detail, imaging, and soundstaging over the already improved Nº380.
In all there are over 50 different parts in the Nº380S that, because of their exotic nature and premium price, cannot be considered in the Nº380. This includes active devices and passive parts as well as the 4 layer cyanate ester circuit board. (The Nº38S differed from the Nº38 by only 30 parts)
The result of these many refinements is perhaps even more significant in terms of sonic performance than the differences between the Nº38 and Nº38S, making the new Nº380S the finest sounding preamplifier we have ever produced.
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